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13: 373, 1939.
13: 373, 1939.
==Chapter VI - Cementum==
1. DEFINITION
2. PHYSICAL CHARACTERISTICS
3. CHEMICAL COMPOSITION
4. CI‘-MIE‘-NTOGENESIS
5 MORPHOLOGY
6. CEMENTO-ENAMEL JUNCTION
7. CEMI'.NTO~DENTINAL JUNCTION
8. FUNCTION
9. EYPERCEMENTOSIS
10. CLINICAL CONSIDERATIONS
1. DEFINITION
Cementum is the hard dental tissue covering the anatomical roots of
the human teeth. It was first microscopically demonstrated in 1835 by
two pupils of Purkinje.5 It begins at the cervical portion of the tooth
at the cemento-enamel junction, and continues to the apex. Cementum
furnishes a medium for the attachment of the fibers that bind the tooth
to the surrounding structures. It can be defined as a specialized, calcified
tissue of mesodermal origin, a modified type of bone covering the anatomic
root of the teeth.
2. PHYSICAL CHARACTERISTICS
The hardness of adult or fully formed cementum is less than that of
dentin.“ 2‘ It is light yellowish and is easily distinguished from the
enamel by its darker hue; it is somewhat lighter in color than dentin.
By means of vital staining and other chemical-physical experiments the
cell containing cementum has been proved to be permeable.”
3. CHEMICAL COMPOSITION
Adult cementum consists of about 45 to 50 per cent inorganic substances and 50 to 55 per cent organic material and water (see table in chapter on Enamel). The inorganic substances consist mainly of calcium
salts. The molecular structure is hydroxyl apatite which, basically, is the
same as that of enamel, dentin and bone. The chief constituent of the organic material is collagen.
4. CEMENTOGENESIS
The development of cementum is known as cementogenesis. During
enamel formation the crown of the tooth is covered by the enamel epithelium. The basal part of the epithelium (inner and outer layers) is the
First draft submitted by Emmerich Kotanyi.
154
CEMENTUM 155
He1'twig‘s epithelial root sheath which is of particular importance in root
development; it forms the mold into which the root dentin is deposited.
Therefore, the newly formed dentin, in this region, is covered at first by
the epithelium, and is separated by it from the surrounding connective
tissue (Fig. 117). Cementum is formed by this connective tissue but it
I‘.
x
 
   
 
Epithelial sheath "
broken, separated from root
\‘ 5
Epithelial sheath-,-.—‘ .
in contact with . .'- ‘dentin
- Epithelial
diaphragm
Fig. 117.—-Hertwig’s epithelial root sheath at end of forming root. At the side of the root
the sheath is broken up and cementum formation begins. (Gottliel).“)
cannot be deposited on the outer surface of the root dentin as long as
the epithelial sheath separates it from the dentin. A contact between
connective tissue and tooth is accomplished by invasion of connective
tissue through the epithelial layers. By this process the epithelial sheath
loses its continuity but persists as a network of epithelial strands which
Gementobluts
156 om. HISTOLOGY AND nnnaronocr
lie fairly close to the root surface. The remnants of the epithelial
sheath are known as “epithelial rests” of Malassez.“ (See chapter
on Periodontal Membrane.) When the separation of the epithelium from
the surface of the root dentin has been accomplished, the periodontal
connective tissue comes into contact with the root surface and cementum
is laid down.
‘x
Enamel epithelium; , it
 
 
- Enamel
— Cemento-enamel
junction
Remnants at epithelial
sheath
 
L’.
Fig. 118.—Epithelia.I sheath is broken and separated from root surface by connective
US$116.
In the first stage of cementum formation two tissue elements can be
observed; First, cells of the connective tissue (undiflferentiated mesonchymal cells) are arranged along the outer surface of the dentin (Fig. 118).
These change into flat," cuboidal cells and are the cementoblasts. At the
same time the second tissue element, pre-collagenous (argyrophil) fibers,
can be seen at right angles to the root surface, and attached to the outer
surface of the dentin (Fig. 119). These fibers soon assume a collagenous
CEMENTUM 157
1% numa“
.9» ’
Argyrophil  H.‘
nbera  _ ,
59.; —— Dentin
"V
4’ ”" " Attach an
‘e . 111
.'$w$ :~_ of fibers
fibers
w‘
Fig. 119.—Argy1-ophil fibers of the periodontal membrane. attached to the dentin (silver
impregnation).
Couagenous _ __M__  ___,_..,,~:, , WW , _ '- Dentin
fibers
* Cementum
 
M _ _
Fir. 120.—-Cementum ground substance develops from fibers of the periodontal membrane
- (silver impregnation).
158 ORAL HISTOLOGY AND EMBRYOLOGY
character and become a. part of the ground substance of the cementum
(Fig. 120). This mechanism is similar to that observed in dentinogonesis
(see chapter on Dentin).
Definite knowledge of the function of the cementoblasts is incomplete,
but it is presumed that they play the same role in cementum formation
Dentln
'1.
Cementoblastsfr ' >-' ' :7 - ‘—:~=~-= ’ " " "*ex
——-V-n--—-~ W cementum
Periodontal ” ’ '—,membrane
,.__—_—————~— -r—— Cementold
' tissue
Cementoblast ' ‘  ’” "'-‘"“:““‘ ' "f"
Fig. 121.—Cementoid tissue on the surfaceflgf calcified cementum. Cementoblasts between
ers.
as the osteoblasts play in bone formation. In the first phase of development the cementoblasts, apparently by enzymatic action, elaborate a
homogenous material, the cementoid tissue. In the second phase, calcification takes place by the deposit of calcium salts in the cementing substance of the intercellular substance. Simultaneously the organic component changes radically, becoming soluble by proteolytic enzymes.“
GEMENTUM 159
During the continuous apposition of cementum a thin layer of non- °¢m°“"°i°
calcified matrix, termed cementoid tissue, which is analogous to osteoid
tissue and predentin, is seen on the surface of the cementum (Fig. 121).
This cementoid tissue is lined by cementoblasts. Connective tissue fibers
from the periodontal membrane pass between the cementoblasts into the
cementum. These fibers are embedded in the cementum and serve as an
attachment for the tooth to the surrounding bone. Their embedded portions are known as Sharpey’s fibers. These were accurately described
in 18872 as an essential part of the suspensory apparatus.
-—» —— -1
 
3:355 25' 7
-f, if In '
.4‘  J»
gag‘!
at .
' ‘r 7 i
Periodontal
membrane
 
T-»"'"‘, .A.ceuu1a.r
3:?“ cementum
ax» .
Alveolar bone
Fig. 122.——Increment2.l lines in the accellular cementum.
5. MORPHOLOGY
From a morphologic standpoint two kinds of cementum can be differentiated: (a) acellular, and (b) cellular cementum. Functionally, however there is no difference between the two.
Acellular
cementum
160 om. HISTOLOGY AND EMBRYOLOGY
Acellular cementum may cover the root dentin from the cemento-enamel
junction to the apex, but is often missing on the apical third of the root.
Here the cementum may be entirely of the cellular type. The aeellular
cementum is thinnest at the cemento-enamel junction (20 to 50 microns),
and thickest toward the apex (150 to 200 microns). The apical foramen
is surrounded by cementum. Sometimes the cementum extends to the
inner wall of the dentin for a short distance, forming a lining of the root
canal.
Both acellular and cellular cementum are separated by incremental
lines‘ into layers that indicate periodic formation (Fig. 122). Acellular
"  "— " ‘“. ‘
.3‘: ' j
_. Principal fibers of
periodontal
membrane
Dentin .
Cementum _
F1E- 123.——'1‘he principal fibers ot the periodontal membrane continue into the surface
layer of the cementum.
cementum consists of the calcified matrix and the embedded Sharpey’s
fibers. The matrix is composed of two elements: the collagenous fibrils
and the calcified cementing substance. The fibrils in the matrix are
perpendicular to the embedded Sharpey’s fibers and parallel to the
cementum surface. The fibrils are less numerous than in lamellated
bone and about as numerous as those of bundle bone. Due to identical
‘The term incremental lines was introduced by Salter in 1874 as including the stripes
of Remus In the enamel, the contour lines at Owen in the dentin and the stratification
In the cementum.
U1‘JJ.V.l.EJN'l'UL1 .10.].
optical qualities, i.e., the same refractive index, the fibrils and interfibrillar cementing substance can be made visible only by special staining methods. Fibrils and Sharpey’s fibers are easily distinguished by
means of silver impregnation. In dried ground sections Sha.rpey’s fibers
are disintegrated and the spaces and channels which they formerly occupied are filled with air; the areas thereby become discernible as dark
lines.
   
  ‘ 'r.-,z Dentin
. ‘
Periodontal ‘
“L I Acellular
membrane —
cementum
Cementoid
tissue ’——«g Cellular
1 cementum
F--“fl Acellular
cementum
.e
Alveolar bone A
Fig. 124.——Cellula.r cementum on the surface or acellular cementum, and again cov
ercd by acellular cementum (incremental lines). The _la.cunae _of the cellular cementum
are empty, indicating that this part of the cementum is necrotic.
While the cementum remains relatively thin, Sharpey’s fibers can be
observed crossing the entire thickness of the cementum. With further
apposition of cementum a larger part of the fibers is incorporated in the
cementum. At the same time, the portion of the fibers lying in the deeper
layers of the cementum becomes obscure. The attachment proper is
probably confined to the most superficial or recently formed layers of
162 ORAL HISTOLOGY AND EMBRYOLOGY
Periodontal Dentin
membrane ‘ ‘
Cementoid __ __ _____
tissue _— —  cellular
cementum
Fig. 125.—Cel1u1'ar cementum forming the entire thickness of cementum. (Orban.W)
F_?  - -—-—-——-v---—-———-—J..-g‘
:
     
Dentin
Apex formed » ~.—_.—— I-~~———~————
by cemen-.
tum
2‘-T ‘
373- 136-——Cementum tyiickest at apex contributing to the length or the root,
cnmrmrun 163
cementum (Fig. 123). This would seem to indicate that the thickness
of the cementum does not enhance functional efficiency by increasing the
strength of attachment of the individual fibers. Continuous apposition
of cementum is essential for the continuous eruptive movements of the
functioning tooth and the continuous reorganization of the periodontal
membrane which is necessitated by these movements. The surface of the
cementum is vital Whereas the inner layers become necrotic as recognized
by empty lacuni in the cellular cementum (Fig. 124) .
The location of acellular and cellular cementum is not definite. Layers
of acellular and cellular cementum may alternate in almost any arrangement. The acellular cementum, which is normally laid down on the surface of the dentin, may occasionally be found on the surface of cellular
cementum (Fig. 124). Cellular cementum is usually formed on the sur
Fig. 127.—Cementum lacuna and canaliculi filled with air (ground section).
face of acellular cementum (Fig. 124), but it may comprise the entire
thickness of the apical cementum (Fig. 125). It is always thickest around
the apex and, in this manner, contributes to the lengthening of the root
(Fig. 126).
The cells in cellular cementum (cementocytes) are similar to osteocytes.
They lie in spaces designated as lacunae. Frequently, the cell body has
the shape of a plum stone, with numerous long processes radiating from the
cell body. These processes may branch, and frequently anastomose
with those of a neighboring cell. Most of the processes are directed
toward the periodontal suflface of the cementum, differing in this respect
from the evenly distributed processes of the bone cells.
Cellular
cementum
164 ORAL HISTOLOGY AND EMBRYOLOGY
Some canaliculi, containing processes of the cementocytes, have been
said to anastomose with peripheral branches of the dentinal tubulifi» 9"
The cells are irregularly distributed throughout the thickness of the
cellular cementum. The cavities can be best observed, however, in
ground sections of dried teeth, where they appear as dark spider-like
figures (Fig. 127). The dark appearance is due to the fact that the
spaces are filled with air; these spaces also can easily be filled with dyes.
Enamel I Enamel
 
 
Enamel ,_,___._-_.__, , ‘ Enamel
epithelium  epithelium
. ff‘ ‘EC:
, Z t .,l u
"’ I  - ‘- ‘ ‘="'::—:-—- cementum over_ . _ lapping enamel
Cemento-enamel «— . ' 7 ~ ‘ .i
junction ‘
Cementum—— -
A. B.
Fig. 128.-—Cemento—enamel junction.
A. cementum and enamel meet in a. sharp line.
B. cementum overlaps enamel.
6. CEMENTO-ENAMEL JUNCTION
The relation between cementum and enamel at the cervical region of
the teeth is variable.“ In about 30 per cent of the examined teeth the cementum meets the cervical end of the enamel in a sharp line (Fig. 128, A).
Here, the cementum, as Well as the enamel, tapers into a knife-edge. In
other teeth, about 60 per cent, the cementum overlaps the cervical end
of the enamel for a short distance (Fig. 128, B). Developmentally, this
CEMENTUM 165
may occur only when the enamel epithelium, which normally covers the
entire enamel, degenerates in its cervical end, permitting the connective
tissue, which is responsible for the deposition of cementum, to come in contact With the enamel surface.
Enamel
 
     
i . Enamel
epithelium
End of —
enamel
Enamel
epithelium
Q7‘ Cemente enamel
- junction
‘ ‘;
Cementum
epithelium
Cementum
Fig. 129.—Variations at the cemento-enamel junction.
4. Enamel epithelium attached to dentin surface preventing cementum formation.
1 BhEnamel epithelium breaking continuity of cementum near the cemento-enamel
unc on.
In about 10 per cent of all teeth various aberrations of the cementeenamel junction may be observed. Occasionally, the enamel epithelium
which covers the cervical part of the root does not separate from the
dentin surface at the proper time.‘ In other words, it remains attached
to the dentin of the root for variable distances (Fig. 129, A), and prevents
the formation of cementum. In such cases there is no cemento-enamel
junction, but a zone of root dentin is devoid of cementum and covered by
166 ORAL HISTOLOGY AND EMBRYOLOGY
enamel epithelium. In other instances cementum is formed at the cemento-enamel junction for a short distance only and, following it apically,
Her-twig’s epithelial root sheath remains in contact with the dentin in a
limited area (Fig. 129, B). Enamel spurs, pearls or drops 1nay be formed
by such epithelium.“
7. CEMEN TO—DENTIN AL J UN GTION
The surface of the dentin upon which the cementum is deposited is
normally smooth in permanent teeth. The eemento-dentinal junction,
- Dentin
Periodontal membrane ,_ 7
Intermediate cementum
layer
-I--—» -- - Acellular
cementum
Fig. 130.—Intermediate layer of cementum.
in deciduous teeth, however, is sometimes scalloped. The attachment of
the cementum to the dentin, in either case, is quite firm although the
nature of this attachment has not been fully investigated.
Sometimes the dentin is separated from the cementum by an intermediate layer, known as the intermediate cementum layer, which does
not exhibit the characteristic features of either dentin or cementum (Fig.
130). This layer contains large and irregular cells which can be regarded
CEMENTUM 167
as embedded connective tissue cells. The development of this layer may
be due to localized, premature disintegration of 1'-lertwig ’s epithelial sheath
after its cells have induced the diflerentiation of odontoblasts, but before
the production of dentinal intercellular substance. It is found mostly
in the apical two-thirds of the root. Sometimes it is a continuous layer;
sometimes it is found only in isolated areas.“
8. FUNCTION
The functions of cementum are, first, to anchor the tooth to the bony
socket by attachment of fibers; second, to compensate by its growth for
loss of tooth substance due to occlusal wear; third, to enable, by its continuous growth, the continuous vertical eruption and mesial drift of the
teeth; and fourth, to make possible the continuous rearrangement of the
principal fibers of the periodontal membrane.
The attachment of the fibers of the periodontal connective tissue to the
surface of the tooth is the medium by which functional connection between tooth and surrounding tissues is established. Due to physiological
movements of the functioning tooth, fibers have to be replaced continually. I11 order to maintain a functional relationship new cementum
has to be deposited continuously on the surface of the old cementum.‘
By this continued formation of cementum new fibers of the periodontal
membrane are attached to the surface of the root, and loosened or degenerated Sharpey’s fibers are thus continuously replaced. By this mechanism an adequate attachment of the tooth to the supporting tissues is
maintained. The morphologic evidence of the continuous formation of
cementum is shown by the presence of cementoblasts and a layer of cementoid tissue on the surface of the cementum. Cementoid tissue may be found
on acellular (Figs. 121, 122, 124), as well as on cellular (Fig. 125) cementum.
The continuous deposition of cementum is of great biologic importance.“ 3' 13 In contrast to the ever alternating resorption and new formation of bone, cementum is not resorbed under normal conditions. If a
layer ages or, functionally speaking, loses its vitality, the periodontal
connective tissue and cementoblasts must produce a new layer of cementum on the surface to keep the attachment apparatus intact. In bone the
loss of vitality can be recognized by the fact that the bone cells degenerate and the bone lacunae are empty. Lowered vitality in acellular
cementum cannot be so readily ascertained but, in cellular cementum, the
cells in the deepest layers may degenerate and the lacunae may be
empty (Fig. 124). This indicates necrosis of the cells. On the surface,
the lacunae contain normal cementocytes. The nuclei of degenerating
cells in the deeper layers are pyknotic and the cells are shrunken: near
the surface the cells fill the entire space of the cementum lacunae (Fig.
125) and the nuclei stain dark.“ 3
168 ORAL HISTOLOGY AND EMBRYOLOGY
9. HYPERGEIVLENTOSIS
Hypercementosis designates an abnormal thickening of the cementum.
It may be difiuse or circumscribed, i.e., it may affect all teeth of the
dentition, or it may be confined to a single tooth. It may even affect
only certain parts of one tooth. If the overgrowth improves the functional qualities of the cementum, it is termed a cementum hypertrophy;
if overgrowth occurs in nonfunctional teeth or if it is not correlated with
increased function, it is termed hyperplasia.
 
 
Hypertrophic
cementum
‘i
5 ‘C
Alveolar ‘bone .
Periodontal. _ _.. -.. N 73- i 1"
membrane
Dentin
3»-:,
1,,
‘S1,.
:1
_,,‘ I-Iypertrophic
cementum
Fig. 131.——Pronglike excementoses.
In localized hypertrophy a spur or pronglike extension of cementum
may be observed (Fig. 131). This condition is frequently found in teeth
which are exposed to great stress. The pronglike extensions of cementum provide a larger surface area for the attaching fibers, thus securing a firmer anchorage of the tooth to the surrounding alveolar bone.’
Localized hyperplasia of cementum may sometimes be observed in areas
where enamel drops have developed on the dentin. The hyperplastic cementum, covering the enamel drops (Fig. 132), is occasionally irregular
CEMENTUM 169
and sometimes contains round bodies which may be calcified epithelial
rests. The same type of embedded calcified round bodies are frequently
found in localized areas of hyperplastic cementum (Fig. 133). Such
knoblike projections are designated as excementosis. They, too, develop
around disintegrated, degenerated epithelial rests.‘
‘V 5%.;
in '9.
3% 1-3,
--1;
Hyper-plastic cementum _: ~ Denun
—-—-- '- Enamel drop
Hyperplastic cementum
as
Fig. 132.—Irreg'ula.r hyperplasia or cementum on the surface or an enamel drop.
Extensive hyperplasia of the cementum of a tooth is found, occasionally, in connection with chronic periapical inflammation. Here the hyperplasia is circumscribed and surrounds the root like a cuff.
A thickening of the cementum is often observed on teeth which are not
in function. The hyperplasia may extend around the entire root of the
nonfunctioning teeth or may be localized in small areas (see chapter
on Periodontal Membrane). Hyperplasia of cementum in nonfunctioning
teeth is characterized by the absence of Sharpey’s fibers.
170 ORAL HISTOLOGY AND EMBRYOLOGY
Excementosis '
cementum
Excementosis
Alveolar bone
‘ ~«__... . . __.
Fig. 133.~—Excementoses in bifurcation of a. molar. (Gottliebfl)
I71
CEMENT Ul\I
Remnants of
fractured cementum
Hype!-plastic cementum
._ Hyperplastic cementum
 
X
e
n.
A
Fig. 134..—E:xtens1ve spikelike hyperplasia of cementum172 omu. HISTOLOGY AND EMBRYOLOGY
The cementum is thicker around the apex of all teeth and in the
bifurcation of multirooted teeth than on other areas of the root. This
thickening can be observed in embedded, as well as newly erupted,
teeth.”
In some cases an irregular overgrowth of cementum can be found with
spikelike extensions and calcification of Sharpey’s fibers, accompanied by
numerous cementicles. This type of cementum hyperplasia can, occasionally, be observed on many teeth of the same dentition and is, at least
in some cases, the sequelae of injuries to the cementum (Fig. 134).
10. CLINICAL CONSIDERATIONS
The fact that cementum appears to be more resistant to resorption than
bone renders orthodontic treatment possible. When a tooth is moved by
means of an orthodontic appliance, bone is resorbed on the side of pressure new bone is formed on the side of tension. On the side toward which
the tooth is moved pressure is equal on the surfaces of bone and cementum.
Resorption of bone, as well as of cementum, may be anticipated. However, in careful orthodontic treatment cementum resorption, if it occurs, is
usually localized and shallow. Moreover, it is readily repaired if the
intensity of pressure is reduced and the surrounding connective tissue
remains intact. If resorption is extensive it may indicate a. systemic
disorder, possibly of the endocrine system.‘
Excessive lateral stress may compress the periodontal connective tissue
between bone and cementum and cause bleeding, thrombosis and necrosis.
After resorption of the damaged tissues, accompanied by bone resorption,
repair may take place.‘~ 9~ “’~ 23
It has been the aim of some investigators to determine why resorption
takes place in some cases and not in others when external conditions
seem to be identical. The reasons are as yet unknown. The potentiality
to form new cementum does not seem to be equal in all individuals; in
some, cementum forms readily; in others it does not. The latter are those
cases which react unfavorably to trauma or any kind of irritation. These
are the cases that develop periodontal diseases easily. The dilference in
cementum formation may be explained by constitutional factors. Cementum resorption without obvious cause is called idiopathic.
Severe resorption of cementum may be followed by resorption of the
dentin. After resorption has ceased the damage is usually repaired,
either by formation of acellular (Fig. 135, A) or cellular (Fig. 135, B)
cementum, or by alternate formation of both (Fig. 135, 0). In most cases
of repair there is a tendency to re-establish the former outline of the
root surface. However, if only a thin layer of cementum is deposited on
the surface of a deep resorption, the root outline is not reconstructed and a
baylike recess remains. In such areas sometimes the periodontal space is
GEMENTUM 173
restored to its normal width by formation of new bone, so that a
proper functional relationship will result. The outline of the alveolar
bone, in these cases, follows that of the root surface (Fig. 136). In contrast to anatomical repair, this change is called functional repair.“
 
 
 
 
I
T  4»:
 
JCT '
X‘
;‘f5.."-‘4K:»:('si
Fig. 135.—Repair of resorbed cementum.
4. Repair by acellular cementum (a:).
B. Repair by cellular cementum (2).
0. Repair flrst by cellular (ac) and later by acellular (wz) cementum.
D = Dentin; I1’. = line or resorption; P = periodontal membrane.
If teeth are subjected to acute trauma, such as a blow, smaller or
larger fragments of cementum may be severed from the dentin. The
tear occurs frequently at the cemento-dentinal junction, but may also be
in the cementum or dentin. Transverse fractures of the root may heal
by formation of new cementum uniting the fragments.
Frequently, hyperplasia of cementum is secondary to periapical inflammation or extensive occlusal stress. The fact is’ of practical significance
174 ORAL HISTOLOGY AND EMBRYOLOGY
in so far as the extraction of such teeth necessitates the removal of bone.
This also applies to extensive excementoses, as shown in Fig. 133.
These can anchor the tooth so tightly to the socket that the jaw or parts
of it may be fractured in an attempt to extract the tooth. These facts
indicate the necessity of taking roentgenograms before an extraction.
Small fragments of roots, left in the jaw after extraction of vital teeth,
may be surrounded by cementum, and remain in the jaw without causing
any disturbance.
   
" 5,
:,.--' Repaired
     
       
 
 
'_;é,'_‘.:__i_uW' 1%“, resorption
----.-I-:a..;.sa£g
. A .- New perio- dontal
membrane
Perio(11:)nta.1._:. \ ‘
mem a. . ‘ ~' "
r ne_rh\g,"",3_.'
Fi8- 136.—-Functional repair of cementum resorption by bone apposition. Normal width
of periodontal membrane re-established.
If the cementum does not cover the cervical part of the root, recession
of the gingiva will expose the highly sensitive dentin in the cervical area.
When calculus is removed it is frequently impossible to avoid the removal of the thin cementum covering the cervical region of the exposed
root. As the individual gets older, more cementum is gradually exposed
and subject to the abrasive action of some dentifrices. Since the ceCEMENTUM 175
inentuin is the softest of the hard dental tissues, a considerable amount
of cementum may be removed by these mechanical means.” The denuded dentin is then highly sensitive to thermal, chemical or mechani
cal stimuli. The hypersensitivity can often be relieved with astringent
chemicals which coagulate the protoplasmic odontoblastic processes.
References
. Becks, H.: Systemic Background of Paradentitis, J. A. D. A. 28: 1447, 1941.
. Black, G. V.: A Study of Histological Characters of the Periosteum and Peridental Membrane, Dental Review 1886-1887; and W. T. Keener 00., Chicago,
1887.
Box, H. K.: The Dentinal Cemental Junction (Bull. No. 3), Canad. Dent. Res.
Found., May, 1922.
Coolidge, E. D.: Traumatic and Functional Injuries Occurring in the Supporting Tissues of Human Teeth, J. A. D. A. 25: 343, 1938.
Denton, G. H.: The Discovery of Cementum, J. Dent. Research 18: 239, 1939.
Gottlieb, B.: Zementexostosen, Schnielztropfen und Epithelnester (Cementexostosis, Enamel Drops and Epithelial Rests), Oesterr. Ztschr. f. Stomatol. 19:
515 1921.
. Gott1ieb’,B.: Tissue Changes in Pyorrhea, J. A. D. A. 14: 2173,1927.
. Gottlieb, B.: Biology of the Cementum, J. Periodont. 13: 13, 1942.
Gottlieb, B., and Orban, B.: Die Veriinderungen der Gewbe bei iibermiissiger
Beanspruchung der Ziihne (Experimental Traumatic Occlusion), Leipzig,
1931.
10. Gottlieb, B., and Orban, B.: Biology and Pathology of the Tooth (Translated
by M. Diamond), New York, 1938, The Macmillan Co.
11. Kitchin, P. G.: ’l‘he Prevalence of Tooth Root Exposure, J. Dent. Research 20:
565 1941.
12. Kitchin,,P. 0., and Robinson, H. B. G.: The Abrasiveness of Dentifrices as
Measured on the Cervical Areas of Extracted Teeth, J. Dent. Research 27:
195 19-18.
13. Kronfeld, R.: Die Zementhyperplasien an nicht funktionierenden Ziihnen (Cementum Hyperplasia on Nonfunctioning Teeth), Ztschr. f. Stomatol. 25:
1218 1927.
14. Kronfeld: R.: The Biology of Cementum, J. A. D. A. 25: 1451, 1938.
15. Malassez, M. L.: Sur le r6le des débris epitheliaux paradentaires (The Epithelial Rests Around the Root of the Teeth), Arch. de Physiol. 5: 379, 1885.
Oppenheim, A.: Human Tissue Response to Orthodontic Intervention, Am. J.
Orthodont. & Oral Surg. 28: 263, 1942.
17. Orban, B.: Resorption and Repair on the Surface of the Root, J. A. D. A. 15:
1768 1928.
18. Orban, B.,: Dental Histology and Embryology, Philadelphia, 1929, P. Blakiston’s
Son & Co.
19. Sicher, H., and Weinmann, J. P.: Bone Growth and Physiologic Tooth Movement, Am. J. Orthodo_n_t.. Kr Oral _Surg. 30: 109, 1944.
20. Skillen, W. G.: Permeability: A Tissue_ Characteristic, _J. A. D. A. 9: 187, 1922.
21. Sorrin, S., and Miller, S. G.: The Practice of Pedodontia, New York, 1928, The
Macmillan Co. _
22. Stones, H. H.: The Permeability of Cementum, Brit. D. J. 56: 273, 1934.
23. Stuteville, O. H.: Injuries Caused by Orthodontic Forces, Am. J. Oi-thpdont.
85 Oral Surg. 24: 103, 1938. _ _
24. Tainter, M. L., and Epstein, S.: A Standard Procedure for Determining Abrasion, J. Am. Coll. Dentists 9: 353, 1942.
25. Thomas, N. G., and Skillen, W. G.: Staining the Granular Layer, Dental Cosmos
26
[Old
?°°~1 9”?‘ 2"‘ 9°
IP’
62: 725, 1920.
. Weinmann, J. P., and Sicher, H.: Bone and Bones. Fundamentals of Bone
Biology, St. Louis, 1947, The C. V. Mosby Co.
CHAPTER VII
PERIODONTAL MEMBRANE
D1‘-I'INITION
FUNCTION
DEVELOPMENT
STRUCTURAL ELELIENTS
PHYSIOLOG-I0 CHANGES
CLINICAL CONSIDERATIONS
9’S"'.“9°!°!"
1. DEFINITION
The periodontal membrane is the connective tissue which surrounds
the root of the tooth and attaches it to the bony alveolus; it is continuous
with the connective tissue of the gingivae. Various terms have been
given to this tissue: peridental membrane; pericementum; dental periosteum; and alveolodental membrane. The variety of terms may be explained by the difficulty of classifying this tissue under any anatomic
group. The term periodontal is derived from the Greek pert meaning
around, and odous meaning tooth, thus signifying the relationship of the
tissue to the tooth. This tissue is called a membrane though it does not
resemble other fibrous membranes, like fasciae, capsules of organs, perichondrium, and periosteum. It has some structural and functional
similarities to these tissues, but is different in that it not only serves as a
pericementum for the tooth, a periosteum for the alveolar bone, but
mainly as the suspensory ligament for the tooth. Therefore, the term
periodontal ligament would be most appropriate.
2. FUNCTION
The functions of the periodontal membrane are formative, supportive,
sensory and nutritive. The formative function is fulfilled by the cementoblasts and osteoblasts which are essential in building cementum and bone,
and by the fibroblasts forming the fibers of the membrane. The supportive function is that of maintaining the relation of the tooth to the surrounding hard and soft tissues. This is achieved by connective tissue
fibers which comprise the bulk of the membrane. Functions which are
sensory and nutritive to the cementum and alveolar bone are carried out
by the nerves and blood vessels.
3. DEVELOPMENT
The periodontal membrane is derived from the follicle, or sac which
envelops the developing tooth germ. Around the tooth germ three zones
can be seen: an outer zone containing fibers related to the bone; an inner
zone of fibers adjacent to the tooth; and an intermediate zone of un
First dratt submitted by Helmuth A. Zander.
176
rmuonommn MEMBRANE 177
orientated fibers between the other two (Fig. 137). During the formation
of cementum, fibers of the inner zone are attached to the surface of the
root. As the tooth moves toward the oral cavity, gradually a functional
orientation of the fibers takes place.“ Instead of loose and irregularly
arranged fibers, fiber bundles extend fi'om the bone to the tooth. When
the tooth has reached the plane of occlusion, and the root is fully formed,
- - Dentin
   
- —— cementum
Bone fibers
Cemental fibers
Bone
Fig. 137.—Three zones in the periodontal membrane of a developing tooth.
this functional orientation is complete. However, due to changes in functional stresses, some changes in the structural arrangement of the periodontal membrane occur throughout life.
4. STRUCTURAL ELEMENTS
The main tissue elements in the periodontal membrane are the principal
fibers, all of which are attached to the cementum?’ 3 The fiber bundles
extend from the cementum to the alveolar wall, or over the alveolar wall
to the cementum of the adjacent tooth, or into the gingival tissue. The
principal fibers of the periodontal membrane are white collagenous connective tissue fibers and cannot be lengthened. There are no elastic fibers in
the periodontal membrane. The apparent elasticity of the periodontal membrane is due to the arrangement of the principal fiber bundles. They follow
a wavy course from bone to cementum, thereby allowing slight movement
178 ORAL msvronomz AND EMBRYOLOGY
of the tooth upon stress. Near the bone the fibers seem to form larger
bundles before their insertion into it. Although the bundles run directly
from bone to cementum, it is most probable that the single fibers do not all
span the entire distance. The bundles are “spliced" together from shorter
fibers and held together by a cementing substance. The principal fibers
are so arranged that they can be divided into the following groups:
Gingiva.
 
Cementeenamel
junction '_
155
«j.
E  ‘L
y‘, ‘\
 
Alveolar
crest
Fig. 138.——Gingival fibers of the periodontal membrane pass from the cementum into
' the gingiva.
The fibers of the gingival group (Fig. 138) attach the gingiva to the cementum. The fiber bundles pass outward from the cementum into the
free and attached gingiva. Usually they break up into a meshwork of
smaller bundles and individual fibers, interlacing terminally with the
fibrous tissue of the gingiva.
The fibers of the transseptal group (Fig. 139) connect adjacent teeth.
The fiber bundles run mesially and distally from the cementum of one
tooth, over the crest of the alveolus, to the cementum of the neighboring
tooth.
The fibers of the alveolar group (Fig. 140) attach the tooth to the bone
of the alveolus; they are divided into five groups: (1) Alveolar crest
PERIODONTAL MEMBRANE 179
group: the fiber bundles of this group radiate from the crest of the alveolar process, and attach themselves to the cervical part of the cementum.
(2) Horizontal group: these fibers run at right angles to the long axis of
the tooth, directly to the bone. (3) Oblique group: the fibers run
obliquely; arising from the bone, they are attached in the cementum somewhat apically from their attachment to the bone. These fibers are ‘most numerous and constitute the main support of the tooth against occlusal stress.
(4) Apical group: the fibers are irregularly arranged and radiate from
the apical region of the root to the surrounding bone (Fig. 1-11). (5)
I ntermdicular group: From the crest of the interradicular septum fibers
extend to the bifurcation of multiradicular teeth.
 
 
 
Enamel cuticle
Enamel cuticle Gingival papilla
Enamel
Enamel
Gingival fibers
Cemento-enamel
Dentin junction
Cemento-enamel
junction
cementum _
Fig 139.——Transseptal fibers of the periodontal membrane connect adjacent teeth.
The arrangement of the fibers in the different groups is Well adapted to
fulfill the functions of the periodontal membrane. No matter from which
direction a force is applied to the tooth, it is counteracted by some or all
of the fiber groups. The principal fibers, as a whole, may be regarded as
a ligament, alveolodental ligament, by which the tooth is attached to
the alveolar bone. Its function is, primarily, to transform pressure
exerted upon the tooth into traction on cementum and bone." The fibers
180 omu. I-IISTOLOGY AND EMBRYOLOGY
 
   
 
Enamel - Gingiva
Cemento-enamel
junction
Alveolar crest fibers
‘ Alveolar crest
Horizontal fibers?--: , T"
‘ Bundle bone
Lamellated bone
Oblique fibers
IP12. 140.——AJveo1a.r fibers or the periodontal membrane.
PERIODONTAL MEMBRANE 181
are arranged in response to functional stimuli. The structure of the
periodontal membrane changes continuously to meet the requirements of
the continuously moving tooth.°» 2°
Most cells of the periodontal membrane are typical fibroblasts. They
are long, slender, stellate connective tissue cells whose nuclei are large
and oval in shape. They lie at the surface of the fiber bundles and are,
probably, active in the formation and maintenance of the principal fibers.
 
 
V.‘ 'r.‘~ ~“I
“_—§‘ . ' Periodontal
membrane
 
Fig. 141.—Apica1 fibers of the periodontal membrane.
( Orban.“ )
Bone is in a constant state of transition. As elsewhere in the body, the
bone of the alveolus is constantly locally resorbed and rebuilt. Resorption
of bone is brought about by the osteoclasts; formation of new bone is
initiated by the activity of the osteoblasts.
Where bone formation is in progress osteoblasts are found along the
surface of the wall of the bony socket, the periodontal membrane fibers
passing between them. These cells are, usually, irregularly cuboid in
shape, with large single nuclei containing large nucleoli and fine chromatin particles. The fibers of the periodontal membrane are secured to the
Fibroblasts
Osteoblasts
and Osteo182 ORAL HISTOLOGY AND EMBRYOLOGY
bone by the formation of new bone around the ends of the fibers. Therefore, osteoblasts seem to be necessary for the attachment and reattachment
of the fibers to the alveolar bone. Osteoclasts are mostly multinucleated,
and are believed to originate from undifferentiated mesenchymal cells in
the periodontal membrane; they are found only during the process of active
bone resorption. Presumably, the cytoplasm of the osteoclasts produces a
substance which dissolves the organic components of bone, while its mineral
Epithelial ——- ————
Test —~"-——~- —"'---*-" Principal
fibers
--‘-‘--2 '* Bundle bone
 
vessels
Cementum - I  V l  , ‘ ,‘ §
, . - ' “ I p . Blood
i i Interstitial
tissue
- —:~- - Principal
i fibers
I
-. — Bundle bone
.— -W
_. .r M .
Fig. 142.—Interstitia.l spaces in the periodontal membrane consist of loose connective
tissue and carry blood vessels and nerves. (0rban.=°)
contents are liberated and either removed in the tissue fluid or ingested
by macrophages. Wherever their cytoplasm lies in contact with bone,
hollows or grooves called “Howship’s lacunae,” or resorption lacunae,
are formed. When bone resorption ceases the osteoclasts disappear.
These cells are also active when resorption of the roots of teeth occurs
(see chapters on Bone and Shedding).
PERIODONTAL Il1EMBR.-\NE 183
Cementoblasts are connective tissue cells found on the surface of °°me’1*°b135t9
cementum betvveen the fibers. They are large cuboidal cells with spheroid
or ovoid nuclei, which are active in the formation of cementum (see chapter on Cementum). The cells have irregular, fingerlike projections which
fit around the fibers as they extend from the cementum.
The blood vessels, lymphatics, and nerves of the periodontal membrane Interstitial
are contained in spaces between the principal fiber bundles (Fig. 142). mm‘
They are surrounded by loose connective tissue (interstitial tissue) in
which fibroblasts and some histiocytes, undifferentiated niesenchymal
cells and lymphocytes are found.
Blood vessels
- Dentin
 
 
- -~ —— Blood vessels
‘ — ~~ Cementum
Periodontal
membrane
7 —— Alveolar bone
Blood vessels
Fig. 143.—Blood vessels enter the periodontal membrane through openings in the alveolar
bone. (Orban.=‘)
The blood supply of the periodontal membrane is derived from three Blood Vessels
sources: (1) blood vessels enter the periapical area together with the
blood vessels for the pulp; (2) vessels branching from the inter-alveolar
arteries pass into the membrane through openings in the wall of the alveolus (Fig. 143); they are the main source of supply; and (3) near the
Lymphatic:
NEWS!
184 om. msronoey AND nmmzvonoor
gingivae, the vessels of the periodontal membrane anastomose with vessels passing over the alveolar crest from the gingival tissue. The capillaries form a rich network in the periodontal membrane, intertwining
between the fibers.”
A network of lymphatic vessels, following the path of the blood vessels,
provides the lymph drainage of the periodontal membrane. The flow is
from the membrane toward and into the adjacent alveolar bone, continuing
to the lymph nodes.“ 23
Epithelial rests- -— -»
" "\-s-rt
 
cementum I: , _.. Alveolar bone
-.
at
l
o
r
Periodontal mem- '
.. __ J1  .
brane “ Q‘, ‘.17 ‘l ‘-7 ' '
Epithelial rests _
Asa:
Fig. 144.—-—Epithe!ta1 rests in the periodontal membrane.
Generally, the nerves of the periodontal membrane follow the path of the
blood vessels, both from the periapical area and from the interdental
and interradicular arteries through the alveolar wall. A rich plexus is
formed in the periodontal membrane. Three types of nerve endings are
found: one terminating in a knob-like swelling; another, forming loops or
PERIODONTAL MEMBRANE 185
rings around bundles of the principal fibers; lastly, free endings of fibers
branching from the main axon. These terminal branches are free of myelin
sheaths. Most of the nerve endings are receptors for proprioceptive stimuli
(deep sensibility). The slightest touch at the surface of the tooth is transmitted to the nerve endings through the medium of the periodontal membrane. All sense of localization is through the periodontal membrane. The
sense of touch is not impaired by removal of the apical parts of the membrane, as in root resection, nor by removal of its gingival portion (gingivectomy). As elsewhere in the body, fibers from the sympathetic system
supply the blood vessels of the periodontal membrane." 13
Cementnm
(tangential ‘
section) ‘ '
Network of 9""
epithelial '.
rests
Network of ‘
epithelial }
rests -f‘
. .—N tw k t ithelial rests in the periodontal membrane. (Tangential section
Fig 145 e or 0 ep almost parallel to root surface.)
In the periodontal membrane epithelial cells are found which, usually, Elgtglictfll-llm
lie close to the cementum but not in contact with it (Fig. 144). They
were first described by Malassez in 1885.“ Since then much research has
been done as to their origin, structural arrangement and function. They
186 omu. I-IISTOLOGY AND EMBRYOLOGY
are, undoubtedly, remnants of the epithelium which forms Hertwig’s
epithelial root sheath“ (see chapter on Tooth Development). At the time of
formation of cementum the continuous layer of epithelium, bordering the
dentin surface, breaks into strands which persist as a network parallel‘ to
the surface of the root (Fig. 145). Only in a surface View, as in sections
almost parallel to the root, can the true arrangement of these epithelial
Alveolar bone
Epithelial
rest
’ -’ Periodontal
Cementurn  membrane
Dentin _.
Blood vessel
Fig. 146.-—Long strand or epithelium in the periodontal membrane.
strands be seen.“ Cross or central sections through the tooth cut through
the strands of the network and, thus, only isolated nests of epithelial cells
appear in the sections. It is not clear whether the epithelial sheath
breaks up because of degeneration of the epithelial cells, or due to active
proliferation of the mesenchyme, or both. This disintegration of the
epithelium enables the connective tissue to approach the outer surface
of the dentin and to deposit cementum on its surface. The frequent
appearane of the epithelial rests, in long strands (Fig. 146) or in tu187
PI*ZRIOD0i\'TAL MEMBRANE
bules (_Fig. 147 l, has given rise to the assumption that they may have
endocrine function. Under pathologic conditions they may proliferate
and give rise to epithelial masses, associated with grannlomas, cysts, or
tumors of dental origin.
Epithelial. rest ', . —.~
   
