Radiologic measurements of the mandible: a comparison between CT-reformatted and conventional tomographic images.

This study was carried out to compare the accuracy of determination of the mandibular contour and the position of the mandibular canal in cadaver mandibles by the multiplanar reconstruction method (MPR-CT), which has recently come to be used widely for preoperative examinations, with those by tomographic techniques and to evaluate the usefulness of MPR-CT. Using three imaging systems, i.e. Quantum CT scanner, Scanora, and OP-100, a total of 6 sites were scanned in the molar regions of 3 cadaver mandibles. The images obtained were measured twice each by 4 radiologists. The anatomic structures measured were the height and thickness of the mandible, distance from the alveolar crest to the mandibular canal, and distance from the buccal cortical bone to the mandibular canal. After scanning, the scanned areas of the mandibles were sliced at a thickness of 2 mm, and soft X-ray images of these slices were obtained. The values of the above 4 anatomic structures obtained by measurements in the soft X-ray radiograms using digital-display calipers were regarded as true values. When compared with the true values, the errors in the distance from the alveolar crest to the mandibular canal were within 1 mm (+/- 1 mm) in 93.7% of the measurements by Direct-CT, 89.6% of the measurements by MPR-CT, 87.5% of the measurements by Scanora, and 47.9% of the measurements by OP-100, and the accuracy of the 4 methods ranked in the order of Direct-CT, MPR-CT, Scanora, and OP-100. A similar tendency was observed in the measurements of other anatomic structures, and statistically significant differences were observed among the methods. Thus, MPR-CT allows more accurate measurements than by the other 2 tomographic techniques,and to be useful as a preoperative examination for implant surgery.