The aim of this study was to evaluate the impact of an estrogen-deficient state and its therapies (estrogen and calcitonin administration) upon bone loss resulting from an experimental periodontitis. Fifty-eight Wistar rats were divided into four groups: group 1 (n = 15): sham operated; group 2 (n = 15): ovariectomized; group 3 (n = 14): ovariectomized plus calcitonin administration; group 4 (n = 14): ovariectomized plus estrogen administration. Twenty-one days after ovariectomy or sham surgeries, the ligature was randomly placed. Sixty days later, the animals were killed and the specimens routinely processed. In addition, serum levels of alkaline phosphatase and calcium were assessed. Intergroup analysis revealed that an estrogen-deficient state significantly increased bone loss resulting from periodontitis and that such an effect could not be prevented either by estrogen or calcitonin administration (0.34 +/- 0.13, 0.65 +/- 0.06, 0.63 +/- 0.19, 0.67 +/- 0.28 for groups 1, 2, 3 and 4, respectively). Furthermore, an estrogen-deficient state presented a direct effect on the alveolar bone regardless of plaque accumulation and this effect may be significantly reduced by estrogen administration (p < 0.05). Serum analysis demonstrated a higher bone turnover for the animals with estrogen deficiency, and estrogen therapy restored bone metabolism. Estrogen administration may prevent the direct effect of an estrogen-deficient state on alveolar bone; however, neither estrogen nor calcitonin administration could prevent this effect when associated with a response to a plaque-related inflammatory process.39107-10