— Cemenmblast
Principal nbers
Fig. 1-l7.—Pseuclo-tubular structure of epithelial rest in the periodontal membrane.
Calcified bodies, cementicles, are sometimes found in the tissues of the
periodontal membrane, especially in older persons. These bodies may
remain free in the connective tissue; they may fuse into large calcified
masses, or they may be joined with the cementum (Fig. 148). As the
cementum thickens with advancing age, it may envelop these bodies in
which event the cemcnticles become interstitial in location. When they
are adherent to the cementum they form excementoses. The origin of
these calcified bodies is not established; it IS presumed that degenerated
cells, usually epithelial, form the nidus for their calcification.
5. PEYSIOLOGIG CHANGES
Several studies of the width of the periodontal membrane, in“human
specimens, have been reportecl.“ 3- “r 12 All reports agree that the thickness of the periodontal membrane varies in different individuals, in dif
cementicles
Measurements
and changes
in Dimensions During
188 ORAL HISTOLOGY AND EMBRYOLOGY
ferent teeth in the same person, and in different locations on the same
tooth as is illustrated in Tables III to V1.5
TABLE III
THICKNESS or PERIODONTAL MEMBRANE or 172 TEETH FROM 15 HUMAN JAWS
AVERAGE AT AVERAGE AT AVERAGE AT AVERAGE OF‘
ALV. CREST MIDROOT APEX TOOTH
14:); MM MM MM
A es 11-10
83 teeth from 4 jaws 0 23 0 17 0 24 0 21
Ages 32-50
36 teeth from 5 jaws 0.20 0.14 0.19 0.18
Ages 51457 [ _
35 teeth from 5 jaws 0.17 0.12 0.16 0.1::
Table III shows that the width of the periodontal membrane decreases with age, and
that it is wider at the crest and apex than at the midroot. (Coo1idge.8)
TABLE IV
THICKNESS or PE1uoBoNTAL Trssuns IN VARYING CoNmTxoNs or FUNcTIoN
ALV. CREST MIDROOT APEX AVERAGE
MM. MM. MM. MM.
Teeth in heavy function
44 teeth from 8 jaws 0.20 0.14 0.19 0.18
Teeth not in function
20 teeth from 12 jaws 0.1-1 0.11 0.15 0.13
Embedded teeth
5 teeth 0.09 0.07 0.08 0.08
_Table IV shows that the width of the periodontal membrane is greater around teeth
which are subjected to heavy stress and decreases with loss of function. (Coolidgefi)
TABLE V
COMPARISON or THICKNESS or PERIODONTAL MEMBRANE or Foua INGISORS AND FOUR
MoLABs (SUBJECT AGED 11 YEARS)
ALv. CREST MIDROOT APEX AVERAGE
MM. MM. MM. MM.
4 incisors 0.33 0.25 0.28 0.29
4 molars 0.22 0.15 0.26 0.21
Table V demonstrates that there is a difierenee in the width of the membrane in
different teeth in the same individual. (Coolidge!)
TABLE VI
COMPARISON or PERIODONTAL MEMBRANE IN DIFFERENT LocAT1oNs AROUND THE SAME
'1‘ooTH (SUBJECT AGED 11 YEARS)
MESIAL DISTAL LABIAL LINGUAL
MM. MM. MM. MM.
Upper ri ht central incisor, mesial
and bial drift 0.12 0.24 0.12 _ 0.22
Upper left central incisor, no
drift 0.21 0.19 0.24 0.24
Upper right lateral incisor, distal
and labial drift 0.27 0.17 0.11 0.15
Table VI shows the variation in width of the mesial, distal, labial, and lingual sides
of the same tooth. (Coolidge!)
PERIODONTAL MEMBRANE 189
The measurements shown in the tables indicate that it is not feasible
to refer to an average figure of normal width of the periodontal membrane. Measurements of large number of cases range from 0.15 to 0.38
mm. The ‘fact that the periodontal membrane is the thilmest in the
m1ddle region of the root shows that the fulcrum of physiologic movement Is in this reglon. The thickness of the periodontal membrane seems
‘ Free cementicle
Alveolar bone
W’ i '_ Attached cementicle
' Periodontal membrane
Embedded cementicle
Fig. 148.—Cementicles in the periodontal membrane.
to be maintained by the ftmctional movements of the tooth. It is thinner
in flmctionless and embedded teeth. The fact that cementum and bone
do not fuse even in functionless teeth might be due to the fact that both
lose their growth potential if function is lost.
Physiologic movement of human teeth is characterized by their tendency
to migrate mesially in compensation for the wear at their contact points.”
In mesial migration a difference can be observed in the periodontal mem
Physiologic
Changes
Marrow
space
190 om. nrsronoor mo nmsmzonoer
brane in the distal and mesial areas (Fig. 149, A and B). On the distal
side of the tooth, the interstitial spaces with their blood vessels, lymph
spaces and nerves, appear in sections elliptic in contrast to those on the
mesial side that appear round.” Bone resorption on the mesial side of the
tooth sometimes opens marrow spaces which become continuous with the
periodontal membrane (Fig. 149, A). Frequently, however, the drift is so
gradual that bone formation in the marrow spaces keeps pace with the resorption on the periodontal membrane side, and the thickness of the alveolar bone is maintained. Due to the shift of the tooth, epithelial rests
may become incorporated in the bone on the side from which the tooth is
shifting.“
Alveolar - ' "
bone
Interstitial
space
Principal
fibers
 
Fig. 149.—Interstitie.1 spaces between the principal fiber bundles are round on the
pressure side (A) and elliptic on the tension side (3). Marrow spaces open up on the
pressure side and become interstitial spaces.
C : Cementum. D : Dentin.
6. CLINICAL CONSIDERATIONS
The complex functional relationship between the teeth and their supporting tissues brings about continuous structural changes during life.
Between the two extremes of occlusal trauma and loss of function there
“ i‘ Lamellated
bone
Bundle bone
l’l<}RIODON'l‘AL MEMBRANE 191
are many intermediate stages. In loss of function the periodontal membrane becomes narrower, due to decreased use of that particular tooth.‘ 1°’ 1‘
The regular arrangement of the principal fibers is lost and the periodontal
membrane appears as an irregularly arranged connective tissue. The
cementum becomes thicker but finally aplastic; it contains no Sharpey’s
fibers. Also, the alveolar bone is in an aplastic (inactive) state and lacks
Sharpey’s fibers (Fig. 150, B).
Bundle —
bone
~ lAlveola.r bone
_ ] (lamellated)
1;.  } - K
Periodontal  I‘ . .
membrane .1 g , .:l§
Bundle —--—---— . _
bone E P H do tal
‘ e o 11
membrane
Lamellated —— '5 .
Haversian “,
bone 1
   
 
59'
we
Fig‘. 150.—~Periodontal membrane or a. functioning (A) and nontunctioning (B) tooth.
In the functioning tooth the periodontal membrane is wide, principal fibers are present.
cementum (C) is thin; bundle bone with Sharpey's fibers. In the nonfunctioning tooth
the periodontal membrane is narrow, no principal fiber bundles are present. Cementu_m
is thick (0 and 0') ; alveolar bone is lamellated with no Shar-pey's fibers. D = Dentin.
For restorative dentistry the importance of these changes in structure is
obvious.” The supporting tissues of a tooth long out of function are
unable to carry the load suddenly placed upon the tooth by restoration.
This applies to bridge abutments, teeth opposing bridges or dentures, and
teeth used as anchorage for removable bridges. This may account for the
192 ORAL HISTOLOGY AND EMBRYOLOGY
inability of a patient to use a restoration immediately following its placement. Some time must elapse before the supporting tissues are again rearranged in response to the new functional demands. This may be termed
an adjustment period which, likewise, must be permitted to follow orthodontic treatment.
The stress, especially of a lateral type, often placed upon the supporting apparatus may be more than the tissue can tolerate. Sudden trauma
of the periodontal membrane, such as in accidental blows, condensing of
foil, rapid mechanical separation, may produce pathologic changes: fractures or resorption of the cementum, tears of the fibers, hemorrhage and
necrosis. The adjacent alveolar bone is resorbed and the periodontal
membrane thickened; the tooth becomes loose. When trauma is eliminated
repair may take place. For practical purposes it is important that, in the
construction of fillings and bridges, the occlusion be carefully considered,
and interference in lateral movements (cusp interference) avoided or eliminated. It is also important that missing teeth be immediately replaced to
avoid tipping and migration of remaining teeth; failure to do so may result
in loss of function and traumatism.
Orthodontic tooth movement depends upon bone resorption and bone
formation stimulated by properly regulated pressure and tension." These
stimuli are transmitted through the medium of the periodontal membrane.
If the movement of teeth is within physiologic limits (Which may vary
with the individual) the initial thinning of the periodontal membrane
on the pressure side, is compensated for by bone resorption, whereas
the thickening of the periodontal membrane, on the tension side, is balanced by bone apposition. If new bone formation is impaired by faulty
manipulation or disease, the periodontal membrane may become wider
and the tooth may loosen, or even be completely lost. Under the stimulus
of inflammation such as occurs in a dental granuloma the epithelial rests
of the periodontal membrane may proliferate to form a periodontal cyst
around the root end of the tooth. The dental granulomas are found frequently, and very careful studies“: 9“ have shown that 100 per cent
of dental granulomas have either proliferating or resting epithelium.
Since all dental granulomas contain this material, they must" all be considered as potential periodontal cysts.
References
1. Berkelbach van der Sprenkel, H.: Zur Neurologie des Zahnes (Neurology of
the Tooth), Ztschr. f. mikr.- anat. Forsch. 38: 1, 1935.
2. Black, G. V.: A Study of the Histological Characters of the Periosteum and
Peridental Membrane, Chicago, 1887, W. T. Keener Co.
3. Black, G. V.: The Fibers and Glands of the Peridental Membrane, Dental Cosmos 41: 101, 1899.
4. Box, K. F.: Evidence of Lymphatics in the Periodontium, J. Canad. D. A. 15:
8, 194.9.
5. Brunn, A. v.: Ueber die Ausdehnung des Schmelzorganes und seine Bedentung
fur die Zahnbildung (The Extension of the Enamel Organ and Its Significance in Tooth Development), Arch. f. mikr. Anat. 29: 367, 1887.
PERIODONTAL MEMBRANE 193
6. Bruszt, P.: Ueber die netzartige Anordnung des paradentalen Epithels (The
Network Arrangement of the Epithelium in the Periodontal Membrane),
Ztschr. f. Stomatol. 30: 679, 1932.
7. Coolidge, E. D.: Clinical Pathology and Treatment of the Dental Pulp and
_Periodontal Tissues, Philadelphia, 1939, Les. & Febiger.
8. Cool1g§e,11;3éi93'17‘he Thickness of the Human Periodontal Membrane, J. A. D. A.
. , .
9. Gottlieb, B.: Paradental Pyorrhoe und Alveolar atrophie (Paradental Pyorrhea
and Alveolar Atrophy), Fortschr. d. Zahnheilk. 2: 363, 1926.
9a. Hilli J.: The Epithelium in Dental Granulomata, J. Dent. Research 10: 323,
10. Kellner,  Histologische Befunde an antagonistenlosen Ziihnen (Histologic
Findings on Teeth Without Antagonists), Ztschr. f. Stomatol. 26: 271, 1928.
11. Klein, A.: Systematische Untersuchungen iiber die Periodontalbreite (Systematic Investigations on the Width of the Periodontal Membrane), Ztschr.
f. Stomatol. 26: 417, 1928.
12. Kronfeld, R.: A Case of Tooth Fracture, With Special Emphasis on Tissue Repair and Adaptation Following Traumatic Injury, J. Dent. Research 15:
429, 1935/6.
13. Lehner, J., and Plenk, H.: Die Ziihne (The Teeth), Moellendorfs Handbuch. d.
mikrosk. Anat. vol. 3, Berlin, 1936, J. Springer, p. 449.
14. Malassez, M. L.: Sur l’existence de masses epithéliales dans le ligament alveolodentaire (On the Existence of Epithelial Masses in the Periodontal
Membrane), Compt. rend. Soc. de biol. 36: 241, 1884.
15. McCrea, M. W.: Histologic Studies on the Occurrence of Epithelium in Dental
Granulomata, J. A. D. A. 24: 1133, 1937.
16. Noyes, F. B.: A Review of Work on the Lyniphatics of Dental Origin, J. A. D. A.
14: 714, 1927.
17. Oppenheim, A.: Human Tissue Response to Orthodontic Intervention of Short
and Long Duration, Am. J. Orthodont. & Oral Surg. 28: 263, 1942.
18. Orban, B.: Entwicklungsgeschichte und Histogenese (Embryology and Histogenesis), Fortschr. d. Zahnheilk. 3: 749, 1927.
19. Orban, B.: Biologic Considerations in Restorative Dentistry, J. A. D. A. 28:
1069 1941.
20. Orban, B’: A Contribution to the Knowledge of the Physiologic Changes in the
Periodontal Membrane, J. A. D. A. 16: 405, 1929.
21. Orban, B.: Dental Histology and Embryology, Philadelphia, 1929, P. Blakiston’s
Son & Co.
22. Robinson, H. B. G.: Some Clinical Aspects of Intra-Oral Age Changes, Geriatrics
2: 9 1947.
23. Schweitzer, G.: Die Lymphgeflisse des Zahnfieisches und der Ziihne (Lymph Vessels
of the Gingivae and Teeth), Arch. 1:‘. mikr. Anat. 69: 807, 1907; '74: 927,
1909.
24. Sicher, H.: Ban und Funktion des Fixationsapparates der Meerschweinchenmolaren ( tructure and Function of the Supporting Apparatus in the Teeth
of Guinea Pigs), Ztschr. f. Z. Stomatol. 21: 580,.1923. .
25. Weinmann, J. P.: Progress of Gingival Inflammation into the Supporting Structures of the Teeth, J. Periodont. 12: 71. 1941. _
26. Weinmann, J. P.: Bone Changes Related to Eruption of the Teeth, Angle
Orthodontist 11: 83, 1941.
CHAPTER VIII
MAXILLA AND MANDIBLE
(ALVEOLAR PROCESS)
1. DEVELOPIMEENT OI‘ MAXJILA AND MANDIBLE
2. DEVELOPMENT 01' ALVEOLAB PROCESS
3. STRUCTURE OI’ AINEOLAR PROCESS
4. PHYSIOLOGIC CHANGES DI '1‘H.'.l':‘. ALVEOLAR PROCESS
5. I'N'TE.'R.N.A.L RECONSTRUCTION OF BONE
6. CLINICAL CONSIDERATIONS
1. DEVELOPMENT OF MAXILLA AND MANDIBLE
In the beginning of the second month of fetal life the skull consists
of three parts: The chondrocranium, which is cartilaginous, comprises
the base of the skull with the otic and nasal capsules; the desmocranium,
which is ‘membranous, forms the lateral walls and roof of the brain case;
the appendicular or visceral part of the skull consists of the cartilaginous
skeletal rods of the branehial arches.
The bones of the skull develop either by endochondral ossification, replacing the cartilage, or by intramembranous ossification in the mesenchyme. Intramembranous bone may develop in close proximity to cartilaginous parts of the skull, or directly in the desmocranium, the membranous capsule of the brain (Fig. 151).
The endochondral bones are the bones of the base of the skull: ethmoidal bone; inferior concha (turbinate bone); body, lesser wings, basal
part of greater wings, and lateral lamella of pterygoid process of the
sphenoid bone; petrosal part of temporal bone; basilar, lateral, and lower
part of squamous portion of occipital bone. The following bones develop
in the desmocranium: frontal bones; parietal bones; squamous and tympanic parts of temporal bone; parts of the greater wings, and medial
lamina of pterygoid process of sphenoid bone; upper part of squamous
portion of occipital bone. All the bones of the upper face develop by intramembranous ossification; most of them close to the cartilage of the nasal
capsule. The mandible develops as intramembranous bone, lateral to the
cartilage of the mandibular arch. This cartilage, Mecke1’s cartilage, is
in its proximal parts the primordium for two of the auditory ossicles:
incus (anvil) and malleus (hammer). The third auditory ossicle, the
stapes (stirrup), develops from the proximal part of the skeleton in the
second branchial arch which then gives rise to the styloid process, stylohyoid ligament and part of the hyoid bone which is completed by the
derivatives of the third arch. The fourth and fifth arches form the
skeleton of the larynx.
First draft submitted by Harry Sicher and Joseph P. Welnmanu.
194
— — ~ - — — — — Greater win of
F '  sphenoid bgone
Medial plate of
pterygoid
A _ process
' 1 Frontal bone
I
Parietal bone 1"‘
i
5
3 xi ‘,2
i  v _/— Nasal capsule
3 1 _— Nasal bone
1 _ 4' .7 _ —_ Lacrlmal bone
l ‘ \ -ll ' es .
~ ‘ “rs .\ «<T'« . = ~; Maxilla
* . _ A.» ‘ was... —
E j (4 LT zygomatic bone
Occipitai —————.—- _
suuama I 0 k ‘ l - 7 ‘.__ Mandible
\ ‘Ir
Lateral part of ;’ \ \
occipital bone . \ Tympanic bone
Petrosal bone '——-é-—-?———’ \ Sm ‘d
0: process
Squama of ' '
temporal bone .
Medial plate or‘ _ Water Wins 0‘
pm-ygoid - sphenoid bone
process
Frontal bone
Parietal bone
4
I ‘ '
Nasal bone L... ‘
/
Nasal capsule —  'A
Lacrimal bone — _ 
‘ ' W‘ .
Maxilla ‘——— _.__;__ ",. j' .
,  ‘H
Palatine bone  _
l -  ' Occipltul
Mandible  squama
" ‘Ui. I
Meckel's ‘ I
cartilage . ‘ / v p , ‘ ,'
Hammer. , [ " . Pel;osa.l bone
‘ » Min 1
Styloid process ' ~ -— -—— --—--—‘--*-‘
Fig. 151.—Reconstruction of the sl_£u1l ot a. human embryo 80 mm. long. gtarfilagez
green. Intramembranous bones: punk. Endochondral bones: white. (Sxeher and
Tandlerfl)
A. Right lateral view.
B. Left lateral view after removal of left int:-amernbranous bones.
MAXILLA. AND MANDIBLE 195
The human maxillary bone is formed, on either side, from the union
of two bones, premaxilla and maxilla, which remain separate in most
other mammals. In man the two bones begin to fuse at the end of the
second month of fetal life. The line of fusion is indicated in young individuals by the intermaxillary (incisive) suture on the hard palate.
Developing
tooth
Inferior Bone
alveolar (mandible)
nerve
Meckel’s
cartilage
man 1 e g
I(Bone d_bI )
Fig. 152.——Deve1opment of the mandible as intramembranous hone lateral to Meckers
cartilage (human embryo 45 mm. long).
The maxilla proper develops from ‘one center of ossification which
appears in the sixth week. The bone is then‘ situated on the lateral side
of the cartilaginous nasal capsule and forms the wall of the nasal cavity
when the cartilage has disappeared. The prernaxilla, or os incisivum,
has two independent centers of ossification. Ultimately, it forms that
part of the maxilla which icarriesthe two incisors, the anterior part of
the palatine process, the rim of the piriform aperture, and part of the
frontal processfi“
Maxilla.
196 ORAL HISTOLOGY AND EMBRYOLOGY
   
' Connective
tissue
‘ Cartilage
Fig. 153.—Deve1opment of mandibular symphysis.
A. Newborn infant: symphysis wide open: mental ossicle (roentgenogram).
B. Child 9 months: symphysis partly closed; mental ossicies fused to mandible
(roentgenogram).
0. Frontal section through mandibular symphysis of newborn infant. Connective
tissue in midline is transformed into cartilage on either side which is later replaced
by bone.
MAXJLLA AND MANDBLE 197
The mandible makes its appearance as a bilateral structure in the sixth
week of fetal life and is a thin plate of bone lateral to, and at some distance from, Meckel’s cartilage (Fig. 152). The latter is a cylindrical rod
of cartilage; its proximal end (close to the base of the skull) is continuous with the hammer, and is in contact with the anvil. Its distal end
(at the midline) is bent upwards and is in contact with the cartilage of the
other side (Fig. 151). The greater part of Meckel’s cartilage disappears
without contributing to the formation of the bone of the mandible. Only
a small part of the cartilage, some distance from the midline, is the site
of endochondral ossification. Here, it calcifies and is invaded and destroyed by connective tissue and replaced by bone. Throughout fetal
life the mandible is a paired bone the two halves of which are joined in
the midline by fibrocartilage. This synchondrosis is called mandibular
symphysis. The cartilage at the symphysis is not derived from Meckel’s
cartilage but differentiates from the connective tissue in the midline. In
it small irregular bones, known as the mental ossicles, develop and, at
the end of the first year, fuse with the mandibular body. At the same
time the two halves of the mandible unite by ossification of the symphysial
fibrocartilage (Fig. 153).
2. DEVELOPMENT OF THE ALVEOLAB. PROCESS
Near the end of the second month of fetal life, the bones of maxilla and
mandible form a groove which is open towards the surface of the oral
cavity (Fig. 152). In a later stage the tooth germs are contained in this
groove which also includes the dental nerves and vessels. Gradually,
bony septa develop between the adjacent tooth germs, and much later the
primitive mandibular canal is separated from the dental crypts by a horizontal plate of bone.
An alveolar process in the strict sense of the word develops only during
the eruption of the teeth. It is important to realize that during growth
part of the alveolar process is gradually incorporated into the maxillary
or mandibular body while it grows at a fairly rapid rate at its free
borders. During the period of rapid growth, a special tissue may develop at the alveolar crest. Since this tissue combines characteristics of
cartilage and bone, it is called ch/(android bone (Fig. 154).
3. STRUCTURE OF THE ALVEOLAB. PROCESS
The alveolar process may be defined as that part of the maxilla and
mandible which forms and supports the sockets of the teeth (Fig. 155).
Anatomically, no distinct boundary exists between the body of the
maxilla or mandible and their respective alveolar processes. In some
places the alveolar process is fused with and partly masked by bone
which is not functionally related to the teeth. In the anterior part of the
maxilla the palatine process fuses with the alveolar process. In the pos
Mandible
198 ORAL HISTOLOGY AND EMBRYOLOGY
terior part of the mandible the oblique line is superimposed upon the
bone of the alveolar process (Figs. 155, D and E’ ) .
As a result of its adaptation to function, two parts of the alveolar process
can be distinguished. The first consists of a thin lamella of bone which
surrounds the root of the tooth and gives attachment to principal fibers
of the periodontal membrane. This is the alveolar bone proper. The
:v'.>--—'‘ “-4
Proliferation
zone at
alveolar
crest
 
   
 
 
Chondroid  —
bone in
 
*-vie,
Chondroid  *--—'
bone - .
Uhwl 11    so 1;‘? V
‘ Resorptlon
ii
Fig‘. 154.—Vex-tical growth of mandible at alveolar crest. Formation of chontlrold bone
which is replaced by typical bone.
second part is the bone which surrounds the alveolar bone and gives support to the socket. This has been called supporting bone.” The latter, in
turn, consists of two parts: the compact bone (cortical plate) forming
the vestibular and oral plates of the alveolar processes, and the spongy
bone between these plates and the alveolar bone proper (Fig. 155).
The cortical plates, continuous with the compact layers of maxillary
and mandibular body, are generally much thinner in the maxilla than in
the mandible. They are thickest in the bicuspid and molar region of the
MAXILLA AND MANDIBLE 199
Fig. 155.—Gross relations of alveolar processes:
A. Horizontal section through upper alveolar process. _,.
B. Labiollngual section through upper lateral incisor.
0. Labiolingual section through lower cuspid.
D. Labiolingual section through lower second molar.
E. Labiolingual section through lower third molar. (Sicher and Tandlerfl)
Fig. 156.—Dia.gra.mma.tic illustration of the relation between the cemento-enamel
junction of adjacent teeth and the shape of the crests of the alveolar septa. (Ritchey,
B., and Orban, B.“".)
200 ORAL HISTOLOGY AND EMBRYOLOGY
lower jaw, especially on the buccal side. In the maxilla the outer cortical plate is perforated by many small openings through which blood and
lymph vessels pass. In the lower jaw the cortical bone of the alveolar
process is dense and, occasionally, shows small foramina. In the region
of the anterior teeth of both jaws the supporting bone is, usually, very
thin. No spongy bone is found here and the cortical plate is fused with
the alveolar bone proper (Figs. 155, B and C).
Circumferential lamel lae
Reversal line
Haversian
sytem
Interstitial -—
lamellae
g Resting line
Fig. 157A.-—Appositiona.1 growth of mandible by formation of circumferential lamellae.
Ehetshe are replaced by Haversian bone; remnants of circumferential lamellae in the
ep .
The outline of the crest of the intraalveolar septa, as they appear in
the roentgenogram, are dependent upon the position of the adjacent
teeth. In a healthy mouth the distance between the cemento-enamel
junction and the free border of the alveolar bone proper is fairly constant. In consequence the alveolar crest is often oblique if the neighboring teeth are inclined. In the majority of individuals the inclination
is most pronounced in the premolar and molar region, the teeth being
MAXILLA AND MANDIBLE 201
tipped mesially. Then, the ceniento-enamel junction of the mesial tooth
is situated in a more occlusal plane than that of the distal tooth and the
alveolar crest, therefore, slopes distally (Fig. 156).
The interdental and interradicular septa contain the perforating canals
of Zuckerkandl and Hiischfeld, which house the interdental and interradicular arteries, veins, lymph vessels and nerves.
 
 
PrinclpaJ
flgyers
o
perio- -I Lgmellated
' one
\.
BK
' "" Haversian
system
Fig. 157B.—Bundle bone and I-Iaversian bone on the distal alveolar wall (silver impregnation).
Histologically, the cortical plates consist of longitudinal lamellae and
Haversian systems (Fig. 157A) . In the lower jaw circumferential or basic
lamellae reach from the body of the mandible into the cortical plates.
The trabeculae of the spongy bone of the alveolar process are placed
in the direction of the stresses to which it is subjected as a result
of mastication (Fig. 158). The functional adaptation of this spongy
bone is particularly evident between the alveoli of molars where the
202 ORAL HISTOLOGY AND EMBRYOLOGY
trabeculae show a parallel horizontal arrangement. From the apical part
of the socket of lower molars trabeculae are, sometimes, seen radiating in
a slightly distal direction. These trabeculae are less prominent in the
upper jaw, because of the proximity of the nasal cavity and maxillary
Fig. 158.—Suppox-ting trabeculae between alveoli.
A. Roentgenogram or a. mandible.
B. Meslodistal section through mandibular molars showing alveolar bone proper and
supporting bone.
sinus. The marrow spaces in the alveolar process may contain hemopoietic, but, usually, contain fatty marrow. In the condyloid process,
angle of mandible, maxillary tuberosity, and other foci cellular marrow
is frequently found, even in adults." 1‘
MAXILLA AND MANDIBLE 203
The alveolar bone proper which forms the inner wall of the socket
(Fig. 158) is perforated by many openings which carry branches of the
interalveolar nerves and blood vessels into the periodontal membrane
(see chapter on Periodontal Membrane). It is called cribriform plate or
lamina dura ; the latter term refers to the dense appearance of the alveolar bone proper in roentgenograms. The alveolar bone proper consists
partly of lamellated, partly of bundle bone. The lamellae of the lamellated bone are arranged roughly parallel to the surface of the adjacent
marrow spaces, others form Haversian systems. Bundle bone is that
bone to which the principal fibers of the periodontal membrane are anchored. The term bundle bone was chosen because the bundles of the
principal fibers continue into the bone as Sharpey’s fibers. The bundle
bone is characterized by the scarcity of the fibrils in the intercellular
substance. These fibrils, moreover, are all arranged at right angles to the
Sharpey’s fibers. The bundle bone appears much lighter in preparations
stained with silver than lamellated bone because of the reduced number
of fibrils (Fig. 157B). Because all the fibrils run in the same direction,
the bundle bone is not lamellated.
4. PHYSIOLOGIG CHANGES IN THE ALVEOLAR PROCESS
The internal structure of bone is adapted to mechanical stresses. It
changes continuously during growth and alteration of functional stresses.
In the jaws this change takes place according to the growth, eruption,
wear and loss of teeth. With advancing age parts of the bone and the
osteocytes lose their vitality, and regeneration has to follow. All these
processes are made possible only by a coordination of destructive and
formative activities. Specialized cells, the osteoclasts, have the function
of eliminating overaged bony tissue or bone which is no longer adapted
to mechanical stresses.
Osteoclasts are multinucleated giant cells (Fig. 159, A). The number of
nuclei in one cell may rise to a dozen or more. However, it is to be noted
that, occasionally, uninuclear osteoclasts are found. The nuclei are
vesicular, showing a prominent nucleolus and little chromatin. The cell
body is irregularly oval or club-shaped and may show many branching
processes. In general, osteoclasts are found in bay-like grooves in the bone
which are called Howship’s lacunae; they are hollowed out by the activity of the osteoclasts. The cytoplasm which is in contact with the
bone is distinctly striated. These striations have been explained as the
expression of resorptive activity of these cells. The osteoclasts seem to
produce a proteolytic enzyme which destroys or dissolves the organic constituents of the bone matrix. The mineral salts thus liberated are removed in the tissue fluid or ingested by macrophages. A decaleification
of bone during life has often been claimed but has never been demonstrated.
Osteoclasts differentiate from young fibroblasts or undifferentiated mescnchymal cells probably by division of nuclei without the usual division of
204 ORAL msronoev AND EMBRYOLOGY
the cytoplasm. Some investigators believe that the osteoclasts may arise by
fusion of osteoblasts, others believe that they difierentiate from endothelial
cells of capillaries. The stimulus which leads to the diiferentiation of mesenchymal cells into osteoblasts or osteoclasts is not known. Osteoclastic
resorption of bone is partly genetically patterned, partly functionally
determined. Also overaged bone seems to stimulate the differentiation
of osteoclasts‘ possibly by chemical changes that are the consequence of
degeneration and final necrosis of the osteocytes.
New bone is produced by the activity of osteoblasts (Fig. 159, B). These
cells also difierentiate from fibroblasts or the undifferentiated mesenchymal
   
.i.«r~$
 
-u.0m
 
E
as
an’
Fig. 159.—Resorption and apposition of bone.
A. Osteoclasts in Howship’s lacunae
B. Osteoblasts al 11 a ho tr b la. La. 1 1
fomafion (high magngflmflolxbe. a ecu yer o osteo 1! tissue as a sign of bone
- cells of the connective tissue. Functioning osteoblasts are arranged along
the surface of the growing bone in a continuous layer, similar in appearance to a cuboidal epithelium.
The osteoblasts are said to produce the bone matrix by secretion. The
matrix is at first devoid of mineral salts. At this stage, it is termed
—--———-up-‘ I. ‘ , ‘ Osteoblas
MAXJLLA AND MANDIBLE 205
osteoid tissue. It is still undecided Whether the fibrils of the matrix are connective tissue fibrils which become embedded in the substance of the matrix,
or whether the fibrils difierentiate in the primarily amorphous matrix. If a
certain amount of matrix is produced some of the osteoblasts become embedded in the matrix, and are known as osteocytes. Normally, the organic
matrix calcifies immediately after formation?’ 1‘ The ratio of organic and
inorganic substance in dry bone is approximately 1 :2. (See Table in
chapter on Enamel for complete data.)
5. INTERNAL RECONSTRUCTION OF BONE
The bone in the alveolar process is identical to bone elsewhere in the body
and is in a constant state of flux. During the growth of jaw bones, bone
is deposited on the outer surfaces of the cortical plates.. The changes
are most readily observed in the mandible, with its thick cortical
layer of compact bone. Here bone is deposited in the shape of basic
or circumferential lamellae (Fig. 157A). When the lamellae reach a certain thickness they are replaced from the inside by Haversian bone. This
is a reconstruction in accordance with the functional and nutritional demands of the bone. In the Haversian canals, closest to the surface, osteoclasts differentiate and resorb the Haversian lamellae, and part of the circumferential lamellae. After a time the resorption ceases and new bone is
apposed onto the old. The scalloped outline of Howsh:1p’s lacunae which
turn their convexity toward the old bone remains visible as a darkly stained
cementing line, sometimes called the “reversal” line. This is in contrast to those cementing lines which seem to correspond to a rest period
in an otherwise continuous process of bone apposition; they are called resting lines (Fig. 157A). Resting and reversal lines are found between
layers of bone of varying age.
Another type of internal reconstruction is the replacement of compact
bone by spongy bone. This can be observed following the growth of the
bone when the compact outer layer has expanded to a certain extent.
The process of destruction can be observed from a section through bone,
by noting the remnants of partially destroyed Haversian systems, or
partially destroyed basic lamellae which form the interstitial lamellae of
the compact bone.
Wherever a muscle, tendon, ligament, or periodontal membrane is attached to the surface of bone, Sharpey’s fibers can be seen penetrating
the basic lamellae. During replacement of the latter by Haversian systems fragments of bone containing Sharpey’s fibers remain in the deeper
layers. Thus, the presence of interstitial lamellae containing Sharpey’s
fibers indicates the former level of the surface.“
Alterations in the structure of the alveolar bone are of great importance in connection with the physiologic movements of the teeth. Thee
movements are directed mesio-occlusally. At the alveolar fundus the con206 ow. HISTOLOGY AND nnmzvonoer
tinual apposition of bone can be recognized by resting lines separating
parallel lavers of bundle bone; when the bundle bone has reached a cer
tain thickness it is partly resorbed from the marrow spaces and then replaced by Haversian bone or trabeculae. The presence of bundle bone indicates the level at which the alveolar fundus was previously situated. During the mesial drift of a tooth, bone is apposed on the distal, and resorbed
 
:4; .
. - ii‘ , ' "i L ‘I
‘ I
.1‘-pl:  __ ‘
‘L’ ’,  Cementum
‘3 V _ 1 fr
;-«-3.  '* ‘
‘  *‘ R ‘ "  ‘.
i. ‘ _ t l ‘
‘ v —- ._.- ———1>-'--—-L Resorptlon
R‘-' L .,z' a
' ; ‘ :t:-‘; v  ,1??  ~-  Lamellated
  ‘ ‘F bone
, is _
lg i_ -‘_ - _- —— -~—-—. Periodontal
3". membrane
:3. «
sat:
lg)!’ ‘/
‘ _ 9 Resorptlon
__‘__-_ _ _ _ _ *9
A B.
Fig. 160.-—-Meslel drift.
.4. Appositlon of bundle bone on the distal alveolar wall.
3. Resorption of bone on the mesial alveolar wall. (Weinmann.”)
on the mesial, alveolar wall (Fig. 160). The distal Wall is made up almost
entirely of bundle bone. However, the osteoclasts in the adjacent marrow
spaces remove part of the bundle bone when it reaches a certain thickness.
In its place lamellated bone is laid down (Fig. 157B).
On the mesial alveolar wall of a drifting tooth signs of active resorption
are observed by the presence of Ho\vship’s lacunae containing osteoclasts (Fig. 160). Bundle bone on this side is present in relatively few
areas. When found, it usually forms merely a thin layer (Fig. 161). This
is due to the fact that the mesial drift of a tooth occurs in a rocking moMAXILLA AND MANDIBLE 207
tion. Thus, resorption does not involve the entire mesial surface of the
alveolus at one and the same time. Moreover, periods of resorption
alternate with periods of rest and repair. It is during these rest
periods that bundle bone is formed, and detached periodontal membrane fibers are again secured. It is this alternating action that stabilizes the periodontal membrane attachment on that side of the tooth.
Islands of bundle bone are separated from the lamellated bone by reversal
lines which turn their convexities toward the lamellated bone (Fig. 161).
Bundle bone
Dentin  1 ' ~  ‘ —~——- Reversal line
Lamellated bone
Periodontal membrane
' " *" Reversal line
Bundle bone
’,1
__ - wan istin fly or simple lamellated bone; islands of
Fig‘ 161 bfiilhslglbghgecfigghoringcggisnd giuoé-s of the periodontal membrane.
6. CLINICAL CONSIDERATIONS
Bone is one of the hardest tissues of the human body. Nevertheless,
bone is, biologically, a highly plastic tissue. Where bone is covered by a
vascularized connective tissue, it is exceedingly sensitive to pressure
whereas tension acts, generally, as a stimulus to the production of new
bone. It is this biologic plasticity which enables the orthodontist to move
208 ORAL HISTOLOGY AND EMBRYOLOGY
teeth Without disrupting their relations to the alveolar bone. Bone is resorbed on the side of pressure, and apposed on the side of 1361131011; thus
allowing the entire alveolus to shift with the tooth.
The adaptation of bone structure to functional stresses is quantitative
as Well as qualitative, namely, decreased function leads to a decrease in
the bulk of the bone substance. This can be observed in the supporting
bone of teeth which have lost their antagonists.’ Here, the spongy bone
around the alveolus shows marked rarefication: the bone trabeculae are
> ;_=; '- _ :75-;_"'  '_“."t’:  .
A. ' B.
Fig. 162.-—Osteoporosis of alveolar process caused by inactivity or the tooth _which has
no antagonist Labiolingual sections through upper molars of the same individual:
4. Disappearance of bony trabeculae after loss of function; plane or mesiobuccal
root; alveolar bone proper remains intact.
3. Normal spongy bone in the plane of mesiobuccal root or functioning tooth.
less numerous and very thin (Fig. 162). The alveolar bone proper, however, is generally well preserved because it continues to receive some
stimuli by the tension exerted upon it via principal fibers of the periodontal membrane. A similar distinction in the behavior of alveolar and
supporting bone can be seen in certain endocrine disturbances and vitamin deficienciesli 2 (Fig. 163).
The independence of the growth mechanisms of the upper and lower
jaws accounts for their frequent variations in relative size. Trauma or
inflammatory processes can destroy the condylar growth center of the
MAXILLA AND MANDIBLE 209
mandible on one or both sides. I-Iyperfunction of the hypophysis, leading
to acromegaly, causes a characteristic overgrowth of the mandible, even
at a time when sutural growth has ceased.“ The maxillary growth in
such cases is confined to bone apposition on the surfaces, because a general enlargement of the upper face is impossible.
During healing of fractures or extraction wounds, an embryonic type
of bone is formed which only later is replaced by mature bone. The
embryonic bone, immature or coarse fibrillar bone, is characterized by
Fig. 163.—Dlflerence in reaction of alveolar bone and supporting bone:
4. Normal bone structure in bifurcation of dog's tooth.
B. Osteoporosis of supporting bone in bifurcation ot dog’s tooth. Dog fed on diet
deficient in nicotinic acid. Alveolar bone proper intact. (Similar conditions could be
produced by other dietary deficiencies.) (Courtesy H. Becks,’ University of California.)
the great number, great size, and irregular arrangement of the osteocytes
and the irregular course of its fibrils. The greater number of cells and
the reduced volume of calcified intercellular substance renders this immature bone more radiolucent than mature bone. This explains why
bony callus cannot be seen in roentgenograms at a time when histologic
examination of a fracture reveals a well-developed union between the
210 omu. HISTOLOGY AND EMBRYOLOGY
fragments and why a socket after an extraction wound appears to be empty
at a time when it is almost filled with immature bone. The visibility in
radiograms lags two to three weeks behind actual formation of new bone.
References
1. Becks, H.: Dangerous Consequences of Vitamin D Overdoage on Dental and
Paradental Structures, J . A. D. A. 29: 1947, 1942. _ _
2. Becks, H.: The Efiect of Deficiencies of the Filtrate Fraction of the Vitamin
B C0mp1eX42 and Nicotinic Acid on Teeth and Oral Structures, J . Periodont.
13: 18 19 .
3. Bloom, W.: and Bloom, M. A.: Calcification and Ossification. Calcification of
Developing Bones in Embryonic and Newborn Rats, Anat. Rec. 78: 497,
1940.
4. Box, H. K.: Red Bone Marrow in Human Jaws, Toronto, 1933, University of
Toronto Press.
5. Breitner, C.: Bone Changes Resulting From Experimental Orthodontic Treatment, Am. J. Orthodont. & Oral Surg. 26: 521, 1940.
6. Brodie, A. G.: Some Recent Observations on the Growth of the Mandible, Angle
Orthodontist 10: 63, 1940.
7. Brodie, A. G.: On the Growth Pattern of the Human Head From the Third
Month to the Eighth Year of Life, Am. J. Anat. 68: 209, 194].
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Therapy of Alveolar Pyorrhea), Oesterr. Ztschr. f. Stomatol. 18: 59, 1920.
9. Kellner, E.: Histologische Befunde an antagonistenlosen Zfihnen (Histological
Findings on Teeth Without Antagonists), Ztschr. f. Stomatol. 26: 271, 1928.
10. Lehner, J., and Plenk, H.: Die Ziihne (The Teeth), Moellendorfis Handbueh d.
mikrosk. Anat., vol. 3, Berlin, 1936, Julius Springer.
11. McLean, F. 0., and Bloom, W.: Calcification and Ossification. Calcification in
, Normal Growing Bone, Anat. Rec. 78: 333, 1940.
12. Orban, B.: Dental Histology and Embryology, ed. 1, Chicago, 1928, Rogers
Printing Co.
13. Orban, B.: A Contribution to the Knowledge of the Physiologic Changes in the
Periodontal Membrane, J. A. D. A. 16: 405, 1929.
139.. Ritchey, B., and Orban, B.: The Crests of the Interdental Alveolar Septa,
J. Period. 1953 (in print).
14. Sclmfier, J .: Die Verkniicherimg des Unterkiefers (0ssification of the Mandible),
Arch. f. mikr. Anat. 32: 266, 1888.
15. Schoenbaner, F.: Histologische Befunde bei Kieferosteomyelitis (Histologic
Findings in Osteomyehtis of the Jaw), Ztschr. f. Stomatol. 35: 820, 1937.
16. Schour, I., and Massler, M.: Endocrines and Dentistry, J. A. D. A. 30: 595, 763,
943, 194.3.
17. Sicher, EL, and Tandler, J.: Anatomie fiir Zahniirzte (Anatomy for Dentists),
Vienna, 1928, Julius Springer.
18. Weinmann, J. P.: Das Knochenbild bei Stiirungen der physiologischen Wanderung der Z§.hne (Bone in Disturbances of the Physiologic Mesial Drift),
Ztschr. f. Stomatol. 24: 397, 1926.
19. Weinmann, J. P.: Bone Changes Related to Eruption of the Teeth, Angle Orthodentist 11: 83, 1941.
19a. Woo, Fu-Kang: Ossification on Growth of the Human Maxilla, Premaxilla
and Palate Bone, Anat. Rec. 105: 737, 1949.
20. Zawisch-Ossenitz, C. v.: Die basophilen Inseln und andere basophile Elemente
im menschlichen Knochen (Basophilic Islands and Other Basophilic Elements
in Human Bone), Ztschr. f. mikr.-Anat. Forsch. 18: 393, 1929.
CHAPTER IX
THE ORAL MUCOUS MEMBRANE
1. GENERAL CHARACTERISTICS
2. TRANSITION BETWEEN SKIN AND MUCOUS MEMBRANE
3. SUBDIVISIONS 01‘ THE ORAL MUCOSA
A. Mastlcatory Mucosa
a. Gingiva
b. Epithelial Attachment and Gingival Sulcus
c. Hard Palate
B. Lining mucosa.
a. Lip and Cheek
b. Vestibular Fornix and Alveolar Mucosa
c. Sublingual Mucosa and Mucous Membrane of the Interior Surface
of the Tongue
(1. Soft Palate
C. Specialized Mucosa or Dorsal Lingual Mucosa
4. CLINICAL CONSIDERATIONS
1. GENERAL CHARACTERISTICS
The oral cavity, as the first part of the digestive tract, serves a variety
of functions. It is both the portal of entry and the place of mastication
of food. It contains the taste organs. Entering it is the fluid saliva
which not only lubricates the food to facilitate swallowing, but also contains enzymes which initiate digestion. The oral cavity is lined throughout by a mucous membrane. This term designates the lining of any
body cavity which communicates with the outside.
The morphologic structure of the mucous membrane varies in the
different areas of the oral cavity in accordance with the functions of
specific zones and the mechanical influences which bear upon them.
Around the teeth and on the hard palate, for example, the mucous membrane is exposed to mechanical influences in the mastication of rough
and hard food, whereas, on the floor of the mouth, it is largely protected
by the tongue. This is the reason why the mucous membrane around
the teeth and on the hard palate varies in structure from that of the
floor of the mouth, cheeks, and lips.
The mucous membrane is attached to the underlying structures by a
layer of connective tissue, the submucosa, which varies in character in
different areas. The oral mucous membrane is composed of two layers;
the surface epithelium and the lamina propria (Fig. 164). A basement
membrane separates the lamina propria from the stratified squamous
First dratt submitted by Balint Orban and Harry slcher.
211
212 om rusronoer AND EMBRYOLOGY
epithelium. The epithelium consists of several layers of cells which flatten out as they approach the surface. All these cells are connected with
each ‘other by intercellular bridges. The innermost is the basal layer,
consisting of cuboid cells which effect the attachment of the epithelium
to the basement membrane of the connective tissue by numerous short
basal processes that fit into grooves of the lamina propria. The more
superficial cells form the so-called “prickle-cell” layer which consists
of several layers of polyhedral cells. The term is derived from the fact
Keratlnous layer
Granular layer Opening 0! duct
Prickle cell layer
Basal layer
Basement
membrane ‘
— Subepithelial
Capillaries M’-We Plexus
Lamina propria.
Nerve
Submucous layer
Artery
Vein
Periosteum
Bone
Fig. 164.-—Diagra.mmatic drawing of oral mucous membrane (epithelium and lamina
propria. and submucosa).
that the intercellular spaces are wide and the intercellular bridges prominent, thus giving the isolated cell a spinous appearance. Basal and
prickle-cell layers are sometimes referred to as germinative layers. Regeneration of epithelial cells, lost at the surface, occurs by mitotic division of cells in the deepest layers.
The cells of the prickle-cell layer flatten and pass into first the granular layer and then the keratinous layer as they move toward the surface.
The cells of the granular layer contain fine kerato-hyalin granules which
are basophil and stain blue in hematoxylin-eosin preparation. The nuclei
ORAL MUGOUS MEMBRANE 213
of the flattened cells are pyknotic. The keratinous layer is characterized
by its acidophil nature; here the nuclei have mostly disappeared. The
structure of the granular and keratinous layers varies in the diiferent
regions of the oral cavity. A stratum lucidum, such as is seen in regions
of the skin where hornification is abundant, is, as a rule, missing in the
oral mucosa.
The lamina propria is a dense connective tissue layer of variable thickness. Its papillae, which indent the epithelium, carry both blood
vessels and nerves. Some of the latter actually pass into the epithelium.
The papillae of the lamina propria vary considerably in length and width
in different areas. The inward epithelial projections between the papillae
are described as epithelial pegs, because of their appearance in sections.
They are in reality, however, a continuous network of epithelial ridges.
The arrangement of the papillae increases the area of contact between
lamina propria and epithelium, and facilitates the exchange of material
between blood vessels and epithelium. The presence of papillae permits
the subdivision of the lamina propria into the outer papillary, and the
deeper reticular layer.
The submucosa consists of connective tissue of varying thickness and
density. It attaches the mucous membrane to the underlying structures.
Whether this attachment is loose or firm depends upon the character
of the submucosa. Glands, blood vessels, nerves, and also adipose tissue
are present in this layer. It is in the submucosa that the larger arteries divide into smaller branches which enter the lamina propria. Here they
again divide, to form a subepithelial capillary network in the papillae. The
veins originating from the capillary network follow the course of the
arteries. The blood vessels are accompanied by a rich network of lymph
vessels which play an important part in the drainage of the mucous membranes. The sensory nerves of the mucous membrane traverse the submucosa. These nerve fibers are myelinated but lose their myelin sheath
in the mucous membrane before splitting into their end arborizations.
Sensory nerve endings of various types are found in the papillae; some
of the fibers enter the epithelium where they terminate in contact with
the epithelial cells as free nerve endings. The blood vessels are accompanied by nonmyelinated visceral nerve fibers which supply their smooth
muscles; other visceral fibers supply the glands.
The oral cavity can be divided into two parts: the vestibulum oris*
(vestibule) and the cavum oris proprium (oral cavity proper). The vestibule is that part of the oral cavity proper which is bounded by the lips
and cheeks on the outer side, and by the teeth and alveolar ridges on the
inner. The oral cavity lies within the dental arches and bones of the
jaw, being limited posteriorly toward the pharynx by the anterior pillars
of the fauces.
‘The use of the terms vestibular instead of labial and buccal, and oral instead of
lingual or palatal, is suggested.
214 ORAL HISTOLOGY AND EMBRYOLOGY
2. TRANSITION BETWEEN SKIN AND MUCOUS MEMBRANE
The transitional zone between the skin covering the outer surface of
the lip and the true mucous membrane lining the inner surface, is the
red area or Vermilion border of the lip. It is present in man only (Fig.
165). The skin of the lip is covered by a hornified epithelium of moderate thickness; the papillae of the connective tissue are few and short.
Many sebaceous glands are‘ found in connection with the hairs; sweat
glands occur between them. The epithelium is typically stratified and
squamous with a rather thick hornified layer. The transitional region
 
