Influencia dos hormonios tireoidianos na densidade ossea e na periodontite : estudo em ratos / The influence of thyroid hormones on bone density and periodontitis : a study in rats

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Thyroid hormones play a critical role on bone metabolism. However, data regarding the effect of thyroid hormones alterations on mandibular bone density and on the progression of periodontal disease are limited. The aim of the present study was to evaluate, in rats, the influence of different serum levels of thyroid hormones on: (1) the bone mineral density and the proportion of cortical and cancellous components in mandibles compared to tibia by radiographic evaluation; and (2) the rate of periodontal bone loss resulting from ligature placement and on the quality of tooth-supporting alveolar bone, as well as on the number of resorbing cells on inflamed and non-inflamed sites by histologic analysis. Thirty-six male Wistar rats were randomly assigned to the following groups: G1 (n=12) - healthy (control); G2 (n=12) - hypothyroidism (1 g propylthiouracil / 1 l drinking water); G3 (n=12) - hyperthyroidism (800 µg T4 and 180 µg T3 / 1 l drinking water). Three months after the beggining of the induction of thyroid dysfunctions, total serum levels of T3 and T4 alterations were confirmed by radioimmunoassay. For periodontitis induction, ligatures were randomly placed around one of the first mandibular molars and, thirty days later, the animals were sacrificed. Digital radiographs were immediately taken from one tibiae and one hemimandible of each animal and, subsequently, the hemimandibles were routinely processed for serial decalcified sections. The radiographic parameters assessed were tibiae and mandibular bone density and the proportion of cortical and cancellous components in both bone types were assessed. In addition, the histologic parameter analyzed were periodontitis-related bone loss, quality of tooth-supporting alveolar bone, and the number of tartrate-resistant acid phosphatase (TRAP)-positive cells. Radiographic data analyses demonstrated that bone density (p<0.05) and the proportion of cortical bone (p<0.01) were influenced in the tibiae when distinct hormonal conditions were compared, with a significant decrease in the parameters for hypothyroidism. However, in the mandibles, there were no significant differences among the groups neither for bone density nor for the proportion of cortical/cancellous components (p>0.05). Regarding histologic data, in the ligated sites, hypothyroidism significantly increased the bone loss resulting from ligatureinduced periodontitis (p<0.05) and the number of TRAP-positive cells on the linear surface of bone crest (p<0.05). In addition, no significant differences were detected regarding the alveolar bone density (p>0.05). Therefore, within the limits of the present study it may be concluded that bone density and the proportion of cortical/cancellous bone in the mandibles seem to be less sensitive than tibia to the hormones changes. Moreover, decreased serum levels of thyroid hormones may enhance periodontitis-related bone loss, as a function of an increased number of resorbing cells

ASSUNTO(S)

tireoide periodontics thyroid periodontia

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