A Three-dimensional Evaluation of the Effects of Functional Occlusal Forces on the Morphology of Dental and Periodontal Tissues of the Rat Incisor

Abstract

We examined the effect of function on tooth and periodontal ligament (PDL) morphology in 40 lower incisors of adult female rats. Ten teeth were exposed to occlusal hyperfunction for three months, ten to hypofunction for three weeks, ten to hypofunction for three months, while ten teeth in normal occlusion served as control. Transverse ground sections were cut at various levels perpendicular to the tooth long axis, and their distances from the apex were calculated. The outlines of the tissues were traced and fed into a computer. We plotted the measurements according to their location and fitted them by second-order polynomials. We calculated tissue volume for the proximal 18 mm of bone-embedded tooth.

Hyperfunction affected tooth shape, in that it became more rounded. The volumes of the dental tissues remained unchanged, while width and volume of the cementum-bordering PDL increased. Hypofunction did not alter tooth shape, but influenced its size: After three weeks, tooth circumference decreased, and after three months, it expanded. Dentin width was reduced, with concomitant increase of pulp size. The amount of enamel diminished initially, but after three months returned to normal values. The PDL bordering enamel expanded proportionally to the duration of hypofunction. The changes in socket size reflected the total dimensional variations in the tooth and its PDL. The results demonstrate that the shape and size of growing teeth and their periodontium are influenced by functional occlusal forces.

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References

Berkovitz, B.K.B. (1972): The Effect of Eruption on the Proliferative Basal Tissue of the Rat Lower Incisor, Arch Oral Biol 17:1279-1288.

Bondevik, O. (1984): Tissue Changes in Rat Molar Periodontium Following Alterations of Normal Occlusal Force, Eur J Orthod 6:205-212.

Carranza, F.A. (1979): Classification of Periodontal Disease. In: Glickman's Clinical Periodontology, Philadelphia: W.B. Saunders Co., pp. 194-208.

Goldman, H.M. and Cohen, D.W. (1980): Lesions of the Attachment Apparatus. In: Periodontal Therapy, 6th ed., St. Louis: C.V. Mosby Co., pp. 239-261.

Gould, T.R.L. ; Brunette, D.M. ; and Dorey, Y. (1984): Cell Turnover in the Periodontium in Health and Periodontal Disease, J Periodont Res 18:353-361.

Grant, D.A. ; Stern, LB ; and Everett, F.G. (1979): Role of Occlusion in Periodontal Disease. In: Periodontics, 5th ed., St. Louis : C.V. Mosby Co., pp. 400-427.

Haskell, B. ; Day, M. ; and Tetz, J. (1986): Computer-Aided Modeling in the Assessment of the Biomechanical Determinants of Diverse Skeletal Patterns, Am J Orthod 89:363-382.

Kiliaridis, S. ; Engstrom, C. ; and Thilander, B. (1985): The Relationship between Masticatory Function and Craniofacial Morphology, Eur J Orthod 7:273-283.

Kjellberg, H. ; Kiliaridis, S. ; and Engström, C. (1987): Effect of Low Masticatory Function on Condylar Growth, Abstr Proceedings 63rd Congress of the European Orthodontic Society, Rhodes, p. 83.

10.

Lowe, A.A. and Takada, K. (1984): Association between Anterior Temporal, Masscter, and Orbicularis Oris Muscle Activity and Craniofacial Morphology in Children , Am J Orthod 86 :319-330.

11.

Matena, V. (1972): The Periodontium of the Enamel Aspect of the Rat Incisor, J Periodontol 43:311-315.

12.

McFadden, L.R. ; McFadden, K.D. ; and Precious, D.S. (1986): Effect of Controlled Dietary Consistency and Cage Environment on the Rat Mandibular Growth, Anat Rec 215:390-396.

13.

Michaeli, Y. and Weinreb, M.M. (1968): Role of Attrition and Occlusal Contact in the Physiology of the Rat Incisor. III: Prevention of Attrition and Occlusal Contact in the Nonarticulating Incisor, J Dent Res 47:633-640.

14.

Michaeli, Y. ; Pitaru, S. ; and Zajicek, G. (1981): On the Derivation of Cell Kinetics from Histomorphology, Observed in the Rat Incisor Odontoblast, Cell Tissue Kinet 14:73-84.

15.

Michaeli, Y. ; Steigman, S. ; and Harari, D. (1985): Recovery of the Dental and Periodontal Tissues of the Rat Incisor Following Application of Continuous Intrusive Loads: A Long-Term Study, Am J Orthod 87:135-143.

16.

Michaeli, Y. ; Steigman, S. ; Weinreb, M., Jr. ; and Zajicek, G. (1982): Histomorphomctric Study of the Impeded and Unimpeded Rat Incisor. In: Current Advances in Skeletogenesis, M. Silberman and H.C. Slavkin , Eds., Amsterdam: Excerpta Medica , pp. 276-283.

17.

Michaeli, Y. ; Weinreb, M.M. ; and Zajicek, G. (1974): Role of Attrition and Occlusal Contact in the Physiology of the Rat Incisor. VIII: Tooth Length and Occlusal Plane as Regulating Factors of Eruption and Attrition Rates, J Dent Res 53:1215-1218.

18.

Michaeli, Y. ; Zajicek, G. ; and Regev, J. (1978): The Adaptation of a Two-Compartment Cell Renewal System to External Demands: A Study of the Rat Incisor Inner Enamel Epithelium , Cell Tissue Res 194:163-170.

19.

Moss, J.P. (1975): Function-Fact or Fiction?, Am J Orthod 67 :625-646.

20.

Picton, D.C.A. (1969): The Effect of External Forces on the Periodontium . In: Biology of the Periodontium, A.H. Melchcr and W.H. Bowen , Eds., London: Academic Press, Inc., pp. 378-381.

21.

Rippin, J.W. (1976): Collagen Turnover in the Periodontal Ligament under Normal and Altered Functional Forces, J Periodonl Res 11:101-107.

22.

Steigman, S. ; Michaeli, Y. ; and Weinreb, M., Jr. (1987): Structural Changes in the Rat Incisor and its Periodontium after Load Application, Am J Orthod Dentofac Orthop 91:49-56.

23.

Steigman, S. ; Michaeli, Y. ; Weinreb, M., Jr. ; and Zajicek, G. (1983): Three Dimensional Reconstruction of the Rat Incisor by Means of Computerized Histomorphometry, Anat Rec 205:455-464.

24.

Takada, K. ; Lowe, A.A. ; and Freund, V.K. (1984): Canonical Correlations between Masticatory Muscle Orientation and Dentoskeletal Morphology in Children, Am J Orthod 86:331-341.

25.

Van Den Bos, T. and Tonino, G.J.M. (1984): Composition and Metabolism of the Extracellular Matrix in the Periodontal Ligament of Impeded and Unimpeded Rat Incisors, Arch Oral Biol 29:893-897.

26.

Weinreb, M., Jr. ; Steigman, S. ; Michaeli, Y. ; and Zajicek, G. (1985): Odontoblast Turnover in the Impeded and Unimpeded Rat Incisor Derived from Computerized Histomorphometry, Anat Rec 211:218-225.