.
4
t.‘» ,  ‘T’ Red zone of
3*‘ _ lip
Mucous mem- —— »
brane of lip
: Skin of lip
Labial glands
‘  orbiculafis
~ "  ' oris muscle
Fig. 165.—Section through lip.
is characterized by numerous densely arranged long papillae of the
lamina propria, reaching deep into the epithelium and carrying large
capillary loops close to the surface. Eleidin in the epithelialcells renders
them translucent. Thus, blood is visible through the thin parts of the
transparent epithelium covering the papillae; hence the red color of the
lips. Because this transitional zone contains only occasional single
sebaceous glands, it is particularly subject to drying if not moistened
by the tongue.
ORAL MUCOUS MEMBRANE 215
The boundary between the red zone of the lip and the mucous membrane is found where hornification of the transitional zone ends. The
epithelium of the mucous membrane of the lip is not hornified.
3. SUBDIVISIONS OF THE ORAL MUGOSA
In studying any mucous membrane the following features should be
considered: (1) type of covering epithelium; (2) structure of lamina
propria, especially as to its density, thickness, and presence or lack of
elasticity; and (3) its fixation to the underlying structures, in other
words, the submucous layer. A submucosa may be present or absent
as a separate and well-defined layer. Looseness or density of its texture
determines whether the mucous membrane is movably or immovably attached to the deeper layers. Presence or absence and location of adipose
tissue or glands should also be noted.
The oral mucosa may be divided primarily into three different types.
During mastication some parts are subjected to strong forces of pressure and friction. These parts, gingiva and covering of the hard palate,
may be termed masticatory mucosa. The second type of oral mucosa is
that which is merely the protective lining of the oral cavity. These areas
may be termed lining mucosa. They comprise the mucosa of lips and
checks; the mucosa of the vestibular fornix and that of the upper and
lower alveolar process peripheral to the gingiva proper; the mucosa of
the floor of the mouth extending to the inner surface of the lower
alveolar process; the mucosa of the inferior surface of the tongue; and
finally, the mucous membrane of the soft palate. The third type of
mucosa is represented by the covering of the dorsal surface of the tongue
and is highly specialized; hence, the term specialized mucosa.
A. Masticatory Mucosa
Gingiva and covering of the hard palate have in common the thickness and hornification of the epithelium, the thickness, density, and firmness of the lamina propria, and, finally, their immovable attachment to
the deep structures. Hornification is absent or replaced by parakeratinization in some individuals whose gingiva otherwise has to be regarded as normal. As to the structure of the submucosa, these two areas
differ markedly. In the gingiva, a well-differentiated submucous layer
cannot be recognized; instead, the dense and inelastic connective tissue
of the lamina propria continues into the depth to fuse with the periosteum
of the alveolar process or to be attached to the cervical region of the
tooth.
In contrast to this, the covering of the hard palate has, with the exception of narrow areas, a distinct submucous layer. It is absent only
in the peripheral zone where the tissue is identical with the gingiva, and
in a narrow zone along the midline, starting in front with the palatine
or incisal papilla and continuing as the palatine raphe over the entire
length of the hard palate. In spite of the presence of a well-defined
216 ORAL HISTOLOGY AND EMBRYOLOGY
submucous layer in the wide lateral fields of the hard palate between
palatine raphe and palatine gingiva, the mucous membrane is immovably
attached to the periosteum of maxillary and palatine bones. This attachment is accomplished by dense bands and trabeculae of fibrous connective tissue Which join the lamina propria of the mucous membrane to
the periosteum. The submucous space is thus subdivided into irregular
intercommunicating compartments of various sizes. These are filled
with adipose tissue in the anterior part and with glands in the posterior
part of the hard palate. The presence of fat or glands in the submucous
layer acts as a hydraulic cushion comparable to that which We find in the
subcutaneous tissue of the palm of the hand and the sole of the foot.
The presence or absence of a distinct submucous layer permits the subdivision of the masticatory oral mucosa into the non—cushioned and the
cushioned zones. The non-cushioned zone consists of the gingiva and
the palatine raphe, the cushioned zone consists of the remainder of the
mucosa covering the hard palate.
A. GINGIVA
The mucous membrane surrounding the teeth, the gingiva, is subjected to forces of friction and pressure in the process of mastication.
The character of this tissue shows that it is adapted to meet these
.7. 7 .. . T.‘
Alveolar R
 
 
mucosa.
-- “T Mucoginglval
Junction
Att hed —— —— ' ‘
{if in « -.,A r, F”? Interdental
g g  .— ,_“,~-~, papilla.
P
Free g'ing'lva.1 Attifilcéligi
g’°°"° Migicogingival
1 * _ junction
Alveo ar 1-vi" ..
mag.
mucosa 9. A \
_ * __ — _
Fig. 166.—Sur1‘a.ce of the gingivu of a young adult.
stresses. The gingiva is sharply limited on the outer surface of both jaws
by a scalloped line (mucogingival junction) which separates it from the
alveolar mucosa (Fig. 166). The gingiva is normally pink, sometimes With
a grayish tinge, a variation which is partly caused by differences in the
thickness of the stratum corneum. The alveolar mucosa is red, showing
numerous small vessels close to the surface. A similar line of demarcation
-‘M. ‘.g;-.;, 7,
Keratinous layer:jg__*,.:£, M  '
cells
Flattened surface  P v w ' , V
 
Parakeratotic ">
layer
3
g > .
3, ’ ._ ‘ ’f‘i
' in ‘ '
Prickle ce11s_" '*‘ 4%
3...
4
' 1’ ""4" *‘ ’ " ' ' ‘——, ’=' Basal layer
Fig. 167.——Varia.tions of glnglval epithelium.
A. Hornmcatlon.
B. No hornmcation.
0'. Paxakeratonia.
218 ORAL HISTOLOGY AND EMBRYOLOGY
is found on the inner surface of the lower jaw between gingiva and the
mucosa on the floor of the mouth. In the palate, there is no sharp dividing
line because of the dense structure and firm attachment of the entire
palatal mucosa.
Normally, the epithelium of the gingiva is hornified on its surface
(Fig. 167, A) and contains a granular layer. In the absence of hornification (Fig. 167, B) there is no granular layer and the flat surface cells contain nuclei which are, frequently, pyknotic. Other cases show a partial
or incomplete hornification (Fig. 167, 0) characterized by a well-defined
 
   
 
Epithelium? —  . f X ' ' H
{Q t,"  -Pngarggrlxted
I layer
‘ V i.
If " ‘ . "~
I Connective
tissue
Fig. 168A..—Pig'ment in basal cells of gingiva. of a. Negro.
surface layer containing flat cells which have lost their boundaries. Nuclei
are present but are extremely flat and pylmotic; this condition is termed
parakeratosis. All transitions from nonhornified to parakeratotic and
hornified epithelium of the gingiva should be considered as Within the
range of normal.
The epithelium covers the margin of the gingiva and continues into the
epithelial lining of the gingival sulcus to terminate on the surface of the
tooth as the epithelial attachment (see section on Epithelial Attachment).
ORAL MUCOUS MEMBRANE 219
The cells of the basal layer may contain pigment granules (melanin)
(Fig. 168:1). While pigmentation is a normal occurrence in Negroes, it is
often found, too, in the white race, especially in people with dark complexion. When found, it is most abundant in the bases of the interdental papillae. It may increase considerably in cases of Addison’s
u— -*‘—"—*“‘ a
Fig. 168B.——Dendritic melanoblasts in the basal layer of the epithelium. Biopsy of
normal gingiva. (x1000.) (Courtesy Esther Carames de Aprile, Buenos Aires.)
1..
'5'-i:..
Fig. 1680.—Macropha.ges in the normal gingiva.._ Rio I-Iortega. stain. ()(1000.)
(Courtesy Esther Carames de Aprile, Buenos Aires.)
disease (destruction of the adrenal cortex). The melanin pigment is
stored by the basal cells of the epithelium, but these cells do not produce
the pigment. The melanin is elaborated by specific cells, melanoblasts,
situated in the basal layer of the epithelium (Fig. 168, B). These cells
have long processes and are also termed “dendritic” cells. In the usual
hematoxylin-eosin specimen, these cells appear with a clear cytoplasm and
are also known as “clear cells.”
220 ORAL I-1I§'l‘0LOGY AND EMBRYOLOGY
The lamina propria of the gingiva consists of dense connective tissue
Which is not highly vascular. Macrophages are present in the normal
ging-iva (Fig. 168, C). These cells play an important function in the defense mechanism of the body. The papillae are characteristically long,
slender, and numerous. The presence of these high papillae permits the
sharp demarcation of the gingiva and alveolar mucosa in which the papillae
are quite low (Fig. 169). The tissue of the lamina propria contains only
few elastic fibers which are, for the most part, confined to the walls of the
 
 
Hard palate
   
—h—- Alveolar
mucosa.
, .- .’
‘ w.a,~;L.i' 1 Emu .
Fig. 169.—Structura1 dlflferences between glngiva. and alveolar mucosa. Region of
- upper bicuspid.
blood vessels. The gingival fibers of the Pariodontal membrane enter into
the lamina propria, attaching the gingiva firmly to the teeth (see chapter
on Periodontal Membrane). The gingiva is also immovably and firmly attached to the periosteum of the alveolar bone; here, a very dense connective
tissue, consisting of coarse collagenous bundles (Fig. 170, A) extends from
the lamina propria to the bone. In contrast, the submucosa underlying the
alveolar mucous membrane is loosely textured (Fig. 170, B). The fiber
bundles of the lamina propria are here thin and regularly interwoven.
The alveolar mucosa and the submucosa contain numerous elastic fibers
which are thin in the lamina propria and thick in the submucosa.
omu. MUCOUS MEMBRANE 221
The gingiva. is well innervated.“ Difierent types of nerve endings can
be observed, such as the Meissner 01- Krause eorpuscles, end bulbs, loops or
fine fibers. Fine fibers enter the epithelium as “ultra-terminal” fibers.
(Figs. 171A and B.)
 
, S. ,
Lamlna propria L "
Submucosa
Epithelium
Lamina proprla.
Submucosa.
Fig. 170.—Differences between ging-Iva. (A) and alveolar mucosa (8). Silver impregnation ot collagenous fibers. Note the coarse bundles of fibers in glngiva. and finer
fibers in alveolar mucosa.
The gingiva can be divided into the free gingiva and attached
gingiva (Figs. 172A and 172B).” The dividing line between these two
parts of the gingiva is the free gingival groove which runs parallel
to the margin of the gingiva at a. distance of 0.5 to 1.5 mm. The free
222 omu. HISTOLOGY AND EMBRYOLOGY
0».
:
Fig. 171A.—Meissner tactile corpuscle in the human gingiva. S_i1veg- impregnation
after Bielschowsky-Gros. (Courtesy F. VV. Gan-ns and J. AltchlS0n.3“)
. 1:
Fig. 171B.——-Intraepithelial “uli:raterminal" extensions and nerve endings in the human
gingiva. Silver impregnation after Bielschowsky-Gros. (Courtesy F. W. Gaitns and J.
A.itchiaon.'-)
ORAL MUCOUS MEMBRANE 223
   
Marginal
   
Inter
—'—‘ glngiva
dental Fr”
pagirlla. / gingiva
. 93 Margin of
gigrgoggé the gingiva.
Inter- ‘' ° ° ° ' ° ‘’ Fr.“
dental o , ° I ,, ° 6 0 II‘ o 0 _ ‘’ H 0 ° ° gmgival
‘°‘‘‘s -» ., ~ ‘’ ., ,° ° ,, ° . " .. ,° . "—_.._._° A‘?'t2‘3’.§a
., ° ' 0 glngive.
3 6
_Muco- ° ” G (stippled)
gmgwal
junction
Alveolar
mucosa
Fig. 172A.—Diag'ram illustrating the surface characteristics of the gingiva.
Margin of the
glngiva.
Free ginglva.
Free gingival
groove
Attached gingiva
( stlppl ed )
Mucogingival
Junction
Alveolar mucosa.
   
-¢_—.r‘.—"‘..
 
—
.4.1‘
 
Fig. 172B.—Diag-ram illustrating the diflerence between the tree ginglva. attached
glnglva, and alveolar mucosa.
224 ORAL HISTOLOGY AND EMBRYOLOGY
gingival groove is, on histologic section (Fig. 173), a shallow V-shaped
groove corresponding to the heavy epithelial ridge which divides the free
and the attached gingiva. The free gingival groove develops at the
level of, or somewhat apical to, the bottom of the gingival sulcus. In
' 9  ’../,2",-I 'j}r""‘_ 
1 .
   
——.-- Free ginglval
groove
- »»»» ——»-—— . —— . A .-«r‘x".‘.&=;
Fi§- 173-—Bi0Dsy specimen of gingiva. showing_ tree gingival groove and stippled at.
tached ging-Ava.
501119 03868, the free gingival groove is not as Well defined as in others,
and then the division between the free and attached gingiva is not clear.
The tree gingival groove and the epithelial ridge are brought about by
functional impacts upon the free gingiva, folding the movable free part
back upon the attached and immovable zone.
ORAL MUCOUS MEMBRANE 225
The attached gingiva is characterized by high connective tissue papillae
elevating the epithelium, the surface of which appears stippled (Fig. 173).
Between the elevations there are small depressions which correspond to
the center of heavier epithelial ridges and show signs of degeneration
and hornification at their depth. The stippling is most probably an expression of functional adaptation to mechanical impacts. The degree of
.,-.,.,3,..,
  ' ‘Oral epithelium
«- K .
~ /, : ‘ Reduced enamel
“ g _ ' " ‘ epithelium
 
 
Enamel
Reduced enamel
epithelium
Pulp
.1 ‘ -’
Cemento-enamel
.  junction
   
iii;
l » ,
-.I----=- :9: _Periodonta.l mem
., ‘; ‘E brane
sea
3,
' ,‘»".
T’ *1
1 .
 
Undeveloped apical
   
Fig. 174.—I-Iuman permanent incisor. The entire surface of the enamel is covered
léybrediiced enamel epithelium. Mature enamel is lost by decalciflcation. (Gottlieb and
1- an. )
stippling varies with different individuals. The disappearance of stippling is an indication of edema, an expression of an involvement of the
attached gingiva in a progressing gingivitis.
The attached gingiva appears slightly depressed between adjacent teeth,
corresponding to the depression on the alveolar bone process between
eminences of the sockets. In these depresssions, the attached gingiva
often forms slight vertical folds.
226 ORAL I-IISTOLOGY AND EMBRYOLOGY
The interdental papilla is that part of the gingiva that fills the space
between two adjoining teeth and is limited at its base by a line connecting the margin of the gingiva at the center of one tooth and the center
Ora.l——— -—-—  2. .'
epithelium , Q "K;
Fusion oi’ oral
and enamel "3 .,g
epithelium , , f V.‘
._ .
I ‘~ _ ""”'—“—'.‘1{e(luced enamel
~ ._ ' __ epithelium
( ,, an
Reduced enamel :15,’ <-‘J
epithelium § 93;‘? . .5‘.
Fusion of oral and enamel
epithelium X
Oral epithelium
Cemento-enamel junction
cementum
Fig. 175.—Rednce_d enamel epithelium fuses with oral epithelium. X in the diagram
indicates area from which the photomlcrograph was taken.
of the next. The interdental papilla is composed of free gingiva and attached gingiva in various relations, depending largely upon the relationship of the neighboring teeth.
ORAL MUCOUS MEMBRANE 227
B. EPITHELIAL ATTACHMENT AND GI.\‘GIVAL SULcus*
At the conclusion of enamel matrix formation the ameloblasts pro- De"91°Pm°nt
duce a thin membrane on the surface of the enamel: the primary enamel
cutwle. It is a. limiting membrane, connected with the intei-prismatic
L
our ll - -- “ oral
epithelium ' " - epithelium
.' F.
4-Gr * .
. in
Enamel ’ "‘-—“  J‘ ".73"
cuticle ‘r.
.-9.
- "3' Y‘
5* -it
” Epithelial
Enamel , attachment
.1: ,
Epithelial
‘I
attachment _.
 
Reduced enamel epithelium
(now epithelial
attachment)
Dentin
Pulp
Cemento-enamel junction
Cementum
Fig. 176.—'I‘ooth emerges through a perforation in the fused epithelial. X in the diagram
indicates area from which the photomicrograph was taken.
enamel substance. The ameloblasts shorte11 after the enamel cuticle
is formed, and the epithelial cells comprising the enamel organ are reduced to a few layers of cuboidal cells which are then called reduced
‘First draft of this section submitted by Bemliard Gottlieb.
228 ORAL HISTOLOGY AND EMBRYOLOGY
enamel epitheliunt. Under normal conditions it covers the entire enamel
surface extending to the cemento-enamel junction (Fig. 174) and remains attached to the primary enamel cuticle. During eruption the tip
of the tooth approaches the oral mucosa and the reduced enamel epithelium fuses with the oral epithelium (Fig. 175).
The epithelium which covers the tip of the crown degenerates in its
center, and the crown emerges through this perforation into the oral
cavity (Fig. 176). The reduced enamel epithelium remains organically
attached to that part of the enamel which has not yet erupted. Once
the tip of the crown has emerged, the reduced enamel epithelium is
termed the epithelial attachment.‘ At the marginal gingiva the epithelial
attachment continues into the oral epithelium (Fig. 177). As the tooth
Erupted enamel
Glngival sulcus
Free gingiva
Oral epithelium
Epithelial attachment
Enamel
Cemento-enamel
junction
Dentin
Pulp
Fig 177.—Diagramma.tic illustration of epithelial attachment and gingival sulcus at an
early stage of tooth eruption. Bottom of the sulcus at x.
erupts, the epithelial attachment is gradually separated from its surface.
The shallow groove which develops between the gingiva and the surface
of the tooth and extends around its circumference is the gingival sulcus
(Fig. 177). It is bounded by the surface of the tooth on one side, and
by the gingiva on the other. The bottom of the sulcus is found where
the epithelial attachment (formerly reduced enamel epithelium) separates
from the surface of the tooth. The part of the gingiva which is coronal
to the bottom of the sulcus is the marginal gingiva. While the epithelial
attachment is separated from the surface of the enamel, it produces often
the secondary enamel cuticle} This is a hornified layer, 2 to 10 microns
in thickness.
ORAL MUCOUS MEMBRANE
A. B. 0.
Fig. 178.-—Three sections oi.’ the same tooth showing different relations of tissues at cemento-enamel junction.
4. Epithelial attachment reaching to cemento-enamel Junction.
B. Epithelial attachment leaves the enamel free at cemento-enamel junction.
0. Epithelial attachment covers part or the cementum. cementum overlaps the end of the enamel.
EA = epithelial attachment; E = enamel (lost in decaiciflcetion); 0 = cementum: X = end of epithelial attachment. (Or-ba.n.")
229
$5
230 omu. HISTOLOGY AND EMBRYOLOGY
In erupting teeth the epithelial attachment extends to the cementeenamel junction (Fig. 177). Occasionally, the epithelium degenerates in the
cervical areas of the enamel; then the surrounding connective tissue
frequently deposits cementum upon the enamel. This does not always
occur aI'Ol111(l the entire surface of a tooth. Different sections of the
same tooth may, and frequently do, show varying relationships in the
area Where enamel and cementum meet (Fig. 178).
Enamel
Cuboidal cells of
epithelial attachment
Flattened cells in
epithelial attachment
Dentin
: Basal cells of
epithelial attachment
 
Cemento-enamel
junction
Fig. 179.——Arra.ngement of cells in the epithelial attachment indicate functional influences. (Orban.“')
The epithelial attachment is the derivative of the reduced enamel
epithelium. In some cases, ameloblasts may still function at the apical
end of the attachment when the tip of the crown has already emerged
through the oral mucosa. The ameloblasts flatten out rapidly and then
the reduced enamel epithelium forms the epithelial attachment. This
is thin at first and consists of 3 to 4 layers of cells (Figs. 181, 182) but
thickens gradually with advancing age to about 10 to 20 rows of cells,
or more (Figs. 183, 184).
The epithelium which forms the attachment is stratified squamous
epithelium. As a rule, the junction between epithelial attachment an_d
connective tissue is smooth. It may be considered as a sign of irritation if the epithelial attachment sends fingerlike projections, epithelial
pegs, into the conective tissue. The cells within the epithelial attachORAL MUCOUS MEMBRANE 231
ment are elongated, and are arranged more or less parallel to the surface
of the tooth (Fig. 179). There is a distinct pattern in the direction of
these flattened cells which may be the result of functional influences
upon the attachment.“ The cells at the surface of the epithelial attachment are firmly fastened to the tooth and must follow all its movements.
The basal layer of the epithelial attachment, on the other hand, is
anchored to the surrounding connective tissue and must follow all the
movements to which the gingival margin is subjected. The cells within
the epithelial attachment are exposed to these different stresses. The
-. Epithelial bridge cross»
ing tear in attachment
Epithelial cells attached
to cementum
p Epithelial bridge crossing tear in attachment
‘ Epithelial attachment
torn from cementum
 
Epithelial cells attached
‘ ‘Q to cementum
¥
Fig. 180.—Artitlcia1 tear in epithelial attachment. Some cells are attached to the
‘ cementum, others bridge the tear. (Orban and Muellenl‘)
attachment of the surface cells to enamel or cementum seems to be more
firm than the connection of these cells to the deeper layers of the epithelium. For this reason tears occur frequently between the cuboidal
cells attached to the tooth and the rest of the epithelial attachment.
Such tears are found as artifacts in microscopic specimens (Fig. 180) but
may also occur during life.“
shift of
Epithelial
Attachment
First Stage
232 omu. HISTOLOGY AND EMBRYOLOGY
The relation between epithelial attachments and the surface of the
tooth changes constantly. When the tip of the enamel first emerges
through the mucous membrane of the oral cavity, the attachment
covers almost the entire enamel (Fig. 181). Tooth eruption is relatively
fast (see chapter on Tooth Eruption) until the tooth reaches the plane
of occlusion. This causes the epithelial attachment to separate from
the enamel surface, gradually exposing the crown. When the tooth
reaches the plane of occlusion, one-third to one-fourth of the enamel is
still covered by the epithelial attachment (Fig. 182). The gradual ex
 
I
I
I
I
/I ‘
I \
rll
II \
I \
I \
F ’ I \
ree(gnn§:;:i \\ Free gingiva
sulcus) \ - ' ’ ' ""‘ Gingival sulcus
Enamel
Dentin - —- - ‘ Enamel
Epithelial —-' E lth ll l tta attachment Bnelfta 8' ch
_ " *"»-"' Pulp
Cementmenamel —— .
junction  _
" '—'- Cemento-enamel
Junction
Fig. 181.—Epithelial attachment and glngival sulcus in an erupt‘ t th.
of enamel is indicated by dotted line. Enamel lost in decalcifllgagtloii? (K1:-J¢!:'ii.i!)etl%1.1°‘))ut
posure of the crown by separation of the epithelial attachment from the
enamel is known as passive eruption. The simultaneous elevation of
the teeth, toward the occlusal plane, is termed active eruption (see chapter on Tooth Eruption).
The bottom of the gingival sulcus remains in the region of the enamelcovered crown for some time, and the apical end of the epithelial attachment stays at the cemento-enamel junction. This relationship of the
epithelial attachment to the tooth characterizes the first stage in passive
omu. MUCOUS MEMBRANE 233
eruption (Fig. 183). It persists in primary teeth almost up to one year
before shedding and, in permanent teeth, usually to the age of about twenty
or thirty; however, this is subject to great variations.
The epithelial attachment forms, at first, a wide band around the cervical
part of the crown which becomes gradually narrower as the separation
of epithelium from the enamel surface proceeds. Long before the bottom
of the sulcus reaches the cemento—enamel junction, the epithelium proliferates along the surface of the cementum and the apical end of the
=‘ as
 
 
Enamel T
‘I
9
Dentin *'“" '*
-:
V \ Gingival sulcus
.. _, ,3,‘
-4 p ’_ Free gingiva.
.
g“‘“ '' " —. Epithelial attachment
Cemento-enamel '— ""
junction
' 4' 4 Alveolar crest
Fig. 182.—Tooth in occlusion. One-fourth of the enamel is still covered by the epithelial
attachment. (Kr-onfeld."')
epithelial attachment is then found in the cervical part of the root, on
the cementum. This is the second stage in the passive eruption of teeth.
In this phase the bottom of the gingival sulcus is still on the enamel; the
apical end of the epithelial attachment has shifted to the surface of the
cementum (Fig. 184).
The downgrowth of the epithelial attachment along the cementum is
impossible as long as the gingival and transseptal fibers are still intact.
It is not yet understood whether the degeneration of the fibers is
Second stage
Third Stage
234 omu. msronoev AND EMBRYOLOGY
primary or secondary to the proliferation of the epithelium.“ Recent
findings indicate that destruction of the fibers is secondary, the proliferating epithelial cells actively dissolving the principal fibers byenzymc action
(desmolysis). A primary destruction of the principal fibers had been explained by the action of bacterial toxins from the gingival sulcus. The
second stage of passive tooth eruption may persist to the age of forty or
Enamel cuticle
Bottom 01
glnglval
snlcus
Enamel
Epithelial
attachment
Cemento-enamel
junction
Cementum
Fig. 183.—-Epithelial attachment on the enamel. First stage in passive tooth eruption.
(Gotflieb and Orbanfi)
later. With advancing age the epithelial attachment further separates
from the enamel surface, and the apical end of the epithelium continues
to grow down along the cementum.
For a short time, the bottom of the gingival sulcus is just at the cementeenamel junction, the epithelial attachment is entirely on the cementum,
and the enamel-covered crown is exposed (Fig. 185). This is the third
stage in passive tooth eruption. Because of the continuous active and
235
ORAL MUCOUS MEMBRANE
 
Fre_e
gmgiva
gingival
sulcus
0-.
0
m
o
t
t
o
B
Epithelial
attachment
to enamel
Cemento-enamel
junction
cementum
Epithelial , . _
attachmentn -‘«‘
to cementum .
End of
epithelial
attachment
Second
Fig. 184.—EpitheIia.l attachment partly 01.1 the enamel, partly on the cementum.
stage in passive tooth eruption. (Gottiieb and Oz-ba.n.')
E‘ourth Stage
236 ORAL HISTOLOGY AND EMBRYOLOGY
passive eruption of the teeth, the epithelium shifts gradually along
the surface of the tooth and the attachment does not remain at the linear
cemento-enamel junction for any length of time. The third stage in
passive eruption marks only a moment in a more or less continuous process. If a part of the cementum is already exposed by separation of the
Enamel
 
1 E
,’ . Bottom of Einglval
. I sulcus
I ‘ !
, .
Cemento-enamel junction
Oral epithelium
Epithelial
attachment ;
End of epithelial - j ' _ "L _ '
attachment , .
Fig. 185.—Epithelial attachment on the cementum; bottom of the gingival sulcus at the
cemento-enamel junction. Third stage in passive tooth eruption. (Gottlieb.')
epithelial attachment from the tooth surface, the fourth stage of passive
eruption is reached. The epithelium is entirely attached to the cementum
(Fig. 186).
It would appear that the epithelial attachment has to maintain a certain Width* to assure normal function of the tooth. Therefore, this
proliferation along the cementum should be considered a physiological
'The width of the epithelial attachment varies from 0.25 to 6 mm.“
ORAL MUCOUS MEMBRANE 237
process, if it is in correlation to active eruption and attrition. If it
progresses too rapidly or precociously and loses, therefore, correlation
to active eruption, it must be considered as a pathologic process.
An atrophy of the gingiva. is correlated with the apical shift of the
epithelial attachment, exposing more and more of the crown, and, later,
of the root, to the oral cavity. The recession of the gingiva is therefore
a physiologic process if it is correlated both to the occlusal wear and to
the compensatory active eruption.
.*"*r.--vj _"“'*'~""""" '
x 1-: - ‘ .» - ,, . a
 
Enamel
‘ .
Cemento~ena.mel
junction
Free gingiva.
Cementum
(exposed)
Bottom of gingival
sulcus
Free gingival groove  -,  V‘
cementum
Oral epithelium " —'
'7 End of epithelial
attachment
Fig. 186.—Epithelial attachment on the cementum; bottom of_the ginglva-1 sulcns also
on the cementum Fourth stage in passive tooth eruption. (Gott1ieb_6)
The rate of passive tooth eruption varies in difierent persons, and in
different teeth of the same individual, as well as on different surfaces
of the same tooth. In some cases, the fourth stage of passive tooth eruption is observed in persons during their twenties; in others, even at the
age of fifty or later, the teeth are still in the first or second stage of eruption. The rate varies also in diflerent teeth of the same jaw: the earlier
,-,.,,_ __ _ K
88%
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A. B. C.
Fig. 187.—-Three sections of the same tooth showing different relationship of soft to hard tissues.
A. Bottom of the sulcua on the enamel (second stage).
B. Bottom of the sulcus at cemento-enamel junction (third stage).
0. Bottom of the aulcua on cementum (fourth stage).
E = enamel lost in decalciflcation—outline indicated by dotted line; EA = epithelial attachment; 5: - bottom of
gingival sulcus: mm = and of epithelial attachment. ’
Mode of Attachment of
Epithelium
ORAL MUCOUS MEMBRANE 239
a tooth erupts, the more advanced can be its passive eruption. Even
around the same tooth there is a variation; one side may be in the first
stage, the other in the second or even the fourth stage (Fig. 187). At
no time are all parts of the bot_tom of the gingival sulcus in the same
relation to the tooth.
Gradual exposure of the tooth to the oral cavity makes it possible
to distinguish between the anatomical and clinical crowns of the tooth
(Fig. 188). That part of the tooth which is covered by enamel is the
anatomical crown; the clinical crown is that part of the tooth exposed
in the oral cavity.“ In the first and second stages, the clinical crown
II III IV
Fig. 188.—Diagrammatie illustration of the four stages in passive tooth eruption:
in Stages I and 11 the anatomic crown is larger than the clinical; in Stage III anatomic
and inical crowns are equal; in Stage IV the clinical crown is larger than the
anatomic. The arrow in the small diagram indicates the area from which the drawings were made.
E = enamel; E4 = epithelial attachment; 0 = cemento-enamel junction; 5.‘ = bottom of gingival sulcus.
is smaller than the anatomical. In the third stage, the enamel-covered
part of the tooth is exposed and the clinical crown is equal to the anatomical. It should be emphasized that this condition is not actually
encountered, because the bottom of the gingival sulcus is never at the
same level all around the tooth. In the fourth stage the clinical crown
is larger than the anatomical because parts of the root have been exposed.
The means by which the epithelium is attached to the enamel is not
as yet fully understood. Several explanations have been advanced.
Formerly it was claimed that the epithelium is not organically attached
to the tooth but is kept in place by tissue tone and elasticity of the con240 ORAL HISTOLOGY AND EMBRYOLOGY
nective tissue of the gingiva pressing the epithelium against the tooth
surface. This concept has been disproved by microscopic evidence,
which shows that there is an organic union between the epithelium and
the tooth surface. The strength of the attachment was demonstrated by
the following experiment: The teeth and surrounding tissues in young
dogs were frozen and ground into relatively thin sections. These were
placed under the dissecting microscope, and the free margin of the
giiigiva was pulled away from the tooth with a needle. By this method
it was possible to demonstrate that the attachment can be severed from
Epithelial
attachment
Epithelial
'3. attachment
to  189.—e-LG:-ound section of hard and soft tissues of teeth. Epithelial attachment
A. General view of inter-dental papilla.
3- Higher ma.g'nifl<‘£ti011 01 Elnsival sulcus and epithelial attachment
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the tooth only to a certain depth; from there on it tears instead of
separating from the tooth.” The firmness of the attachment may be
further shown by studying ground sections prepared by a. special method
of investing soft and hard tissues (Fig. 189). In such specimens the
enamel. is not lost as in decalcified sections, and the relations between
epithelium and enamel are undisturbed. Another confirmation of the
organic connection between tooth surface and epithelium is the fact that,
omar. MUCOUS MEMBRANE 241
after extraction of teeth, epithelium is often found adherent to the extracted tooth,’ The firm connection between epithelium and enamel is
a primary 11111011, the enamel being a cuticular product of the ameloblasts.
The layer of the epithelial attachment that is attached to the surface of the
enamel is the regressed ameloblast layer.
It has also been claimed that the secondary cuticle plays an important
role in cementing the epithelium to the surface of the tooth. This cuticle‘
is a hornified structure, homogenous and brittle. It lies outside the primary enamel cuticle (see chapter on Enamel) and stains bright yellowishred in hematoxylin-eosin preparations. It is resistant to acids and
Secondary '< ' l
enamel
cuticle
   
 
Epithelial  . .
attachment a l
‘ .
Cemento- —— -enamel
junction
Cements.)
cuticle ;
(dental .’
cuticle)’  fl “j
s §:}is._.
31
Fig. 190.—Seconda.ry enamel cuticle follows epithelial attachment to the cementum
forming the “dental cuticle." Arrow in diagram indicates area. from which the photomicrograph was taken.
 
