A method for quantifying positional change of the condyle on lateral tomograms by means of digital subtraction

A method is described for quantifying the positional change of the condyle on lateral tomograms of the temporomandibular joint (TMJ) by use of digital subtraction. This method permits rotational and translational changes of condylar reference points for easy measurement. Accuracy was evaluated in vitro using both TMJs of two dry human skulls and in vivo with seven volunteers. The average absolute error of the angle of rotation in vitro was 0.67 degrees. For the anterior-posterior element of translation the average absolute error was 0.07 mm, and for the superior-inferior element of translation it was 0.06 mm. From these results, we could conclude that the method provides clinically acceptable measurement accuracy. To verify the usefulness of the method, a clinical application is presented.