Region-specific bone mass changes in rat mandibular condyle following ovariectomy

The effects of estrogen deficiency on the mandible have been indicated; however, there have been only a few reports on the mandibular condyle. To clarify the region-specific changes of condyles following estrogen deficiency, we histomorphometrically studied the anterior and posterior regions of condyles in sham-operated (Sham) and ovariectomized (Ovx) female Fischer rats, since it has been reported that rat occlusal force loads mainly onto the anterior part of the condyle. The anterior and posterior regions of condyles showed significantly different bone dynamics. The bone volume in the anterior region of the Sham group increased to 79.9% with aging, but that of the posterior region remained at ca. 60%. In the Ovx group, the bone volume of the posterior region significantly declined to 42.7% until 60 days post-ovariectomy, although no changes occurred in the anterior region. As compared with the Sham counterparts, both regions of the Ovx group showed high bone turnover and revealed significantly low bone volume at 60 days (p < 0.01). Regional differences between anterior and posterior regions were more emphasized in the Ovx than in the Sham group. The osteoclast number and amount of eroded surface in the Ovx were higher in the posterior than in the anterior region, with significance at 30 and/or 60 days (p < 0.05). The mineralized surface at 14 days and the bone formation rate at 60 days in the Ovx posterior region were significantly lower than those in the Ovx anterior region (p < 0.05). Consequently, a net bone loss occurred in the posterior region of the mandibular condyle in ovariectomized rats, owing to region specificity and estrogen deficiency.