alkalies and may act as a protective layer on the tooth surface. Even
yet its method of formation is not quite clear: some investigators claim‘
that it develops by transformation of the cells which are adjacent to
the tooth surface in a manner similar to normal hornification. Others
contend that this cuticle is a secretory product of the epithelial cells.“
The secondary cuticle is not limited to the surface of the enamel, as
is the primary cuticle, but follows the epithelial attachment when it shifts
along the cementum; hence it is designated by the term cuticula. dentis
The Gtngival
suleus
242 ORAL msronocv AND EMBRYOLOGY
(dental cuticle) (Fig. 190). The formation of the dental cuticle by the
epithelial attachment is believed to be a reaction of the epithelium to
its contact with a hard structure. It is further assumed that formation
of the cuticle is the first phase of a process which, ultimately, leads to
separation of the epithelium from the tooth. However, some investigators claim that this cuticle is a pathologic structure, induced by inflammation of the gingiva."
~7
Cuticle
:l'l‘
F."
cementum  '
xx’,
‘.1:
5'3:
'  Extension or cuticle Into
_ ' space in cementum
Dentin _ "
Fig. 191.—Horny substance of the dental cuticle extends into the spaces of the cementum.
(Gottlieb and Orbanfi)
The mechanism of attachment of the epithelium to the enamel is still
open to further investigation. The attachment of the epithelium to the
cementum is accomplished by fine processes of the epithelial cells, extending into minute spaces of the cementum where Sharpey’s fibers were
previously located. This mode of attachment can be likened to the attachment of the basal cells of an epithelium to the underlying basement
membrane. When the dental cuticle is formed on the surface of the
cementum,-the horny substance extends into these spaces (Fig. 191).
The erupting crown is surrounded by a tissue formed by the fusion
of the oral and reduced enamel epithelium. The gingival suleus forms
when the tip of the crown emerges through the oral mucosa. It deepens
as a result of separation of the reduced enamel epithelium from the
actively erupting tooth. Shortly after the tip of the crown has appeared
in the oral cavity the tooth establishes occlusion with its antagonist.
otm. MUCOUS MEMBRANE 243
During this interval the epithelium separates rapidly from the surface
of the tooth. Later, when the tooth reaches its occlusion, separation
of the epithelial attachment from the surface of the tooth slows down.
Actual movement of the tooth (active eruption) and peeling off of
the epithelial attachment (passive eruption) are the two integral factors
of tooth eruption. The normal correlation between the two may be broken.
In accelerated active eruption (teeth Without antagonists), the rate of passive eruption does not necessarily increase. On the other hand, in the case
of a pathologic recession of gingiva, the peeling off of the epithelial attachment may be accelerated without appreciable change in the rate of
active eruption.
E E E
EA EA
II III IV
_ Fig. 192.—Dia.grarnmatic illustration of diflerent views on the formation of the
gmgival sulcus as discussed in the text. Arrow in the small diagram indicates area.
from which the drawings were made.
The formation and relative depth of the gingival sulcus, at different
ages, has proved an extremely controversial subject. Until the epithelial
attachment was recognized, it was believed that the gingival sulcus extended to the cemento—enamel junction, immediately after the tip of the
crown pierced the oral mucosa (I in Fig. 192). It was assumed that
the attachment of the gingival epithelium to the tooth was linear
and existed only at the cemento—enamel junction. Since the epithelial attachment has been first described, it has been recognized that no cleft exists
between epithelium and enamel, but that enamel and epithelium are in firm
organic connection. The gingival sulcus is merely a shallow groove, the
bottom of which is at the point of separation of the attachment from the
tooth (II in Fig. 192) . The separation of the epithelium from the tooth is
now considered a physiologic process.
244 ORAL HISTOLOGY AND EMBRYOLOGY
Some investigators contend that the deepening of the gingival sulcus is
due to a tear in the epithelial attachment itself (III in Fig. 192). Tears
may deepen the gingival sulcus when the free margin of the gingiva is exposed to excessive mechanical trauma.
Others claim‘, 22 that the gingival sulcus forms at the line of fusion between the enamel epithelium attached to the surface of the enamel, and the
oral epithelium (IV in Fig. 192). Accordingly, the oral epithelium proliferates at the connective tissue side of the epithelial attachment and replaces the former enamel epithelium which degenerates progressively.
The depth of the normal gingival sulcus has been a frequent cause of
disagreement, investigations, and measurements.“ Under normal conditions, the depth of the sulcus varies from zero to six millimeters; 45 per
cent of all measured sulci were below 0.5 mm., the average being about 1.8
mm. It can be stated that the more shallow the sulcus, the more favorable
are the conditions at the gingival margin. Every sulcus may be termed
“normal,” regardless of its depth, if there are no signs of a pathologic
condition in the investing tissues.
The presence of leucocytes and plasma cells in the connective tissue at
the bottom of the gingival sulcus should not, in itself, be considered a
pathologic condition. It is evidence, rather, of a defense reaction in
response to the constant presence of bacteria in the gingival sulcus.
These cells form a barrier against the invasion of bacteria and the penetration of their toxins.“
The blood supply of the gingiva is derived chiefly from the branches of
the alveolar arteries which penetrate the alveolar septum,” and from
arteries lying on the outside of the alveolus and jawbones. The blood
vessels of the gingiva anastomose with those of the peridontal membrane.
There is a rich network of lymph vessels in the gingiva along the blood
vessels leading to the submental and submaxillary lymph nodes. There
is also a rich plexus of nerve fibers and numerous nerve endings in the
gingiva.
C. HARD PALATE
The mucous membrane of the hard palate is tightly fixed to the underlying periosteum and, therefore, immovable. Its color is pink, like that
of the gingiva. The epithelium is uniform in character throughout the
hard palate, with a rather thick hornified layer and numerous long pegs.
The lamina propria, a layer of dense connective tissue, is thicker in the
anterior than in the posterior parts of the palate. Various regions in
the hard palate differ because of the varying structure of the submucous layer. The following zones can be distinguished (Fig. 193): (1)
the gingival region, adjacent to the teeth; (2) the palatine raphe, also
known as the median area, extending from the incisive (palatine) papilla
posteriorly; (3) the anterolateral area, or fatty zone between raphe and.
gingiva, (4) -the posterolateral zone or glandular zone, between raphe
and gingiva.
om. MUCOUS MEMBRANE 245
 
   
 
E Palatine papilla
Gmgiva
Raphe
Soft palate
.... ..
._.., _
Alveolar crest _
Fig. 194.—Structura.l differences between gglngivs. and palatine mucosa. Region or first
m a.r.
246 ORAL rnsronocv AND EMBRYOLOGY
The marginal area shows the same structure as the other regions of
the gingiva. Therefore, in this zone, a submucous layer cannot be differentiated from the lamina propria or periosteum (Fig. 194). Similarly,
the layers of the lamina propria, submucosa, and periosteum cannot be
distinguished in the palatine raphe, or median area (Fig. 195). If a
palatine torus is present, the mucous membrane is noticeably thin and
the otherwise narrow raphe spreads over the entire torus.
In the lateral areas of the hard palate (Fig. 196), in both fatty and
glandular zones, the lamina propria is fixed to the periosteum by strands of
dense fibrous connective tissue which are at right angles to the surface
and divide the submucous layer into irregularly shaped spaces. The distance between lamina propria and periosteum is smaller in the anterior
than in the posterior parts. In the anterior zone the connective tissue
 
‘. Nasal septum
Median palatine
suture
‘-'Connective tissue
' ‘i. strands
Fig. 195.—'1‘r-ansverse section through hard palate. Palatine raphe; fibrous strands connecting mucosa and periosteum; palatlne vessels. (E. C. Pendletonfi)
spaces contain fat (Fig. 195) while in the posterior part lobules of mucous glands are packed into the spaces (Fig. 196). The glandular layer of
the hard palate extends posteriorly into the soft palate.
In the sulcus between alveolar process and hard palate, the anterior palatine vessels and nerves are found surrounded by loose connective tissue.
This area being wedge-shaped in cross section (Fig. 197) is relatively large
in the posterior parts of the palate and gradually diminishes in size anteriorly.
The pear-shaped or oval incisive (palatine) papilla is formed of dense 1“°i‘iY°
connective tissue. It contains the oral parts of the vestigial nasopalatine mun‘
ducts. These are blind epithelial ducts of varying lengths. They are
lined by a simple or pseudostratified columnar epithelium, rich in goblet
cells; small mucous glands open into the lumen of the ducts. Frequently,
ORAL mucous MEMBRANE 247
the ducts are bordered by small irregular islands of hyalin cartilage, vestigial extensions of the paraseptal cartilages. The nasopalatine ducts
are patent in most mammals a11d, together with Jacobson ’s organ, are
considered as auxiliary olfactory sense organs. The cartilage is sometimes found in the anterior parts of the papilla; it then shows no apparent relation to nasopalatine ducts (Fig. 198).
The transverse palatine ridges (palatine rugae), irregular and often
asymmetric in man, are ridges of mucous membrane -extending laterally from the incisive papilla and the anterior part of the raphe. Their
core is a dense connective tissue layer with finely interwoven fibers.
In the midline, especially in the region of the palatine papilla, epithelial pearls may be found in the lamina propria. They consist of concentrically arranged epithelial cells which are frequently hornified. They
are remnants of the epithelium in the line of fusion between the palatine
processes (see chapter on Development of the Face).
B. Lining Mucosa
All the zones of the lining mucosa are characterized by a relatively
thin, nonhornified epithelium and by the thinness of the lamina propria.
They differ from one another in the structure of their submucosa. Where
the lining mucosa reflects from the movable lips, cheeks and tongue to
the alveolar bone, the submucosa is loosely textured. In regions where
the lining mucosa covers muscles, as on the lips, cheeks, and underside
of the tongue, it is immovably fixed to the epimysium or fascia of the
respective muscle. In these regions the mucosa is also highly elastic.
These two characteristics safeguard the smoothness of the mucous lining
in any functional phase of the muscle and prevent a folding which
would interfere with the function; for instance, the teeth might injure
the lips or cheeks if such folds protruded between the teeth. The mucosa
of the soft palate is a transition between this type of lining mucosa and
that which is found in the fornix vestibuli and in the sublingual sulcus
at the floor of the oral cavity. In the latter zones, the submucosa is
loose and of considerable volume. The mucous membrane is loosely and
movably attached to the deep structures which allows for a free movement of lips and checks and also tongue.
Thus, it is possible to subdivide the lining mucosa into the two main
types of tightly and loosely attached zones; the tightly fixed area, however, should be subdivided once more on the basis of the absence or
presence of a distinct submucous layer. This layer is lacking on the
underside of the tongue but is present in the lips, cheeks, and soft palate.
In the latter areas, the mucous membrane is fixed to the fascia of the
muscles, or to their epimysium, by bands of dense connective tissue between which either fat lobules or glands are situated.
A. Ln> AND CHEEK
The epithelium of the mucosa on the lips (Fig. 165) and the cheek
(Fig. 199) is typically stratified and squamous, Without hornification.
Palatine Eugae (transverse palatine ridges)
Epithelial
Pearls
Soft palate
End of hard palate
Lamlna. propria.
 
Musculua inclslvus
Alveolar crest
Fig. 196.—Longltudlna.l section through hard and soft palate lateral to mldllne. Fatty and glandular zones of hard palate.
Palatine vessels
' . and nerves
Alveolar crest
Fig‘. 197.—'1‘z-ansverse section through posterior part of hard palate, region or second
molar. Loose connective tissue in the furrow between alveolar process and hard palate
around palatine vessels and nerves.
, Incisal canal
Cystic remnant of
nasopalatine duct
Central lncior—
Fig. 198.—Sa.gitta.l section through palagne pai1l>lll.la and anterior palatine canal. Cartilage
Dan
250 ORAL HISTOLOGY AND EMBRYOLOGY
The surface layer consists of very flat cells containing pyknotic nuclei.
These superficial cells are continuously shed and replaced.
The lamina propria of the labial and buccal mucosa consists of dense
connective tissue which sends irregular papillae of moderate length into
the epithelium.
"The submucous layer connects the lamina propria to the thin fascia of
the muscles and consists of strands of densely grouped collagenous fibers.
Between these strands loose connective tissue containing fat and small
mixed glands is found. The strands of dense connective tissue limit
the mobility of the mucous membrane against the musculature and prevent its elevation into folds. Small Wrinkles appear in the mucosa during
the contraction of the muscles, thus preventing the mucous membrane
of the lips and cheeks from lodging between the biting surfaces of the
teeth during mastication. The mixed glands of the lips are situated in
the submucosa, While in the check the larger glands are usually found
between the bundles of the buccinator muscle, and sometimes on its outer
surface. A horizontal middle zone on the cheek, lateral to the corner
of the mouth, may contain isolated sebaceous glands (“Fordyce spots”).
These occur in the zone of embryonic fusion between the lateral parts of
the primary lips during the development of the cheek (see Chapter I).
The epithelium and lamina propria of the mucous membrane in the
vestibular fornix do not differ from those of the lips and cheeks. However, the submucosa here consists of loose connective tissue, which often
contains a considerable amount of fat. This layer of loose connective
tissue is thickest at the depth of the fornix. The labial and buccal frenula
are folds of the mucous membrane, containing loose connective tissue. No
muscle fibers are found in these folds.
B. VESTIBULAR FORNIX AND ALVEOLAR MUCOSA
The vestibular fornix is the area where the mucosa of lips and checks
reflects to become the mucosa covering the jaws. The mucous membrane of the cheeks and lips is firmly attached to the buccinator
muscle in the cheeks and the orbicularis oris muscle in the lips. In the
fornix, the mucosa is loosely tonnected to the underlying structures
and thus permits the necessary movements of lips and cheeks. The mucous membrane covering the outer surface of the alveolar process is
loosely attached to the periosteum in the area close to the fornix. It
continues into, but is sharply limited from, the gingiva, which is firmly
attached to the periosteum of the alveolar crest and to the teeth.
Gingival and alveolar mucosae are separated by a scalloped line,
muco-gingival junction. The altered appearance of tissues on either
side of this line is due to a difference in their structures. The attached gingiva is stippled, firm, thick, lacks a separate submucous layer,
is immovably attached to the bone, and has no glands. The gingival
epithelium is thick and hornified; the epithelial ridges and the papillae
omu. MUGOUS MEMBRANE 251
of the lamina propria are high. The alveolar mucosa is thin and loosely
attached to the periosteum by a well-defined submucous layer of loose
connective tissue and may contain small mixed glands. The epithelium
is thin, not hornified, and the epithelial ridges and papillae are low
and: are often entirely missing. Structural differences also cause the
difference in color between the pale pink gingiva and the dark red lining
mucosa.
Epithelium
Dense connectlve
tissue
strands
Submucosa
Buccinator  _ , . _ _.
muscle _ —; » . pi
Fig. 199.—Section through mucous membrane of check. Note the strands ot dense connective tissue attaching the mucous membrane to the buccinator muscle.
0. Mucous IVIEMBRANE or TI-IE INFERIOR SURFACE on THE TONGUE
AND on THE FLOOR on‘ THE ORAL CAVITY
The mucous membrane on the floor of the oral cavity is thin and loosely
attached to the underlying structures to allow for the free mobility of
the tongue. The epithelium is not hornified and the papillae of the
252 ORAL msvronoev AND EMBRYOLOGY
 
   
   
Epithelium
Lamina propria
Submucosa
Submucosa
Lamina. propria :
Fig. 201.—Mucous membrane on interior surface of tongue.
can. MUCOUS MEMBRANE 253
lamina propria are short (Fig. 200). The submucosa contains adipose
tissue. The sublingual glands lie close to the covering mucosa in the sublingual fold. The sublingual mucosa joins the lingual gingiva in a sharp
line that corresponds to the mucogingival line on the vestibular surface of
both jaws. At the inner border of the horseshoe-shaped sublingual sulcus,
the sublingual mucosa reflects onto the lower surface of the tongue and continues as the ventral lingual mucosa.
The mucous membrane of the inferior surface of the tongue is smooth
and relatively thin (Fig. 201). The epithelium is not hornified; the
papillae of the connective tissue are numerous but short. Here, the submucosa cannot be identified as a separate layer; it binds the mucous
membrane tightly to the connective tissue surrounding the bundles of
the striated muscles of the tongue.
D. SOFT PALATE
The mucous membrane on the oral surface of the soft palate is highly
vascularized and of reddish color, noticeably differing from the pale
color of the hard palate. The papillae of the connective tissue are few
and short. The stratified squamous epithelium is not hornified (Fig. 202).
Fig. 202.—Mucous membrane from oral surface of soft palate.
254 ORAL HISTOLOGY AND EMBRYOLOGY
The lamina propria shows a distinct layer of elastic fibers separating it
from the submucosa. The latter is relatively loose and contains an almost continuous Iayer of mucous glands. Typical oral mucosa continues
around the free border of the velum palatinum and is replaced, at a
variable distance, by nasal mucosa with a pseudostratified, ciliated, col
umnar epithelium.
G. Specialized Mucosa or Dorsal Lingual Mucosa
The superior surface of the tongue is rough and irregular (Fig. 203).
A V-shaped line divides it into an anterior part, or body, and a posterior
part, or base of the tongue. The former comprises about two-thirds
of the length of the organ, the latter forming the posterior one-third.
The fact that these two parts develop from different areas of the
branchial region (see chapter on Development of the Face) accounts
for the different source of nerves of general sense: the anterior twothirds is supplied by the trigeminal nerve through its lingual branch; the
posterior one-third by the glossopharyngeal nerve. '
The body and base of the tongue differ widely in the structure of their
covering mucous membrane. On the anterior part are found numerous
fine-pointed, cone-shaped papillae which give it a velvet-like appearance.
These projections, the filiform papillae (thread-shaped) are built of a
core of connective tissue which carries secondary papillae (Fig. 204, A).
The covering epithelium is hornified, especially at the apex of the papillae.
This epithelium forms hairlike tufts over the secondary papillae of the
connective tissue.
Interspersed between the filiform papillae are the isolated mushroomshaped or fungiform papillae (Fig. 204, B) which are round, reddish
prominences. Their color is derived from a rich blood supply visible
through the relatively thinner epithelium. Some fungiform papillae contain a few taste buds.
In front of the dividing V-shaped line, between the body and base of the
tongue, are found the vallate or circumvallate (walled—in) papillae (Fig.
205) ; they are 8 to 10 in number. They do not protrude above the surface of the tongue, but are bounded rather by a deep and circular furrow
which seems to cut them out of the substance of the tongue. They are
slightly narrower at their base. Their free surface shows numerous secondary papillae which are covered by a thin and smooth epithelium. On
the lateral surface of the vallate papillae and occasionally on the walls surrounding them, the epithelium contains numerous taste buds. Into the
trough open the ducts of small albuminous glands (von Ebner’s glands)
which serve to Wash out the furrows into which the soluble elements of
food penetrate to stimulate the taste buds.
At the angle of the V-shaped line on the tongue is found the foramen I
cecum which is a .remnant of the thyroglossal duct (see chapter on Development of the Face). Posterior to the vallate papillae, the surface of
ORAL MUCOUS MEMBR.-XNE 255
the tongue is irregularly studded with round or oval pron1inences known as
the lingual follicles. Each of the latter show one or more lymph nodules,
sometimes containing a germinal center (Fio-. 206). Most of these prommences have a small pit at the center, the lingual crypt, which is lined with
stratified squamous epithelium. Innumerable lymphocytes migrate into the
crypts through the epithelium. The ducts of the medium—sized posterior
lingual mucous glands open into the crypts. Together the lingual follicles form the lingual tonsil.
Filiform
papillae
         
 
Fungitorni - - - — — — — _
papilla
Foliate
papillae
Vallate
D9-Dilla.
z’ Foramen
cecum
335' 2)-r’ Lingual tonsil
hr» Entrance to
larynx
, , Pha.ryngo_ _ . 1 .' . , epiglottic
Eplglottis“ "‘ p, " _ * .  I -‘ : fold
" L‘ '  .‘,,—' Cuneiform
~ tubercle
. _ P’?
: §«:,...— Fold of supe‘ I, rlor laryn"" geal nerve
i‘_' " ‘ ' Corniculate
; ' tubercle
c. ,7 “~ Piriform
sinus
Interarytenoid - * — — - -* ‘
notch
Fig. 203.—Surtace view of human tongue. (Sicher and Tandler.)
On the lateral border of the posterior parts of the tongue sharp parallel
furrows of varying length can often be observed. They bound narrow
folds of the mucous membrane and are the vestiges of the large foliate
papillae found in many mammals. They may contain taste buds.
Taste Buds
256 ORAL ELISTOLOGY AND EMBRYOLOGY
The taste buds are small ovoid or barrel-shaped intra-epithelial organs
of about 80 microns in height and 40 microns thickness (Fig. 207). They
touch with their broader base the basement membrane while their narrower tip almost reaches the surface of the epithelium. The tip is cov
wefcfl 4 395
Fig. 204.——-Filiform (A) and fungiform (B) papillae.
ered by a. few flat epithelial cells, which surround a small opening, the
taste pore. It leads into a narrow space between the peripheral ends of
the sustentacular (supporting) cells of the taste bud. The outer supporting cells are arranged like the staves of a barrel, the inner and shorter ones
ow. MUOOUS mmmmm 257
   
 
 
,5-5 Taste bud
5  3%:
 
 
“ of v. Ebnel-'5
{——— _..._’  Opening of duct
' " ' gland
zland
Lymph nodule
with germinal _
center
Fig. 206.—L1ng'u8.l follicle.
258 ORAL HISTOLOGY AND EMBRYOLOGY
are spindle-shaped. Between the latter are arranged 10 to 12 neuroepithelial cells, the receptors of taste stimuli. They are thin, dark-staining
cells that carry a stiff hairlike process at each superficial end. This hair
reaches into the space beneath the taste pore.
A rich plexus of nerves is found below the taste buds. Some fibers
enter the taste bud from the base and end in contact with the taste cells.
Others end in the epithelium between the taste buds.
Taste buds are numerous on the inner wall of the trough surrounding
the vallate papillae, in the folds of the foliate papillae, on the posterior
surface of the epiglottis and on some of the fungiform papillae at the
tip and the lateral borders of the tongue.
Stratified
squamous
epithelium
Taste pore
Taste cells
Supporting cells
Connective tissue
Supporting cells
Fig. 20'l'.—Taste buds from the slope of a. vallate papilla. (From .1’. Schafter.)
The primary taste sensations, namely, sweet, salty, bitter, and sour,
are not perceived in all regions of the tongue. Sweet is tasted at the
tip, salty at the lateral border of the body of the tongue. Bitter and
sour are recognized in the posterior part of the tongue, bitter in the
middle, sour in the lateral areas. The distribution of the receptors for
primary taste qualities can, diagrammatically, be correlated to the different types of papillae. They are mediated by different nerves. The
vallate papillae recognize bitter, the foliate papillae sour, taste. The
ORAL MUCOUS MEMBRANE 259
taste buds on the fungiform papillae at the tip of the tongue are receptors for sweet, those at the borders for salty, taste. Bitter and acid
(sour) taste are mediated by the glossopharyngeal, sweet and salty taste
by the intermediofacial nerve via chorda tympani.
4. CLINICAL CONSIDERATIONS
To understand the pathogenesis of periodontal diseases and the pathologic involvements of the difierent structures, it is essential to be thoroughly familiar with the structure of cementum, periodontal membrane,
alveolar bone, and the structure of the marginal gingiva, gingival sulcus,
and epithelial attachment, as Well as their biologic relation to each
other. Periodontal disturbances, frequently, have their origin in the
gingival sulcus and marginal gingiva, leading to the formation of a deep
gingival pocket.‘ Moreover, the safe and speedy reduction of the depth
of the gingival pocket is the primary objective of treatment. The superiority of any given method of treatment should be judged by its
ability to accomplish this end whether the method be surgical, chemical,
or electrical.
In restorative dentistry, the extent of the epithelial attachment plays
an important role. In young persons, this attachment of the epithelium
to the enamel is of considerable length and the clinical crown is smaller
than the anatomical. The enamel cannot be removed entirely without
destroying the epithelial attachment. It is, therefore, very difficult to
prepare a tooth properly for an abutment or crown in young individuals. On the other hand, the preparation may be mechanically inadequate
when it is extended only to the bottom of the gingival sulcus. It should
be understood, therefore, that, in young persons, a restoration may serve
merely as a temporary measure and require ultimate replacement.
When large areas of the root are exposed, and a restoration is to be
placed, the preparation need not cover the entire clinical crown. The
first requirement is that the restoration be adapted to mechanical needs.
In extending the gingival margin of any restoration in the direction
of the bottom of the gingival sulcus, the following rules should be observed: If the epithelial attachment is still on the enamel, and the
gingival papilla fills the entire proximal space, the gingival margin of a
cavity should be placed below the marginal gingiva. Special care should
be taken to avoid injury to the gingiva and epithelial attachment, to
prevent premature recession of the gingiva. When the gingiva is pathologically affected, treatment should precede the placing of a filling. If
the gingiva has receded from the enamel, if the gingival papilla does
not fill the interproximal space and if the gingival sulcus is very shallow,
the margin of a cavity need not necessarily be carried below the free
margin of the gingiva. The gingival margin of a cavity should be placed
far enough from the contact poi11t to permit proper cleansing.
‘The term gingival pocket designates the pathologic condition of the gingival sulcus.
260 ORAL msrronocv AND EMBRYOLOGY
When the anatomical root is exposed, a predisposition to cemental
caries and abrasion exists. Improperly constructed clasps, overzealous
scaling, and too abrasive dentifrices may result in marked abrasion.
After loss of the cementum the dentin may be extremely sensitive to
thermal or chemical stimuli. Drugs, judiciously applied, may be used
to accelerate sclerosis of the tubules and secondary dentin formation.
It is desirable to keep the depth of the gingival sulcus at a minimum.
The more shallow the sulcus, the less opportunity for irritating material
to be deposited. This can be done in part by proper massage and brushing.
The diflerence in the structure of the submucosa in various regions
of the oral cavity is of great practical importance. Wherever the submucosa consists of a layer of loose connective tissue, edema or hemorrhage causes much swelling and infections spread speedily and extensively. Generally, inflammatory infiltrations in such parts are not
very painful. If possible, injections should be made into loose submucous connective tissue. Such areas are the region of the fornix and
the neighboring parts of the vestibular mucosa. The only place in the
palate where larger amounts of fluid can be injected without damaging
the tissues is the furrow between the palate proper and alveolar process
(Fig. 197). Also, it will be found that in the areas where the mucosa
is loosely fixed to the underlying structures, it is easier to suture surgical wounds than in those places where the mucous membrane is immovably attached.
The gingiva is exposed to heavy mechanical stresses during mastication. Moreover, the epithelial attachment to the tooth is relatively
weak, and injuries or infections can cause permanent damage here.
Strong hornification of the gingiva may afford relative protection.
Therefore, measures to increase hornification can be considered a prevention against injuries. One of the methods of inducing hornification is
mechanical stimulation, such as massage or brushing.
Unfavorable mechanical irritations of the gingivae may ensue from
sharp edges of carious cavities, overhanging fillings or crowns, and accumulation of calculus. These may cause chronic inflammation of the
gingival tissue.
Many diseases show their symptoms, initial and otherwise, in the oral
mucosa. For instance, metal poisoning (lead, bismuth) causes characteristic discoloration of the gingiva margin. Leukemia, pernicious anemia, and other blood dyscrasias can be, and often have been, diagnosed by
characteristic infiltrations of the oral mucosa. In the first stages of
measles, small red spots with bluish-white centers can be seen in the
mucous membrane of the cheeks, even before the skin rash appears; these
spots are known as Koplik’s spots. Endocrine disturbances, including
those of the estrogenic and gonadotropic hormones and of the pancreas
may be reflected in the oral mucosa.
ORAL MUCOUS MEMBRANE 261
In denture construction it is important to observe the firmness or
looseness of attachment of the mucous membrane to the underlying bone.
Denture—bearing areas should be those where the attachment of the
mucosa is firm. The margin of dentures should not reach into areas
where the loose mucous membrane is moved by muscle action.“’v 2°
In old age, the mucous membrane of the mouth may atrophy in the
cheeks and lips; it is then thin and parchment-like. The atrophy of the
lingual papillae leaves the upper surface of the tongue smooth, shiny
and varnished in appearance. A senile atrophy of major and minor
salivary glands may lead to xerostomia and sometimes an accompanying
atrophy of the mucous membrane. In a large percentage of individuals,
the sebaceous glands of the cheek may appear as fairly large, yellowish
patches. Such a condition is known as Fordyce’s disease, but does not
represent a pathologic change.
References
1. Aprile, E. C. de: Contribucion al estudio de los elementos reticulo endoteliales
de la mucosa gingival, Arch. Hist. normal y Pat. 3: 473, 1947.
la. Becks, H.: Normal and Pathological Pocket Formation, J. A. D. A. 16: 2167,
1929.
2. Bodecker, C. F., and Applebaum, E.: The Clinical Importance of the Gingival
Crevice, Dental Cosmos 176: 1127, 1934.
3. Fish, E. W.: Bone Infection, J. A. D. A. 26: 691, 1939.
3a. Gairns, F. W., and Aitchison, J. A.: A Preliminary Study of the Multiplicity
of Nerve Endings in the Human Gum, The Dental Record 70: 180, 1950.
4. Gottlieb, B.: Der Epithelansatz am Zahne (The Epithelial Attachment),
Deutsche Monatschr. f. Zahnh. 39: 142, 1921.
5. Gottlieb, B.: Aetiologie und Prophylaxe der Zahnkaries (Etiology and Prophylaxis of Caries), Ztschr. f. Stomatol. 19: 129, 1921.
6. Gottlieb, B.: Tissue Changes in Pyorrhea, J. A. D. A. 14: 2178, 1927.
7. Gottlieb, B., and Orban, B.: Biology of the Investing Structures of the Teeth,
Gordon ’s Dental Science and Dental Art, Philadelphia, 1938, Lea av Febiger.
8. Gottlieb, B., and Orban, B.: Biology and Pathology of the Tooth (Translated by
M’. Diamond), New York, 1938, The Macmillan Co.
9. Kronfeld, B.: The Epithelial Attachment and So-Called Nasmyth’s Membrane,
J. A. D. A. 17: 1889, 1930.
10. Kronfeld, 3.: Increase in Size of the Clinical Crown of Human Teeth With
Advancing Age, J . A. D. A. 18: 382, 1936.
11. Lehner, J.: Ein Beitrag zur Kenntniss vom Schmelzoberhiiutchen (Contribution
to the Knowledge of the Dental Cuticle), Ztschr. f. mikr.-anat. Forsch. 27:
613, 1931.
12. Meyer, W.: Ueber strittige Fragen in der Histologie des Schmelzoberhiiutchens
(Controversial Questions in the Histology of the Enamel Cuticle), Vrtljsschr.
f. Zahnh. 46: 42, 1930.
13. Orban, B., and Kohler, J.: Die physiologisiche Zahnfleischtasche, Epithelansatz
und Epitheltlefenwucherung (The Physiologic Gingival Sulcus), Ztschr.
f. Stomatol. 22: 353, 1924.
14. Orban, B., and Mueller, E.: The Gingival Crevice, J. A. D. A. 16: 1206, 1929.
15. Orban, B.: Hornification of the Gums, J . A. D. A. 17: 1977, 1930.
16. Orban, B.: Zahnfleischtasche und Epithelansatz (Gingival Snlcus and Epithelial
Attachment), Ztschr. f. Stomatol. 22: 353, 1924.
17. Orban, B.: Clinical and Histologic Study of the Surface Characteristics of the
Gingiva, J . Oral Surg., Oral Med., Oral Path. 1: 827, 1948.
18. Orban, B., and Sicher, 11.: The Oral Mucosa, J. Dent. Educ. 10: 94-103, 163-164,
1946.
19. I-‘endleton, E. 0.: The Minute Anatomy of the Denture Bearing Area, .1’. A. D. A.
21: 488, 1934. _ _
20. Pendleton, E. 0., and Glupker, 11.: Research on the Reaction of Tissues Supporting Full Dentures, J. A. D. A. 222 76, 1935262 ORAL HISTOLOGY AND EMBRYOLOGY
21. Robinson, H. B. G., and Kitchin, P. 0.: The Effect of Massage With the Tooth
brush on Keratinization of the Gingivae, Oral Surg., Oral Med., Oral Path.
1: 1042, 1948.
22. Skillen, W. G.: The Morphology of the Gringivae of the Rat Molar, J. A. D. A.
17: 645, 1930.
23. Toller, J. R.: Studies of the Epithelial Attachment on Young Dogs, Northwestern
U. Bull. 11: 13, 1940.
24. Wassermann, F.: Personal communication.
25. Weinmann, J. P.: Progress of Gingival Inflammation Into the Supporting
Structures of the Teeth, J. Periodont. 12: 71, 1941.
26. Weinmann, J. P.: The Keratinization of the Human Oral Mucosa, J. Dent.
Research 19: 57, 1940.
27. Wermuth, J.: Beitrag zur Histologie der Gregend seitlich Von der Papilla palatina (Histology of the Region Lateral to the Incisive Papilla), Deutsche
Monatschr. f. Zahnh. 45: 203, 1927.
CHAPTER X
GLANDS OF THE ORAL CAVITY
INTRODUCTION; SALIVA
EISTOGENESIS
CLASSIIPICATION OF SALIVARY G-LANDS
SEGRETORY CELLS OI‘ THE SALIVARY G-LANDS
MYOEPITHELIAL CELLS
DUCT ELEMENTS
INTERSTITIAL TISSUE
SAI.-IVARY G-LAITDS OI‘ MAJOR SECRETION
SALIVABY G-LANDS O1‘ MINOR SECRETION
. CLINICAL CONSIDERATIONS
H
°S°9°.“.°°9‘!*“."°!°!"
1. INTRODUCTION
The salivary glands of man are exocrine glands, the primary function
of which is to transform and secrete materials brought to them via the
circulating fluids of the body. This function represents active Work in
producing and discharging complex substances, such as mucin and
ptyalin, which are not found in the circulating blood and lymph. The
cells give morphologic evidence of their secretory function, and because
they remain intact throughout a cyclic process of formation and discharge, these glands are classified as merocrine in type.
A secondary function of the salivary glands is to excrete certain substances. Evidence of this may be seen in comparing the constancy of
the ratio between salivary and blood urea, nitrogen and creatinine.”
Saliva is the term applied to the accumulated secretory and excretory
products discharged by the salivary glands into the oral cavity. The
saliva is the first of many digestive fluids to act upon the food elements
in the diet, its main actions being to assist in the mastication of food
and to act as a solvent for bringing components into solution, thus
facilitating the stimulation of the taste organs. Albuminous or serous
cells of the glands liberate the enzyme ptyalin or amylase which
causes a preliminary breakdown of carbohydrates. The mucous celLs liberate mucin which counteracts tendencies to desiccation of the oral membranes and dental hard structures, and aids in the lubrication of the
bolus of food for deglutition. The proteins and salts of saliva act as
bufiers which tend to counteract the acids and alkalies in the oral cavity.
Saliva is mechanically protective inasmuch as it serves to flush the sur
Flrst draft submitted by Virgil D. Cheyne.
263
264 emu. HISTOLOGY AND ammevocoev
faces of the teeth and mucous membranes of food and debris. Its action of
removing bacteria from ducts and surfaces is a safeguard against infection.
There is some indication that saliva, normally, contains an antibacterial
factor which inhibits the growth and activity of aciduric bacteria in the
oral cavity, and may act to prevent dental caries.‘ 1° There is also evidence, however, that the saliva of some individuals may supply the proper
culture medium needed for the bacteria found in the mouth. Because of
these contradictions the role of saliva in dental caries is as yet unsettled
and requires further investigation.
The total daily amount of saliva secreted by man is approximately
1,500 c.c. This quantity is subject to great variation, depending upon
age, exercise, and diet. It is materially influenced by physical and psychologic stimulation and varies Widely in different individuals. Of the total
amount secreted, the large salivary glands (parotid, submaxillary, and
sublingual) contribute by far the greatest amount. The quality is directly
dependent upon the type of glands which participate in its formation.
The methods of collection and the type of stimulus have an important
influence upon the composition of saliva. In man, the mixed excretions
from the glands may be collected in the unstimulated or resting state by
simply cxpectorating into a receptacle or, in the stimulated or active state,
by chewing parafiin. Pure secretions from the individual glands may be
collected by the use of Lashley’s double metal cup instrument which can be
applied to the mucous membrane surrounding the papillae of the salivary
ducts,” or by direct canalization of the ducts of the parotid, submaxillary,
or sublingual glands. Saliva obtained in this manner is a clear, colorless
fluid. The function of certain glands or groups of glands in animals has
been clarified by selectively removing salivary tissue,‘ or by the experimental production of a fistula, the duct being diverted to the outside of
the oral cavity.
Mixed saliva is a frothy, slightly opalescent fluid containing water,
proteins, mineral salts, ptyalin, mucin, food particles, desquamated epithelial cells and salivary corpuscles. Its viscosity is dependent upon the
predominating type of saliva secreted. Serous saliva imparts the Watery
characteristics to the fluid; mucin in the saliva renders it thick and ropy.
The specific gravity of mixed saliva varies from 1.000 to 1.020, the freezing point being lower than for the other secretions of the digestive glands.
Results of hydrogen-ion determinations (pH) of saliva vary greatly, owing
to individual variation, time of day, and difierence in methods used for
its determination. The mean or average pH of resting saliva is approximately 6.8, ranging from 5.6 to 7.6 and being highest just before meals.‘
Undoubtedly, oral hygiene and the nature of the oral flora are also influencing factors.
Chemically, human, mixed saliva is a dilute solution containing about 0.2
per cent inorganic solutes and 0.5 per cent organic matter. The bulk of the
inorganic portion consists of potassium and phosphate ions. The following
Quantity
Methods of
Study
characteristics
GLANDS on THE ORAL CAVITY 265
elements, however, are found in appreciable amounts: Cl, P. Na, K, Mg,
Ca, and S. The amount of NaCl is approximately 90 mg. per 100 c.c.; the
amount of carbonate, as C0,, 13.0 mg. The C0._., Ca, and K present in the
saliva exceed the concentration in the blood, While the sodium chloride concentration is lower in saliva. Oxygen is present in the human parotid
saliva in amounts varying from 0.84 to 1.46 c.c. per 100 c.c.
Leucocytes
Epithelial
Leucocytes
Fig. 208.—Smear of human saliva (Wright's stain). (Orban and Weinmannfl)
A large portion (0.4 per cent) of the organic matter in mixed secretions
is mucin. With the exception of mucin, the principal organic constituents
of saliva are albumin, globulin, amylase, and cholesterol. Urea, uric acid,
creatinine, maltase, and ammonia are found in varying amounts. The
ammonia originates largely from the decomposition of urea. In normal
subjects values range from 1.28 to 13.66 mg. of ammonia nitrogen per
100 c.c. of saliva.” Total nonprotein nitrogen, urea plus ammonia, nitrogen, and uric acid average 37 per cent and 40 per cent, respectively, of
the corresponding constituents of blood.” Blood amino-acids and polypeptides are not found in appreciable amounts in the saliva.
Histology
266 can. msronocr AND snnsronoer
Sulfocyanate is generally present in the saliva to the extent of several
milligrams per cubic centimeter. It is greatest in habitual smokers. The
significance of sulfocyanate in the saliva is not known, but it probably
comes from ingested cyanides present in certain fruits, tobacco, and from
the disintegration of protein material. It is, apparently, not related to
tooth decay.”
The opacity of saliva is attributed mainly to the presence of desquamated epithelial cells and salivary corpuscles (Fig. 208), the latter consisting of polymorphonuclear leucocytes and lymphocytes. The epithelial
cells are large and flat with oval nuclei. They may be round or roughly
irregular, with a granular cytoplasm. The salivary corpuscles are derived from the mucous membrane of the mouth, the tonsils and salivary
glands. The average number of salivary corpuscles is, usually, less than
25 cells per cubic mm. of saliva, but higher counts (500 to 1,000) have been
reported.” Lymphocytes constitute a relatively minor proportion of this
number. Corpuscle counts are high after a night’s rest, low after meals.
Their role is as yet imperfectly understood but it is the opinion of some
investigators that they are phagocytic, reducing the bacterial flora of
the mouth.
2. HISTOGENESIS
The salivary glands are formed during fetal life as solid buds of oral
epithelium with club-shaped ends pushing into the subjacent mesoderm.
As the bud or anlage grows it proliferates distally, forming a cord of
cells. The most distal portion forms the alveoli or fimctional elements of
the gland. Cords and buds are at first solid and are later hollowed out
to form ducts and alveoli.
The bud of the parotid salivary gland appears as a shelflike outgrowth
of epithelium during the fourth week of fetal life at the angle of the
maxillary process and the mandibular arch (sulcus buccalis) ; the bud of
the submaxillary appears in the sixth week, and that of the major sublingual (Bartholinian) during the eighth to ninth week from similar outgrowths located at the medial angle of the hollow between the tongue
and mandibular arch (sulcus lingualis). The minor sublingual glands
(Rivinian) arise as independent proliferations in the alveolingual region
associated with the sulcus lingualis at the lateral margin of the plica sublingualis. Accessory and secondary lobes of the parotid and submaxillary glands become visible during the eighth to ninth weeks, as outgrowths arising from the cords of their respective glands. All the elements of the smaller sublingual, glossopalatine and palatine groups
develop from the primitive oral epithelium. The anterior lingual glands
are noticeable for the first time at ten weeks. They start as epithelial
proliferations located on the ventral surface near the tip of the tongue on
both sides of the median line. Development of the labial glands takes
place simultaneously with the anterior lingual glands. Lymphoid tissue
GLANDS on THE ORAL CAVITY 267
is, frequently, found in the fetal salivary glands; this is especially common
in the parotid. Occasionally, remnants of lymphatic tissue are found in
the adult.
3. CLASSIFICATION OF THE SALIVARY GLANDS
The human salivary glands are usually classified either according to
the type of cells or according to the location of the gland. Cells
which liberate mucin are named mucous cells, and those Which secrete some form of protein (enzyme) are called albuminous or serous
cells, but it is now quite evident that all mucous cells, as Well as
all albuminous cells, do not produce identical products. In many cases
the secretory granules of albuminous cells give a distinct reaction for
mucin with mucicarmine stain. This would indicate that it is possible
for these cells to secrete both mucin and protein substances. Although a
simple classification of the glands according to the chemical qualities of
their secretion remains unsatisfactory, the glands are best classified as
albuminous, mixed and mucous glands. The parotid gland of the adult
is a pure albuminous gland. Glands with very few or no mucous cells are
those of the vallate papillae. Glands in which both serous and mucous
cells are present (true mixed glands) are referred to as predominantly
serous or predominantly mucous, depending upon the ratio of the cell
types. Those with a few mucous cells include the submaxillary gland
(and the parotid gland of the newborn). Those predominantly of mucous
character include the labial glands, small buccal glands, anterior lingual
glands, and the sublingual gland. In man pure mucous glands are those
at the base and border of the tongue, the glossopalatine glands and the
palatine glands.
Classification of the Oral Glands According to Location?‘
A. Glands of the vestibule:
1. labial glands:
a. superior labial glands
b. inferior labial glands
2. buccal glands:
a. minor buccal glands
b. parotid gland
B. Glands of the oral cavity proper:
1. glands of the floor of the mouth (alveolingual complex)
a. submaxillary (submandibular) gland
b. major sublingual gland
c. minor sublingual glands
d. glossopalatine glands
The
Albuminous
Cell
means
268 ORAL msronoov AND nmnnvonoev
2. glands of the tongue:
a. anterior lingual glands
b. posterior lingual glands
(1) glands of the vallate papillae
(2) glands of the base of the tongue
3. palatine glands
4. SECRETORY CELLS OF THE SALIVARY GLANDS
Both albuminous and mucous cells vary in appearance with the flinctional changes of the gland.
The albuminous or serous cells of the parotid gland and other glands
of the mouth probably do not perform an identical function; the cells,
however, resemble each other closely. Their secretion is a thin watery
fluid containing a high percentage of organic and inorganic substances.
Albuminous cells are roughly pyramidal or polyhedral in shape, and
form globular alveoli, the lumina of which are very narrow. The cells
drain, for the most part, by intercellular secretory capillaries or canaliculi. In resting cells of a fixed specimen the small highly refractive
secretory granules, embedded in a closely reticulated cytoplasm, obscure
the cell boundaries. These zymogen granules are the antecedents of the
enzyme ptyalin. They accumulate between the nucleus and the free end
of the cell. They are easily dissolved by chemical agents, but are more
stable than the granules in the mucous cell. Following stimulation they
diminish in number (Fig. 210).
In addition to the secretory granules the cytoplasm contains rod-shaped
mitochondria, a Golgi net, and a cytocentrum which can be demonstrated
only by special staining methods (Fig. 210). Intracellular fat droplets
are common. The nucleus of the albuminous cell is large, spheroidal,
and filled with abundant chromatin substance. Its size and location are
somewhat dependent upon the stage of activity of the cell.
The mucous cell of the salivary glands secretes mucin, a glycoprotcin
which, dissolved in water, becomes a lubricating solution called mucus.
It makes the saliva highly viscid. In man, mucous cells are studied best
in sublingual glands, the mucous glands of the tongue, the glossopalatine
and palatine glands. They are also found in small mixed glands where
they make up the greater number of alveoli; in the submaxillary gland
they are few in number.
The mucous cells are irregularly cuboidal in form and aligned against
a basement membrane (Fig. 211). Mucous alveoli vary from globular to
long branching masses, their lumina forming large ovals or elongated
tubules. In the fixed preparation the nucleus is often deformed, shrunken;
it is located at the base of the cell. The accumulation and removal of
‘,'.~
Buccal mt pad ".
. “K, ‘In...
Parofid gland -"""" 3’~‘“
I
Minor sublingual --.-/‘V g’ ':-4-_..,m».“‘
ducts »
Sublingual gland ———— —— Ii‘ '
V
Submaxillary duct — — — — ~ — — - J
Submaxillary _. L _' ______ .../
gland
Fig. 209.-Salivary glands of mad 1:1
muscle mug: ed.5°°?esi:11l1(-er a1;3&flT:‘f1dlt:1:P;nudib1e and mylohyold
5
_—:
.3.
‘a
Different functional stages at
(zknmermannfi)
Fig. 210.——A1buminoua gland.
cycle is indicated by the letters 9. to g.
   
