A special apparatus was developed for standardization of the lateral oblique projection of the mandible (LOPM) in order to apply the digital subtraction method. Geometric reproducibility was examined over an 8-week period using a dry skull. Angulation errors were determined by the relation to image noise in the subtraction image. It was found that the relation between image noise and angulation error was approximated by a second-order polynomial. Geometric reproducibility was within 1° over the experimental period. These results suggest that this standardized LOPM is satisfactory for clinical application of digital subtraction. Two cases are presented where this technique was used to demonstrate longitudinal changes in bone density.
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