Site-specific and time-course changes of postmenopausal osteoporosis in rat mandible: comparative study with femur

Although the effects of osteoporosis on the skeleton are well studied, site-specific and long-term studies on the mandible are still lacking. This study investigated the time-course changes of the bone microarchitecture in the mandibular condyle in comparison to the corresponding changes in the alveolar bone, body of the mandible, and femur. Thirty-six 11-week-old female Sprague-Dawley rats were divided into ovariectomized (OVX) (24 rats) and sham (12 rats) groups. The right femur and mandible were obtained from 6 OVX rats and 3 sham rats at 8, 12, 26, and 36 weeks after surgery, respectively. The histomorphometric analysis was performed using micro-computed tomography and histologic assessments from the (1) distal femur; (2) the alveolar bone and (3) the body of the mandible; (4) the subchondral and (5) the central region of the condyle. The Brown-Forsythe test was used to verify the assumptions for statistical analysis, and the Mann-Whitney U test was then performed. The mandibular condyle showed increased trabecular bone in both the OVX and sham groups, while the bone density was reduced in the distal femur and the mandible interradicular septum and body. When comparing the OVX group to the sham group, only the central condyle showed a significant reduction in bone density at 36 weeks. Osteoporosis behaves in different manners in different parts of the skeleton, and clinicians should be aware that patients displaying osteoporotic changes in the mandible are expected to show severely advanced bone mineral density reduction in other bones, such as the femur.