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.

Submerging of deciduous molars was examined in 1,042 preschool children. The process of submerging was detected as early as the age of 3 years. First deciduous molars were affected more often than second deciduous molars. Submerging was more frequent in the mandible than in the maxilla. Differences were found between sexes and between age groups.The phenomenon of submerged teeth appears clinically as a disruption in the continuity of the occlusal plane of the dental arch. The distance from the marginal ridges of the submerged tooth to the existing occlusal plane can vary between fractions of a millimeter to complete "submerging" of the tooth within bone.Reports on the epidemiology of submerged teeth based on random samples are sparse, although the subject itself has received considerable attention in the literature. It is not clear at which age this local disturbance first becomes apparent clinically because most of the investigations on submerged teeth have been carried out with children older than 7 years of age.1-4

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Dental study casts of 1530 Israeli rural children aged 3-13 years, evenly represented by the sexes, were examined for submersion of their primary molars, 24.8% of the children had one or more of these teeth affected. Out of 8250 teeth at risk, 8.81% were submerged to various degrees. Over 50% of them were primary mandibular first molars, close to 26% were primary mandibular second molars. The number of affected teeth rose with age in both sexes. Sex differences were significant only at 5-7 years, when girls were more frequently affected. Children with one or two affected teeth predominated. The submerged teeth were predominantly located in one or in both quadrants of the same arch. The degree of submersion became more severe with age.

This study assessed quantitatively the vascular system in the cementum-related periodontal ligament (PDL) along the rat incisor. The lower left incisors of six rats (+/- 200 g) were subjected to routine histological procedures and cross-sectioned serially (2 microns), and the distance between each section and the apex was computed. The PDL of five sections at different levels along the tooth was divided into mesial, lingual, and lateral parts. The number and area of small and terminal arterioles, capillaries (C), sinusoids (S), post-capillary venules (PCV), and connecting venules, as well as the area of the PDL, were established. Blood vessels (BV) occupied 47 +/- 2% of the PDL area in the apical half and 4 +/- 2% at the incisal end. Of the total BV area, 41%, 32%, and 27% were located on the lingual, mesial, and lateral tooth sides, respectively. The majority of BV belonged to the venous system (98.5 +/- 0.6% and 82.5 +/- 3.0% in the apical and incisal parts, respectively). The apical venous system comprised 95.4 +/- 1.6% S and 3.2 +/- 1.0% PCV, reversing to 27.2 +/- 14.2% S and 55.2 +/- 11.3% PCV in the incisal half. The number of arterial profiles increased gradually from 6.8 +/- 1.5 at the apex to 25.3 +/- 2.4 in the incisal part and that of C from 9.0 +/- 1.18 to 25.0 +/- 4.3. The extensive vascularization in the apical half of the PDL is consistent with the high metabolic demands and with the need for protective cushioning of the constantly growing dental and periodontal tissues.2+_