| Masticatory system comprises the temporomandibular joint, masticatory muscles and occlusion, and the three parts function as a whole under the control of nervous system. The abnormity of any one part will lead to abnormal changes or dysfunction of the other parts. The mechanoreceptor in the periodontium, the periodontal Ruffini endings, is in charge of receiving the mechanical stimuli, such as occlusive force. The incoming mechanical signal is then tranmitted to the central nervous system by the afferent nerve to coordinate mastication. In the present study, SD rats were used as the objects. The left maxillary and right mandibular third molars were pushed distally by an elastic band, and thus an unbalanced occlusal cusp-fossa relation was formed. We focuses on the changes in the microscopic and ultramicroscopic of periodontal Ruffini endings, and changes in Schwann cell marker S-100 protein and neurotrophin-3 (NT-3) expression in the opposite molar of the orthodontically moved molar.First part: Twenty-four 8-week-old female SD rats were randomly assigned to opposite molar group, moved molar group and control group. The opposite molar group (right maxillary third molar) served as experimental group, and the moved molar group (left maxillary third molar) as the positive control on the same animal of the experimental group. Animals were sacrificed at 3d, 14d and 28d respectively after tooth moving. The slices of alveolar bone sections that include separately the right side and left side maxillary third molars were stained with haematoxylin-eosin (HE), and were observed under microscopy. The maxillary third molar of rat has three roots: mesio-buccal root, distal-buccal root and distal root. We chose the gross distal root to observe so as to make the standard uniform. In control groups, the periodontal cavities of both third molars were even around the root. In the moved molar, at 3d after tooth moving, the mesial half of the periodontal cavity was compressed and the distal half was extended, indicating a mesial inclination of the root apex of the moved molar. At 14d after tooth moving, the opposite molar also displayed a slightly compressed mesial half and extended distal half, indicating a lighter mesial inclination of its root apex. At 28d after tooth moving, the length of the periodontal cavity recovered in both molars. Conclusion: Orthodontic tooth movement could induce reconstruction of the periodontium in the opposite molar, but the reconstructive process occurred later and slighter and completed faster than in the moved molar.Second part: Sixty-four 8-week-old female SD rats were divided into to two units. The first units contained 16 rats and the second 48 rats. The rats in each unit were randomly redivided into opposite molar group, moved molar group and control group. The rats in control group (n=4) of the first unit were sacrificed after 3 days of adaptive feeding, and the rats in the other two groups of the first group were sacrificed at 3d, 14d and 28d (n=4) after tooth moving, and specimens of the apical 1/3 of the distal root of the maxillary third molars were used for ultra-microscopic observation. Rats of the second unit were sacrificed at 1d, 3d, 7d, 14d, 21d and 28d respectively after tooth moving, and the slices of alveolar bone sections that include separately the left side and right side maxillary third molars were stained with protein gene product 9.5 (PGP 9.5) antibody by immunofluorescence technique. In control groups: The periodontal Ruffini endings showed relatively normal ultra-structure with typical mitochondria, microfilaments and microtubules and basal lamina; The PGP 9.5 positive structures were mainly distributed in the alveolar-side of the periodontal cavity. In the moved molar: The mitochondria with decreased number, a swollen mitochondrion, a vacuole-like structure, an amorphous structure with high electron-density, deranged microfilaments and microtubules and unclear and deranged basal lamina were observed in the ultra-structure of the periodontal Ruffini endings, and these changes were most obvious at 3d after tooth moving; The PGP 9.5 positive structures were detected in the alveolar-side and middle zone of the periodontal cavity, and quantitative analysis indicated that percentage of PGP 9.5 positive area decreased temporarily, to its lowest level at 3d after tooth moving; In the opposite molar: Eccentrically distributed mitochondria were observed in the axon terminal at 3d after tooth moving, and decreased and deranged microfilaments and microtubules and structurally abnormal basal lamina was viewed at 14d after tooth moving; The PGP 9.5 positive structures were detected in the alveolar-side and middle zone of the periodontal cavity, and quantitative analysis indicated that percentage of PGP 9.5 positive area decreased temporarily, to its lowest level at 14d after tooth moving. At 28d after tooth moving, PGP 9.5 positive area gradually recovered to baseline in both moved and opposite molars. Conlusion: Orthodontic tooth movement could induce temporary changes of ultra-structure, distribution pattern and quantity of periodontal Ruffini endings in the opposite molar, and the changes were slighter and completed faster than in the moved molar.Third part: Fourty-eight 8-week-old female SD rats were randomly assigned to opposite molar group, moved molar group and control group. Animals were sacrificed at 1d, 3d, 7d, 14d, 21d and 28d respectively after tooth moving. The slices of alveolar bone sections that include separately the left side and right side maxillary third molars were stained with Schwann cell marker S-100 protein antibody and NT-3 antibody by immunofluorescence and double-labeling technique. In the moved molar, the percentage of S-100 positive area and relative NT-3 optical density showed a temporary increase, to its top level at 3d after tooth moving. In the opposite molar, the percentage of S-100 positive area and relative NT-3 optical density also showed a temporary increase, to its top level at 14d after tooth moving. Immunofluorescent double-labeling of S-100 and NT-3 showed that there existed extensive co-expression of S-100 and NT-3. the percentage of S-100 positive area and relative NT-3 optical density gradually recovered to baseline at 28d after tooth moving in both moved and opposite molar. Conlusion: Orthodontic tooth movement could induce a temporary increase of Schwann cell structure and NT-3 in the opposite molar, and the changes occurred later and recovered faster than in the moved molar. Conlusions:Orthodontic tooth movement could induce similar changes of periodontal cavity of opposite molar to the moved molar, and could lead to reconstruction of periodontal Ruffini endings and changes in expression of Ruffini endings marker PGP 9.5, Schwann cell marker S-100 and NT-3. The mechanism of these changes lies in the abnormal occlusal force caused by unbalanced cusp-fossa relation, which result from the orthodontic tooth movement. |
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