RESUMO
AIM: The aim of this study was to investigate the effects of acute and chronic systemic stress response on orthodontically induced root resorption. METHODS: Male Wistar rats were restrained during 1 hour a day by stress models of short (3 days) and long duration (40 days), while control group was not submitted to restraint (N.=10/group). The upper left first molars of all rats were moved mesially by a fixed orthodontic appliance exerting 50 g force upon insertion during the last 14 days of the experiment. Then, animals were killed for blood collection and mensuration of plasmatic corticosterone by radioimmunoassay; the tissues around mesial root of the first molar were processed for histological and histochemical techniques with tartrate-resistant acid phosphatase. The degree of root resorption and the number of odontoclasts were evaluated, being the contralateral side of each animal serving as its control (split-mouth design). RESULTS: The results revealed that the plasmatic levels of corticosterone were significantly higher in both the stressed groups than in the control one. There were no significant differences in the degree of root resorption and in the number of odontoclasts on the root between the 3 groups studied. CONCLUSIONS: These results indicate that systemic stress alone can not be considered a risk factor for root resorption induced by orthodontic tooth movement.
Assuntos
Aparelhos Ortodônticos/efeitos adversos , Reabsorção da Raiz/etiologia , Estresse Psicológico/fisiopatologia , Técnicas de Movimentação Dentária/efeitos adversos , Fosfatase Ácida/análise , Animais , Biomarcadores , Contagem de Células , Corticosterona/sangue , Isoenzimas/análise , Masculino , Dente Molar/enzimologia , Dente Molar/patologia , Desenho de Aparelho Ortodôntico , Osteoclastos/patologia , Ratos , Ratos Wistar , Restrição Física , Reabsorção da Raiz/sangue , Reabsorção da Raiz/patologia , Estresse Psicológico/sangue , Estresse Psicológico/etiologia , Fosfatase Ácida Resistente a Tartarato , Fatores de Tempo , Técnicas de Movimentação Dentária/métodosRESUMO
Resection of the odontogenic region or root transection of normal (impeded) rat lower incisors showed that eruption ceased from 1 to 13 weeks when the base of the resected teeth (87.5%) or of the distal segment of the transected ones (86%) reached the alveolar-crest region. When the operated teeth reached the crestal region, the enamel-related periodontal tissues were absent and the periodontal ligament (PDL) was the only periodontal tissue that remained. The PDL of the crestal region may be considered as mature PDL, showing a length of approx. 5-6 6 mm at the mesial face of the tooth, 4-5 mm at lingual face and 1 mm at distal face; from these limits towards the apical end of the socket the PDL becomes gradually immature. The mature PDL seems not to have a role in the process of tooth eruption. Several factors can be suggested to explain the more frequent retention, at the crestal region of the socket, of impeded rather than unimpeded incisors submitted to the same procedures. The connective tissue that develops between the base of the tooth and the bone that fills the alveolus may have more time to organize itself in impeded than in unimpeded teeth, which erupt at a faster rate; this tissue could support and retain the impeded operated teeth longer than the unimpeded ones. The decrease in the mechanical properties of the PDL in the unimpeded condition may ease the traumatic effects and lead to exfoliation. Eruption might be stopped by the increase in occlusal forces, per unit area of root surface, as the root becomes shorter; this effect is likely to be greater in impeded than unimpeded teeth.