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Effect of axial plane deviation on cross-sectional height in reformatted computed tomography of the mandible
D Kohavi1, J Bar-Ziv, Y Marmary
1Department of Prosthodontics, Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel.
Objective:
To assess the effect of angular deviation on the measured height 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 transaxial planes parallel to the lower border, was 0% (s.d. 3.6). Deviations 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) respectively. When the angulation between the deviated transaxial plane and the lower border was greater than 10 degrees, the maximum error was about +/- 30%.
Conclusion:
The use of different transaxial planes along the mandible may result, in a small proportion of cases, in discrepancies in height when measured from the cross-sectional images obtained. This may lead to incorrect interpretation of the depth of bone available for implants.