Book - Oral Histology and Embryology (1944) 5
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Orban B. Oral Histology and Embryology (1944) The C.V. Mosby Company, St. Louis.
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Chapter V - Pulp
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 elements of the vessels.
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.
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 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 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.
Fig. 97. Age changes in the pulp chamber or the first permanent molar. Decalciﬂed sections; enamel lost. A. Age 8 years. B. Age 55 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)
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 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).
- The ﬂoor of the pulp chamber is the wall opposite the occlusal wall (root) regardless of the position of the tooth in the Jaws.
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.
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.
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 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).
Flg. 100.—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’).
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 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.
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.)
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).
Fig. 103. Age changes of the dental pulp. Cellu cellular substance increases with advancing age.
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.
Fig. 104. Cellular and ﬁbrous elements in the pulp. .4. Cellular elements stained with hematoxylin and eosin. 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.
Odontoblasts are highly differentiated connective tissue cells, columnar in shape, with an oval nucleus (Fig. 105). From each cell a cytoplasmic 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.
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 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.
Fig. 106. Variatlon o! odontablasts in different regions of one tooth. A. High columnar odontoblasts in the pulp chamber. B. Low columnar odontoblasts in the root canal. C. Flu odontoblasns in the apical region.
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.
Flg. 101. Cell-free subodontoblastic zone of wall.
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 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.
Fig. 108. Defense cells in the Pulp. Blood Vessels
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 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.
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 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.
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 common histological technique does not reveal them. The presence of lymph vessels has been demonstrated by the application of dyes into the pulp which are carried into the regional lymph nodes. Injection methods have also been tried successfully.
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.
Fig. 111. Perlcytes 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 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).
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 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.
Fig. 113. Denticles (pulp stones). A. True denticle.
B. False denticle.
C. Diﬂluse calciﬂcations.
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.
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 induce 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 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 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.
Fig. 115p-Pulp stones in close proximity to a nerve.
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.
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 usually 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.
Fig. 116. Pulp horn reaching far into the cusp of a molar. (0rban.)
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.
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Cite this page: Hill, M.A. (2020, October 22) Embryology Book - Oral Histology and Embryology (1944) 5. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Oral_Histology_and_Embryology_(1944)_5
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