Comparison of the effect of ovariectomy on bone mass in dentate and edentulous mandibles of adult rats.

We investigated the effect of ovariectomy (OVX) on bone changes in the edentulous and dentate mandibles and compared these to changes in tibiae and femorae using dual energy x-ray absorptiometry (DEXA) and histomorphometric measurements. One hundred and fifteen female rats had their molars and the incisor on one side of the mandible extracted at six months of age and allowed to heal for 4 months. At 10 months of age, animals were divided into an experimental group, which underwent bilateral ovariectomy, and a control group of intact animals. Sixteen OVX and sixteen control animals were sacrificed at 6-weeks, and at 6- and 9-months post-OVX. In addition 12 animals were sacrificed at the time of OVX to act as an internal control group. Bone mineral density measurements (BMD) using DEXA and bone volume measurements on undecalcified sections evaluated under backscattered electron microscopy were investigated in the edentulous and dentate mandibles as well as in tibiae and femorae. At 6-weeks post-OVX, there were no significant differences between the edentulous mandibles, dentate mandibles, tibiae and femorae of OVX and control groups. At 6 months post-OVX, BMD and cancellous bone volume were significantly decreased in the edentulous mandibles (-15.9%; -21.8%), proximal tibiae (-15.6%; -38.5%) and proximalfemorae (-9.7%; -39.6%) of OVX group as compared to the control group. At 9 months post-OVX, BMD and cancellous bone volume were further decreased in the edentulous mandibles (-17.2%; -24%), proximal tibiae (-16.1%; -58.9%) and proximal femorae (-10.3%; -49.9%) of the OVX group as compared to the control group. On the other hand, OVX had no effect on the BMD and cancellous bone volume of the dentate mandibles at 6-weeks and at 6- and 9-months post-OVX. These results show that loss of bone mass in the edentulous mandible of OVX animals is similar to that occurring in the tibiae and femorae, while lack of a significant effect of OVX on bone mass in the dentate mandible suggests that functional loading related to biting force prevented bone loss in the dentate mandible.