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This prospective study compared the sensitivity of panoramic tomography (zonography) and helical computed tomography (CT) in diagnosing 73 mandibular fractures in 42 consecutive patients and correlated the results with known surgical findings. The purpose of the study was to determine the optimal radiologic examination for the diagnosis and operative management of mandibular fractures. The attending surgeons' interpretations of panoramic tomograms and helical CT images in the axial plane were compared with the patients' known surgical findings. A series of questions assessed the relative contribution of these two radiologic examinations in formulating an optimal operative plan for each patient. In the 42 patients studied, the sensitivity of helical CT was 100 percent in diagnosing mandibular fractures; this compared with 86 percent (36 of 42) for panoramic tomography, in which significantly more fractures were missed (p = 0.0412). In the six patients with fractures not visualized, the operative management was altered because of the new fracture visualized on helical CT. Of the seven missed fractures, six were in the posterior portion of the mandible. Comparing fracture detection by region, seven fractures found on helical CT were not visualized on panoramic tomography. Helical CT improved the understanding of the nature of mandibular fractures by providing additional information regarding fracture displacement and comminution and by locating injuries missed using panoramic tomography. This study suggests that helical CT alone may be more diagnostic than panoramic tomography alone in evaluating mandibular fractures. Helical CT sufficiently demonstrated details of fractures in 41 of 42 patients; in one patient, the nature of a dental root fracture was better delineated by panoramic tomography.