0" - Mucous cell
Arrangement
o1'_ cells in
Glands
Intercellular secre
270 ORAL HISTOLOGY AND EMBRYOLOGY
mucigen can be studied under favorable conditions. As the stimulated
cell liberates its contents, the nucleus rises from the base and assumes an
ovoid shape.
Mucigen granules cannot be observed because of their labile character
except in fresh condition or by special methods of fixing and staining,
whereby they can be stained specifically with mucicarmine and mucihematin. Mucous cells which have lost their granules have an empty appearance and the remaining cytoplasm takes a faintly blue stain with
hematoxylin. In properly prepared specimens a few irregular mitochondria, a Golgi net and a cytocentrum can be demonstrated; fat glob
ules are a constant feature.
 
 
Albuminous
cell of
demllune
Lumen of
alveolus
— Mucous cell
tory capillary
Fig. 212.-7Semidiagr-ammatic drawing or a. section through a mixed alveolus in the submaxillary gland. Serous cells forming a. demllune around the mucous cells.
In mixed glands mucous and serous cells are combined in such a Way
that either all the cells of some alveoli are serous, and all the cells of
others mucous; or that within the same alveolus both serous and mucous
cells are present. In a mixed alveolus the albuminous cells occupy a
position at the terminal or peripheral region. They are found as small
crescent-shaped clumps which cap the mucous cells: crescents or demilunes of Gianuzzi (Figs. 212 and 215, a). Crescent cells are somewhat
smaller, more finely granular, and darker staining than mucous cells in
ordinary preparations.
Albuminous cell
Process of myoepithelial cell
GLANDS or run om. cmrr 271
The secretory surfaces of the mucous cells form the lumen of a mixed
alveolus. The cells of the crescents do not reach the lumen and discharge
their secretion through fine secretory capillaries which pass between the
mucous cells (Fig. 212).
5. MYOEPITHELIAI. CELLS
In all salivary glands a syncytium of branching stellate cells surrounds
the ducts and cells of the terminal secretory portions. They are in close
contact with the bases of the glandular cells and lie between them and the
basement membrane. They lie in a similar location in the ducts. Viewed
cell
Fibroblast
Fat
Fibroblast
 
 
 
s
2 .‘  Basement
Blood vessel
duct
Fig. 213.—A1buminous alveoli and striated duct or subma.xilla.ry gland with myoepithelial
cells. (Modified after Zimmennannfi)
from the periphery, they appear as spider—like structures embracing
the alveoli (Fig. 213). Although probably of epithelial origin, these
cells function as a part of the supporting structure of the glandular
elements and are called basal or basket cells, or myoepithelial cells.
The body of the myoepithelial cell is made up of a dark, angular nucleus
with a scanty amount of cytoplasm containing fine, straight fibrils
which continue into many tentacle-like processes that encircle the
basal portion of the alveolar cells. In cross section only their nuclei
are visible. The cells become especially prominent after treating fresh
glandular tissue in the state of active secretion with osmic acid or by
teasing fresh glandular substance in water.“
It is generally believed that myoepithelial cells are contractile cells
which facilitate the movement of the secretion into and through the ducts.
The phenomenon which is known as motor effect of the sympathetic
Myoepithelial
membrane
Lumen of striated
Location
Albumlnous cell
' ‘ Myoepithelial cell
.— Striated cell
_._ __. Excretory duct
4.
.1 _._ Striated duct
__ Intercalated duct
Secretory alveoll
__ Excretory duct
B.
———. — Striated duct
Intercalated duct
Secretory alveoll
.__ ;._ Excretory duct
__ __ Striated duct
0.
8] 214.——Dia.g-rams of the duct system and terminal‘ secretory portions or salivary
A. Parotid.
B. Subma.xil.Ia.ry.
G’. Sublzlngual. (Modified after Brauafi)
GLANDS on THE ORAL CAVITY 273
nerves on the large salivary glands is probably caused by contraction of
these cells under nervous stimulation.“ True muscular tissue is absent
in the salivary glands.
6. DUCT ELEMENTS
The duct system of the salivary glands is complex and branching (Fig.
216). The smallest excretory channels are the intercalated ducts or the
so-called necks or isthmuses. These connect the terminal alveoli with the
Albumlnous cell
-  Myoepithelial
_, . cell
, .
I’
serous alveolus I’-ll’-31'¢°11“18!‘
secretory
capillary
Demllune
Myoeplthelial
cell
Basement
membrane
Mucous cells
Intercalated duct
Striated duct
Fi . 216.—Reconstruc1:ion of a terminal portion and its duct or a salivary gland (a).
(b) ross section through serous alveolus. (0) Cross section through mucous alveolus.
(d) Qross section through lntercalated duct. (a) Cross section through striated duct.
(Maximow and Bloom“)
excretory system. An outstanding characteristic of the intercalated
ducts is their thin Wall and relatively small diameter. They are always
surrounded by moyepithelial cells ‘(Fig 213). The cells are simple, low
cuboidal in type, remain relatively undifferentiated, and take ordinary
stains very poorly. They are of variable length depending on the type
of gland which they drain. The parotid gland has long intercalated
very short and inconspicuous (Fig. 214). In pure mucous glands the
cells abut directly upon the distal tubules of the larger excretory ducts.
In the parotid and submaxillary glands striated ducts (secretory ducts,
salivary tubules) intervene between the intercalated ducts and the larger
excretory ducts. These ducts are believed to secrete water and inorganic
salts which act to dissolve the antecedents secreted by the alveolar cells.
In the striated ducts the epithelial cells are regular and columnar in form
274 ORAL HISTOLOGY AND EMBRYOLOGY
and arranged in a single layer. The cytoplasm is finely granular and
contains a nucleus which is centrally placed. The perpendicular striations from which the cells derive their name are confined to the outer or
basal zone near the basement membrane (Figs. 215, 217). In the larger
ducts (parotid, submaxillary, major sublingual) the epithelium is columnar and pseudo-stratified; a basement membrane is distinct between
epithelium and connective tissue wall. Where the ducts open into the
oral cavity the walls fuse with the mucous membrane.
A common feature of compound glands in general is the presence of
secretory capillaries or canaliculi which arise from the smallest excretory
ducts and penetrate between the functional cells at their boundaries (Figs.
212, 215). The purpose of secretory capillaries is to increase the drainage
capacity of alveoli composed of multiple layers of cells and, for that
reason secretory capillaries are a constant feature of mixed alveoli. The
capillaries are most effectively demonstrated with silver impregnation.
7. INTERSTITIAI. GONNECTIVE TISSUE; BLOOD, LYMPH
AND NERVE SUPPLY
The interstitial substance of the salivary glands is loose connective
tissue made up of a large number of fibers. The fibers run in all directions to form networks which surround and support the various elements.
In it are fibroblasts, macrophages, plasma and fat cells which vary in
relative number with the type of gland. Around the terminal alveoli
and ducts, located peripherally to the myoepithelial cells, the connective
tissue forms a basement membrane.
The salivary glands possess a rich blood supply. The larger arteries
follow the course of the excretory ducts, giving off branches which accompany the divisions of the ducts to the lobules; the capillaries form
dense networks on the outer surface of the basement membrane of alveoli
and ducts. The veins and lymph vessels follow the arteries in reverse order
to drain the gland. The main branches of the nerves supplying the salivary
glands also follow the course of the vessels to break up into terminal plexuses in the connective tissue adjacent to the alveoli. Both sympathetic and
parasympathetic fibers pass through the basement membrane and end in
varicose filaments and budlike expansions between the secretory cells.
8. MAJOR SALIVARY GLANDS
The parotid, submaxillary and sublingual glands are often classified
as the salivary glands proper. Because of their size and the volume of
saliva which they contribute they deserve special consideration. Physiologic investigations have been, for the most part, carried out on these
glands but conclusions which have been drawn from their study can probGL.-LNDS or THE ORAL oavrrr 275
ably be applied with little change to the numerous smaller glands of the
oral cavity. A comparison of the anatomic features of the three large
salivary glands is presented in the accompanying table.
Tasnn IX
COMPARISON or rm: MAJOR Sanrvucr GLANDS
(Amen Cownnv)
 
   
 
 
 
     
   
 
   
   
 
 
   
SUBMAXILLARY SUBLINGUAL
Size and Largest; main and ac- Intermediate; well lim-Smallest; major gland
 
 
   
   
 
 
 
 
 
       
 
shape cessory parts both en- ited and encapsulated; and several minor
capsulated; compound, compound, branched, ones; no capsule; com
branched, alveolar alveolar, partly tubular poxmd, b ranch e d,
tubnlo-alveolar
Posifion A r ound mandibular Beneath mandible (also In floor of mouth
ramus anterior to ear called submandibular
gland)
Ducts Parotid (Stenson’s)ductSubma.xi1lary (Whar- Major sublingual (Baropens opposite second ton’s) duct opens on tholin’s) duct opens
upper molar; double either side of frenu- near submaxillary
layer columnar cells on lum of tongue; struc- sometimes by common
in a r k e d basement ture same aperture, also several
membrane minor sublingual
(Rivinian) ducts;
structure same
Secretory Single layer very con- Same but somewhat Rare or absent
ducts spicuously striated longer and may coneolumnar cells tain yellow pigment
Inter- Long, narrow, brancl1- Much shorter but similar Absent
calated ing made of single structure
ducts layer of flattened cells
59°79“?! 5610115 8-1V601i, 1111160115 Serons alveoli predom-Major gland: mucous
e_pithe- alveoli rare (in new- inate, some mucous al- alveoli predominate,
hum born) veoli have serous cres- many serous crescents
cents and alveoli. Minor
glands all mucous
Interstitial Fat cells most abundant Connective tissue septa
‘$188118 most abundant
Ni’-"73 Sensory: fifth nerve. Sens fifth nerve. Sensory: fifth nerve
WPP1)’ Secretary: (1) sympa- Secretory: (1) sympa-Secretory: same as subthetic, superior cer- thetic, same; (2) maxillary gland
vical ganglion (vaso- parasympathetic,
constriction); seventh‘ nerve, chords
(2) parasympathetic, tympam, subrnamllary
ninth nerve, fitic gan- ganglion (vasod1laglion (vasodilation) tion)
The parotid gland (glandula parotis) is the largest of the salivary
glands. Its superficial portion is located in front of the external car on
the lateral surface of the masseter muscle and extends slightly backward
below the external auditory meatus. Its upper corner never transgresses
the zygomatic arch, the lower corner reaches into the neck as cervical
lobe (Fig. 209). The deep part of the parotid gland fills the retromandibular fossa. The gland is enclosed within a strong capsule which is
tightly adherent and continuous with the connective tissue separating
lobes and lobules. Accessory parotid glands are often found alongside
the parotid duct.‘
Parotid Gland
276 our. HISTOLOGY mu mmnmzonoey
The parotld gland empties by the parotid duct (ductus parotideus,
Stenson’s duct) which is given off at the anterior corner of the gland,
continues forward, turns around the anterior border of the masseter
muscle, pierces the buccinator muscle and mucous membrane of the cheek
to open opposite the upper second molar. Usually a small papilla marks
the opening.
. 1:, yrs ‘;f'::.&v:h ‘,.
‘  ‘xi  an
   
Branching
duct
'$;':‘I".‘;‘3|. ’ - ;’V
Fig. 216.—Section through a human parotid gland.
Intercalated ' ~  *~-~—v~—
duct
Striated duct ,, new W4, A *-W’-r—‘ ' - - --— striated duct
Fig. 217.—I-Iigher magnification of field X in Fig. 216.
GLANDS on THE omu. csvrrr 277
 
 
   
- Albuminous
alveoll
3-Mucous
alveoli
5 ‘i id 57>‘ i« I‘ ./
.:"‘-  ‘ii. . .‘:-  ’  ‘Zn :1" i 
Fig. 218.—Section through a human submaxillary gland.
7)" Albuminous
Demilune _* ‘mean
Mixed -alveolus
Interlobulsr
septum
Fig. 219.—Higher magnification or fleld X in Fig. 218.
The parotid gland of the adult is made up entirely of albuminous cells
(Fig. 216). The alveoli which form small tightly packed oval masses are
drained by long thin branching intercalated ducts; striated tubules are
conspicuous (Fig. 217).
The parotid gland produces a thin and watery saliva which serves for
the moistening and cleansing of the mouth cavity. It contains, besides
278 ORAL HISTOLOGY AND EMBRYOLOGY
Interlobular ‘
septum
Fig. 220.—-Section through a. human major sublingual gland.
Fig. 221.-—Higher magnification of field X in Fig. 220.
GLANDS or THE osar. oavrrr 279
salts and proteins, the enzyme ptyalin (amylase) which acts chemically
to hydrolize starch into simpler compounds.
The submaxillary gland (submandibular gland; glandula submaxillaris)
of man comprises one component of the group of glands in the floor of
the mouth sometimes designated as the alveolingual complex.‘ It is
ovoid in form, loosely encapsulated and about the size of a walnut. The
greater part of the gland is located in the submaxillary triangle behind
and below the free border of the mylohyoid muscle (Fig. 209). It is
usually divided into several large lobes by deep incisures penetrating to
the hylus. A tongue—like extension of the gland usually lies above the
mylohyoid muscle close to the sublingual glands. It, occasionally, extends forward under cover of the lesser sublingual gland, nearly to the
midline, and is designated as the secondary submaxillary gland proper.
The submaxillary gland including its accessory portions drains by the
submaxillary duct (Wharton’s duct) which is composed of many smaller
ducts arising in the lobules of the gland. The submaxillary duct is much
thinner than the parotid duct. The supporting stroma contains a few
longitudinal smooth muscle cells. It opens by a narrow orifice on the
summit of a small papilla, caruncula sublingualis, at the side of the
lingual frenulum at the floor of the mouth.
In man, the submaxillary gland is of the mixed type with albuminous
elements predominating (Fig. 218). Many purely serous alveoli are present; infrequently occurring mucous alveoli are usually capped by demilunes of serous cells. The intercalated ducts of the submaxillary gland
are relatively short (Fig. 214), but similar in structure to those of the
parotid gland (Fig. 219). The striated tubules are also structurally similar to those of the parotid but are somewhat longer (Fig. 214).
The secretion of the submaxillary gland contains mucin and is, consequently, more viscid than that of the parotid gland. It is described as
clear and abundant. It varies, however, both in quantity and quality
with the type of stimuli.
The sublingual glands form a composite of one larger and several smaller
glands which open independently into the oral cavity. The larger or
major sublingual gland (Bartholinian gland) is drained by a single duct,
major sublingual duct, Bartholin’s duct. The smaller glands, Rivinian
glands, are usually 8 to 20 in number and drain by separate openings,
Rivinian ducts. The greater and lesser sublingual glands plus the supramylohyoid submaxillary gland sometimes carry the inclusive designation
of “massa sublingualis.”‘
The sublingual gland or glands of the adult are the smallest of the units
comprising the salivary glands proper. The greater sublingual is narrow, flattened and elongated; it is situated in the floor of the mouth in
the sublingual fold (Fig. 209). The course of the duct which drains it
is roughly parallel to and a little lateral to the submaxillary duct. It
opens into the mouth at the side of the frenulum of the tongue on the
submaxillary
Gland
sublinguai
tion
Tubulo-alveolar :
terminal por- _
A Albumlnous
alveolus
septum
Demllune
Mucous
alveoli
fiiual Glands
Minor Buccal
Glands
Demllune .7
280 out HISTOLOGY AND EMBRYOLOGY
salivary caruncle with Wharton’s Qluct, in most cases; occasionally, however, the duct opens independently into the oral cavity near the submaxillary duct.
Some of the ducts of Rivini which do not take part in the formation of
the larger sublingual duct, join the submaxillary duct, others open separately into the mouth on an elevated crest of the mucous membrane, plica
sublingualis.
The large sublingual gland in man is a mixed gland in which the
mucous elements predominate (Figs. 220, 221, 222). Most alveoli are
purely mucous, the albuminous cells are mostly found as demilunes in
mixed alveoli. Purely serous alveoli are rare. The smaller sublingual
glands are, for the most part, mucous glands.
 
Fig. 222.--Section thro h a human sublingual gland with long tubulo-alveolar terminal
no ons. (Courtesy Army Medical Museum.)
10. MINOR SALIVARY GLANDS
The labial glands, which are located in the inner surface of the lips, are
of the mixed type. They are variable in size and closely packed in the
submuoosa where they may be easily palpated. They are not encapsulated. The secretory portions may contain both serous and mucous cells
lining the same lumen but more often typical demilunes are formed. A
considerable number may contain only mucous cells (Fig. 223). The cells
have a distinct muco-albuminous character, the intercalated ducts are short.
The buccal glands, which are a continuation of the labial glands, bear a
marked resemblance to those of the lips. The glands which lie in the immediate vicinity of the parotid duct opening, and drain in the third molar
region, are frequently designated as the molar glands (Fig. 224).
GLANDS or THE ORAL CAVITY 281
The glossopalatine (isthmian or faucial) glands are pure mucous glands; G1‘(’}*:;P;:‘”"°
they are located in the isthmus region and are a continuation, posteriorly,
of the lesser sublingual glands. They ascend in the mucosa of the glosse
Fig. 224.—Section through a human retromolar gland.
Palatine
Glands
Glands of the
Tongue
282 ORAL HISTOLOGY AND EMBRYOLOGY
palatine fold. They may be confined to the anterior faucial pillar or extend
into the soft palate to fuse with the palatine glands pI‘0PeI‘- They may
also be seen on the lingual side of the retromolar area of the mandible.
The palatine glands which occupy the roof of the oral cavity can be
topographically divided into ( 1) glands of the hard palate; (2) glands of
the soft palate and uvula. They are composed of independent glandular
aggregates numbering approximately 250 in the hard palate, 100 in the
soft palate, and 12 in the uvula. In the posterior area of the hard palate
the glands lie between the mucous membrane and bone supported by a
Fig. 225.——'.l.‘he palatine glands. (Sicher and Tandlerfi)
dense framework of connective tissue characteristic of this region. Continuing backward, the lateral groups become arranged into compact rows
and take on considerable size (Fig. 225). They merge with those of the
soft palate and form a thick layer between the mucous membrane and
palatal musculature (see chapter on Mucous Membrane).
The structure of the palatine glands is that of long branched tubulo~
alveoli connecting with single ducts. The predominating cell produces
only mucus. Cells of the so-called intercalated ducts are converted into
mucous cells in the palatal glands, and function as part of the elongated
alveoli.
The glands of the tongue are of three types: serous, mucous, and mixed,
the mucous being the most numerous. The anterior lingual gland (gland
GLANDS or ran oaar. cavrrx 283
of Blandin-Nuhn) is located close to the inferior surface of the tongue, one
on each side of the frenulum near the apex. The structure is composed of a
group of raccmose glands embedded deeply Within the structure of the
tongue (Fig. 226). Approximately five small ducts open Imder the tongue
on the plica fimbriata. The gland is of the mixed type although chiefly
mucous in its anterior part. In its posterior part are found mucous alveoli
capped with delicate demilunes, with a distinctly serous character.
The glands of the base and border of the tongue are of the pure mucous
variety. The glands which are located on the surface of the tongue -bear
long mucous tubular alveoli and ill-defined ducts. In the immediate region of the vallate and foliate papillae they are replaced by the serous
glands of the gustatory papillae (glands of v. Ebner). These glands
pour a watery secretion into and serve to wash out the furrows of the
circumvallate papillae. (See chapter on Mucous Membrane.)
 
Anterior lingual
gland ,’
Fig. 226.-Longitudinal section through the tip of the tongue of a. newborn child.
Anterior lingual gland.
11. GLINIGAL CONSIDERATIONS
Pathologic disturbances of the salivary glands are relatively infrequent.
When they do occur the result may be either an increase in the flow of
saliva (sialism) or a decrease (xerostomia). Secretion is increased in
mental and nervous affections, occasionally in acute fever and during
attacks of generalized stomatitis. Injections of certain drugs, particularly mercury and iodine compounds, are likely to produce an abundance
of saliva. Other than the discomfort. an abundance of saliva results in
no known harm. Disturbances that cause a reduction of saliva, however.
bring about loss of the protective action which this fluid exerts upon
284 ORAL I-IISTOLOGY AND EMBRYOLOGY
the teeth and oral tissues. Atrophy of the secretory elements and their
replacement by adipose tissue occurs in old age. The resulting xerostomia
may cause discomfort to a. patient wearing artificial dentures. Through
its loss the lubricating, cleansing and neutralizing power of the saliva
is forfeited. Moreover, a normal flow of saliva is a mechanical guard
against infection.
Inflammation is frequently the cause of disturbances in the flow of
saliva. It is common in the parotid gland, less common in the submaxillary, sublingual and smaller glands. Pyogenic organisms are the chief
offenders in acute infections. Most frequently in debilitated individuals
suffering from infectious fever or general postoperative complications,
the infection may be confined to the ducts (sialodochitis) or, less frequently, spread through the parenchyma of the gland (sialadenitis). Inflammation of the glandular substance itself, when it occurs, is usually
severe. When it progresses to suppuration, surgery is indicated.
Glass blowers and players of wind instruments are especially subject
to infection of the salivary ducts. The heightened intraoral pressure
tends to dilate the ducts, counteract the normal outflow of saliva, and
bacteria are forced into the ducts.
Infection of the ducts of a salivary gland may cause a mass of dead
cells or bacterial debris to become lodged in a constricted area of the
ducts. If allowed to remain, such a mass acts as a nidus in which calcium
salts are deposited. This leads to the formation of a salivary calculus.
Salivary calculi occur most often in the submaxillary duct (90 per cent)
where they vary in size from minute particles to deposits several
centimeters in length. If they are retained their obstructive influence
invites inflammatory exacerbations afiecting the parenchymatous tissues;
or, if saliva is retained under pressure for any length of time, atrophy
and fibrosis of the gland may result. Salivary duct calculi are easily
detected by palpation or roentgenologic examination, and are removed
by gentle pressure or by excision. When calculi involve the glandular sub
stance proper, total extirpation of the gland may be advisable.
Infectious parotitis (mumps) is the most common example of a virus
infection of the salivary glands. This disease shows tender swelling
of the parotid region, usually bilateral, with mild fever but no leukocytosis. Tuberculosis, syphilis, and actinomycosis may occasionally affect
the salivary glands. The etiologic agents may be hematogenous or carried to the glandular substance through the ducts.
Mikulicz’ disease is a type of granulomatous inflammation, rare in occurrence, which affects both the salivary and lacrimal glands, and occasionally, the lips and eyelids. It makes its appearance as a symmetrical,
indolent enlargement which may last several years. A dry mouth is one
of the accompanying symptoms. Histologically, there is a lymphocytic
infiltration of the interstitial connective tissue and, if persistent, ultimate
GLANDS or THE omu. CAVITY 285
destruction of the parenchymatous elements.“ The blood picture remains normal. It must be diflerentiated from Mikulicz’ syndrome which
is associated with such general processes as leukemia, Hodgkin’s disease,
and syphilis. A variety of tumors have been described in connection with
the salivary glands: mixed tumors, carcinoma, sarcoma, and several other
types are found of which about 75 per cent occur in the parotid. Of this
number about 95 per cent are of the mixed variety.’
Congenital malformations of the salivary glands may vary from atresia
of the ducts to complete aplasia of the gland. Such disturbances are more
common in the floor of the mouth in connection with the alveolingual
complex, but they are not uncommon in the parotid area. Atresia is less
common than aplasia, but when present causes disfiguring cysts or tumorlike growths. The large sublingual gland is most frequently afiected,
giving rise to the so-called ranula, in the floor of the mouth. The glands
of Blandin-Nuhn, located in the anterior part of the tongue, are susceptible
to cystic involvement as a result of closure of their ducts. These cysts
are designated as mucous cysts or mucoceles. Mucoceles are quite commonly found in connection with the smaller glands of the oral cavity,
where they probably result from trauma, a mild infection of the duets with
consequent closure. They are, however, of little concern and usually disappear after rupture and discharge of their contents.
Aberrant glands are encountered occasionally in the alveolingual area.
They are accessory glands which have become detached from the duct
system. These glands remain functional but because they-lack an excretory duct, the secretion accumulates within their structure and causes
distention with cyst formation.
The use of rubber dam or prolonged pressure by cotton rolls can
occlude the opening of one of the salivary ducts. The resulting swelling
occurs at the time the work is in progress, and disappears soon after the
obstruction is removed and the saliva has an opportunity to discharge.
References
1. Appleton, J. L. T.: Bacterial Infection, Philadelphia, 1925, Lea &; Febiger.
2. Babkin, B. P.: The Physiology of the Salivary Glands, in Gordon, S. M.: Dental
Science and Dental Art, Philadelphia 1938, Lea & Febige .
3. Braus, H.: Anatomic des Menschen (Human Anatomy), Book 2, ed. 2, Berlin,
1934, Julius Springer.
4. Brawley, R. E.: Studies of pH of Normal Resting Saliva: Variations With Age
and Sex; Diurnal Variation, J. Dent. Research 15: 55, 79, 1935.
5. Car-malt, Churchill: Contribution to the Anatomy of the Adult Human Salivary
Glands, IV, Part 1, Geo. Cracker Special Research Fund, 1913.
6. Cheyne, V. D.: Efiects of Selective Salivary Gland Extirpation Upon Experimental
Dental Caries in Rat, Proc. Soc. Exper. Biol. & Med. 42: 587, 1939.
7. Cheyne, Virgil D., Tiecke, Richard W., and Home, Eleanor V.: A Review of
So-Called Mixed Tumors of the Salivary Glands Including an Analysis of
Fifty Additional Cases, Oral Surg., Oral Med., Oral Path. 1: 359, 1948.
8. Gies, W. J., and Kahn, M.: An Inquiry Into the Possible Relation of Sulfacyanate to Dental Caries, Dental Cosmos 55: 40, 1913.
9. Hill, T. J .: Salivary Factor Which Influences Growth of L. Acidophilus and Is an
Expression of Susceptibility or Resistance to Dental Caries, J. A. D. A. 26:
239, 1939.
286
10.
1 1.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
ORAL I-IISTOLOGY AND EMBRYOLOGY
Hill, '1‘. J.: The Influence of Saliva Upon the Growth of Oral Bacteria, J . Dent.
Research 18: 214, 1939.
Inouye, J. M.: Biochemical Studies of Salivary Mucin, J. Dent. Research 10: 7,
1930.
Langley, J . N .:
261, 1379.
Lashley, K. S.: Reflex Secretion of the Human Parotid Gland, J . Exper. Psychol.
1: 461, 1916.
Lehman, J. A., and Leaman, W. G.:
1940.
Mathews: The Physiology
Maximow, A. A., and Bloom, W.:
1942, W. B. Saunders Co.
Orban, B., and Weinmann, J. P.: Cellular Elements of Saliva and Their Possible
Role in Caries J. A. D. A. 26: 2008, 1939.
Rosemann, B.: Iihysikalische Eigenschaften und chemische Zusammenstezung
der Verdauungssiifte unter normalen und abnormen Bedingungen. Handb.
der normalen und pathologischen Physiologic (Physical Properties and
Chemical Constitution of the Digestive Juices Under Normal and Abnormal
Conditions. I. Saliva, Handbook of Normal and Pathologic Physiology),
Berlin, 1927, Julius Springer, vol. 3, p. 819.
Sicher, H., and Tandler, J .: Anatomie fiir Zahniirzte (Anatomy for Dentists),
Berlin, 1928 Julius Springer.
Stephens, D. J.,’and Jones, E.: Leukocytes in the Saliva in Normal and Abnormal Subjects, Proc. Soc. Exper. Biol. & Med. 31: 879, 1934.
Thoma, K. E.: A Contribution to the Knowledge of the Development of the
Snbmaxillary and Sublingual Salivary Glands in Human Embroys, J . Dent.
Research 1: 95, 1919.
Updegrafi, H., and Lewis, H. B.: A Quantitative Study
stituents of Saliva, J. Biol. Chem. 61: 633, 1924.
Youngberg, G. E.: Salivary Ammonia and Its Relation to Dental Caries, J . Dent.
Research 15: 247, 1936.
Zimmermann, K. W.: Die Speicheldriisen der Mundhiihle und die Bauchspeicheldriise. Handb. der mikr. Anat. des Menschen (The Salivary Glands
and the Pancreas. Handbook of Human Microscopic Anatomy), Book 5,
Part 1, Berlin, 1927, Julius Springer.
On the Changes in Serous Cells During Secretion, J. Physiol. 2:
Mikulicz’s Disease, Internat. Clin. 3: 105,
of Secretion, Ann. New York Acad. Sc. 11: 293, 1898.
A Textbook of Histology, ed. 4, Philadelphia,
of Some Organic ConCHAPTER XI
ERUPTION OF THE TEETH
1. INTRODUCTION
2. EISTOLOGY OI‘ ERUTTION
a. Preemptive Phase
1:. Pre1'uncti.ona.1 Phase
c. Functional Phase
3. MEGEANISM OF ERUPTION
4. CLINICAL CONSIDERATIONS
1. INTRODUCTION
The human teeth develop in the jaws and do not enter the oral cavity
until the crown has matured. In the past, the term eruption was generally applied only to the appearance of the teeth in the oral cavity.
It is, however, known that the movements of the teeth do not cease when
the teeth meet their antagonists.“ 7 Movements of eruption begin at the
time of root formation and continue throughout the life span of a tooth.
The emergence through the gingiva is merely an incident in the process of
eruption. The eruption of deciduous as well as permanent teeth can be
divided into the prefunctional and functional phases. At the end of the
prefunctional phase the teeth come into occlusion. In the functional
phase the teeth continue to move to maintain a proper relation to the jaw
and to each other.
Eruption is preceded by a period in which the developing and growing
teeth move to adjust their position in the growing jaw.’ A knowledge
of the movements of the teeth during this preeruptive phase is necessary
for a complete understanding of eruption. Thus, the movements of the!
teeth can be divided into three phases: (1) preeruptive phase; (2) prefunctional phase; (3) functional phase.
During these phases the teeth move in difierent directions.” These
movements can be termed: ( 1) axial: occlusal movement in the direction
of the long axis of the teeth; (2) drifting: bodily movement in a distal,
mesial, lingual or buccal direction; (3) tilting: movement around a transverse axis; (4) rotating: movement around a longitudinal axis.
2. HISTOLOGY OF ERUPTION
During the first, preeruptive phase the enamel organ develops to its Preemptive
full size, and formation of the hard substances of the crown takes place. Pm“
First draft submitted by Joseph P. Weinmann.
287
288 ORAL HISTOLOGY AND EMBRYOLOGY
At this time the tooth germs are surrounded by the loose connective tissue of the dental sac and by the bone of the tooth crypt.
The development of the teeth and the growth of the jaw are simultaneous and interdependent processes. The microscopic picture of the
growing jaw indicates that extensive growth takes place in that area of
the jaws where the alveolar crest ultimately develops (Fig. 227). The
tooth germs maintain their relationship to the growing alveolar margin
by moving occlusally and buccally.‘
 
. fxi
.  Anlage of
. permanent
tooth
Fig. 227.—-Cross section through lower jaw and deciduous molar or human fetus (4th
month). Tooth germ moves bucoally by excentric growth indicated by resorption at
inner surface of.’ the buccal alveolar plate and lack of apposition at the inner surface
of the lingual plate.
Two processes are responsible for the developing teeth attaining and
maintaining their position in the growing jaw, especially in relation to
the alveolar ridge: the bodily movement of the teeth, and the excentric
growth of the tooth germs. Bodily movement is characterized by a shift
of the entire tooth germ. It is recognized by apposition of bone behind
the moving tooth, and by resorption of bone in front of it. In excentric
growth one part of the tooth germ remains fixed: the growth gives rise
ERUPTION or ran TEETH 289
to a. shift of the center of the tooth germ. Excentric growth is characterized solely by resorption of the bone at the surface toward which the
tooth germ grows.
During most of the time when the deciduous teeth develop and grow,
upper and lower jaws grow in length by apposition in the midline and
at their posterior ends. Accordingly, the growing germs of the deciduous
teeth shift in vestibular direction; at the same time the anterior teeth
move mesially, the posterior distally, into the expanding alveolar
arches." These movements of the deciduous teeth are partly bodily
movements, in part caused by excentric growth. The deciduous tooth
germ grows in length at about the same rate as the jaws grow in height.
The deciduous teeth maintain, therefore, their superficial position throughout the preeruptive phase.
The permanent teeth which have temporary predecessors undergo an intricate movement before they reach the position from which they emerge.
Each permanent incisor (Fig. 228) and cuspid develops at first lingually to
the deciduous tooth germ at the level of its occlusal surface.“ At the
close of the preemptive phase they are found lingual to the apical region
of their deciduous predecessors. The permanent bicuspids (Fig. 229)
begin their development lingually to and at the level of the occlusal plane
of the deciduous molars.“ Later, they are found between the divergent
roots and, at the end of the preeruptive phase, below the roots of the
deciduous molars (see chapter on Shedding). The changes in axial relationship, between deciduous and permanent teeth, are due to the occlusal
movement of the deciduous teeth and the growth of the jaw in height.
The germs of the bicuspids move by their buccally directed excentric
growth into the interradicular space of the deciduous molars.
The second phase of tooth movement, the prefunctional phase of erup-. pmucflom
tion, begins with the formation of the root (page 42) and is completed! P1350 01
when the teeth reach the occlusal plane. In the beginning of this phase nmptm
the crown is covered by enamel epithelium. While the crown moves toward
the surface, the connective tissue between the reduced enamel epithelium
and the oral epithelium disappears, probably by the desmolytic action
of the enamel epithelium. When the cusp of the crown approach the oral
mucosa, the oral epithelium and reduced enamel epithelium fuse. In the
center of the area of fusion the epithelium degenerates and the tip of the
cusp emerges into the oral cavity. The gradual emergence of the crown
is due to the occlusal movement of the tooth (active eruption), and also
to the separation of the epithelium from the enamel (passive eruption).
The reduced enamel epithelium remains in organic connection with that
part of the crown which has not yet emerged. (See section on Epithelial
Attachment.) The growth of the root or roots of a tooth occurs by simultaneous and correlated proliferation of Hertwig’s epithelial root sheath
and the connective tissue of the dental papilla. The proliferation of the
290 ORAL HISTOLOGY AND EMBRYOLOGY
epithelium takes place by mitotic division of the cells of the epithelial
diaphragm. The proliferation of the connective tissue cells is concentrated in the area above the diaphragm.
During the prefunctional phase of eruption the primitive periodontal
membrane, derived from the dental sac, is adapted to the relatively rapid
movement of the teeth. Three layers of the periodontal membrane can
be distinguished around the surface of the developing root: one, adjacent to the surface of the root (dental fibers); another attached to the
9 1110.
Fig: 228.——BuccoIingua1 sections through lower central incisors of seven consecutive
stages, from newborn infant to 9 years 01.’ age.
primitive alveolus (alveolar fibers) ; and a third, the intermediate plexus
(Fig. 137). The intermediate plexus’ consists mainly of precollagenous
fibers, whereas the alveolar and dental fibers are mainly collagenous.
The collagenous fibers can be traced into the intermediate plexus for a
short distance. The intermediate plexus permits continuous rebuilding
and rearranging of the periodontal membrane during the phase of rapid
eruption.“ 2°
ERUPTION or THE TEETH 291
In the region of the fundus, the dental sac differentiates into two
layers: one, close to the bone, consists of loose connective tissue, whereas
the other, adjacent to the growing end of the tooth, consists of a network
of rather thick fibers and contains a large amount of fluid in the tissue
spaces between the fibers (Fig. 230). Strong strands of fibers from the
‘periodontal area at the side of the root curve as a strong ligament around
the edge of the root, and then divide into a network forming spaces that
are filled with fluid. This entire structure is designated as “cushioned
hammock ligament.”-'1
In the prefunctional phase of eruption the alveolar ridge of the jaws
grows rapidly. To emerge from the growing jaws the deciduous teeth
must move more rapidly than the ridge increases in height. Growth of
the root is not always suflicient to meet these requirements. A rapid
formation of bone begins at the alveolar fundus Where it is laid down in
trabeculae, parallel to the surface of the alveolar fundus” (Fig. 231).
The number of trabeculae increases markedly during the prefunctional
292 om. HISTOLOGY AND EMBRYOLOGY
phase, and varies in difierent teeth: the smallest number of trabeculae
is found at the fundus of the molars. This variance in the number of
trabeculae seems to depend upon the distance which the teeth have to
cover during this phase of tooth eruption.
The germs of most permanent teeth develop in a crowded position. They
occupy, therefore, a position which difiers markedly from their ultimateposition after emergence. The molars are tilted; the occlusal surface of
the upper molars, which develop in the maxillary tuberosity, is directed
distally and downward. The occlusal surface of the lower molars, which
develop in the base of the mandibular ramus, is directed mesially and
upward. The long axis of the upper cuspids deviates mesially. The
lower incisors are frequently rotated around their long axis. In the later
stages of the prefunctional phase of eruption these teeth undergo intri
   
 
i\ en:-"' ”"“"-‘-”»'%’.f’v". ,. 1
Fig. 229.—Bucco1ingus.i sections through lower deciduous flrst molar and flrst bicuspid
or eight consecutive stages, from newborn infant to 14 years.
cate movements to rectify their primary position. During these tilting
and rotating movements, bone apposition takes place in those areas of the
tooth crypt from which the tooth moves away, and resorption occurs in
the areas toward which the tooth moves. In all other details, the his
tologic changes correlated to eruption are identical in permanent and deciduous teeth..
ERUPTION or run TEETH 293
The histologic findings in erupting multirootecl teeth present a picture
quite diflerent from that in single-rooted teeth. The epithelial root
sheath does not form an epithelial diaphragm, a cushioned hammock ligament is absent, and the proliferating pulp protrudes beyond the root
end. The bone at the crest of the interradicular septum shows all signs
of rapid growth. Apposition of cementum is also evident at the bifurcation. , _
After the erupting teeth have met their antagonists their movements are 1-uncuoml
not easily ascertained For a long time it was believed that functioning §h“°_°f
teeth do not erupt any longer. However, clinical observations and his- mph”
tologic findings show that the teeth continue to move throughout their life
span. The movements are in an occlusal as well as in a mesial direction.
..,,..... .... __ _ ...
 
