Distortions in panoramic radiographs.

This study was designed to investigate the factors affecting linear distortion in orthopantomography A test model was constructed with metallic rods positioned to simulate maxillary teeth from the first permanent molar to the lateral incisor. In addition to examining the effects of varying the tilts of the test rods in a mesiodistal or bucco-palatal direction, spatial position changes (sagittal displacement, transverse displacement and horizontal rotation) of the test model were evaluated by determining the magnification changes in the width and length of the test rods. Results showed that significant errors occurred with all variations in magnification when test rods were inclined buccopalatally (p < 0.001) at or exceeding 5 degrees relative to the true perpendicular, and for spatial positioning errors (p < 0.05) at or exceeding +/- 5 degrees and +/- 5 mm. Bucco-palatally inclined objects in the lateral incisor-canine region were particularly susceptible to large changes in horizontal magnification. Linear measurements and clinical assessments from panoramic radiographs should therefore be undertaken cautiously. To minimise errors in orthopantomography, it is important to position the patient in the focal trough precisely according to the manufacturer's specification.