Histomorphometric study of the periodontal vasculature during and after experimental tipping of the rat incisor.

The periodontal vasculature encircling the entire length of the rat lower incisor was studied at the time of tipping movement and 3 months later. In 12 rats (212+/-4 g b.w.), loads (0.19+/-0.016 N) were applied to the lower left incisor in a linguointrusive direction. After 2 weeks of loading, six experimental animals were killed with the loading springs in place. The springs were removed in the six remaining rats, which were killed 12 weeks later. Six additional rats with intact teeth served as control. All incisors were fixed, demineralized, embedded in glycol methacrylate and cross-sectioned perpendicular to the long axis of the tooth. The distance of each section (2 microm) from the apex was calculated. A computerized image-analysis program was used to measure the width and area of the labial and lingual periodontal ligament to establish whether the measured segments corresponded to the compressed or expanded zones. In each cross-section, the various types of blood vessels were counted and the cross-sectional area of all venous vessels was measured. The results showed that after 2 weeks of loading (1) the general trend of vascular changes was similar under pressure and tension; (2) the large-diameter vessels were unaffected by loading; (3) the mean number of terminal arterioles had decreased significantly, while the number of capillaries and postcapillary venules had increased significantly in the apical tooth part; (4) the venous blood vessel area had decreased significantly in the apical tooth part; (5) the intensity of the vascular reaction was dependent on the degree of tissue distortion; and (6) after 12 weeks' recovery the vascular changes were still present, demonstrating a rebound effect. The findings suggest that microvascular alterations following tooth loading are not directly related to the spatial effect of loading itself and are of a much longer duration than expected.

Histomorphometric study of the periodontal vasculature of the rat incisor.

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+_

The effect of toxic doses of 1,25-dihydroxycholecalciferol on dental tissues in the rat.

Vitamin D-depleted rats 4-weeks old were divided into three groups and given daily for 5 weeks cholecalciferol (0.25 microgram) or 1,25(OH)2D3 (0.075 microgram). The third group received no treatment with vitamin D sterols. A fourth control group was fed a diet containing vitamin D. The animals were killed after 5 weeks, plasma was prepared for calcium analysis, and incisors and molars were taken for histology. Growth was monitored throughout. Plasma calcium, body weight and the physical condition of the 1,25(OH)2D3-treated animals indicated that they were toxemic. The pulp-dentine complex of their incisors showed premature aging of fibroblasts and odontoblasts, disturbances in the dentinal matrix and osteodentine formation. That of molars was not affected. There was hypercementosis and bone-like tissue formation in the periodontal-ligament which in the incisors was considerably enlarged; some molars were ankylosed. The pulp-dentine complex of the incisors and molars of the rats in the remaining three groups appeared normal except for zones of hypomineralization in incisors of the third group. The supporting tissues of the teeth of the rats in the other three groups were within normal limits. Thus toxic doses of 1,25(OH)2D3 affected the dental tissues of both developing and mature teeth.