Subtraction radiography to assess reproducibility of patient positioning in cephalometrics.

Subtraction radiography is a way to measure differences in landmark positions between cephalometric films without using tracings that introduce another source of error. This method was used to evaluate the reproducibility of head positioning in 54 pairs of cephalometric films taken within hours of each other, before and after splint removal in orthognathic surgery patients. There were no statistically significant changes in two cranial and four maxillary landmarks; the expected changes in mandibular landmark served to validate the method. The results suggest that patient positioning is not a major contributor to the error of cephalometric methods.