Investigation into the relationship between deviations in X-ray angulation and images of proximal overlapping on...

Eleven child skulls were radiographed through a range of 50 degrees by varying the horizontal angulation of the X-ray beam in steps of 2 or 5 degrees. The changes in the width of overlapping contact images and the ranges through which no overlap occurred were measured. A linear relationship between changes in X-ray beam angulation and overlap width was found in all the skulls. Using the data it was calculated that for each increase in overlap width of 0.1 mm, 95% of the deviations in X-ray beam angulation were less than 2.5 degrees. The findings of this study suggested that the positioning of the X-ray beam so as to cause no overlapping is at best difficult, and at worst impossible. They also emphasize the importance of using identical projections in estimating the progress of carious lesions on radiographs since small changes can cause overlaps. The use of methods that reduce the error in repositioning the X-ray beam may be important in reducing methodological errors in clinical research.