The effect of ovariectomy on mandibular cortical thickness in the rat.

OBJECTIVES

The purpose of this study was to investigate the effects of long-term oestrogen deficiency on mandibular cortical thickness in ovariectomized rats.

METHODS

Twelve female rats either underwent ovariectomy or received a sham-operation. One year later images of the left side of the mandible were made using a standardized radiographic protocol. Manual measurements were made of the lower mandibular cortical thickness at three locations. The mean cortical thickness was also assessed using a specially developed image analysis program by placing points at three positions, identical to those used for the manual measurements, and additionally at 20 points evenly distributed along the mandibular cortex.

RESULTS

The mean mandibular cortical thickness of the ovariectomized mandibles was significantly less than that of the sham-operated rats, measured using the computer image analysis (p=0.016, 95% CI=0.125, 0.016) and measured manually (p=0.011, 95% CI=0.0218, 0.1309). When 20 computational points were used, the mean mandibular cortical width of the ovariectomized rats was significantly less than that for the control rats (p=0.016, 95% CI=0.127, 0.018).

CONCLUSIONS AND CLINICAL IMPLICATIONS: Long-term oestrogen deficiency in ovariectomized rats decreased the mandibular cortical thickness. If our result is applicable to human studies, a considerable duration of oestrogen deficiency may be necessary before a reduction of mandibular cortical bone loss can be observed. Because mandibular cortical bone is resistant to resorption, the value of clinically determined mandibular cortical thickness measurements as a method of detecting patients at risk of osteoporosis may have a reduced importance in younger postmenopausal patients.