The influence of thyroid hormones on periodontitis-related bone loss and tooth-supporting alveolar bone: a histological study in rats.

BACKGROUND AND OBJECTIVE: Recent studies have pointed to potentially periodontal risk indicators, however no information is available on the impact of changes in thyroid hormone levels on the progression of periodontitis and on the quality of alveolar bone. Thus, the aim of the present study was to evaluate histologically, in rats, the influence of thyroid hormones on the rate of periodontal bone loss resulting from ligature placement and on the quality of tooth-supporting alveolar bone. MATERIAL AND METHODS: Thirty-six male Wistar rats were randomly assigned to the following groups: healthy (control, n = 12), hypothyroidism (n = 12) and hyperthyroidism (n = 12). Once alterations were confirmed by total serum levels of triiodothyronine and thyroxine, ligatures were randomly placed around one of the first mandibular molars. Thirty days later, the animals were killed and specimens routinely processed for serial decalcified sections. The parameters assessed were periodontitis-related bone loss, quality of tooth-supporting alveolar bone and the number of cells positive for tartrate-resistant acid phosphatase (TRAP), a marker of bone resorption. RESULTS: At the ligated sites, intergroup analysis revealed that hypothyroidism significantly increased the bone loss resulting from ligature-induced periodontitis (p = 0.02) and the number of TRAP-positive cells on the linear surface of bone crest (p = 0.01). In addition, no significant differences were detected regarding the quality of the bone (p = 0.24) or the number of TRAP-positive cells in the area of the interradicular bone for ligated teeth among the groups (p = 0.17). CONCLUSION: It may be concluded that decreased serum levels of thyroid hormones may enhance periodontitis-related bone loss, as a function of an increased number of resorbing cells, whereas the tooth-supporting alveolar bone seems to be less sensitive to alterations in hormone levels.