This study was aimed to investigate the use of panoramic radiography in patients with low bone mineral density (BMD) in order to diagnose and prevent osteoporotic fractures. Panoramic radiographs of 60 patients (20 men and 40 women) aged from 40 to 70 years with cortical thicknesses of less than 3 mm in the mandibular angle were selected from patients referred to a dentomaxillofacial radiology clinic and were then examined for mandibular cortical angles. These were measured using Computed Radiography (CR) software. The bone densitometry was carried out using Dual Energy X-ray Absorptiometry (DEXA). Cortical thicknesses at the lower border of the mandibles were also measured by panoramic radiographs. Statistics analyses were then undertaken using Fisher's exact test, Chi-square, t-test, ANOVA and receiver operating characteristic (ROC) curve. In most cases, no significant difference in mandibular angle cortical thickness was found between those patients with a normal BMD and those patients with a lowered BMD (P=0.621). There was a relationship between the cortical thicknesses of the mandibular lower border, and vertebral and femoral BMD (P<0.0001), and there was a significant difference between the thickness of the mandibular lower border and BMD. The results of this study also revealed a new marker of osteoporosis on the mandibular lower border under the third molar. A thickness of 2.80 mm of the mandibular lower border was detected as a threshold for the measurement of bone densitometry in the chosen Iranian population. Panoramic radiography is effective for screening patients who are at risk of having decreased bone mineral density. Patients with a threshold of 2.80 mm thickness of the mandibular lower border should be considered as individuals likely to have osteoporosis associated low bone density.