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.

Effect of occlusal functional forces on incisor socket morphology and location in the rat mandible

“…Thus, it was found that adaptations occur in the craniofacial skeleton in response to altered functional stress (Washburn, 1947;Avis, 1961;Kreiborg et al, 1978;Schneiderman and Carlson, 1985). The dental supporting structures also react to changes in functional demands, and it has been shown that decreased or increased function causes dimensional changes in the periodontal ligament (PDL) (Kronfeld, 1931;Coolidge, 1938;Grant et al, 1979;Bondevik, 1984;Steigman et al, 1989). Other studies reported significant changes in tooth morphology of the rat as a result of disrupted eruption (Berkovitz, 1972;Steigman et al, 1983Steigman et al, , 1988 or of altered function (Steigman et al, 1989).…”

“…The dental supporting structures also react to changes in functional demands, and it has been shown that decreased or increased function causes dimensional changes in the periodontal ligament (PDL) (Kronfeld, 1931;Coolidge, 1938;Grant et al, 1979;Bondevik, 1984;Steigman et al, 1989). Other studies reported significant changes in tooth morphology of the rat as a result of disrupted eruption (Berkovitz, 1972;Steigman et al, 1983Steigman et al, , 1988 or of altered function (Steigman et al, 1989). No information is available, however, about a possible change in the location of the lower incisor within the mandibular border following increased or decreased functional loads.…”

Alveolar bone Sharpey fibers of the rat incisor in normal and altered functional conditions examined by scanning electron microscopy

“…However, this decrease in area density may not reflect an actual decrease in the total number of fibers. In rat incisors after 3 months of hypofunction, a significant increase was observed in the cross-sectional area of the socket, but this increase was not significant after 3 weeks of hypofunction (Steigman et al, 1989). The figures of region 1 (Fig.…”

“…The eruption of these teeth was in an unimpeded or hypofunctional condition. The contralateral incisors were impeded, occluding with both upper incisors, thus in a hyperfunctional condition (Steigman et al, 1989). The lower incisors of the remaining nine rats were kept during the period in normofunctional conditions.…”

MT1-MMP expression in the odontogenic region of rat incisors undergoing interrupted eruption

“…In the interrupted condition, the eruption rate was markedly interrupted (&10 fold less than that of the normal eruption group), in agreement with a previous study from our laboratory (Neves et al 2009), confirming that the immobilization by steel wire efficiently impeded the incisor eruption. Steigman et al (1989) studied the incisor under hypofunction eruption conditions, in which there is an increase in the eruption rate, reported some morphological alterations such as variation in tooth size components (decreased dentin and increased pulp size). In contrast, in the present study, the incisor tooth was immobilized to interrupt the eruption and, in this condition, we demonstrated for the first time, visible alterations in the morphology of the tooth germ and socket area.…”