Objective: To assess the diagnostic accuracy of panoramic radiography (PR), panoramic radiography combined with intraoral radiography (PR + IR), and CT in detecting the superoinferior extent of tumor invasion of the mandible by gingival carcinoma. Method: PR, PR + IR, and CT images of the mandible in 37 patients with gingival carcinoma were evaluated by five oral radiologists for the supero-inferior extent of bone invasion using ROC analysis. The mean ROC curve area (Az) of each observer for the different imaging modalities was analysed by nonparametric two-way ANOVA. P <0.05 was considered statistically significant. Results: The mean Az for the detection of bone invasion were 0.88 ±0.03 for PR, 0.77 ± 0.12 for PR + IR, and 0.87 ± 0.03 for CT (P=0.0907). The mean Az for the detection of bone invasion beyond the alveolus was 0.89 ± 0.07 for PR, 0.85 ± 0.08 for PR + IR, and 0.83 ± 0.06 for CT (P = 0.5438). The mean Az for the detection of bone invasion beneath the mandibular canal were 0.94 ± 0.04 for PR, 0.94 ± 0.02 for PR + IR, and 0.91 ± 0.04 for CT (P = 0.2466). No statistically significant differences were observed in Az between PR, PR + IR, and CT. Conclusion: We consider that PR + IR should be adopted as the initial imaging modality to determine the extent of supero-inferior invasion of the mandible in gingival carcinoma.
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