Mandibular bone mineral density as a predictor of skeletal osteoporosis.

A considerable amount of work has been performed on methods of detecting individuals with low bone mass at an early stage. Some researchers have considered if dental radiographs could have a role in the detection of individuals with osteoporosis. A basic requirement for this would be that bone mass in the jaw relates significantly to that of other skeletal sites in which osteoporosis is a significant problem. The first aim of this study was to investigate the relationship between mandibular bone mineral density (BMD) and that of other skeletal sites commonly used for bone densitometry in the detection of osteoporosis. The second aim was to assess the validity of mandibular BMD as a predictor of BMD in these other sites. 40 edentulous females underwent dual energy X-ray absorptiometry (DXA) of the lumbar spine (L2-L4), DXA of the right femoral neck, single photon absorptiometry (SPA) of the proximal and distal forearm and DXA of the mandible. Significant correlations were observed between BMD in the mandibular body, ramus and symphysis and all other skeletal sites (p < 0.02). Five patients (12.5%) had age matched Z-scores of -1.0 or lower in all three non-mandibular sites (lumbar spine, femoral neck and forearm). Using these patients as the proportion of the population with a positive finding of "low bone mass", the sensitivity and specificity of mandibular BMD in predicting low bone mass for these patients was determined. Where a diagnostic threshold for low mandibular BMD was set at one standard deviation below the mean, the mandibular body BMD measurement gave high sensitivity (0.8) and specificity (0.97), the symphysis BMD low sensitivity (0.4) but a high specificity (0.77), while the ramus BMD had a moderate level of sensitivity (0.6) and high specificity (0.91). It is concluded that mandibular BMD assessed by DXA correlates significantly with BMD measurements of other important skeletal sites. The higher correlation coefficients and the greater sensitivity and specificity for the body of mandible suggest that this site should be used for any potential clinical application of dental radiographs in detection of osteoporosis.