EFFECT OF AXIAL-PLANE DEVIATION ON CROSS-SECTIONAL HEIGHT IN REFORMATTED COMPUTED-TOMOGRAPHY OF THE MANDIBLE

Objective: To assess the effect of angular deviation on the measured h eight of the mandible in reformatted cross-sectional CT scans. Methods : Reformatted cross-sectional CT scans were obtained from three dried mandibles, at three angulations, in a special holding and positioning device for perpendicular measurements. The radiographic lengths of 321 measurements were compared with the actual bone length. Results: The mean difference between actual bone length and image length, with tran saxial planes parallel to the lower border, was 0% (s.d. 3.6). Deviati ons of 10 degrees and 20 degrees from the lower border of the mandible resulted in a mean error of 1% (s.d. 4.5) and 2.8% (s.d. 8.0) respect ively. When the angulation between the deviated transaxial plane and t he lower border was greater than 10 degrees, the maximum error was abo ut +/-30%. Conclusion: The use of different transaxial planes along th e mandible may result, in a small proportion of cases, in discrepancie s in height when measured from the cross-sectional images obtained. Th is may lead to incorrect interpretation of the depth of bone available for implants.