Ovariectomy decreases the bone area fraction of the rat mandible

Although osteoporosis is a major public health concern, the effect of this condition on oral bone has not been determined. Using the ovariectomized rat, we tried to determine if estrogen depletion and aging affect the mandible of the rat. Sixty-one ovariectomized (ovx) and shamoperated (sham) 6-month-old Sprague Dawley rats were divided equally into six groups. The baseline, adult, and old rats were euthanized 14, 114, 200 days post-ovx, respectively. The bone mineral density of the mandible was measured using high resolution dual energy x-ray absorptiometry. The failure load and stiffness of the mandible were measured in three-point bending. The bone area fraction and area moment of inertia of digitized images of mandible sections were measured using image analyzing software. In adult rats, ovx led to a 15% and 28% increase in failure load and stiffness, respectively, but no change in bone area fraction or bone mineral density. In the old rats, ovx led to an 8% decrease in bone area fraction, but no change in failure load, stiffness, or bone mineral density of the mandible. In the ovx rats, aging led to a 20% and 7% decrease in stiffness and bone area fraction of the mandibles in the old rats compared with that in the adult rats. In the adult ovx rats, the increase in structural properties of the mandible may be a consequence of an increase in masticatory function as it has been reported that ovx rats eat approximately 10% more than sham controls. Overall, ovx led to a decrease in bone area fraction in the mandible and a decrease in bone area fraction and stiffness in the mandible of the aging rat. These findings indicate that in this model, estrogen depletion affects the mandible and may contribute to oral bone loss and that this loss may be accentuated with aging.