 
 
  a l V E
*’*s..,.. /A .
3 yr. 41,5 yr. 11 yr. 14 yr.
Clinically, the continued active movement of teeth can be proved by
an analysis of the so-called shortened and submerged teeth (see page
322). Histologically, the changes in the alveolar bone furnish concrete
evidence for the movements of the teeth in their functional period (see
page 205).
During the period of growth, the occlusal movement of the teeth is.
fairly rapid. The bodies of the jaws grow in height almost exclusively at‘
the alveolar crests and the teeth have to move occlusally as fast as the
294 ORAL HISTOLOGY AND EMBRYOLOGY
   
   
 
 
- -  Prollferzttlon
zone of pulp
‘ §~-,-— -—-—————» Epithelial
' _-V ' diaphragm
4 m4 —-»— V — Cushioned
. hammock
ligament
Fig. 230.—Cushioned hammock ligament Root end or an erupting 10WeI' cuspid.
Proliferation zone of the pulp above the epithelial diaphI'a€m- Note the numerous tissue
spaces in the ligament. (slcher-.3‘)
I Deciduous
tooth
Bone Q  ' ’
trabeculae ,- —.’ u
at fundus ,‘ -‘ .3 Enamel
Permanent
tooth
trabeculae
at tundus
F13-. 231.—-Erupting upper deciduous cuspicl (A) and lower permanent cuspid (B),
Note formation of numerous parallel bone trebeculae at alveolar fundus. Formation of
bone trabeculae at the alveolar crest of deciduous cuspids (A) is 9. sign or rapid growth
or the maxilla in height. (Kronteldfi)
Bundle bone at
fundus
     
 
 
me5ia-l- ;  ‘.5 ‘  Bundle bone on
alveolar ‘ ‘f  distal
wall .3 "I.  ,  alveolar
r;_'.,:l - i  wall
’ 7“ Alveolar
! ; septum
First bzcuspid. 2" ’ _, _  Second bicuspm"
-2‘
~. M «
‘  \
L . ‘E
Fig‘. 232—-—1\_£[esia._l drift and vertical eruption. Meslodistal section through upper first.
and second bxcuspids. Arrow indicates direction of drifting movement. Apposition or
bundle bone at the distal, resorption of bone on the meslal surfaces or the alveoli. Ap
Dosition of bundle bone at the tundus and alveolar crest. (Weinma.nn.")
Periodontal
membrane
. . Periodontal
Apposition ,
o! bundle membrane
bone
- Resorption
First __.._.. p or bone
bicuspid
- Second
J bicuspid
Avposition of - W - '‘
bundle bone
Fig. Z33.—I-Iigher magnification of crest of interdental septum between first and
second upper bicuspids of Fig. 232. Arrows indicate direction of movement. Apposition
or bundle bone on surface of septum facing the flrst blcuspid and at alveolar crest, resorption of bone on surface of septum facing the second bicuspid. (Wein1na.nn.")
296 ORAL HISTOLOGY AND EMBRYOLOGY
jaws grow, in order to maintain their functional position. The eruptive
movement in this period is masked by the simultaneous growth of the
jaws. _
The continued vertical eruption also compensates for occlusal. or mcisal attrition. Only in this way can the occlusal plane and the distance
between the jaws during mastication be maintaincd—a condition which
is essential for the normal function of the masticatory muscles.
Epithelial
rest
Epithelial
rest
Epithelial
rest
Epithelial
rest
Epithelial
rests
Fig. 234.—-A. Bundle bone at tundus of alveolus and in wall of canal leading blood
vessels and nerves to apical roramina. Epitl-ielial rests some distance from apex
along blood vessels and nerves. B. High magnification of epithelial rests of A.
The mobility of the individual teeth leads to friction at the contact
points and to increasing wear in these areas. Sharp contact of the teeth
is maintained despite the loss of substance at the proximal surfaces only
because of the continuous movement of the teeth toward the midline.
This movement is termed physiologic mesial drift.
Apposition of cementum continues along the entire surface of the root,
but the apposition of bone is restricted principally to the fundus, alveolar
crest, and distal Wall of the socket (Fig. 233). The mesial wall of the
ERUPTION or THE TEETH 297
socket shows resorption in wide areas. However, even on the mesial
surface of the alveolus, zones of reparative bone apposition can always
be found.
The tissue changes in the diiferent phases of tooth movements are summarized in Table V11.
TABLE VII
Trssun CHANGES DURING Tm: PHASES or Tooru MOVEMENTS
”"‘E°"-'I°N cmuens or
OF EPITIIELIUM ————e———— 1>,1),M_
MOVEMENT TOOTH BONE
- 0ccluso-ax- Enamel organ Eccentric Growth of jaw Dental sa,
Prefihrzgrve ial; buccal growth of G
tooth germ
Prefunc- 0ccluso-ax- Fusion of re- Root growth Apposition Intermeditional ial; duced enamel (trabecular ate plexus;
Phase _straighten- organ with _ bone) at fun- cushioned
of Eruption mg oral ep1thel1- due and a.1veo- hammock
tuirn; ffonnagh lar ridge ligament
on o 1 elial attac ment. Hert
wig ’s sheath;
epithelial rests
Functional 0ccIuso-ax- Down growth Attrition. Root Apposition Functional
Phase ial; mesial of epithelial resorption and (bundle bone) arrange
of Eruption attachment shedding of at fundus and ment of
(passive erup- deciduous alveolar ridge suspensory
' tion) teeth. Ce- and distal al- apparatus
mentum appo- veolar wall;
sition of per- resorption at
manent teeth mesial wall
3. MECHANISM OF ERUPTION
Many theories have been advanced on the causes of tooth eruption}
The following factors have been eonsidered:"”' 1‘ growth of the root;?
growth of dentin; proliferation of the dental tissues; pressure from mus-p
cular action; pressure from the vascular bed in the pulp and periapieal
tissue; apposition and resorption of bone.
The eruptive movements of a tooth are the effect of differential growth. #
One speaks of diiferential growth if two topographically related organs,
or parts of an organ, grow at different rates of speed. Changes in the
spatial relations of such organs, or of the parts of an organ, are the inevitable consequence of differential growth. The ontogenesis of almost
any organ and of the whole embryo proves that diiferential growth is
one of the most important factors of morphogenesis. In the jaws, it is
the differential growth between tooth and bone which leads to the movement of a tooth.
The most obvious eruptive “force” is generated by the longitudinal
growth of the root of the tooth. However, the different movements of
an erupting tooth cannot be explained by the development of its root?
alone. Some teeth, even while their roots develop, travel a. distance
293 ORAL HISTOLOGY AND EMBRYOLOGY
which is longer than the fully developed root. An auxiliary factor must
account for the additional distance. Most teeth move in different directions, for instance by tilting, rotating, drifting; the growth of the root
can only account for the axial or vertical movement. The “force” that can
explain the variety of eruptive movements is generated by the growth of
bone tissue in the neighborhood of the tooth germ.
1 It is also a fact that the teeth move extensively after their roots have
been fully formed. The continued growth of the cementum covering
}the root and of the surrounding bone causes the movements of the tooth
3' in this period.
Before the development of the root starts, the outer and inner enamel
epithelium continue from the region of the future cemento-enamel junction as a double epithelial layer, the epithelial diaphragm, which is bent
into the plane of the dental cervix. It forms a definite boundary between
the coronal pulp of the tooth germ and the underlying connective tissue
which intervenes between tooth germ and bony wall of the crypt. Thus,
’ growth and development of the root is possible only under active proliferation of the pulpal tissue.
The importance of this single fact for the eruption of the tooth can
best be realized by comparing our knowledge of root development with
the long disproved, old concept of the function of Her-twig’s epithelial
root sheath. It was thought that this double layer of epithelium g_rew
into the underlying mesenchyme, punching out, as it were, part of this
tissue, isolating it and transforming it into pulpal tissue. If this were
true, the growth of the pulp would be by incorporation of new tissue
and therefore passive rather than active. The presence of the epithelial ‘
diaphragm makes an inward growth of the epithelial sheath impossible
and the pulp is “forced” to grow by multiplication of its cells and new
formation of intercellular substance ;, in other words, the pulp enlarges
by active growth, which creates the tissue pressure which can be seen
'- as the primary “force” of eruption.
1 The pressure generated by the increase in volume of the pulp in the
restricted space of the dental crypt would act against the bone in the
_bottom of the crypt and cause resorption of this bone and could not
cause an eruptive movement of the tooth germ if there were no auxiliary
structure. The auxiliary structure, which protects the bone at the bot'; tom of the crypt from pressure, prevents resorption of the bone, and
causes the tooth to grow or move away from the bottom of the crypt,
is the “hammock ligament.” If, by the proliferation of the growing
pulp, tissue pressure increases, this ligament is tensed, the pressure is
transmitted as traction to the bone to which the ligament is anchored,
and no pressure is directed against the bone at the bottom of the crypt.
Thus, the hammock ligament is the fixed base or plane from which the
tooth erupts because elongation of the tooth can only result in growth
toward the surface of the jaws.
ERUPTION or THE TEETH 299
It has been mentioned before that the growth of the root alone cannot move a crown as far as is necessary to reach the occlusal plane. Some
teeth, for instance the cuspids, develop far from the surface of the jaws.
While all the teeth are erupting, the jaws continue to grow at their
alveolar borders. The vertical erupting movement of these teeth is aided
by growth of bone at the bottom of the crypt, lifting the growing tooth
with the hammock ligament toward the surface. The formation of bone 3
at the bottom of the crypt occurs in diiferent teeth at a different rate of
speed. Where the production of new bone is slow, new layers of bone
are laid down upon the old bone and a more or less compact bone results.
Where growth of bone is rapid, spongy bone is formed in the shape of a,
framework of trabeculae. These trabeculae develop by the growth of
small projections of bone from the old surface, which then, at a given
distance, seem to mushroom and to form new trabeculae parallel to the
old surface (Fig. 231). In this way, tier after tier of bone tissue develops
in the deep part of the socket.
The increased tissue pressure which is inevitably linked with the proliferation of bone in the crypt would tend to compress the hammock ligament, thereby destroying the fixed base which is essential for the normal
eruption of a tooth; finally, the bone would encroach upon tooth andj
pulp, bringing the eruption to a standstill. These consequences are prevented by a peculiar structural differentiation of the hammock ligament.
Teleologically speaking, the hammock ligament is rendered incompressible by the accumulation of a fluid or a semifluid substance between the
fibers and thus transformed into the “cushioned hammock ligament.”
The fluid is distributed throughout the ligament in small round drop- ,
lets. The presence of fluid in confined spaces is, of course, the cause of
the incompressibility of this ligament. The incompressibility is relative
but gives entirely sufficient protection if one considers the low intensity
of the pressure forces generated during tooth eruption. That this pressure normally never reaches any higher intensity is explained by the
simple fact that reactive tissue changes immediately follow the increase
of tissue pressure and relieve it. '
While the hammock ligament and tooth are lifted toward the surface,
the anchoring fibers of the hammock ligament have to be continually
reconstructed. In other words, the hammock ligament has to shift its
anchoring plane toward the surface of the jaws. Details of the mechanism of this shift are, as yet, not known.
Enlargement of the root does not cease when the root is fully formed.
By continuous apposition of cementum, the root grows slightly in its
transverse diameters and more rapidly in length. Cementum apposition
is not only increased in the apical area of roots but the bifurcation of
two or three-rooted teeth is also a site of fairly intensive cementum apposition. It is also well known that there is continuous apposition of
bone at the fundus of the socket and at the crests of the alveolar process.
300 omu. HISTOLOGY AND EMBRYOLOGY
The bone apposition at the fundus and at the free border of the alveolar
process is very rapid in youth, slows down in the thirties, but normally
never ceases. Apposition at the alveolar crest, however, is found only
‘when the tissues are entirely normal. The frequency of inflammatory
changes at the gingivodental junction accounts for the fact that this
site of bone growth has been overlooked for a long time. There is also
constant apposition of bone on the distal wall of each socket while the
mesial wall shows resorption of the bone alternating with reparative
apposition.
Though the correlation of bone changes and movement of the teeth
is self-evident, the question still must be raised whether the bone changes
are primary and thus the cause of the movement of the teeth, or not.
The impossibility of finding any internal or external “forces” which
would account for the continuous vertical eruption and mesial drift is an
indication that the apposition of bone in the functional period plays the
same role which one can ascribe to it in the preeruptive and prefunctional
eruptive movements.
The apposition of bone can lead to a movement of a tooth only if the
root surface is protected against resorption. This protection is actually
given by the surface layers of uncalcified cementum, the cementoid tissue, which regularly covers the surface of the cementum. The resistance
of cementoid tissues to resorption has been demonstrated repeatedly.
The mechanism of tooth movement in the functional period can therefore be described in the following way: The entire surface of the root
is protected against resorption by the growth pattern of the cementum
which shows continuous, though not even, apposition throughout the
life of the tooth. If apposition of bone occurs at the bottom of the crypt,
the" slight increase of tissue pressure can lead to a movement of the tooth
in occlusal direction only. This is because a relief of the pressure is not
possible by resorption of the root. For the normal occlusal movement
of a tooth in the functional period, the normal general growth of the
cementum and the patterned growth of the bone are of equal importance.
It is necessary to point out that only simultaneous growth of the opposing surfaces of cementum and bone can lead to a movement of a
itooth. It is therefore clear that the apposition of cementum at the apex
- can compensate only in part for the loss of tooth substance at the occlusal surface, that is, for the shortening of the tooth by attrition. A con
sequence of this behavior is the fact that the teeth do shorten during the
functional period.
In the life of every tooth there comes a time in which the “forces” of
eruption change abruptly. It is, of course, the time when the pulp is fully
grown and the root is fully formed. From now on, it is the differential
growth of bone and cementum, and not that of pulp and bone, which
causes the continued vertical movement of the tooth. The eruptive mechanism of multirooted teeth differs in that the shift from one to the
ERUPTION or arm: mam 301
other mechanism of eruption occurs much earlier, namely, as soon as the
bifurcation is fully formed, though the roots are still growing.
The mesial drift is caused, in principle, by similar changes of bone
and tooth which seem to be an adaptive, genetically determined process.
However, this movement is greatly complicated by the fact that extensive
bone resorption at the mesial alveolar walls has to open the space into
which the teeth move, while the vertical movement is not opposed by
bone.
Apposition of bone on the distal surface of the socket leads to an increase of the interalveolar pressure. This can be relieved only by resorption of bone at the mesial wall of the socket since the growing surface of the bone and the entire surface of the root are protected by their
own growth, that is, by the presence of a thin layer of uncalcified ground
substance on their surface.
With both vertical and mesial movement of the functioning teeth, a
continual rearrangement of the principal fibers of the periodontal membrane has to be postulated. Details of this process, however, are al
most entirely unknown. The changes which prevent a destruction of the
ligamentous anchorage of the tooth on its mesial surface during the con
tinuous mesial drift are explained by the peculiar reaction of bone to.
pressure (or during modeling resorption) which could be called “thel
law of excessive resorption.” Resorption of bone under pressure is, as '~
a rule, more extensive than necessary to relieve the pressure. The sur-'
face layers of a bone are structurally adapted to the functional needs of _
the particular area. If they are destroyed during resorption, the newly
exposed surface lacks this adaptation. Therefore, the resorption con
tinues until room is provided for a reconstruction of a functionally ,
adequate new surface. This is the reason that, under normal circumstances, resorption is almost never a continuous process but instead occurs in waves, periods of resorption alternating with periods of reparative or reconstructive apposition.
This sequence of events can also be observed during the mesial drift
of a tooth. Some principal fibers lose their attachment during the period
of bone resorption and are then reattached, or replaced by new fibers,
which are anchored in the bone apposed during the period of repair.
Furthermore, it can be observed that bone resorption does not occur at
the same time on the entire extent of the mesial alveolar surface. Instead, at a given moment, areas of resorption alternate with areas of
reparative apposition. It seems that the tooth moves mesially in a complicated manner. Thus, resorption occurs only in restricted areas in one
period and reconstruction occurs in the same area, while the tooth,
minutely tilting or rotating, causes resorption in another area. Only this
can account for the fact that the functional integrity of the tooth is maintained in spite of its continued movements.
302 ORAL HISTOLOGY AND EMBRYOLOGY
4. CLINICAL CONSIDERATIONS
The eruption of teeth is a part of general development and growth, and
therefore the progress of tooth eruption may serve as an indicator of the
physical condition of a growing individual. The time of emergence of a
tooth is readily observed by clinical examination. Considerable work has
been done in compiling data regarding this particular stage of eruption.
Table VIII illustrates that the time of emergence of all teeth varies
widely.” 5' 13 Only those cases which are not within the range of variation
may be considered abnormal. Retarded eruption is by far more frequent
than accelerated eruption and may have a local or systemic etiology.
Local causes, such as premature loss of deciduous teeth and closure of
the space by a shift of the neighboring teeth, may retard the eruption
of some permanent teeth. Severe acute trauma may result in an arrest of
active tooth eruption during the functional phase if the periodontal mem
- brane of the tooth has been injured. Resorption of the root may ensue
in which event deposition of bone in the spaces opened by resorption
may lead to an ankylosis by fusion of alveolar bone and root.‘‘» 29 The
movement of such a tooth is then arrested whfle the other teeth continue
to erupt. If this disturbance takes place in the permanent dentition, a
so-called “shortened” tooth results. An ankylosed deciduous tooth may,
eventually, be covered by the rapidly growing alveolar bone. Such teeth
are called submerged teeth (see chapter on Shedding).
If the eruption of the entire deciduous or permanent dentition is delayed,
hereditary or systemic factors may be responsible. Among the systemic
causes are: disturbances of the endocrine system and nutritional deficiencies. Hypothyroidism is of the former, and vitamin D deficiency of
the latter group. The eifects of hypothyroidism and vitamin D deficiency
on tooth eruption can be explained by a retardation of the growth of
teeth and bone. Delayed eruption of the teeth usually accompanies
cleidocranial dysostosis, a hereditary disease aifecting membrane bones.
The movements of the teeth, during eruption, are intricate and are
accomplished by minute coordination of growth of tooth, growth of the
alveolar bone, and growth of the jaws. Any break in this correlation may
affect the direction of the movements; this, in turn, may lead to an impaction or embedding of a tooth. At the time the third molars develop, the jaw
has not reached its full length. Normally, the oeclusal surface of a third
lower molar turns anteriorly and upward. It is frequently prevented from
straightening out because of a lack of correlation between growth in length
of the lower jaw and tooth development. In such cases, the eruption of the
lower third molar is arrested because its crown comes in contact with the
roots of the second molar. If, at this time, the roots of the third molar are
not as yet fully developed, they will grow into the bone and may become
deformed. Cuspids, sometimes found in an oblique or horizontal position,
due to crowding of the teeth, may also fail to correct this malposition and
remain embedded.
TABLE VIII
Cnnoxonoov or THE HUMAN’ Dr.N'rI'rIoN
Logan and Kronfeld (slightly modified by McCall and Schour)
FORM.A'.l‘rON
ENAMEL MATRIX AMOUNT OF ENAMEL ENAMEL EMER/GENOE ROOT
TOOTH AND DEN,-MN MATRIX FORMED COMPLETED INTO ORAL COMPLETED
BEGINS AT BIRTH CAVITY
Central incisor 4 mo. in utero Five-sixths 1'} m0- 7% 1110- 1} )7!‘
Lateral incisor 4} mo. in utero Two-thirds 21} mo. 9 mo. 2 yr.
Maxillary Cuspid 5 mo. in utero One-third 9 mo. 18 mo. 31 yr.
First molar 5 mo. in utero Cusps united 6 mo. 14 mo. 2} yr.
Deciduous Second molar 6 mo. in utero Cusp tips still isolated 11 mo. 24 mo. 3 yr.
5931310“ Central incisor 4} mo. in utero Three-flftlis 2-} mo. 6 mo. 1'} yr.
Lateral incisor 4} mo. in utero Three-fifths 3 ma. 7 mo. 1-} yr.
Mandibular Ouspid 5 mo. in utero One-third 9 mo. 16 mo. 3% yr.
First molar 5 mo. in utero Cnsps united 5-} mo. 12 mo. 2} yr.
Second molar 6 mo. in utero Cusp tips still isolated 10 mo. 20 mo. 3 yr.
7- 8 yr. 10 yr.
8- 9 yr. 11 yr.
11-12 yr. 13-15 yr.
10-11 yr. 12-13 yr.
10-12 yr. 12-14 yr.
6- 7 yr. 9-10 yr. 512-13 yr. 14-16 yr.
17-21 yr. 18-25 yr.
6- 7 yr. 9 yr.
7- 8 yr. 10 yr.
9-10 yr. 12-14 yr.
10-12 yr. 12-13 yr.
11-12 yr. 13-14 yr.
6- 7 yr. 9-10 yr.
11-13 yr. 14-15 yr.
17-21 yr. 18-25 yr.
   
         
   
     
Central incisor 3 - 4 mo _-_..___.._-_..___..
Lateral incisor 10 -12 mo. .___-___.._..__-..Cuspid 4 - 5 mo. ________ __---___
First bicuspid 1§- 15 yr. ______________ __
Second bicuspid 2 - 2% yr. ______________ __
xFirst molar At birth Sometimes a. trace
Second molar 24- 3 yr. _--_--.._..__.._-..Permanent Third molar 7 - 9 yr. ___-- ____ -__..__
dentition Central incisor 3 - 4 mo. _______ _______-_
Lateral incisor 3 - 4 mo. ........... ----
Cuspid 4 - 5 mo. ...... ..--..----....
. First bicus id 15- 2 . .----_-_----.._..
M‘“‘d‘b“1‘“' Second bicgspid 21- 2; $1. __--______-_____
First molar At birth Sometimes a trace
Second molar 21- 3 yr. _________ ..----_..
Third molar 8 -10 yr. .......... --_--- 1
ilk‘:-Isl
Maxillary
hhhmiii
_;_.
Iii.
1.!
.
sis‘. sis: 1.2
>a§=>:>a?a>~.>.
-oLoL~u=r.~=ooo<o inn-n.~<oL~:.~ono:o
'7‘ _..".'7‘
«swan:-seer:-‘cl vcwsucn.-::ocxn.~:u
ERUPTION on THE TEETH 303
304 ORAL HISTOLOGY AND EMBRYOLOGY
Resorptlon ** —
Repaired
resorption
Enamel -'—
Resorption  ‘ 4" .
Alveolar
bone
Alveolar
bone
Periodontal
membrane
 
B. . D.
Fig. 235.—-Root resorption on distal surface or second lower molar caused by pressure
or erupting third molar. and repair.
4. Relation of germ or third molar to second molar at the beginning of pretunctional
phase of eruption. Note oblique position of the crown ot third molar.
B. Area. of contact between tooth erm oi third molar and root of second molar in
high magnification Resorption rea into dentin.
0. Relation or lower second and third molars when third molar has a.tta.ined its up~
right position.
D. High magnification of alveolar crest. Resorption on distal root surface is partly
repaired by apposition or cementum. (Orba.n.1')
ERUPTION or THE TEETH 305
Erupting teeth may cause resorption on the roots of neighboring teeth.“
This has been observed very frequently on the lower second molars, due
to the oblique position of the erupting third molar (Fig. 235). This tooth
turns its occlusal surface mesially and upward, and attains its upright
position only in the last stages of eruption. Therefore, its crown comes
into closest relation to the distal surface of the distal root of the second
molar, and exerts pressure leading to resorption of cementum and dentin
to a varying depth; it can be so extensive that the pulp may be exposed.
When the pressure is relieved during the normal movement of the wisdom
tooth, repair by apposition of cementum follows. Such resorption was
observed in about two-thirds of investigated jaws. A horizontal position
of the lower third molar might later lead to impaction. In such cases the
destruction on the root of the second molar may be severe.
Impacted or embedded upper third molars may cause similar resorption
of the root of the second molar. Embedded upper cuspids may exert
pressure upon the root of the lateral incisor. During the time of eruption of teeth, the reduced or united enamel epithelium may undergo
changes which result in cyst formation. Such a cyst forms around the
crown of the developing tooth and is known as a dentigerous cyst. Those
which arise late may cause a noticeable swelling on the surface and are
sometimes known as eruptive cysts, although they are simply forms of
dentigerous cysts.
References
1. Brash, J. 0.: The Growth of the Alveolar Bone and Its Relation to the Movements of the Teeth, Including Eruption, Int. J. Orthodont., Oral Surg. &
Badiogr. 14: 196, 283, 393, 487, 1928.
2. Brauer, J. C., and Bahador, M. A.: Variations in Calcification and Eruption of
the Deciduous and Permanent Teeth, J. A. D. A. 29: 1373, 1942.
3. Brodie, A. G.: Present Status of Our Knowledge Concerning Movement of the
Tooth Germ Through the Jaw, J. A. D. A. 24: 1830, 1934.
4. Brodie, A. G.: The Growth of Alveolar Bone and the Eruption of the Teeth,
Oral. Surg., Oral Med., Oral Path. 1: 342, 1948.
5. Cattell, P.: The Eruption and Growth of the Permanent Teeth, J. Dent. Research
8: 279, 1928.
6. Gottlieb, B.: Scheinbare Verkiirzun eines oberen Schneidezahnes (So-called
Shortening of an Upper Lateral cisor), Ztschr. f. StomatoL 22: 501, 1924.
7. Gottlieb, B., Orban, B., and Diamond, M.: Biology and Pathology of the Tooth
and Its Supporting Mechanism, New York, 1938, The Macmillan Co.
8. Gross, H.: Histologische Untersuchungen iiber das Wachstum der Kieferknochen beim Menschen (Histologic Investigations of the Growth of the
Human Jaw Bone), Deutsche Zahnh. 89: 1934.
9. Herzberg, F., and Schour, I.: Effects of the Removal of Pulp and 1Iertwig’s
Sheath on the Eruption of Incisors in the Albino Rat, J. Dent. Research 20:
264 1941.
10. Hoflman’, M. M.: Experimental Alterations in the Rate of Eruption of the Rat
Incisor; Master’s Thesis, University Illinois Graduate School, 1939.
11. Hoffman, M. M., and Schour, I.: Quantitative Studies in the Development of
the Rat Molar, II. Alveolar Bone, Cementum and Eruption (From Birth to
500 Days), Am. J. Orthodont. & Oral Surg. 26: 856, 1940.
12. Kronfeld, B.: The Resorption of the Roots of Deciduous Teeth, Dental Cosmos
74: 103. 1932.
13. Logan, W. H. G., and Kronfeld, B.: Development of the Human Jaws and Surrounding Structures From Birth to the Age of Fifteen Years, J. A. D. A.
20: 379,1933.
14. Logan, W. H. G.: A Histologic Study of the Anatomic Structures Forming the
Oral Cavity, J. A. D. A. 22: 3, 1935.
306
15.
16.
17.
18.
19.
.a.a.
23.
24.
25.
26.
27.
28.
29.
ORAL HISTOLOGY AND EMBRYOLOGY
Massler, M., and Schour, I.: Studies in Tooth Development: Theories of Eruption, Am. J. Orthodont. 8: Oral Surg. 27: 552, 1941.
Orban, B.: Growth and Movement of the Tooth Germs and Teeth, J. A. D. A.
15: 1004, 1928.
Orban, B.: Resorption of Roots Due to Pressure From Erupting and Impacted
Teeth, Arch. Clin. Path. 4: 187, 1940.
Orban, B.: Epithelial Rests in the Teeth and Their Supporting Structures, Proc.
Am. A. Dent. Schools, 1928, p. 121.
Reichborn-Kjennerud: Ueber die Mechanik des Durchbruches der bleibenden
Ziihne beim Menschen (Mechanism of the Eruption of the Permanent Teeth
in Man), Berlin, 1934, Hermann Meusser.
Sicher, IL: Tooth Eruption: The Axial Movement of Continuously Growing
Teeth, J. Dent. Research 21: 201, 1942.
Sicher, B.: Tooth Eruption: The Axial Movement of Teeth With Limited
Growth, J. Dent. Research 21: 395, 1942.
Sicher, B.: Oral Anatomy, St. Louis, 1949, The G. V. Mosby Co.
Sicher, H., and Weinmann, J. P.: Bone Growth and Physiologic Tooth Movement, Am. J. Orthodont. & Oral Surg. 30: 109, 1944.
Stein, G., and Weinmann, J. P.: Die physiologische Wanderung der Ziihne
Physiologic Drift of the Teeth), Ztschr. f. Stomatol. 23: 733, 1925.
Wassermann, F.: Personal communication.
Weinmann, J. P.: Das Knochenbild bei Stiirungen der physiologischen Wanderung der Zahne (The Bone Picture in Cases of Disturbances of the
Physiologic Movement of Teeth), Ztschr. f. Stomatol. 24: 397, 1926.
Weinmann, J. P.: Bone Changes Related to Eruption of the Teeth, Angle
Orthodontist 11: 83, 1941.
Weinmann, J. P., and Sicher, H.:
Bur 46: 3, 1946.
Willman, W.: An Apparent Shortening of an Upper Incisor, J. A. D. A. 17: 444,
1930.
(The
Correlation of Active and Passive Eruption,
CHAPTER XII
SHEDDING OF THE DECIDUOUS TEETH
1. IN TBODUCTION AND DEFINITION
2. PROCESS OI‘ SHZEDDING
3. CLINICAL CONSIDERATIONS
a. Remnants of Deciduous Teeth
b. Retained Deciduous Teeth
c. Submerged Deciduous Teeth
1. INTRODUCTION AND DEFINITION
Human teeth develop in two generations known as the deciduous and
permanent dentitions. The deciduous teeth are adapted in their number,
size and pattern to the small jaw of the early years of life. The size of
their roots, and therefore the strength of the suspensory ligament (periodontal membrane), are in accordance with the developmental stage of
the masticatory muscles. They are replaced by the permanent teeth
which are larger, more numerous, and possess a stronger suspensory liga—
ment. The physiologic elimination of deciduous teeth, prior to thereplacement by their permanent successors, is called shedding.
2. PROCESS OF SHEDDING
The elimination of deciduous teeth is the result of the progressive resorption of their roots by osteoclasts. In this process both cementum
and dentin are attacked (Fig. 236). The osteoclasts differentiate from
the cells of the loose connective tissue in response to the pressure exerted
by the growing and erupting permanent tooth germ. The pressure is
directed against the bone separating the alveolus of the deciduous tooth
from the crypt of its permanent successor and, later, against the root
surface of the deciduous tooth itself (Fig. 237). Because of the position
of the permanent tooth germ the resorption of the deciduous roots of the
incisors and cuspids starts at the lingual surface in the apical third (Fig.
238). The movement of the permanent germ, at this time, proceeds in
occlusal and vestibular directiori.) In later stages, the germ of the permanent tooth is frequently found directly apical to the deciduous tooth (Fig.
236, A). In such cases the resorption of the deciduous root proceeds in
transverse planes, thus causing the permanent tooth to erupt later in the
exact position of the deciduous. However, the movement in vestibular
direction is frequently not complete when the crown of the permanent tooth
breaks through the gingiva. In such cases, the permanent tooth appears
lingual to its deciduous predecessor (Fig. 238). In the first described
First draft submitted by Myron S. Aisenberg.
307
308 ORAL HISTOLOGY AND Emntwonoav
   
R°s°rpfl°n area  " Resorptlon ot
     
 
 
_ root
.T* ‘'''’'''_T" Resorptlon or
Permanent cuspid ‘ ' b°“°
1*’.
‘ cementum
   
I '~ A
_....s ..
“°‘°’P“°'* 'S
(°3t°°°13-533) ' W .. Periodontal
Jr “ membrane
' —--——,—- Resorptlon
of bone
B.
F . 236.—Resox-ption of root of deciduous cus id during eruption of permanent successor.
Kronteld!) A. General view. B. Linguafreaorption area in higher magnification.
sauonme or DECIDUOUS TEETH 309
Deciduous incisor
deciduous tooth
and successor
 
Enamel of permanent incisor
Dentin
Fig‘. 23'I.~—.A thin lamclla of bone separates permanent tooth germ from its predecessor.
310 ORAL EISTOLOGY AND EMBRYOLOGY
r ._ _ ,,_ W , _  /._—...~_..,
Deciduous incisor -—'—-~ I
Enamel of Der-mar
Root resorption .nent incisor
Dentin
..r'
Fig. 23S.—Resorption of root of deciduous incisor due to pressure of erupting successor.
SHEDDING on THE DECIDUOUS TEETH 311
alternative the deciduous tooth is lost before the permanent tooth erupts,
whereas in the latter the permanent tooth may erupt while the Qleciduous
tooth is still in its place.
In most cases, resorption of the roots of the deciduous molars begins
on the surfaces of the roots next to the interradicular septum. This is
due to the fact that the germs of the bicuspids are frequently found
between the roots of the deciduous molars (Fig. 239). In such cases,
extensive resorption of the roots can be observed long before actual shedding. However, during the continued active eruption the deciduous teeth
_ . . --w.....gs—.
I
 
deciduous :3
molar  .
’  .,  4,!’ ‘X
~-_; g ' 1'.‘ V '
‘J \ .;'~. ' ' 3‘-:,
' " - - . _ _ ,, \'_‘
, ‘wt . ”
*4’
.
R8S01‘Dl-303 ;_->':.i"'* '
 
.,_,__‘L.g-'3 Repaired resorp
 
°"' r°°t . ‘ tion of dentin
Penngrlient ,,. .. (X)
too
germ
Fig. 239.——Germ or lower flrst bicuspid between the roots of lower flrst deciduous molar.
Repaired resorption on the roots of the deciduous tooth (see Fig. 241).
move away from the growing permanent tooth germs which, for the most
part, soon come to lie apical to the deciduous molars (Fig. 240). This
change in position allows the growing bicuspid adequate space for its
development. The areas of early resorption on the deciduous molar are
then repaired by the apposition of new cementum and the alveolar bone
regenerates’ (Fig. 241). In later stages, however, the erupting bicuspids
again overtake the deciduous molars and, in most cases, their roots become entirely resorbed (Fig. 242). The resorption may even proceed far
312 ORAL msronomz AND EMBRYOLOGY
up into the coronal dentin; occasionally, greater or less areas of the
enamel may be destroyed. The bicuspids appear with the tips of their
crowns in the place of the deciduous teeth.
The osteoclastic resorption which is initiated by the pressure of the
permanent tooth is the primary reason for the elimination of a deciduous
tooth. Two auxiliary factors have to be taken into consideration. These
are, first, the weakening of the supporting tissues of the deciduous tooth,
due to resorption of wide areas of its roots; and continued active and
passive eruption which seems to be accelerated during the period of
 
   
—— Second
deciduous
‘ molar
‘ Traumatic
changes In
periodontal
membrane
,' (x)
"1
. ‘V  Second
‘ bicuspld
germ
-'4 ' '  I . \ 1’
-. ,,_;  -,-1. ~ , ,/ ,
3» r K I / - 5”: ‘ / ' " w‘.‘.''.
.‘ . A‘ ’ f/ «r ; V: - ‘
.‘—.
\ / ,
r  p ‘A ‘Ti 2", X1! ti _
6
“"‘
Fig. 240.—Germs or bicuspids below roots of deciduous molars. Traumatic changes in
the periodontal membrane or the deciduous teeth. Z. See Fig. 243.
shedding. The epithelial attachment of the deciduous tooth grows down
along the cementum at this time, thus causing the clinical crown of the
tooth to be enlarged and the clinical root to which the suspensory fibers
are anchored, to be shortened. Second, the masticatory forces increase
during this period, due to the growth of the masticatory muscles, and
combine with the root resorption and eruption to initiate a vicious circle
resulting in rapid loosening of the deciduous tooth. The masticatory
stresses act as traumatic forces upon the tooth at this stage!’ 7: ¥° Due to
the loss of large parts of the suspensory apparatus the masticatory forces
SHEDDING OF THE DEGIDUOUS TEETH
tooth
Repaired
     
dentin
Loose connec- ‘ ' ‘
five tissue
surrounding
permanent
germ
313
cementum of
deciduous
resorption
Resorption of
Fig. 241.——High magniflcaton of a. repaired resorption; from area. I of Fig. 239; new
bone formed during rest period.
314 out. HISTOLOGY AND EMBRYOLOGY
4..
\
Deciduous molar
Contact between
deciduous and
permanent
 
V f
t°°th lmiaaiglliesxpgjd
4 _ , _ §—— New formation
Bone resorption - . ‘ »» ' of bone
_Fig'..242.—_—Eoots of deciduous molar completely resorbed. Dentin of deciduous tooth
iii contact with enamel of the bicuspid. Resorption of bone on one side. new formation
of bone on the opposite side or the bicuspid due to transmitted excentric pressure to
the bicuspid. (Grimmer!)
SHEDDING on THE nncmvous TEETH 315
may be transmitted to the alveolar bone not as tension but as pressure.
This leads to compression and injury of the periodontal membrane with
subsequent bleeding, thrombosis and necrosis (Fig. 243). These changes
are most frequently found in the bifurcation and interradicular surfaces
of deciduous molars. Resorption of bone and tooth substance, therefore,
occurs most rapidly in such areas, thus relieving pressure. Repair of
resorbed areas may be excessive and may even lead to ankylosis between
bone and tooth (Fig. 24-1).
Deciduous tooth
Necrotlc tissue
remnants
—.g .- Traumatic destruc‘ tion of perio_ ; dental membrane
Alveolar bone  " ——-—
~ '3 - Repaired
' re resorption
Necrotic tissue
remnants
51?’
   
Fig. 243.—Tx-aumatic changes of periodontal tissues. High magnification from area.
X in Fig. 240.
The process of shedding is not necessarily continuous. Periods of great
resorptive activity alternate with periods of relative rest.’ During the
rest periods resorption not only ceases but repair may actually occur
by apposition of cementum or bone upon the resorbed surface of cementum or dentin. Even repair of resorbed alveolar bone may take place
316 mun ms-ronoenz AND EMBRYOLOGY
Deciduous molar v \
 
 
 
Reaorption of
bone in
area. of L.
ankylosis
Permanent tooth . _. ‘
p.‘ ,r -
Resorptionr:  l _ . «T
a.
_L
.\ 7:
L43.
i<'s.«.a..'f..-4'1;
Fig. 244.—Ankylosl.s ot deciduous tooth as a. sequence of trauma.
4. General view.
B. High magnification of area. X in A.
{ Resorption of
cementum
' Ankylosis
SHEDDING or THE DECIDUOUS TEETH 317
durillg rest periods (Fig. 241). The phases of rest and repair are, probably, lengthened by relief of pressure upon the deciduous tooth by its
own eruptive movement. r
The pulp of the deciduous teeth plays a passive role during shedding.
Even in late stages the ocelusal parts of the pulp may appear almost
normal, with functioning odontoblasts (Fig. 245). However, since the
cellular elements of the pulp are identical with those of loose connective
tissue, resorption of the dentin may occur at the pulpal surface by the
‘W - -— Odontoblasts
Pu1p¢V—’—j——
Dentin
Fig. 245.—High magnification 01' the pulp of resorbed deciduous molar of Fig. 242. Pulp
of normal structure with odontoblasts.
differentiation of osteoclasts from the cells of the pulp. The persistence of
the pulpal tissue, and its organ.ic connection with the underlying connective tissue, explain the fact that deciduous teeth show, to the last, a
fairly strong attachment even after total loss of their root (Fig. 242). In
such cases, shedding may be unduly retarded and the erupting permanent
tooth may actually come into contact with the deciduous tooth. The
masticatory forces are then transmitted to the permanent tooth” before its
suspensory ligament is fully differentiated, and traumatic injuries in the
periodontal membrane of the permanent tooth may develop (Fig. 242).
Remnants of
Deciduous
Teeth
Deciduous
Retained
Teeth
318 om. 1-nsvronocr AND EMBRYOLOGY
3. CLINICAL CONSIDERATIONS
Parts of the roots of deciduous teeth which are not in the path of erupting permanent teeth may escape resorption. Such remnants of roots,
consisting of dentin and cementum, may remain in the jaw for a considerable time.‘’'‘’ In most cases, such remnants are found along the
bicuspids, especially in the region of the lower second bicuspids (Fig.
246). This can be explained by the fact that the roots of the lower second
deciduous molar are strongly curved or divergent. The mesiodistal diameter of the second bicuspid is much smaller than the greatest distance
between the roots of the deciduous molar. Root remnants may later be
found deep in the jaw bone, completely surrounded by, and ankylosed to,
the bone (Fig. 247). Frequently, they become encased in heavy layers of
cellular cementum. In cases where the remnants are close to the surface of the jaw (Fig. 248) they may, ultimately, become exfoliated. Progressive resorption of the root remnants and replacement by bone may
cause the disappearance of these remnants. Cysts occasionally develop
around the retained roots of deciduous teeth. They appear between the
roots of the permanent teeth.
Root remnant of - - ,,  .— — -.---.—
declduous , ~ —. Root remnant of
tooth “ deciduous tooth
Fig. 246.—Remna.nts of roots of deciduous molar embedded in the interdentai septa.
(Roentgenogram courtesy G. M. Fitzgerald, University of California.)
Deciduous teeth may be retained for a long time if the corresponding
permanent tooth is congenitally missing.‘ This is most frequently observed in the region of the upper lateral incisor (Fig. 249, A), less frequently in that of the second bicuspid, especially the lower (Fig. 249, B),
and rarely in the central lower incisor region (Fig. 2-19, 0). Also, if a
permanent tooth is embedded, its deciduous predecessor may be retained
(Fig. 249, D). This type of retained deciduous tooth is found mostly in
the upper cuspid region as an accompaniment of the impaction of the
permanent cuspid.
SHEDDING or THE zorzcmuous TEETH 319
 
First bicuspid second bicuapld
Remnant of
deciduous root
' - Ankylosls
Fig. 247.———Remna.nt of deciduous tooth embedded in, and ankylosed to, the bone.
( Schoenbauez-.5 )
320 mun HISTOLOGY AND EMBRYOLOGY
Interdentul papilla
31¢‘-“PW Blcusvld
-~——-V7 A Remnant of deciduous
tooth
Fig. 248.—-Remnant of deciduous tooth at alveolar crest.
SHEDDING or THE nncmuous TEETH 321
The fate of retained deciduous teeth varies. In some cases they persist
for many years in good functional condition (Fig. 249, A); more often,
however, resorption of the roots and continued active and passive eruption cause their loosening and final loss (Fig. 249, B). The loss of retained
deciduous teeth has been explained by the assumption that such teeth may
undergo regressive changes in their pulp, dentin, cementum, and periodontal membrane, thus losing their regenerative faculties which are necessary to compensate for the continued injuries during function? It is, however, more probable that such teeth, because of their smaller size, are not
adapted to the strength of the masticatory forces in adult life. The roots
are narrow and short, thus rendering the area available for attachment of
principal fibers relatively inadequate. Their loss is then due to traumatism.
Fig. 249.—Roentgenogra.ms of retained deciduous teeth.
A. Upper lateral permanent incisor missing’. deflduous tooth retained (age 55)
B. Lower second bicuspid missing, deciduous molar retained: r00tS D8-N’-1y !‘eS°1'be5~
(Courtesy M. K. Hine, University of Indiana.)
0'. Lower central permanent incisors missing. deciduous teeth retained.
D. Upper permanent cuspid embedded; deciduous cuspid retained. (Courtesy Rowe
Smith, Texarkana.)
If the permanent lateral incisor is missing, the -deciduous tooth is.in
many cases resorbed under the pressure of the erupting permanent cuspid.
This resorption may be simultaneous with that of the deciduous cuspid
Submerged
Deciduous
Teeth
322 oasr. HISTOLOGY AND EMBRYOLOGY
(Fig. 250). Sometimes, the permanent cuspid causes resorption of the
deciduous lateral incisor only, and erupts in its place. In such cases,
the deciduous cuspid may be retained distally to the permanent cuspid.
Traumatic lesions, on the other hand, may lead to ankylosis of a deciduous tooth, rather than its loss. The active eruption of an ankylosed
tooth ceases and, therefore, the tooth appears shortened later on (Fig.
Fig. 250.—Upper permanent lateral incisor missing. Deciduous lateral _incisor and
deciduous cuspid are resorbed due to pressure of erupting permanent cuspid.
A. At the age of 11.
B. At the age of 13.
;,.‘
Fig. 251.—Submerging lower deciduous second molar. Second bicuspid missing.
(Courtesy M. K. Hine, University of Indiana.)
251), due to continued eruption of its neighbors and the relative height
of their alveolar processes. The “shortening” of such a tooth may even
lead to its eventual overgrowth by the alveolar bone and the tooth may
become submerged in the alveolar bone.‘ The roots and crowns of such
teeth show extensive resorption and apposition of bone in the tortuous
cavities.
SHEDDING on THE DEGIDUOUS TEETH 323
Submerged deciduous teeth prevent the eruption of their per
manent successors, or force them from their position. Submerged deciduout teeth should, therefore, be removed as soon as possible.
1.
9°
10.
.“.°’.°‘!“S'°.“"
References
Aisenberg, M. 8.: Studies of Retained Deciduous Teeth, Am. J. Orthodont. 85
Oral Stu‘ . 27: 179, 1941.
Grimmer, E. .: Trauma in an Erupting Premolar, J. Dent. Research 18: 267,
1939.
Kotanyi, E.: Histologische Befunde an Milchzahnreste (Histologic Findings on
Deciduous Tooth Remnants), Ztschr. f. Stomatol. 23: 516, 1925.
Kronfeld, R.: The Resorption of the Roots of Deciduous Teeth, Dental Cosmos
74: 103 1932.
Kronfeld, R.: and Weinmann, J’. P.: Traumatic Changes in the Periodontal Tissues
of Deciduous Teeth, J. Dent. Research 19: 441, 1940.
Noyes, F. B.: Snbmerging Deciduous Molars, Angle Orthodontist 2: 77, 1932.
Oppenheim, A.: Histologische Befunde beim Zahnwechsel (Histo1ogic Findings
in the Shedding of Teeth), Ztschr. f. Stomatol. 20: 543, 1922.
Schoenbauer, F.: Kniichern eingeheilte Milchzahnreste bei iilteren Individuen
(Ankylosed Deciduous Teeth Remnants in Adults), Ztschr. f. Stomatol. 29:
892 1931.
Stafne,  0.: Possible Role of Retained Deciduous Roots in the Etiology of
Cysts of the Jew, J. A. D. A. 24: 1489, 1937.
Weinmann, J. P., and Kronfeld, R.: Traumatic Injuries in the Jaws of Infants,
J. Dent. Research 19: 357, 1940.
CHAPTER XIII
TEMPOROMANDIBULAR JOINT
1. AN ATOMIC REMARKS
2. HISTOLOGY
a.. Bony Structures
b. Articular Pibrocartilage
c. Articular Disc
d. A1-ticular Capsule
3. CLINICAL CONSIDERATIONS
1. AN ATOMIC REMARKS
The mandibular articulation (temporomandibular joint) is a diarthrosis
between mandibular fossa and articular tubercle of the temporal bone,
and capitulum (head, condyle) of the mandible. A fibrous plate, the
articular disc, intervenes between the articulating bones.
The articulating surface of the temporal bone is concave in its posterior,
convex in its anterior part. The 91131 concavity, articular fossa, extends
from the squamotympanic and petrotympanic fissure in the back to the con
vex articular tubercle in front. Th latter is strongly convex in a sagittal
and slightly concave in a frontal plane. The convexity varies considerably,
the radius ranging from 5 to 15 mm. The long axes of fossa and tubercle
are directed medially and slightly posteriorly. The articular surface of
the mandibular head is, approximately, part of a cylinder the axis of
which is placed in the same direction as that of the articular surfaces on
the temporal bone. The articulating parts of the temporomandibular
joint are covered by a fibrous or fibrocartilaginous tissue and not by
hyaline cartilage, as in most other articulations of the human body. The
hyaline cartilage in the mandibular condyle which is present during its
growth period does not reach the surface.
The articular disc is an oval fibrous plate which is united around its
margin with the articular capsule (Fig. 252). It separates the articular
space into two compartments: a lower, between condyle and disc, and an
upper, between disc and temporal bone. The disc appears biconcave in
sagittal section. Its central part is thin, in rare cases perforated;
the anterior and especially the posterior borders are thickened (Fig. 253).
Fibers of the external pterygoid muscle are attached to its anterior border.
The disc serves to adapt the bony surfaces to each other, especially in a
forward position of the mandible when the convex condyle approaches the
aonvex articular tubercle. The disc is, at the same time, the movable
socket for the mandibular head.
First draft subxpitted by Donald A; Kerr.
324
TEMPOROMANDIBULAR JOINT 325
The articular capsule consists of an outer fibrous sac which is loose.
It IS strengthened on its lateral side by the temporomandibular ligament.‘
The inner synovial membrane is divided like the articular space. The
superior part reaches from the margin of the articular surfaces on the tem
poral bone to the disc; the inferior extends from the disc to the neck of
the mandible.
2. HISTOLOGY
The condyle of the mandible is composed of typical cancellous bone Bony
covered by a thin layer of compact bone (Fig. 253). The trabeculae are smmm
grouped in such a way that they radiate from the neck of the condyle and
 
