Mandibular radiomorphometric indices in the diagnosis of reduced skeletal bone mineral density

Diagnosis of osteoporosis allows the delivery of preventive and therapeutic intervention and is usually achieved using bone densitometric techniques. One referral criterion for densitometry is osteopenia on radiographs. The aim of this study was to measure the validity of mandibular cortical indices measured on panoramic radiographs in the diagnosis of reduced skeletal bone density. Seventy-four women underwent bone densitometry of the femoral neck, lumbar spine and the forearm. Fifty-five patients (74%) were classified as having a reduced bone density (T-score < or = -1). Twenty-seven patients had a T-score of < -2.5 observed at one or more of the three measurement sites. A panoramic radiograph was taken of each patient and two observers made measurements of cortical thickness at the mental foramen (mental index, MI), antegonion (antegonial index, AI) and gonion (gonial index, GI) regions. Logistic regression and receiver operating characteristic (ROC) curve analyses were used to measure the validity of cortical indices in the diagnosis of reduced bone mineral density. Only MI contributed significantly to a diagnosis of low skeletal bone mineral density (T-score < or = -1). The 95% limits of agreement between observers in measurement of MI were 1.32 to +1.32 mm. When data for both observers were combined, the area under the ROC curve was 0.733 (SE = 0.072; 95% confidence interval = 0.618 to 0.83), indicating moderate accuracy. A diagnostic threshold for MI of 3 mm (or less) is suggested as the most appropriate threshold for referral for bone densitometry. However, the study provided only limited support for the use of panoramic radiomorphometric indices in diagnosing low skeletal bone mineral density. They might, questionably, be used as part of a method of osteoporosis risk assessment.