The accuracy of 4 panoramic units in the projection of mesiodistal tooth angulations

The purpose of this study was to compare the mesiodistal tooth angulations determined with a typodont/skull testing device with the images of mesiodistal tooth angulations from 4 contemporary panoramic units (OP 100, Cranex 3+, Orthophos, PM 2002 EC). A typodont testing device was constructed, and the true mesiodistal tooth angulations relative to an orthodontic archwire were determined with a 3-dimensional coordinate-measuring machine and custom-designed software. A human skull served as the matrix into which the typodont was fixed for imaging. The skull was repeatedly imaged and repositioned 5 times for each panoramic unit. The images were scanned and digitized with custom software to determine the image mesiodistal angulations. Results revealed that the majority of image angles from the 4 panoramic units were statistically significantly different from the true angle measurements. However, definite trends were noted among the panoramic units. For the maxillary teeth, the images projected the anterior roots more mesially and the posterior roots more distally, creating the appearance of exaggerated root divergence between the canine and the first premolar. For the mandibular teeth, the images projected almost all roots more mesially than they really were, with the canine and the first premolar the most severely affected. The largest angular difference for adjacent teeth occurred between the mandibular lateral incisor and the canine, with relative root parallelism projected as root convergence. It was concluded that the clinical assessment of mesiodistal tooth angulation with panoramic radiography should be approached with extreme caution and with an understanding of the inherent image distortions.