The effect of ovariectomy on bone changes in the mandible of adult female rats

Concerns have been raised about the outcome of therapeutic oral rehabilitation procedures in elderly patients with osteoporosis. A review of the literature, however, reveals that the effects of postmenopausal osteoporosis on the mandible are not clearly understood. The aim of this project is to investigate the effect of estrogen depletion on bone changes in the edentulous and dentate mandibles in the ovariectomized adult female rat model.; To establish the time required for healing after extraction, the mandibular molars and the incisor on one side of the mandible were extracted and animals sacrificed at 0-, 2, 4-, 8- and 16-weeks post-extraction. Using bone mineral density and histomorphometric measurements, we established that healing was completed 16 weeks post-extraction. Furthermore, we found that the edentulous mandible undergoes significant reduction in size, height and width up to 16 weeks post-extraction.; In the next series of experiments, mandibular teeth were extracted and animals were ovariectomized at 16 weeks post-extraction. 12–14 animals were sacrificed at 6 weeks, 6- and 9-months post-ovariectomy. Bone changes in the edentulous and dentate mandibles as well as the tibia and femur were evaluated using bone mineral density measurements and histomorphometry using backscattered electron microscopy, light and fluorescent microscopy. Ovariectomy induced bone loss in the edentulous mandible, tibia and femur and had no effect on the dentate mandible. The bone loss observed in the edentulous mandible was due to reduction in cancellous bone volume, while the cortical bone volume was not affected. Ovariectomy had no effect on the size, height and width of the mandible. Measuring static and dynamic parameters of bone histomorphometry showed that bone loss in the cancellous bone of the edentulous mandible and in the tibia was accompanied by an increase in bone turnover rate where both bone formation and resorption indices were increased. On the other hand, ovariectomy had no significant effect on histomorphometric bone formation and resorption parameters in the dentate mandible. Our results suggest that while normal function did not prevent bone loss in the tibia and femur of ovariectomized animals, functional stresses due to masticatory force prevented post-ovariectomy bone loss in the dentate mandible.