[The effects of local stress on bone mass of mandibles in ovariectomized rats]

To observe the relationship between the change of stress environment of mandibles and their bone mass in normal and ovariectomized(OVX) rats.

The high and low stress environment models of mandibles were established by unilateral maxillary molars extraction. The masticatory sides of the mandibles were regarded as the high stress sides and the non-masticatory sides were regarded as the low stress sides. Ovariectomized rats were utilized as postmenopausal osteoporosis models and Sham-ovariectomized(Sham-OVX) rats as control group. According to these ideas, 48 female rats were divided into 4 groups: 1) OVX + extraction group; 2) OVX + non-extraction group; 3) Sham-OVX + extraction group; 4) Sham-OVX + non-extraction group. The bone mineral densities (BMD) of all mandibles were measured by single-photon absorptiometry bilaterally 1.5 months and 3 months after extraction.

The mandibles of ovariectomized rats had lower BMD than those of normal rats(P < 0.05). To normal rats, the BMD of mandibles in low stress sides were lower than the high stress sides 3 months after extraction(P < 0.05), but the BMD of the two sides were not significantly different to those of the non-extraction control ones(P > 0.05). To ovariectomized rats, the BMD of mandibles low stress sides were much lower than the high stress sides(P < 0.01). The BMD of mandibles in low stress sides were much lower than non-extraction ones of OVX group after 3 months(P < 0.05). The BMD of the high stress sides were much higher than those of the non-extraction control ones of OVX group(P < 0.05), but they were still lower than those of the non-extraction control ones of Sham-OVX group(P < 0.05).

The results indicate that the masticatory functions(the high stress environment) tend to conserve the mandibular bone mass in patients with systemic osteopenia such as postmenopausal osteoporosis and the masticatory deficiency (the low stress environment) tends to aggravate mandibular bone loss induced by systemic osteopenia. The masticatory functions should be rehabilitated for these patients as early as possible.