Ma.ndibula.r  ..
V‘
rossa. =. _
Articular
tubercle
Mandibular
head
Fig. 252.—Sagitta1 section through the temporomandibular joint. (Courtesy W. Bauer,‘
St. Louis University School oi‘. Dentistry.)
Fig. 253.—Sagitta1 section through the temporomandibular joint of a 28-year-old man.
(Courtesy S. W. Chase. Western Reserve University.)
326 ORAL HISTOLOGY AND EMBRYOLOGY
reach the cortex at right angles, thus giving maximal strength to the
condylar bone While still maintaining a light construction. In young
individuals the trabeculae are thin and may contain islands of hyaline
cartilage near the surface (Fig. 254, A). In older individuals these car
 
   
 
- 3- Fibrous
. covering
. - .. Cartilage
V; , -I islands
. A! .-.1:-::. '
1 -§'Fibrous
‘ " covering
 
Fig. 254.—-Sections through the mandibular head.
A. Newborn infant.
R. Young adult.
tilaginous islands are resorbed and replaced by bone (Fig. 254, B). The
marrow spaces are large at first, but decrease in size with progressing age
by a marked thickening of the trabeculae. The marrow in the condyle
TEMPOROMANDIBULAR JOINT 327
is of the myeloid or cellular type; in older individuals it is sometimes
replaced by fatty marrow.
In young individuals the bone of the condyle is capped by a layer of
hyaline cartilage which develops as a secondary growth center in
three-month-old embryos. It is interposed between the fibrocartilage and
the bone. It may still be present in the jaw of a person in his twenties
(Fig. 254). The cartilage grows interstitially and by apposition from
the deepest layer of the covering fibrous tissue; at the same time it is,
gradually, replaced by bone on its inner surface.
. Ii-,,.’
, i . <:
k'V.‘»} ' I,‘ I‘ .
Fig. 255.—Higher magnification of part of the mandibular condyle of Fig. 253.
The bone of the mandibular fossa varies considerably from that of the
articular tubercle (Fig. 253). In the fossa it consists of a thin compact
layer; the articular tubercle is composed of spongy bone covered with a
thin layer of compact bone. In rare cases islands of hyaline cartilage are
found in the articular tubercle.
The condyle as well as the articular fossa and tubercle are covered by
a rather thick layer of fibrous tissue containing a. variable number of
cartilage cells. The fibrous or fibrocartilaginous covering of the mandibular condyle is of fairly even thickness (Fig. 255). Its superficial
layers consist of a network of strong collagenous fibers. Cartilage cells
or chondrocytes may be present and have a tendency to increase in number
with age. They can be recognized by their thin capsule which stains
heavily with basic dyes. The deepest layer of the fibrocartilage is rich in
Bone
Articular
Fibro
cartilage
Arflcularbisc
ORAL HISTOLOGY AND EMBRYOLOG3.
chondroid cells as long as hyaline cartilage is present in the condyle; it
contains only a few thin collagenous fibers. In this zone the appositional
growth of the hyaline cartilage of the condyle takes place.
The fibrous layer covering the articulating surface of the temporal
bone (Fig, 256) is thin in the articular fossa and thickens rapidly on the
posterior slope of the articular tubercle (Fig. 253). In this region the
fibrous tissue shows a definite arrangement in two layers, with a small
transitional zone between them; the two layers are characterized by the
different course of the constituent fibrous bundles. In the inner zone the
fibers are at right angles to the bony surface; in the outer zone they run
parallel to that surface. As in the fibrous covering of the mandibular
condyle, a variable amount of chondrocytes is also found in the tissue on
the temporal surface. In adults the deepest layer shows a thin zone of
calcification.
Bone
Calcification
\ p " ~ - ' zone
v -- --s Inner fibrous
layer
-— --——a Outer fibrous
layer
Fig. 256.—Higher magnification of articular tubercle of Fig. 253
There is no continuous cellular lining on the free surface of the fibrocartilage. Only isolated fibroblasts are situated on the surface itself;
they are, generally, characterized by the formation of long flat cytoplasmic processes.
In young individuals the articular disc is composed of dense fibrous
tissue which resembles a ligament because the fibers are straight and
tightly packed (Fig. 257). Elastic fibers are found throughout the disc,
but only in relatively small numbers. The fibroblasts in the disc are
TEMPOROMANDIBULAR JOINT 329
elongated and send flat cytoplasmic wing-like processes into the interstices between the adjacent bundles. The mandibular disc does not show
the usual fibrocartilaginous character of other interarticular discs. This
may be regarded as a functional adaptation to the high mobility and
plasticity of this disc.
Articular
tubercle
Superior articular
space
 
 
__ Articular disc
--- Inferior articular
space
- -—=  Mandibular head
43
Fig. 257.—-Higher magnification of articular disc of Fig. 253.
With advancing age some of the fibroblasts develop into chondroid
cells Which, later, may become real chondrocytes. Even small islands of
hyaline cartilage may be found in the discs of older persons. Chondroid
cells, true cartilage cells and hyaline ground substance develop in situ by
difierentiation of the fibroblasts. In the disc as well as in the fibrous
tissue covering the articular surfaces, this cellular change seems to
be dependent upon mechanical influences. The presence of chondrocytes
increases the resistance and resilience of the fibrous tissue.
Articulal:
capsule
330 ormr. HISTOLOGY AND EMBRYOLOGY
As in all other joints, the articular capsule consists of an outer fibrous
layer which is strengthened on the lateral surface to form the temporamandibular ligament. The other parts of the fibrous capsule are thin
and loose. The inner or synovial layer is a thin layer of connective tissue.
'It contains numerous blood vessels which form a capillary network close
«to its inner surface. In many places larger and smaller folds or finger
like processes, synovial folds and villi protrude into the articular cavity
(Fig. 258). The former concept of a continuous cellular covering of the
free synovial surface has been abandoned. Only a few fibroblasts of the
synovial membrane reach the surface and, with some histiocyte and
lymphatic‘ wandering cells, form an incomplete lining of the synovial
membrane.
 
I ‘ T synovial villl
Fifi 258.—Villi on the synovial capsule of ternporomandibular joint.
A small amount of viscous fluid, synovial fluid, is found in the articular spaces. It is a lubricant and also a nutrient to the avascular coverings
of the bones and to the disc. Its origin is not clearly established. It is
possibly in part derived from the liquefied detritus of the most superficial elements of the articulating surfaces. It is not clear whether it is
a product of filtration from the blood vessels or a secretion of the cells
of the synovial membrane; possibly it is both.
TEMPOROMANDJBULAR JOINT ' 331
3. CLINICAL CONSIDERATIONS
The thinness of the bone in the articular fossa is responsible for fractures if the mandibular head is driven into the fossa by a heavy blow.
In such cases injuries of the dura mater and the brain have been reported.
The finer structure of the bone and its fibrocartilaginous covering depends upon mechanical influences. A change in force or direction of
stress, occurring especially after loss of posterior teeth, will cause structural changes. These are brought about by resorption and apposition of
bone, and by degeneration and reorganization of fibers in the covering
of the articulating surfaces and in the disc.“
There is considerable literature on the disturbances after loss of teeth
or tooth substance due to changes in the mandibular articulation.“ The
clinical symptoms are said to be: impaired hearing, tinnitus (ear buzzing), pain localized to the temporomandibular joint or irradiating into
the region of ear or tongue. Many explanations have been advanced for
these variable symptoms: pressure on the external auditory meatus exerted by the mandibular condyle which is driven deeply into the articular
fossa; compression of the auriculotemporal nerve; compression of the
chorda tympani; compression of the auditory tube; impaired function
of the tensor palati muscle. Anatomical findings do not substantiate
any one of these explanations. Probably, all the diverse symptoms are
but consequences of a traumatic arthritis in the mandibular joint.“ 2 It is
caused by an increase and a change in direction of the forces of the
masticatory muscles upon the structures of the joint.
References
1. Bauer, W.: Anatomische und mikroskopische Untersuchungen iiber das Kiefergelenk Anatomical and Microscopic Investigations on the Temporo-Mandibular oint), Ztschr. f. Stomatol. 80: 1136, 1932.
2. Bauer, W. H.: Osteo-Arthritis Deformans of the Temporo-Mandibular Joint, Am.
J. Path. 17: 129, 1941.
3. Baecker, B.: Zur Histologie des Kiefergelenkmeniskus deg Menschen und der
Siiu er (Histology of the Temporo-Mandibular Disc in Man and Mammals),
Zts . f. mikr.-anat. For-sch. 26: 223, 1931.
Breitner, 0.: Bone Changes Resulting From Experimental Orthodontic Treatment,
Am. J. Orthodont. 26: 521 1940.
Cabrini, R., ‘and Erausquin,  La. Articulacion Temporomaxilar de la Rata
(Temporo-Mandibular Joint of the Rat), Rev. Odont. de Buenos Aires, 1941.
Cowdry, E. V.: Special Cytology, ed. 2, New York, 1932, Paul B. Hoeber, Inc.,
pp. 981-989, 1055-1075.
Hammer, J. Aug.: Ueber den feineren Bau der Gelenke (The Microscopic Architecture of the Joints), Arch. f. mikr. Anat. 43: 266, 1894.
Marquart, W.: Zur Histologie der Synovialmembran (Histology of the Synovial
Membrane), Ztschr. f. Zellforsch. u. mikr. Anat. 12: 34, 1931.
Peterson, H.: Die Organe des Skeletsystems (Organs of the Skeletal System),
Moel1endorf’s Handb. d. mikr. Anat. d. Menschen. Book 2, Part 2, Berlin,
1930, Julius Springer.
10. Schaefler, J. P.: Morris’ Human Anatomy, ed. 10, Philadelphia, 1942, The
Blakiston Co.
11. Schafler, J.: Ueber den feineren Bau und die Entwicklung dos Knorpelgewebes
und iiber verwandte Formen der Stiitzsubstanz (On the Microscopic Structure and Development of Cartilage and Related Forms of Supporting Tissue),
Ztschr. f. wissensch. Zoo]. 80: 155, 1905.
S°9°.“‘.°’S"'."
332 omu. HISTOLOGY AND EMBRYOLOGY
12. Schaffet, J.: Die Stiitzgewebe (Supporting Tissues), Moe11endorf’s Handb. f.
mikr. Anat. d. Menschen, Book 2, Part 2, Berlin, 1930, Julius Springer.
13. Shapiro, H. IL, and Ti-uex, R. 0.: The Temporo-Mandibular Joint and the Auditory
Function, J. A. D. A. 30: 1147 1943.
14. Sicher, Harry: Temporomandibufar Articulation in Mandibular Overclosure,
J. A. D. A. 36: 131, 1948.
15. Sicher, Harry: Some Aspects of the Anatomy and Pathology of the Temporamandibular Articulation, New York State D. J. 14: 451, 1948.
16. Steinhardt Gr.: Die Beanspruchun der Gelenkfliichen bei versehiedenen Bissarten ( vestigations on the tresses in the Mandibular Articulation and
Their Structural Consequences), Deutsche Zahnh. in Vortr. 91: 1, 1934.
CHAPTER XIV
THE MAXILLARY SINUS
IN'1'RODUC'.|'.'ION
DEVELOPMENT
ANATOMIG REMARKS
FUNCTION
HISTOLOG-Y
CLINICAL CONSIDERATIONS
9‘S"'."9°!°'."
1. INTRODUCTION
The relation of the maxillary sinus to the dentition was first recognized
by Nathaniel Highmore. In his Work Carports Humawi Disquisitio Anatomicafi (1651) he described the adult state of the cavity in detail, and
pointed out that his attention had been called to it because a patient had
an abscess there which was drained by the extraction of a cuspid tooth.
This proved to be one of those misleading first observations, since it is
now known that the cuspid‘ root seldom is related to this space in
such a way that its simple extraction would drain it. However, the
erroneous idea still persists that this relationship is generally true. The
molar roots most often, and the bicuspid roots less frequently, are the
dental structures which lie closest to the sinus (Fig. 259). Individual
variations are great and can be determined only by careful interpretation of
good roentgenographs.’
2. DEVELOPMENT
The maxillary sinus begins its development in about the third monthof fetal life. It arises by a lateral evagination of the mucous membrane of
the middle nasal meatus, forming a slitlike space. In the newborn its
measurements are about 8 x 4 x 6 mm. (Fig. 260); thereafter, it gradually expands by pneumatization of the body of the maxilla. The sinus
is well developed when the second dentition has erupted, but it may continue to expand, probably throughout life.5
3. ANATOMIG REMARKS
The maxillary sinus, or antrum of Highmore, is situated in the body
of the maxilla. It is pyramidal in shape; the base of the pyramid is
formed by the lateral wall of the nasal cavity; the apex extends into the
zygomatic process; the anterior wall corresponds to the facial surface
of the maxilla, and the roof to its orbital surface. The posterior wall is
formed by the infratemporal surface of the maxilla; the floor, usually,
reaches into the alveolar process (Fig. 261).
First draft submitted by Paul C. Kitchin in collaboration with L. F. Edwards. Department of Anatomy, Ohio State University.
333
334 ORAL msronoev AND nmsnvonocv
There is a considerable variation in size, shape and position of the maxillary sinus, not only in different individuals, but also on the two sides of
the same individual. Its average capacity in the adult is about one-half of
one fluid ounce (14.75 c.c.) with average dimensions as follows: anteroposteriorly, 3.4 cm.; transversely, 2.3 cm.; and vertically, 3.35 cm. The
maxillary sinus communicates with a recess of the middle meatus of the
nasal cavity (semilunar hiatus) by means of an aperture, the ostium maxillare, which is located high on its nasal or medial wall and is, therefore,
unfavorably situated for drainage (Fig. 261). An accessory ostium may
occur which is, usually, lower and thus more advantageously placed for
drainage than is the normal ostium.
 
 
Bony floor
of sinus
Buccal
« alveolar
plate
.2
, :3
Fig. 259.—Bucco1ingua1 ection throu h n t b‘ ‘d. ' ;
fzéom the sinusg by is thiirgpgfatenbisliione. The apex ls iepamted
Variations in the size of the maxillary sinus are explained on the basis
of the degree or extent of pneumatization of the body of the maxilla
(ho11owing—out by an air-filled pouch of the nasal cavity). In genera], the greater the pneumatization the thinner the walls of the sinus
will be, since pneumatization occurs at the expense of bone. During
THE MAXILLARY sums 335
enlargement of the sinus various recesses or accessory fossae may form.
Thus, subcompartments or recesses may be present in the palatine, zygomatic, frontal and alveolar processes. The floor of the sinus may extend
downward not only between adjacent teeth but also between the roots
of individual teeth so that their apices cause elevations in the floor and
appear to protrude into the sinus. The type and number of teeth whose
,1. : ,,,
   
.7!
 
Nasal septum
Maxillary sinus
"y Inferior nasal
concha.
Fig. 260.—Fronta1 sections through the head.
A. Newborn infant
B. Nine-month-old child.
Compare the size of maxillary sinus.
apices indent the floor of the space depend upon the degree and shape ofpneumatization. In the majority of cases the roots are covered by a. thin
layer of bone (Fig. 259). In some instances, they are covered only
by the mucous membrane which lines the cavity and by the periodontal
membrane of the root of the tooth. The floor of the sinus may be on the
336 omu. HISTOLOGY AND EMBRYOLOGY
 
 
Ethmoidal cell ‘
Aperture of ,- .lnus
1
Maxillary sinus - —-—‘
Nasal septum
Inferior nasal
concha
Maxtllary sinus
   
~ 3'.  ‘;bhéiF'w.;\?L( $-or‘ '
Fig. 261.—Rela.tion or the maxillary sinus and its opening into the nasal cavity.
A. Frontal section showing marked asymmetry between right and left sinus.
B. Relation of sinus to root apicea.
rm: MAXILLARY sINUs 337
same level with that of the nasal cavity, or higher or lower than that.
In some cases the sinus may be incompletely divided by osseous and membranous ridges, commonly known as septa.
Unilateral supplemental maxillary sinuses have been observed.‘ They
occur posteriorly to the sinus proper and are, from the standpoint of origin,
overdeveloped posterior ethmoid cells. Clinically, they must be considered
as maxillary sinus.
4. FUNCTION
In the past, various functions have been ascribed to the maxillary sinus
and the other accessory nasal sinuses. It has been claimed by some, for
instance, that they aid in warming and moistening inhaled air, thus acting
as air-conditioning chambers. Others believe that the sinus plays an
important role in vocalization. However, the most probable explanation
of the development of all nasal sinuses is that bone which has lost its
mechanical function is resorbed. An example is the marrow cavity in
long bones where fatty tissue develops in the place of the disappearing
bone. The disappearance of useless bony substance in the neighborhood
of the air-filled nasal cavity leads to development of air-filled pouches
which grow into the bone and occupy the place of bony tissue which
is no longer needed to withstand mechanical stresses. The supporting
function of bone is maintained but with a minimum of material. This
is in accord with principles of economy which exist in the animal body.
5. HISTOLOG-Y
The maxillary sinus is lined by a mucosa covered with an epithelium
typical of the respiratory passages. It is thinner and more delicate than
that of the nasal cavity.
The lamina propria of the mucosa is fused to the periosteum of the underlying bone and consists of loose bundles of collagenous fibers with
very few elastic fibers; it is only moderately vascular (Fig. 262, A).
Glands of the mucous and serous type are confined largely to that part
of the tunica propria which is located around the opening, or openings,
into the nasal cavity.
The epithelium is pseudostratified ciliated columnar, rich in goblet cells
(Fig. 262, B). The nuclei of the individual columnar cells are‘located at
different distances from a delicate basement membrane. Actually, each
columnar cell rests upon the basement membrane, but not all the cells
reach the surface. The goblet cells secrete mucus which moistens the
surface of the sinus mucosa. The cilia beat in such a way as to move
any surface material toward the opening communicating with the nasal
cavity, and hence act to clear the sinus cavity of inhaled substances, and
mucus.
6. GLINIGAI. CONSIDERATIONS
Pulpal infection in teeth whose root apices are in close approximation
to the floor of the sinus are dangerous because it can be a cause of sinus
Maxillary sinus
Epithelium
- —"- ‘ “ ‘ - Mucous membrane
‘T’ --- “F” and perlosteum
Incomplete bony
floor of sinus
_ _ ,_,......\‘. 7»;-w
Fig. 262.——Mucous membrane and epithelium of maxillary sinus.
A. Apical region of :1 second bicuspid. The lining oi.’ the sinus is continuous with the
periapicsl tissue through openings in the bony floor of the sinus.
B. High magnification of the epithelium of maxillary sinus. (Courtesy W. 11. Bauer.‘
St. Louis University School of Dentistry.)
.- - -j-—-A .g.g3;‘.I“&'
‘S
-2‘Q
es.
F'iE- 263.—Roentgenogrs.m or upper jaw. Maxillary sinus extends toward alveolar crest
after loss of flrst molar.
Tl-IE MAXILLARY SINUS 339
infection.‘= 3 Thus, the prevention of the dental type of sinusitis is possible by prevention or elimination of pulpal infection. Any root canal
operation in maxillary bicuspid or molar areas should be carried out with
particular care, in order to prevent infection of the sinus.
The dentist should always keep in mind that disease of the maxillary
sinus may produce referred dental pain. The superior alveolar nerves run
in narrow canals in the thin wall of the sinus and, frequently, these canals
are partly open toward the sinus. When this happens the nerves which
supply the teeth are in contact with the lining of the sinus where they
may become involved in an inflammation affecting the mucosa. In such
cases, the pain resembles pulpal pain but involves a group of teeth or
even all the teeth in one maxilla. If apices of some roots are in contact
with the lining of the sinus the affected teeth may show symptoms of
periodontitis during sinus infection. In cases where there is doubt whether
the teeth or sinus are the cause of pain, the patient should be referred to
a rhinologist before an extraction is performed.
In the course of an extraction a root may be forced into the sinus.
If it cannot be easily removed through the socket the patient should be
informed of the circumstances and be referred to a rhinologist. Even
if it is possible for the dentist to remove the root of the tooth, subsequent treatment by the sinus specialist is advisable. Any invasion of the
field of sinus surgery by the dentist operating through the alveolar wall
should be discouraged by both dental and medical professions.
After loss of a single maxillary molar or, more rarely, bicuspid, the
bony scar is, sometimes, hollowed out by the sinus (Fig. 263). The risk
of opening the sinus during extraction of a tooth adjacent to such an
extension has to be recognized. If a single molar remains in the maxilla
for a long time after loss of the neighboring teeth, downward extensions,‘
of the maxillary sinus may occur mesially and distally to this tooth. If [
greater force is applied in extracting such a tooth, tooth and socket are
removed together rather than extracting the tooth from its socket. To
minimize the necessary force the crown should be removed, the roots separated and extracted singly. The expansion of the maxillary sinus (and
other sinuses) in old individuals should not be considered a process of
growth. It is rather the consequence of progressive disuse atrophy of
the bones, especially after loss of teeth, or of senile osteoporosis. The
senile expansion of sinuses strengthens the belief that they develop as
fill-ins in bones whose core is under reduced mechanical stress.
References
1. Bauer. W. ‘EL: Maxillary Sinusitis of Dental Origin, Am. J. Orthodont. & Oral Surg.
29: 133, 1943. _
2. Ennis, L. M., and Batson, 0.: Variations of the Maxillary Sinus as Seen in the
Roentgenogram, J. A. D. A. 23: 201, 1936.
3. Hofer, 0.: Dental Diseases and Their Relation to Maxillary Antrum, J. Dent.
Research 17: 321, 1938 (Abstract).
340 omu. HISTOLOGY AND EMBRYOLOGY
4. MacMilla.n, H. W.: The Relationship of the Teeth to the Maxillary Sinus; Anatomic
Factors glnderlying the Diagnosis and Surgery of This Region, J‘. A. D. A. 14.:
1635, 19 7.
5. Schaefier, J. I’.: The Sinus Maxillaris and Its Relations in the Embryo, Child and
Adult Man, Am. J. Anat. 10: 313, 1910.
6. Schaefler, J. P.: The Nose, Paranasal Sinuses, Nasolacrymal Passageways and
Olfactory Organ in Man, Philadelphia, 1920, P. B1a.kiston’s Son & Co.
7. Sedwick, H. .1'.: Form, Size and Position of the Maxillary Sinus at Various Ages
Studied by Means of Roentgenograms of the Skull, Am. J. Roentgenol. 32: 154,
1934.
8. Zuckerhandl, E.: N ormale und pathologische Anatomie der N asenhiihle und ihrer
pneumatischen Anhiinge (Anatomy of the Nasal Cavity), Leipzig, 1893.
CHAPTER XV
TECHNICAL REMARKS
1. INTRODUCTION
2. PREPARATION OF EISTOLOGIC SPI:GIM:E:N S
a. Dissection
b. Fixation
c. Decalciflcation
d. Embedding
e. Sectioning
f. staining
g. Altmann-Gersh Technique
3. PREPARATION OI‘ G-ROUND SECTIONS
4. PREPARATION OI‘ ORGANIC STRUCTURES IN THE ENAMEL
5. PEOTOMICROGRAPHY
1. INTRODUCTION
This chapter is intended to give the student a general idea of the preparation of microscopic slides, rather than to cover fully the subject of
microscopic technique. For detailed information specialized textbooks
should be consulted." 11’ 12' 1’ The various processes to which a tissue is
subjected from the time it is taken from the body until it is ready to be
examined under the microscope, are termed microtechnique. Its object
is to prepare the specimen for examination of its microscopic structure.
2. PREPARATION OF I-IISTOLOGIC SPECIMENS
Dissection is the first step in the preparation of a specimen; the material may be secured by a biopsy (excision during life) or at an autopsy
(postmortem examination). Pieces of tissue are cut as small as possible
to insure satisfactory fixation and impregnation. A very sharp knife
should be used to prevent tissue structures from being distorted and
squeezed.
Immediately after the specimen is removed and the surface washed
free of blood, it is placed in fixing solution. The object of fixing is to
preserve the tissue elements in the same condition in which they are at
the moment the reagent acts upon them, and harden or so affect them
that they will not be altered by the processes of dehydration, embedding,
staining, clearing and mounting. The amount of the fixing solution should
be at least 20 times the volume of the tissue. The fixing tissue coagulates
the protein content of the cells, thus preventing decomposition.
First draft submitted by Joan Launspach, research technician or the Foundation for
Dental Research, Chicago College of Dental Surgery.
341
Dissection
Fixation
Lciflcation
342 ORAL msronocr AND EMBRYOLOGY
There are several fixing agents in general use, the most common of
which are formalin, formalin-alcohol, Zenker-formol solution, and Bouin’s
fluid. A good and rapidly penetrating fixative for small specimens is
Zenker-formol solution, a mixture of 9 parts of potassium bichromate and
bichloride of mercury with 1 part of neutral formalin. Formalin (5 to 10
per cent) is used for large pieces of tissue, e.g., jaws. It does not deteriorate and it penetrates very rapidly. Formalin-alcohol fixes and dehydrates simultaneously, and is used mostly for surgical specimens. Bouin’s
fluid is a solution of picric acid and formalin, and is especially applicable
in studying cell outlines, but is rather slow to penetrate.
The length of time necessary for a fixing agent to act upon a tissue
varies according to the size of the specimen and penetrating power of the
fixative. Generally, it should be just long enough for the agent to saturate the piece thoroughly without allowing it to become brittle. Small
pieces of tissue, e.g., gingiva, are left in Zenker-formol solution only 4
to 8 hours, while larger pieces such as jaws may be left in formalin for
days. In order to obtain good fixation of pulp in an intact tooth, the
surface of enamel and dentin is ground away to a thin layer of dentin
around the pulp. This process not only insures rapid and thorough penetration of the fixing agent but also reduces the time of decalcification
and permits a thorough impregnation with cellodin. When fixing biopsy
specimens, the solution should be at approximately body temperature.
After the specimens are thoroughly fixed, they are washed in running
water for twenty-four to forty-eight hours to remove all acids and reagents. Occasionally, however, special treatment is required to remove
the precipitates caused by certain agents. Example: specimens fixed in
Zenker-formol solution are treated with Lugol’s (iodine) solution and
sodium thiosulfate, and specimens fixed in formalin are placed in a mixture of potassium hydroxide before staining. However, there is no need
of this if neutral formol is used.
Animal tissues may be classified as hard and soft, or calcified and noncalcified. The dental histologist is particularly interested in the hard
tissues, namely, the enamel, dentin, cementum and bone. These are impregnated with a variable quantity of calcium salts and cannot be seetioned on the microtome unless decalcified.
Decalcification of a tissue is the removal of its mineral content by an
acid such as nitric, hydrochloric, trichloracetic, formic, or sulfosalycilic
acid. The length of time a specimen remains in the decalcifying agent
is influenced by the choice and concentration of the acid, and the size of
the specimen; however, the shorter the time the better is the staining.
A 5 per cent solution of nitric acid seems to be most satisfactory and is,
therefore, widely used. It acts quickly without causing swelling of the
tissue or any other undue changes in its elements; it does not interfere
with the staining process to any marked degree.
While tissues are being decalcified they should be suspended in a large
quantity of the fluid in order that the salts dissolved may sink to the
TECHNICAL REMARKS 343
bottom of the jar. Occasional stirring or gentle agitation of the specimen
and heating of the acid may hasten the process of decalcification, but
great care should be taken not to injure the tissues.
To ascertain whether the inorganic salts have been completely removed,
the specimen can be pierced with a sharp needle or pin: when no gritty
substance is detected, the decalcification is sufficient. Roentgenographic
check-up can also be employed. After decalcification a tooth should be
as pliable as a piece of cartilage. The enamel disappears almost entirely
owing to its low percentage of organic matter. The decalcifying agent
may also be tested for calcium; the acid is changed periodically until the
test is negative.
Following decalcification the specimen is washed thoroughly in running water for at least 24 hours. From this point it is treated as a soft
tissue and is ready for the embedding process. It is possible, however,
to embed hard tissues first and decalcify them later: the specimen is run
through the solutions in routine fashion and, after it is blocked, the
excess celloidin is cut away and the tissue is suspended in acid until
decalcified. This takes much longer than the usual procedure and the
results are often uncertain.
In order that a tissue may be sectioned on the microtome it has to have
a certain rigidity to offer sufficient resistance to the cutting edge of the
knife. This may be accomplished by freezing the tissue or, as is more
commonly done, by using an embedding medium which fills the interstices of the tissue. The freezing technique is employed where immediate
investigation of the specimen is required, as in the course of a surgical
operation. Some substances (fat, lipoids, etc.) are dissolved during embedding: tests for such substances can be made only in frozen sections.
Embedding is a much more lengthy process but results are more satisfactory. Before the specimen is embedded, i.e, impregnated with a suitable substance such as paraffin or celloidin, the water has to be removed
from the tissues. Paraffin embedding is more rapid and is used for small
pieces, usually soft tissue, as decalcified pieces become brittle during the
heating which is necessary in using this method. Celloidin embedding
takes longer but causes less shrinkage. This technique is more commonly
used in dental histology when large blocks of decalcified material have
to be sectioned.
Dehydration is accomplished by placing the specimens in ascending
alcohols (50, 70, 95, 100 per cent) for approximately one day each; the
length of time depends on the size and permeability of the specimen.
Two consecutive changes of absolute alcohol are used. As, however,
paraifin or celloidin is not soluble in alcohol it has to be replaced by a
fluid which is a solvent for the embedding medium.
When paraffin is selected as the embedding medium, the absolute alcohol is replaced by xylol or oil of cedarwood. The specimens are placed
in the solvent 12 to 24 hours, and are then placed in liquid parafiin in the
Embedding
Sectioning
344 ORAL HISTOLOGY AND EMBRYOLOGY
incubator (56 C.) for several hours. Finally the specimen is placed in a
form filled with molten parafiin and quickly cooled. It is then ready to
be sectioned.
If celloidin, a solution of nitrocellulose in absolute alcohol and ether,
is selected as the embedding medium, a mixture of equal parts of ether
and alcohol is used as a solvent in which the tissue remains for 12 hours.
It is then carried through a thin (6 per cent) and medium (121/; per
cent) into thick (25 per cent) solution of celloidin. The length of time
which is necessary for each of the solutions to penetrate the specimen
depends upon size and permeability of the tissue. Soft tissue is well
infiltrated with celloidin after three weeks while decalcified specimens
require at least six weeks; to insure thorough impregnation, it is wise
to leave teeth longer in the lower concentration of celloidin and a somewhat shorter time in the stronger concentration. When it is necessary
to “rush” a specimen the tissue in thin celloidin may be placed in a
50° C. oven in a tightly stoppered container; the embedding period is
thus shortened to two or three days. This method causes considerable
shrinkage. Small pieces of tissue may be placed directly on a fiber block
and left to harden in a desiccator filled with chloroform vapor. Large
pieces of tissue, e.g., jaws, are placed in an evaporating dish filled with
celloidin which is allowed to harden down slowly. When the celloidin
has reached the desired degree of hardness, blocks are cut out and, after
being softened in thin celloidin a few minutes, are placed on fiber blocks,
allowed to air dry, and then placed in 70 per cent alcohol for storage or
sectioning.
Tissues are sectioned by means of a microtome, ‘a machine equipped
with a knife. There are three different types of microtomes: the freezing, rotary, and sliding, the use of which depends on the kind of tissue
and embedding medium used. Each is a heavy specially designed machine precisely constructed, capable of slicing prepared tissues into exceedingly thin sections. The knife is wedge-shaped and made of heavy
steel to aflord the greatest possible rigidity; it must have a very keen
edge as the slightest nick would tear a section. Sharpening a microtome
knife is one of the most important as well as the most difficult tasks of
a technician. Larger nicks are removed on a coarsely grained stone,
and a fine edge is achieved by grinding the knife on a fine hone. The
final cutting edge is obtained by stropping on a finishing leather microtome strop. A much more rapid and just as satisfactory a method that
has recently been developed is the use of a grinding machine, consisting
of an ebony wheel mounted on a rotary motor. A strop, dusted with
abrasive powder, is used to put the finishing edge on the knife. The
possibility of making good sections depends upon the type of tissue,
its preparation, and the condition of the knife. Sections of 5 to 15
microns (174000 millimeter equals 1 micron) are considered thin.
TECHNICAL REMARKS 345
The importance of the freezing technique in preparing surgical specimens has been mentioned. It is well known that, by exposing tissues
to an extreme degree of cold, they become hard and can be easily sectioned with the freezing microtome. The cold is generated by means of
carbon dioxide which is sprayed onto the stage holding the specimen:
rapid evaporation produces the required temperature.
The rotary microtome is used only for sectioning paraffin blocks; the
knife is immovably fixed at a right angle to the block which is carried
past the sharp edge of the knife by turning a wheel. With this machine
it is possible to out long ribbons of serial sections. The ribbons are placed
in lukewarm water where the wrinkles are removed as the paraffin becomes soft. The desired sections are then floated onto slides smeared
with egg albumen and placed in a 37° C. oven for a few minutes. Before
staining, the paraffin is dissolved in xylol. the slides rinsed in absolute
alcohol, the sections are carried through descending concentrations of
alcohols into distilled water; then they can be stained by water-soluble
dyes.
A celloidin block is sectioned by a different method. For this purpose
the sliding microtome, a heavy sledgetype instrument, is used. The longitudinal angle of the knife is adjusted to each specimen so that the entire
cutting edge is used in sectioning. The angle of the cutting edge of the
knife should be changed according to the hardness and density of the material. To obtain the most satisfactory results the knife should be in an
almost horizontal position for large decalcified pieces, at an acute angle
for soft tissue. During sectioning both specimen and knife are continually moistened with 70 per cent alcohol; the sections are placed in distilled
water before staining. The celloidin is usually not removed from the
section as the stain penetrates the tissues in spite of this embedding medium. However, it has to be removed from the section in the case of
specific stains, i.e., Mallory, azure-eosin, etc. For this procedure the section is mounted on a slide smeared with egg albumen and is flooded with
oil of cloves to dissolve the celloidin; the slide is rinsed in 95 per cent
alcohol and placed in 70 per cent until ready for staining.“ When serial
sections are desired, sections are mounted on glass slides which are then
blotted and flooded with a very thin solution of collodion. After a coating is formed, the slides are marked with a diamond pencil or India ink,
and stored in 70 per cent alcohol until ready for staining.“
Some special staining methods can be applied only to sections of undecalcified teeth and bone. To obtain such sections mature enamel has
to be removed from the teeth. The tissue impregnated With celloidin is
placed in a shallow dish and covered with celloidin. The solution is
allowed to evaporate slowly until the celloidin is very hard (two to four
weeks) . A very hard knife should be used which has been sharpened and
stropped ; when checked under the microscope it has deep and even teeth
and should be clamped in the microtome at a 13° angle.
Staining
Altmann-Gersh
Technique
346 orm. ursronoev AND nmasvonoer
Dyes used to stain specimens for microscopic examination may be classified as basic or acid, according to their affinity for different cellular
elements. Basic dyes, sometimes called nuclear dyes, primarily stain
nuclear chromatin, basic substance of cartilage and mucus; the more
commonly used are hematoxylin, methylene blue, safranin, and carmin.
Acid dyes color the cytoplasm of the cell, uncalcified bone and dentin
matrix, some connective tissue fibers; eosin and phloxin are representative
of this group. By using combinations of the two groups, due to their
different affinities, a marked difierentiation of the cellular elements of
the specimen is possible.
Sections may be stained on the slide or floating in dishes; in the latter
case better differentiation is afiorded. Although the steps of the various
staining methods differ considerably, they may be arranged in the following order: staining, differentiating, decolorizing, dehydrating, clearing and mounting.
Hematoxylin and eosin is one of the most commonly used combinations
of stains because it is the simplest to handle. For the differentiation of
more specialized tissues the following are recommended: Mallory stain,“
or Heidenhain’s Azan“ (modification of Mallory’s stain) for connective
tissue; the latter is more brilliant and has greater capacity for differentiation; Silver Impregnation (modification of Foot’s stain by Gomori)
for connective tissue fibers and nerve elements ;’ Van Gieson’s stain, a
counterstain to hematoxylin, for differentiation of white connective tissue," and Weigert’s stain for elastic tissue.“
After sections of tissues have been stained and differentiated, they are
dehydrated and then passed through a medium that will mix with the
dehydrating fluid as well as the reagent in which the sections are to be
mounted. These intermediary fluids are called clearing agents because
they have a high refractive index, thus rendering the sections more or
less transparent.
For celloidin sections a variety of clearing agents is used: terpineol
(Lilacine), carbol-xylol, oil of cloves, oil of cedar wood, oil of origanum
and beechwood creosote; for paraffin sections usually only two are used:
xylol or toluol.
After clearing, the sections have to be placed in some medium which
will preserve the stain and prevent the tissue from drying. Such solutions are termed mounting agents: among the most common are Gum
damar, Canada balsam, and clarite. Loose celloidin sections are floated
onto the slide and straightened out with the aid of a fine camel’s hair
brush; they are carefully blotted and covered with a drop of mounting
medium and a coverslip. Weights are placed on the coverslips to prevent
the formation of air bubbles. When dry, they are carefully cleaned with
xylol and labeled with India ink.
The Altmann-Gersh freezing and drying technique for special microchemical studies should also be mentioned. The tissues are frozen inTECHNICAL REMARKS 347
stantaneously when placed in a tube of isopentane in a Liquidair container
and are dehydrated under vacuum while still frozen, thus avoiding a redistribution of minerals. Fixation, alcohol dehydration, and clearing
are omitted as the dehydrated tissue can be immediately infiltrated with
paraffin and sectioned according to the usual methods. This technique
has proved valuable in the preparation of tissues for micro-incineration,
and for special micro-chemical reactions.
Many submicroscopic structures may be seen with the electron microscope, not visible in sections prepared in the routine manner.
3. PREPARATION OF GROUND SECTIONS
Ground sections are prepared by using abrasive stones upon a tooth
or bone until the tissue is reduced to translucent thinness. It is the principal method of examining the enamel which has so little organic material
that it disappears almost entirely when the teeth are decalcified by ordinary methods. Therefore, this technique should complement the decalcification method. i
To prepare a ground section of a tooth it is first ground down on one
side on a carborundum stone which rotates at high speed on a laboratory
lathe. It is important that the tooth be kept wet constantly with cold
water to lessen the heat produced by friction and to prevent the section
from drying. If it is allowed to dry its organic constituents will shrink
and present a picture untrue to the conditions during life. The tissue is
likewise more apt to crack and break up during preparation if it becomes
dry. When the desired level is reached and the ground surface is perfectly plane, this surface is polished on wet ground glass and, finally, on
an Arkansas stone. The other side of the specimen is then ground down
until the section is sufficiently translucent. This second side is also
polished in the above described manner, to remove the gross scratches
produced by the carborundum stone. The finished ground sections should
have an average thickness of 25 to 50 microns and, if desired, may be
stained before they are dehydrated, cleared and mounted.”
For surface staining of ground sections the surface is well polished and
the section is covered with a 0.25 per cent H01 to decalcify it slightly;
then it is stained lightly with hematoxylin.“ By this method only the
surface of the ground section is stained and the stained layer can be
viewed with high power lenses as it is only a few microns in thickness.
This method, however, causes slight decalcification of the enamel making
a marked differentiation of rods from sheaths and cementing substance,
:3. condition not representative of normal enamel. Enamel that has been
partially decalcified by caries, or a poorly formed enamel has this
appearance.
If it is necessary to investigate an undecalcified tooth with the surrounding soft tissue, ground sections can be made by using the petrification method. The specimen is embedded in Kollolith-chloroform solution
348 omu. HISTOLOGY AND EMBRYOLOGY
or in Canada balsam”, 15 where it is left until it is sufficiently hard before
it is ground down to a desired thickness. Thin “serial” ground sections of
teeth and jaws may be cut in one operation by infiltrating the specimen
with a plastic material and using a cutting device made up of steel wheels
set at various distances."
4. PREPARATION OF ORGANIC STRUCTURES IN THE ENAMEL
The routine decalcification of whole teeth in an aqueous solution of
acid usually destroys the enamel completely. At most, merely shreds of
the organic structures remain near the cervical areas in a tooth of a
young person.
The organic structures may be demonstrated by C. F. Bodecker’s celloidin decalcifying method.‘ When dentin is included in the specimen
sections are rarely satisfactory because this tissue becomes very brittle
as a result of the many media through which it passes. It is necessary
only for study of the organic structures in the enamel under high magnification. In general, this method is erratic and a high percentage of
failures must be expected.
The Cape-Kitchin modification‘ 5 of Bodecker’s method is quite simple
and gives satisfactory results if the structures of the matrix are not magnified more than about 500 diameters.
Frisbie, Nuckolls, and Saunders’ have recently developed a technique
for the successful recovery of the enamel matrix. The fresh specimen
is immediately fixed in neutral formalin for a long period of time (six
months) ; most of the dentin is then removed with a dental bur and the
tooth is placed in the fixative again for a shorter period of time, depending on the penetrability of the specimen. The completely fixed enamel
is decalcified by placing the specimen on a gauze stretched over a platinum wire frame, and immersing it in a 5 per cent solution of nitric acid
in 80 per cent alcohol for 24 to 48 hours. Dehydration is begun with 70
per cent alcohol without preliminary washing. The specimen is infiltrated with celloidin at 56 C. for two weeks and then allowed to harden
down slowly at room temperature until the block is very hard. Sectioning is done with a sliding microtome at 3 to 4 microns.
An aqueous decalcification of enamel under a cover-glass is the simplest
but the least satisfactory method for its study. It is sufficient to show
enamel lamellae, cuticle, tufts, and can be used to demonstrate gross
differences in quantity of organic structures of enamel in recently erupted
teeth and in teeth of old persons. However, the disadvantages are that
only low magnifications up to 100 diameters are possible and that the
specimens are not durable.
Another method of differentiating the organic from the inorganic content of the enamel is by incineration. It has been shown that the heating
of sections of human adult enamel up to 800° 0. causes a destruction of
the organic content but leaves enamel rods intact.
TECHNICAL REMARKS 349
5. PHOTOMICROGRAPHY
Photomicrographs are photographs of small microscopic objects, made
with the aid of a microscope. Most of the illustrations in this book are
such pictures. Transmitted light is the most commonly used method of
illumination as it permits the sharpest differentiation of details and the
highest magnification of tissue structures in stained decalcified sections.
Refiected light is used in oral histology in photographs of ground
sections of enamel and dentin. These sections should be ground perfectly smooth. There is no need for extreme thinness because the specimen is viewed only from the surface from which the light is reflected.
Polarized light also is useful in the study of the dental tissues. It
vibrates in a single known plane and requires special equipment and
technique. By this means it is possible to determine details of the submicroscopic structure of tissues, due to the differences in optical properties of various elements. Polarized light is particularly useful in the
study of calcified tissues, but is not confined to these, because fibrous and
keratinized structures also yield information when studied by this method.
Grenz rays are a form of exceedingly soft roentgen rays. When ground
sections of teeth are photographed in this way, slight variation in calcification may be defined thus rendering this method useful in the study of
calcified structures." 13
A method has recently been developed by Gurney and Rapp” for
studying the fine structural details of tooth surface by adapting the Fax
Film technique used for study of metallographic surfaces. Micro-impressions are made of the specimen, using a plastic film which may then
be mounted on a glass slide for a permanent preparation. Scott and
Wyckoff“ obtained similar results by shadowing collodion replicas with
vaporized metal in a high vacuum, a more complicated method. The
eifect of chemical agents on tooth structure and the changes in tooth
surfaces (caries) may be observed using these methods. When examined
under the electron microscope, many submicroscopic structures are
visible.
Ultraviolet light technique‘ and fluorescence light microscopy, likewise, have been applied in special studies of dental tissues, but have not
yet attained wide use.
References
1. Applebaum, E.. Hollander, F., and Bodecker. C. F.: Normal and Pathological
Variations in Calcification of Teeth as Shown by the Use of Soft X-rays,
Dental Cosmos 75: 1097, 1933. _
Bensley, R. R., and Bensley, S. 8.: Handbook of Histological and Cytological
Technique, Chicago, University of Chicago Press. _ _
Bodecker, C. F.: Cape-Kitchin Modification of Celloidin Deoalcifymg Method for
Dental Enamel, J. Dent. Research 16: 143, 1937. _ _ _ '
Bodecker, C. F.: Enamel of Teeth Decalcifled by Celloidin Decalcifying Method
and Examined by Ultra Violet Light, Dental Review 20: 317, 1906.
Cape, A. T., and Kitchjn, P. 0.: Histologic Phenomenon of Tooth Tissues Observed
Under Polarized Light, With a Note on Roentgen Ray Spectra of Enamel and
Dentin, J. A. D. A. 17: 193, 1930.
S"l“9°.l‘-"
350 ORAL HISTOLOGY AND EMBRYOLOGY
6. Cowdry, E. V.: Microscopic Technique in Biology and Medicine, Baltimore,
1943, Williams & Wilkins Co.
7. Frisbie, H. E., Nuckolls, J., and Saunders, J. B. de G. M.: Distribution of
Organic Matrix of Enamel in Human Teeth and Its Relation to Histopathology of Caries, J. Am. Coll. Dent. 11: 243, 1944.
8. Gurney, B. R, and Rapp, G. W.: Technic for Observing Minute Changes on
Tooth Surfaces, J. Dent. Research 25: 367, 1946.
9. Guyer, M. F.: Animal Micrology, Chicago, 1943, University of Chicago Press.
10. Hotchkiss, R. D.: Microchernical Reaction Resulting in Staining of Polysaccharide Structures in Fixed Tissue Preparation, Arch. Biochem. 16: 131,
1948.
11. Loosli, C. G.: Outline of Histological Methods, Chicago, University of Chicago
Press.
12. Mallory, F. B.: Pathological Technique, Philadelphia, 1938, W. B. Saunders Co.
13. McClung, C.  Microscopic Technique, New York, 1937, Paul B. I-Ioeber, Inc.,
pp. 353-401.
14. McLean, F. 0., and Bloom, W.: Calcification and Ossification. Calcification in
Normal Growing Bone, Anat. Rec. 78: 133, 1940.
15. Meyer, W.: Die Anfertigung histologicher Schlifie (Preparation of Histologic
Ground Sections), Vrtljschr. f. Zahnheilk. 41: 111, 1925.
16. Scott, D. B., and Wyckofi, R. W. G.: Shadowed Replicas of Tooth Surfaces,
Pub. Health Rep. 61: 697, 1946.
17. Sognaecs, R. F.: Preparation of Thin Serial Ground Sections of Whole Teeth
and Jaws and Other Highly Calcified and Brittle Structures, Anat. Rec.
99: 133, 1947.
17a. Sognnaes, R. F.: The Organic Elements of the Enamel. I, II, III, IV, J. Dent.
Research 27: 609, 1948; 28: 549, and 558, 1949; 29: 260, 1950.
18. Willman, M.: Technique for Preparation of Histological Sections Through Teeth
and Jaws for Teaching and Research 16: 183, 1937.
19. Wolf, J.: Plastische Histologie der Zahngewebe (Plastic Histology of Dental
Tissues), Deutsche Zahn-, Mund- und Kieferheilkunde 7: 265, 1940.




