Technique for standardization of panoramic radiographs using helium-neon laser guided positioning

A limitation of the use of panoramic radiography in implant dentistry has been variations in patient positioning, which can produce dissimilar radiographs and is a serious problem in longitudinal investigations. Previous techniques to standardize panoramic radiographs have been cumbersome and technique sensitive. Bilateral helium-neon lasers were mounted on two-axis micrometer translation stages and projected as cross-hairs on a phantom skull. The cross-point of each pattern was superimposed on a facial soft tissue landmark on either side of the skull. Laser coordinates were recorded and an initial radiograph was produced for each of three experimental groups. Two investigators repeated radiographs for each group six times using the original settings. The radiographs were digitized and the variance calculated and compared using a video digital analysis program. Repeat radiographs were compared to the originals by superimposing each pair and measuring the variance in radiographic markers. The variance ranged from 0.1 to 2.2 mm with the experimental groups and from 2.5 to 38.7 mm with the control group. Repeated measures analysis of variance showed no statistical significance (P > 0.125) among each of the experimental groups using the laser system and a significant difference (P < 0.001) when the control group is included in the analysis. Variance for experimental groups was not significant between the examiners (P > 0.45). A laser repositioning system may have application in implant dentistry by standardizing panoramic radiographs for comparisons in long-term investigations.