Histological Identification of Radiographic Features in Ovariectomized Monkey Mandibles

Objectives: The erosion of endosteal margin of mandibular cortex is proposed as a useful screening tool for spinal osteoporosis in postmenopausal women. The purpose of this study was to clarify the relationship between morphological changes and radiographic features in mandibular inferior cortex of ovariectomized monkeys. Methods: Subjects consisted of two groups of six adult (9+ years) female cynomolgus monkeys. The experimental group was ovariectomized (OVX), and the controls received sham surgery (Sham). 76 weeks later, subjects were terminated and their mandibles excised. Lumbar bone mineral density (BMD) and mandibular inferior cortical BMD were measured and dental panoramic radiographs were taken. The mandibular cortical bone was observed using micro CT, confocal laser scanning microscope, and fluorescence microscopy. Results: In OVX group, lumbar and mandibular cortical BMDs were significantly lower than those of Sham group. In Sham group, endosteal margin of the cortex looked sharp in panoramic radiographs, however, in OVX group, it was eroded and striped shadows were detected inside cortex. In Sham's cortical bone, narrow canal structures passed medio-distally through the cortex and flattened osteoblast-like cells appeared along internal surface of the canals. Whereas, in OVX group, some enlarged canals with osteoclasts located on their internal surfaces were found, in the transverse sections, Haversian canals surrounded by lamellar bone in shape of concentric circles were observed in Sham group. In OVX group, several enlarged canals with eroded surfaces, osteoid and active bone formation surfaces were found, reflecting remodeling of Haversian system. Conclusion: In mandibular inferior cortex of ovariectomized monkeys, bone loss and high bone turnover were caused by estrogen deficiency. There were lots of enlarged canals with bone resorptive and formative surfaces in the cortex, representing a “remodeling of osteon”. The erosion of endosteal margin of mandibular cortex on dental radiographs would reflect these enlarged canals induced by estrogen deficiency.