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Orban B. Oral Histology and Embryology (1944) The C.V. Mosby Company, St. Louis.

Orban 1944: 1 Development of the Face and Oral Cavity | 2 Development and Growth of Teeth | 3 Enamel | 4 The Dentin | 5 Pulp | 6 Cementum | 7 Periodontal Membrane | 8 Maxilla and Mandible (Alveolar Process) | 9 The Oral Mucous Membrane | 10 Glands of the Oral Cavity | 11 Eruption Of The Teeth | 12 Shedding of the Deciduous Teeth | Temporomandibular Joint | The Maxillary Sinus | 15 Technical Remarks


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Chapter V - Pulp

I. FUNCTION Formative Nutritive Sensory Defensive

II. ANATOMY

Pulp Chamber Root canal Apical Poramen

HI. DEVELOPMENT

IV. STRUCTURAL ELEMENTS

Fibroblasts and Fibers Odontoblasts Defense Cells

3.. Histiocytes b. Undifferentiated Mesenchymal cells c. Lymphocytes Blood Vessels

Lymph Vessels Nerves

V. REGBESSIVE CEANGES

Pulp Stones Galcifications Secondary Dentin Fibrosis

VI. GLDTICAI. CONSIDERATIONS

I. FUNCTION

The dental pulp is of mesenchymal origin and contains most of the cellular and fibrous elements which are present in connective tissue. The primary function of the dental pulp is the production of dentin. This function is discussed in the chapter on Dentin. The pulp furnishes nourishment through the odontoblastie processes to the dentin. Nutritional elements are contained in the tissue fluid. The pulp also contains nerves. Some of these nerves give sensation to the tooth structures, others serve to regulate the blood supply of the pulp itself by ending on the muscular ele—

ments of the vessels.

First draft submitted by Balint Orban. 127 Defensive

128 (um. HISTOLOGY AND EMBRYOLOGY

The pulp is well protected against external irritations as long as it is surrounded by an intact wall of dentin. It can evolve a very effective reaction if exposed to irritation whether it is of mechanical, thermal, chemical or bacterial nature. The defenive reaction may be expressed in the formation of irregular dentin (see chapter on Dentin) if the irritation is mild, or as an inflammatory reaction in cases of more severe irritation. While the rigid dentinal wall has to be considered as a protection to the pulp it also endangers its existence under certain conditions. During inflammation of the pulp the hyperemia and the exudate cause increasing pressure which, by occlusion of the blood vessels, may lead to necrosis—self-strangulation of the pulp.

H. ANATOMY

The dental pulp occupies the pulp cavity which consists of the coronal pulp chamber and the root canals. The pulp is continuous with the periapical tissues through the apical foramen or foramina. Roughly the

--:-qr’; v-,"'* "—— ~.ws¢§§


Fig. 97.—Age changes in the pulp chamber or the first permanent molar. Decalcifled sections; enamel lost.

4. Age 8 years. B.Ase55 years.

Reduction of the pulp chamber in height is greater than in mesiodlsfal diameter. Pulp stones narrowing the entrance into the root canals in B. (Kronteld, R34)

shape of the pulp chamber follows, in young individuals, the outline of the tooth. The extensions into the cusps of the tooth are called pulpal horns. At the time of eruption the pulp chamber is large, but becomes smaller with advancing age, due to continuous deposition of dentin“ (Fig. 97). The decrease in the size of the pulp cavity in molars does not occur at the same rate throughout the pulp chamber. Formation of dentin PULP 129

progresses fastest on the floor‘ of the pulp chamber; some is formed at the occlusal wall and, lem still, on the side walls of the pulp chamber so that the pulp dimension is reduced in an occlusal direction. The chamber may

be further narrowed and its shape may become irregular by formation of irregular dentin. The formation of pulp stones (Fig. 97, B) may also

reduce the size and change the shape of the formerly Wide pulp cavity, occasionally even occluding it.

=_ ' ‘,“""’”'.j


Pulp

lEpithella.l iiaphragm

Apical foramen


Fig. 98.—Deve1opment of the apical toramen. A. Undeveloped root end; wide apical foramen, partly limited by epithelial diaphragm

B. Apical foramen fully formed. Root canal straight; apical roramen surrounded by cementum (Coolidge, E. D.’)

Advancing age induces similar changes in the root canals. During Root canal root formation the apical foramen is a wide opening, limited by the epithelial diaphragm (Fig. 98, A), the continuation of Hertwig’s root sheath at the root end. The dentinal walls taper and the shape of the pulp

canal is like a wide, open tube. As growth proceeds more dentin is formed so that, when the root of the tooth has matured, the root canal is considerably narrower. In the course of root formation Hertwig’s epithelial root sheath breaks up into epithelial rests, and cementum is laid down on the root surface (Fig. 98, B). This cementum will influence the size and shape of the apical foramen in the fully formed tooth. Root canals are not

‘The floor oi.’ the pulp chamber is the wall opposite the occlusal wall (root) regardless of the position of the tooth in the Jaws. 130 ORAL HISTOLOGY AND EMBRYOLOGY

Fig. 99.-Drawings of teeth a.1.'t_er filling or the _root canals with India. ink and clear_ing. (After Okumura. 1“ and Apr1le.1) A. Upper incisors. B. Upper cuspids. C‘. Lower mcisors. D. Lower cuspids. F. Upper molars. G. Lower premolars. molars.

Fig. 99 Contd.—E. Upper premolars.

H. Lower

.3

PULP

131 132 ORAL HISTOLOGY AND nmmzvonocv

always straight and single but vary by the occurrence of accessory canals, as seen in corrosion specimens“ or after filling of the root canals with india ink and clearing (Fig. 99).

At any distance from the apex of the tooth (Fig. 100, A) side branches of the root canal may be present. In multi-rooted teeth these are observed even at, or close to, the floor of the pulp chamber (Fig. 100, B and C). A possible explanation for the development of all side branches of the pulp canals may be a defect in HertWig’s epithelial root sheath during development of the root at the site of a larger supernumerary blood vessel.



‘ p Accessory

canal

Fig. 100.—Accessory canals in microscopic sections. A. Close to the apex. B. Close to the bifurcation.

Apical There are variations in shape, size, and location of the apical foramen.’ Poramen A regular, straight apical opening is rare (Fig. 98, B); occasionally, the cementum can be traced from the outer surface of the dentin into the pulpal canal. Sometimes, the apical opening is found on the lateral side of the apex (Fig. 101, B) although the root itself is not curved. Frequently, there are two or more distinct apical foramina, separated by a band of

dentin and cementum, or cementum only. The location and shape of the apical foramen may also undergo changes,due to functional influences upon the teeth.“ A tooth maybe tipped, due Flg. 1000.—Roentgenogram or lower molar with accessory canal filled. (H. B. J'ohnston.")

Fig. 101.—Varlatlons of the apical to:-amen.

A. sum ot the apical roramen by resorption of dentin and cementum on one surface md apposition of cementum on the other.

8. Apical fornmen on the side of the apex (Coolidge. E. D’).

Apex 134 ORAL HISTOLOGY AND EMBRYOLOGY

to horizontal pressure, or may migrate mesially causing the apex to deviate in the opposite direction. Under these conditions the tissues entering the pulp through the apical foramen exert pressure on one wall of the foramen, causing resorption. At the same time cementum

is laid down on the opposite side of the apical root canal, resulting in a change in the relative position of the original opening (Fig. 101, A).

III. DEVELOPMENT

The development of the dental pulp begins at a very early stage of embryonic life, about the fifty-fifth day, in the region of the incisors; later in the other teeth. The first indication is a proliferation and condensation of mesenchymal elements, lmown as the dental papilla, at the

Oral epithelium

Epithelial enamel organ

Basement membrane



._ Dental papilla

i Mandi bular bone

Fig. 102.——Development at the pulp. Dental papilla or an embryo two and one-halt months old. The papilla contains a. rich network of tine argyrophil fibers. Basement

membrane between mesenchyrne and epithelium. Silver impregnation.’ (Courtesy Dr. P. Gruenwald.) ‘ ' w A ' ‘ PULP 135

basal end of the enamel organ (Fig. 102). Due to the rapid development of the epithelial elements of the tooth germ into a bell-shaped enamel organ. the future pulp is well defined in its outline. In a silver-impregnated section the arrangement of the fibers in‘ the embryonic dental papilla, is clearly visible (Fig. 102). ' In the future pulp area the fibers are fine and irregularly grouped, and much denser than in the surrounding tissue. At the boundary toward the epithelium a basement membrane is formed, and the fibers of the dental papilla radiate into it.

The fibers in the embryonic pulp are pre-collagenous, i.e., reticular or argyrophil. There are no collagenous fibers in the embryonic pulp, ex cept where the fibers follow the course of the blood vessels." °~ ”' As the development of the tooth germ progresses the pulp becomes increasingly vascular, and the cells develop into star-shaped connective tissue cells (fibroblasts) (Fig. 103, A). The cells are more numerous in the periphery of the pulp. Between the epithelium and the pulp cells is a cell-free layer. This contains numerous fibers, forming the basement or limiting membrane (see chapter on Development of Dentin);

IV. STRUCTURAL ELEMENTS

The pulp is a specialized loose connective tissue. It consists of cells (fibroblasts) and the intercellular substance. The latter, in turn, consists of fibers and a cementing substance. In addition, defense cells and the cells of the dentin, the odontoblasts, are part of the dental pulp. The fibroblasts of the pulp and the defense cells are identical to those found elsewhere in the body. The fibers of the pulp are in part collagenous, in part precollagenous. Elastic fibers are absent. The cementing substance of the pulp seems to be of a much higher consistency than that in the loose connective tissue outside of the pulp.

‘In the course of development the relative number of cellular elements in the dental pulp decreases, whereas the intercellular substance increases (Fig. 103, B). With advancing age there is a progressive reduction in the number of fibroblasts, accompanied by an increase in the number of fibers (Fig. 103, C’). In the embryonic and immature pulp, the cellular elements are predominant, in the mature tooth the fibrous constituents. In a fully developed tooth the cellular elements decrease in number toward the apical region and the fibrous elements become more numerous (Fig. 106).

A microscopic specimen of a mature pulp, stained with hematoxylin eosin, does not present a complete picture of the structure of the pulp, because not all the fibrous elements are stained by means of this method (Fig. 104, A). A great abundance of fibers are revealed by silver impregnation (Fig. 104, B), especially, the so-called Korfl:"s fibers between the odontoblasts. These fibers are the primary elements in forming dentin ground substance (see chapter on Dentin).

Argyrophil Fibers B. Nine months old. 0. Adult.

. Newborn in1a.nt_

6'. Fig. 103.—Age changes of the dental pulp. Cellu cellular substance increases with advancing age.




epithelium Blood vesel P Blood vessel ‘ Blood vessel lax elements decrease, fibrous inter 136

ORAL HISTOLOGY AND EMBRYOLOGY PULP 137

The Korff’s fibers originate from among the pulp cells as thin fibers, thickening at the periphery of the pulp, to form relatively thick bundles which pass between the odontoblasts. They are pre-collagenous, staining black with silver; hence the term argyrophil fibers. The remaining part of the pulp contains a dense irregular network of collagenous fibers.


Dentin-— Odontobiasts — A. . . n, H is Q!" U 3: L 3:" 9: ' - s. .e' _ l "N r: 15‘ H . Dentin ~ V/3; . ‘ c ,_ _ _,_ _ , capillary

Collagenous fibers

Arzyrophu fibers =--‘ “ or Kori!

B.

Fig. 104.-Cellular and fibrous elements in the pulp. .4. Cellular elements stained with hematoxylin and eosin.

gi Fibrous elements stained by silver impregnation. Specimms are from the same too .

The most significant change in the dental pulp during development Odonfioblagtg is that the connective tissue cells adjacent to the enamel epithelium diiferentiate into odontoblasts. Dentin development sets in approximately in the fifth embryonic month and, shortly before this, the odontoblasts begin to differentiate. The development of odontoblasts starts at the highest point in the pulpal horn and progresses apically. T

Odontoblasts are highly differentiated connective tissue cells, columnar in shape, with an oval nucleus (Fig. 105). From each cell a cytoplasmic OR.-\L HISTOLOGY AND EMBRYOLOGY

process extends into a tubule in the dentin matrix. These processes are known as Tomes’, or dentinal, fibers. The ends of the odontoblasts, adjacent to the dentin, are separated from each other by intercellular eondensations, the so-called terminal bars. In a section the terminal bars appear as fine dots or lines. The odontoblasts are connected with each other and with the adjacent cells of the pulp by intercellular bridges. Some odontoblasts are long, others short, the nuclei being irregularly placed.


Odon toblasls

Predentin __.

Dentin

Odontoblastic ___ _ process

, Pulp

/,:\,

Terminal bars ___

Odontoblastic __ , . process

Odontoblasts

at

i.~J.
.

Fig. 105.——Odontobla.sts.

The form and arrangement of the odontoblasts are not uniform throughout the pulp. They are more cylindrical and longer in the crown (Fig. 106, A), and become cuboid in the middle of the root (Fig. 106, B). Close

to the apex of an adult tooth the odontoblasts are flat and spindle-shaped,

and can be recognized as odontoblasts only by their processes entering

the dentin as odontoblastic processes. In areas close to the apical foramen PULP


Odontoblaata

Dentin —

Odontob last!

.’ If ? c-. g

Fig. 106.—Varia.tlon o! odontablasts in different regions of one tooth. A. High columnar odontoblasts in the pulp chamber.

3. Low columnar odontoblasts in the root canal.

0. Flu odontoblasns in the apical region.

139 Defense cells

140 om. HISTOLOGY AND EMBRYOLOGY

the dentin is irregular (Fig. 106, C). This change in the shape of odontoblasts, toward the apical foramen, may be caused by mechanical factors, e.g., movement of the apex when the tooth is in function, or by changes in the blood and lymph stream producing varying pressure at the narrow apical portion of the root} canal.

The odontoblasts are associated with the formation of the dentin matrix (see Chapter on Dentin) -and mediate its nutrition. Histogenetically and biologically they have to be regarded as cells of the dentin. Whether they play a part in the sensitivity of the dentin is still debatable.


".2s<

wig‘,

' * "“‘ “ ' ‘ " Cell-rich zone

Odontoblasts

Predentin

Dentin —-—» - .g ,


Flg. 10'I.—Ce11-tree subodontoblastic zone of Well.

In the crown of the pulp a cell-free layer can be found, just inside the layer of odontoblasts (Fig. 107). This layer is known as the zone of Weil or subodontoblastic layer and it contains nerve fibers. Most unmyelinated nerve fibers are a continuation of the myelinated fibers of the deeper layers and continue to their terminal arborization in the odontoblastic layer. The zone of Weil can be found but rarely in young teeth.

In addition to fibroblasts and odontoblasts there are other cellular elements in the human pulp, usually associated with small blood vessels and PULP 141

Undiflerentlated -


mesenchymal Capillary B. Endothelial cell Capillary _ . ~- _"f"3.Und1flerent1atad 

ifilsmcbrmu

""'57-I-Iiatiocyte ii “ Hf" """“J;T ‘“'* 0. . qi Lymphoid wan- —» ~-vi‘ dering cell A M ‘*1? Fibroblast Undifrerentiated — °‘“’m”’ mesenchymal cell , " '7 ' "‘Histiocyte

Fix. 108.-Defense cells in the Pulp. Blood Vessels

142 ORAL msronocr AND EMBRYOLOGY

capillaries. They are important for the defense activity of the tissues, especially in inflammatory reaction.” Several types of cells belong to this group; they are classified partly as blood elements and partly as belonging to the reticuloendothelial system. In the normal pulp these

cells are in a resting state.

One group of these cells is that of the histiocytes or adventitial cells or, according to Maximow’s nomenclaturefil» 1“ the resting wandering cells. These cells are, generally, located along the capillaries. Their cytoplasm has a notched, irregular, branching appearance; the nuclei are dark and oval. They may have diverse forms in the human pulp but, usually, can be easily recognized (Fig. 108). Intravital staining methods have revealed that histiocytes are able to store dyes. It is assumed that they produce antibodies and, consequently, have an important relation to immune reactions. During an inflammatory process the histiocytes withdraw their cytoplasmic branches, assume rounded shape, migrate to the site of inflammation, and develop into macrophages.

Another cell type of the reticulo-endothelial system is described by Maximow as undifferentiated mesenchymal cells (Fig. 108). These are also associated with capillaries, have oval elongated nuclei similar to those of fibroblasts or endothelial cells, and long, faintly visible cytoplasmic bodies. They are in close proximity to the vessel wall. These cells can be differentiated from endothelial cells only by their location outside the vessel wall. According to Maximow, they possess multipotency which means that, under the proper stimulus, they can develop into any type of connective tissue element. In an inflammatory reaction they form macrophages.

A third type of cell which cannot be classified as belonging strictly to the reticulo-endothelial system, but which plays an important part in defense reactions, is the ameboid wandering cell, or lymphoid wandering cell (Fig. 108, 0). These cells are migrating elements which probably originate in the blood stream. Their cytoplasm is sparse and shows fine extensions, pseudopodia, suggesting a migratory character. The dark nucleus fills almost the entire cell and is often kidney-shaped. In chronic inflammatory reactions they migrate to the site of injury and, according to Maximow, change into macrophages. They may develop into plasma cells which are a cell type characteristic of chronic inflammation. However, their function is not as yet fully known.

The blood supply of the pulp is abundant. The blood vessels of the dental pulp enter through the apical foramen. Usually, one artery and one or two veins enter each foramen. The artery, carrying the blood into the pulp, branches out into a rich network of blood vessels, soon after entering the root canal. The veins gather blood from this capillary network and carry it back through the apical foramen into larger vessels (Fig. 109). The arteries are clearly identified by their straight 1=~u1,p 143

course and thicker walls, whereas the thin-walled veins are wider and, frequently, have an outline similar to a row of beads. The capillaries form loops close to the odontoblasts, near the surface of the pulp, and may even reach into the odontoblast layer.

Vein _.. ’.

Artery _ _T_f_,___.


,itA__.--__

Fig. 109.-—-Blood vessels or the pulp. A. La.rger vessels in the center of the pulp.

B. Dense 111 tw rk in the periphery or the pulp. Arteries narrow, with thick walls and ev3pou?:l11'1y1eI:evel2:s wide with thin walls and irregular outline.

The larger vessels in the pulp, especially the arteries, have a typical circular muscular coating (Fig. 110). These muscular elements can be traced to the finer branches. Along the capillaries are found branching Lymph Vessels

144 ORAL HISTOLOGY AND EMBRYOLOGY

cells, the pericytes (R0uget’s cells). It has been claimed that they are modified muscular eleinents.“

Occasionally, it is difiicult to differentiate between pericytes and undifferentiated mesenehymal cells. However, some specimens show both types of cells and, thereby, it is possible to identify them (Fig. 11111). The nuclei of the pericytes can be distinguished as round or slightly oval bodies outside the endothelial wall of the capillary. A very thin cytoplasm can be seen between the nuclei and the outside of the endothelium.

, E ., .

Circular muscle coating

Circular muscle coating '



1 ‘ ' I-Iistlocyte

Fig. 110.—Branching artery in the pulp; circular muscle coating.

The endothelial cells can be recognized in the continuation of the vessel wall. The undiflerentiated mesenchymal cells lie outside the pericytes, and have finger-like projections. If no pericytes are present the undifferentiated mesenchymal cells are in close proximity to the endothelial wall (Fig. 108).

It has been repeatedly stated that lymph vessels are present in the dental pulp. Special methods are required to render them visible; the PULP 145

common histological technique does not reveal them. The presence of

lymph vessels has been demonstrated by the application of dyes into the

pulp1°’ 21' 22 which are carried into the regional lymph nodes. Injection methods have also been tried successfully.” 2’

' The nerve supply of the dental pulp is abundant. Thick nerve bundles mm. enter the apical foramen and pass into the crown portion of the pulp

where they split into numerous fiber groups and, ultimately, into single

fibers and branches (Fig. 112). Usually, the nerve bundles follow the

blood vessels into the root canal; the finer branches can be seen following

the smaller vessels and capillaries.


Undlflerentlated mesenchymal cell

,..,..;...

pay A...

Undifferentiated » mtlalsenchymal

Fig. 111.—Perlcyte.s of capillaries in the pulp. Note the differences in location and nuclear shape between endothellal cells, pez-Icytes and undifferentiated mesenchymal

Most nerve elements which enter the pulp are of the myelinated type; but, there are also unmyelinated elements. These unmyelinated nerve fibers are of the sympathetic nervous system and are the nerves of the blood vessels, regulating their contraction and dilation.

The bundles of myelinated fibers follow closely the arteries, dividing coronally into-smaller and smaller branches. Individual fibers form a 146 ORAL HISTOLOGY AND EMBRYOLOGY

layer beneath the subodontoblastic zone of Wei], the parietal layer. From there the individual fibers pass through the subotlontoblastic zone and, losing their myelin sheath, begin to branch. Their te1'1ni11al arborization occurs in the odontoblastic layer (See chapter on Dentin).



Histlocyte .- .4 far-Af ‘ ‘

Blood vessel v._

Fig. 112.—Nerves in the pulp.

It is a peculiar feature that, whatever stimulus reaches the pulp, it will always elicit only pain sensation. There is no possibility in the pulp to differentiate between heat, cold, touch, pressure, chemicals, and so forth; the result is always pain. The cause of this behavior is the fact PULP 147

that only one type of nerve endings, free nerve endings, are found in the P111P- The free nerve endings are specific for the reception of pain. The nerves do not have the faculty of localizing the stimulus.

_.ié____ _ 2

'4

_~/‘ *



  • 1


”=:“""* ‘ "" ‘ True denticle

False denticle

False dentlcle

‘ Difluse calciflcations

"** Dentln

Fig. 113.—Denticles (pulp stones). A. True denticle.

B. False denticle.

0. Diflluse calciflcations. Pulp stones

148 omu. HISTOLOGY AND EMBRYOLOGY

V. REGRESSIVE CHANGES

Certain formations in the dental pulp, such as pulp stones or denticles, are on the borderline of pathologic conditions. Their discussion in this chapter is justified only by their frequent occurrence. Pulp stones are often found in teeth which appear to be quite normal in all other re spects. They have been found not only in functioning teeth but also in embedded teeth.

' '4 '¢.c-1-hp:-nu =1 . E .



'5».

s

i ‘ Free dentlcle

Adherent dentlcle


’ Embedded dentlcle

Fig. 114.—Free, attached, and embedded denticles.

Pulp stones are classified, according to their structure, as true denticles, false denticles, and diffuse calcifications (Fig. 113). True denticles consist of dentin, showing traces of dentinal tubuli and odontoblasts (Fig. 113, A). They are comparatively rare and are usually found close to the apical foramen. A theory has been advanced“ that the development of this type of pulp stones is caused by remnants of Hertwig’s epithelial root sheath, which become enclosed in the pulp, due to some local disturbance during development. These epithelial remnants may inPULP 149

duce cells of the pulp to form true denticles. This explanation is based upon frequent observation of true denticles, close to the apical foramen, and also the frequent presence of epithelial rests in this region. It is an accepted fact that epithelial cells (enamel epithelium) are necessary for the differentiation of odontoblasts and the onset of dentin formation.‘ False clenticles are calcified formations in the pulp Which do not show the structure of true dentin. They consist of concentric layers of calcified

Pulp stone ""' ' *‘ if


Nerve

1?‘ ”"‘ —’ Pulp stone

‘. ,Z'l:*'A‘§

Fig. 115p-Pulp stones in close proximity to a nerve.

tissue (Fig. 113, B). In the center of these concentric calcified structures there are usually remnants of necrotic and calcified cells. Calcification of thrombi in blood vessels (phlebolite) may also be the starting point for false denticles. Once calcification has begun, more layers of calcified tissue are laid down on the surface of the pulp stones, thereby increasing their size continuously. The surrounding pulp tissue may be quite normal (Fig. 113, B); no pathologic changes can be detected in the cells or intercellular Calcification:

Secondary Dentin

fibrous

150 ORAL n1s'ro1.ocY AND nmnmronocr

fibrous matrix. Sometimes, pulp stones of this character fill the pulp chamber almost completely. They increase in number and size with advancing age. Overdoses of vitamin D may cause formation of numerous denticles.‘

Diffuse calcifications (Fig. 113, C‘) are irregular calcific deposits in the pulp tissue, usually following collagenous fiber bundles or blood vessels. Sometimes, they develop into large bodies; at other times they persist as fine spicules. They are amorphous, having no specific structure, and are usually the final outcome of a hyalin degeneration of the pulp tissue. The pulp, in its coronal portion, may be quite normal without any sign of inflammation or other pathologic changes. These diffuse calcifications are, usually, located in the root canal, seldom in the pulp chamber; advancing age favors their development.

Pulp stones are classified, not only according to their structure, but also according to their location in relation to the dentiual wall. Free, attached, and embedded denticles can be distinguished (Fig. 114). The free denticles are entirely surrounded by pulp tissue; attached denticles are partly fused with the dentin; embedded denticles are entirely surrounded by dentin. They are formed free in the pulp, and some become attached or embedded as formation of the dentinal wall progresses.

Pulp stones are frequently found close to nerve bundles, as shown in Fig. 115. Occasionally, this may bring about a disturbance if the pulp stones come close enough to the nerves to exert pressure. This may entail pain in the jaw in which the affected tooth is located, rendering a satisfactory diagnosis difficult. The close proximity of pulp stones to blood vessels may cause atrophy of the pulp if the growing pulp stones exert pressure upon the vessels. It is improbable that the pulsation of the blood in the arteries, close to pulp stones, causes suflicient movement of the stone to irritate nerves and cause pain. Pulp calcifications are more common in older teeth. Diffuse calcium deposits may be found in and around the pulpal vessels especially in the roots of older teeth. Well-outlined calcified bodies are more frequently found in the coronal portion of the pulp. In twenty-nine teeth from individuals between ten and thirty years of age, Hill" found pulp calcifications in 66 per cent; in sixty-two teeth from individuals between thirty and fifty years of age, 80 to 82.5 per cent showed calcification in the pulp, and in thirty-one teeth from individuals over fifty years of age, 90 per cent had pulp calcification.

With advancing age the pulp chamber and the root canals become narrower due to secondary dentin formation. In secondary dentin the dentinal tubuli are sparse and irregular. This is due to the fact that odontoblasts degenerate with advancing age, or are destroyed by some

irritation, whereas the matrix formation persists or even increases (see chapter on Dentin).

It has been pointed out that, with advancing age, the cellular elements decrease 111 number whereas the fibrous components increase in the pulp. PULP 151

In older individuals this shift in tissue elements can be considerable and fibrosis may thus develop in the pulp. Thereby, the vitality of the pulp may be lowered without any consequence to the function of the teeth.

VI. CLINICAL CONSIDERATIONS

For all operative procedures it is important to bear in mind the shape of the pulp chamber, and its extensions into the cusps, the pulpal horns. The wide pulp chamber, in the tooth of a young person, will make a deep cavity preparation hazardous to the pulp, and it should be avoided if possible. In some rare instances the pulpal horns remain projected high into the cusps and this may, in some cases, explain the exposure of a pulp when it is least anticipated” (Fig. 116). Sometimes, a roentgenogram will help to determine the size of a pulp chamber and the extensions of the pulpal horns. Roentgenograms of anterior maxillary teeth often lack detail concerning the exact location of pulp horns and the presence of denticles. Information on this subject can be obtained by allowing the rays to strike the crown at almost right angles and double the exposure. Such a film will not only show greater detail concerning pulp horns and pulp calcification, but also orient the position of the pulp chamber more reliably.

If it becomes necessary to open a pulp chamber for treatment, its size and variation in shape must be taken into consideration. With advancing age the pulp chamber becomes smaller and, due to excessive dentin formation at the roof and floor of the chamber, it is sometimes difficult to locate the root canals. In such cases, it is advisable, when opening the pulp chamber, to advance toward the distal root in a lower molar and toward the lingual in the upper molar; in this region, one is most likely to find the opening of the pulp canal without risk of perforating the floor of the pulp chamber. In the anterior teeth the extreme coronal part of the pulp chamber may be filled with secondary dentin, making it difficult to locate the root canal. Pulp stones lying at the opening of the root canal may cause considerable difficulty when an attempt is made to locate the canals (Fig. 97, B).

The shape of the apical foramen, and its location, may play an important part in the treatment of root canals, especially as regards the root canal filling. When the apical foramen is narrowed by cementum formation it is more readily located, because further progress of the broach will be stopped at the foramen. If the apical opening is at the side of the apex, as shown in Fig. 101, A, not even the roentgenograms will reveal the true length of the root canal, and this may lead to misjudging the length of the canal and the root canal filling.

The problem of accessory canals, in root canal work, plays an important part in making the outcome of the root canal treatment questionable. Side branches of the pulp are rarely seen in the roentgenograms and are usu152 oruu. HISTOLOGY AND EMBRYOLOGY

ally overlooked in the treatment and filling of the root canal. If these accessory canals are infected they may cause a recurrence of inflammation.

There "is another condition in which accessory canals may play an important part, especially if they are located in the bifurcation, or high up toward the crown (Fig. 100, B). In periodontal diseases, e.g., where pocket formation progresses, accessory canals may be exposed and infection of the pulp may follow. This may account for some causes of pulp necrosis in periodontal diseases, not only in molars but also in single-rooted teeth.



Enamel (lost in decals]flcatlon)

Fig. 116.-—Pulp horn reaching far into the cusp of a molar. (0rba,n.")

For a long time it was believed that an exposed pulp meant a lost pulp. The fact that “defense cells’ ’ have been recognized in the pulp has changed this contention.” Extensive experimental work has shown that exposed pulps can be preserved if proper pulp capping or pulp amputation procedures are applied.“ 2° This is especially so in noninfected, accidentally exposed pulps in young individuals. In many instances new dentin was formed at the site of the exposure, forming a dentin barrier or bridge. Thus, the pulp may remain in a healthy and vital condition. Pulp capping of deciduous teeth has been shown to be remarkably successful. PULP 153

References

1. Aprile, E. C. de and Aprile, H.: Topografia de los conductos radiculares, Rev. Odontologia 35: 686, 1947. la. Becks, Hermann: Dangerous Eifects of Vitamin D Overdosage on Dental and Paradental Structures, J. A. D. A. 29: 1947, 1942. Bodecker, C. F.: The Soft Fiber of Tomes, J. Nat. Dent. A. 9: 281, 1922. . Bodeglsrerbgg. 117‘S.),3and Applebaum, E.: Metabolism of the Dentin, Dental Cosmos

1.

Bodecker, C: F., and Lefkowitz, W.: Concerning the “Vitality” of the Calcified Dental Tissues, J. Dent. Research 16: 463, 1937. Boling, L. R.: Blood Sup ly of Dental Pulp, J. Dent. Research 20: 247, 1941. Brunn, A. v.: Die Aus ehnung des Schmelzorganes und seine Bedeutung fiir die Zahnbildung (The Extension of the Enamel Organ and Its Significance in the Formation of Teeth), Anat. Anz. 1: 259, 1886. Formation of Teeth, Anat. Anz. 1: 259, 1886. 7. Cooligge,‘ 1151 Anatomy of Root Apex in Relation to Treatment Problems, . . . . 6: 1456 1929. 8. Ebner, V. v.: Ueber die Entwicklung der leimgebenden Fibrillen im Zahnbein lglgtse Development of Collagenous Fibrlls in Dentin), Anat. Anz. 29: 137, 9. Ebner, V: v.: Histologie der Ziihne (Histology of the Teeth, Schefi’s Handbook of Dentistry), ed.' 4, Vienna, 1922, A. Hoelder. 10. Fish, E. W.: An Experimental Investigation of Enamel, Dentin and the Dental Pulp, London, 1932, John Bale Sons & Danielsson, Ltd. 11. Hess, W., and Zurcher, E.: The Anatomy of the Root Canals, London, 1925, John Bale Sons & Danielsson, Ltd. 12. Hill, T. J.: Pathology of the Dental Pulp, J. A. D. A. 21: 820, 1934. 13. Johnston, H. B., and Orban, B.: Interradicular Pathology as Related to Accessory Root Canals, J. Endodontia 3: 21, 1948. 14. Kronfggif Igefitgl Histology and Comparative Dental Anatomy, Philadelphia, 1 ea e iger. 15. Lehner J., and Plenk H.: Die Ziihne (The Teeth) M6llendorfi’s Handb. der Mikrosk. Anat. vol. 5, pt. 3, p. 449, 1936. 16. Magnus, G.: Ueber den Nachweis der Lymphgefiisse in der Zahn Pulpa §D;n]11on:tr4:(1)t1o1:5 of Lymph Vessels in the Dental Pulp), Deutsche Monatschr. . an. :611922. 17. Maximow, A. A.: Morphology of the Mesenchymal Reactions, Arch. Path. &: Lab. Med. 4: 557, 1927. 18. Maximow, A. A., and Bloom, W.: Textbook of Histology, Philadelphia, W. B. Saunders Co. ed. 4 1942. 19. Meyer, W.: Ist’ das ’Foramen Apicale stationiirl (Is the Apical Foramen Stationary?) Deutsche Monatschr. f. Zahnh. 45: 1016, 1927. 20. Noyes, F. B., and Dewey, K.: Lymphatics of the Dental Region, J. A. M. A. 71: 1179 1918. 21. Noyes, F.’ B.: Review of the Work of Lymphatics of Dental Origin, J. A. D. A. 14: 714 1927. 22. Noyes, F. Bi, and Ladd, R. L.: The Lymphatics of the Dental Region, Dental Cosmos 71: 1041 1929. 22a. Okumura, '11: Anat’om_v of the Root Canals, .T. A. D. A. 14: 632,1927. 23. Orban B.: Contribution to the Histolo of the Dental Pulp J. A. D. A. 16: 9%" 1929 gy ’ o, . 24. Orban, B.: Epithelial Rests in the Teeth, Proc. Am. Assn. of Dental Schools, 5th Annual Meeting Washington, D. C. 1929, p. 121. 25. Orban, B.: Biologic Cohsiderations in Restorative Dentistry, J. A. D. A. 28: 1069 194]. 26. Restarski: J. S.: Preserving Vitality of Pulps Exposed by Caries in Young Children Illinois Dent. J. 9: 2, 1940. 27. Schweizer, Gt: Die Lymphgefiisse des Zahnfleisches und der Ziihne (Lymph Vessels of the Gingiva and Teeth), Arch f. mikr. Anat. 69: 807, 1907; 74: 927 1909. 28. Wasserniann, F.: The Innervation of Teeth, J. A. D. A. 26: 1097, 1939. 29. Zander, H. A.: Reaction of the Pulp to Calcium Hydroxide, J. Dent. Research

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