Book - Oral Histology and Embryology (1944) 12

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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 XII - Shedding of the 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 ligament. 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 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.


First draft submitted by Myron S. Aisenberg.


Fig. 236. Resorption of root of deciduous cus id during eruption of permanent successor. Kronteld!) A. General view. B. Linguafreaorption area in higher magnification.


Fig. 23S.—Resorption of root of deciduous incisor due to pressure of erupting successor.


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 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 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.


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).


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 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 of bone on the opposite side or the bicuspid due to transmitted excentric pressure to the bicuspid. (Grimmer!) 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).




Fig. 240.—Germs or bicuspids below roots of deciduous molars. Traumatic changes in the periodontal membrane or the deciduous teeth. Z. See Fig. 243.


Fig. 241. High magniflcaton of a. repaired resorption; from area. I of Fig. 239; new bone formed during rest period.

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



Fig. 243. Traumatic 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 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.


Fig. 244. Ankylosl.s ot deciduous tooth as a. sequence of trauma. A. General view. B. High magnification of area. X in A.

{ Resorption of cementum


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 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).


Fig. 245. High magnification of the pulp of resorbed deciduous molar of Fig. 242. Pulp of normal structure with odontoblasts.

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.


Fig. 246. Remnants 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.


Fig. 247 Remnant of deciduous tooth embedded in, and ankylosed to, the bone. ( Schoenbauez-.5 ) 320 mun HISTOLOGY AND EMBRYOLOGY


Fig. 248. Remnant of deciduous tooth at alveolar crest.


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: roots (Courtesy M. K. Hine, University of Indiana.) C. 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 (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. 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.


Fig. 250. Upper permanent lateral incisor missing. Deciduous lateral _incisor and deciduous cuspid are resorbed due to pressure of erupting permanent cuspid.


Fig. 251.Submerging lower deciduous second molar. Second bicuspid missing. (Courtesy M. K. Hine, University of Indiana.)



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.

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.



Cite this page: Hill, M.A. (2020, October 23) Embryology Book - Oral Histology and Embryology (1944) 12. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Oral_Histology_and_Embryology_(1944)_12

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