Accuracy of CBCT for linear measurements in the mandible

Objectives: To evaluate the accuracy of linear measurements in cone beam CT (CBCT) by comparing radiographic measurements to direct linear measurements. Methods: Seven porcine mandibles were used. Six cross-sectional planes were defined in each mandible by Gutta Percha filled drillings. Mandibles were scanned in a CBCT apparatus, cross-sectional planes were defined, landmarks were identified and four radiographic linear measurements (RAD) between landmarks were recorded in each plane. Mandibles were sectioned in their cross-sectional planes and the same respective linear measurements were performed directly on the sectioned mandibles (DIR). The difference between RAD and DIR was calculated (ΔRAD-DIR), expressed as mean±SD. Results: A total of 164 pairs of measurements were obtained. ΔRAD-DIR was -0.17±0.53 mm (range: -1.42 and 1.09mm), indicating a mean underestimation of RAD relative to DIR. 36% of cases were positive, indicating overestimation of RAD relative to DIR in these cases. In 8% of the cases (95% confidence interval: 3.8%, 12.2%), ΔRAD-DIR was between 0.5 and 1 mm, and in 1.8% of the cases (95% confidence interval: -0.2%, 3.9%), ΔRAD-DIR was greater than 1 mm. Conclusions: A mean underestimation of RAD compared to DIR linear measurements was found in the present study. However, in an appreciable portion of the cases there was overestimation equal to or greater than 0.5 mm. This indicates a potential error and a need for safety margins, especially when utilizing CBCT for dental implant planning.