A new method for measuring three-dimensionally the joint space using a TMJ digital reconstruction technique

The purpose of this study was to develop a new method for effective visualization of the three-dimensional joint space using a reconstruction of the temporomandibular joints' (TMJs) osseous components based on computed tomography (CT) . Axial CT scans, with a 2 mm-thickness and a slice space of 1mm, were made from the right and left TMJs of one subject. In order to relate the digitally reconstructed TMJ images to the upper dentition, he wore a reference face bow unit that had three markers attached onto it through alminum tubes. The three-dimensional data points from the serial CT scans were measured to reconstruct digitally the TMJs. The TMJ images composed of approximately 12000 points and the fossa of approximately 24000 points were reconstructed using graphic software. A triangle indicating the occlusal plane was described simultareously on the display. The distance distribution map was composed of the reconstructed condylar surface shaded with pseudo-colors according to the calculated joint space distance of 0-5mm at 1mm intervals between each fossa and condyle measurement point. The distance distribution map with pseudo-colors could be observed on the screen at any direction. The results were as follows: 1. The axial CT scanning required only one examination to reconstruct the right and left TMJs in the same coordinate system. 2 . By the three-dimensional reconstruction of the TMJs with the occlusal plane indicated by the triangle, it was possible to estimate the positional relationship of the TMJs to the upper dentition by means of the reference face bow unit. 3. The distance distribution map made it possible to visualize effectively the morphologic characteristics of the condyle and the relationship between the condyle and the fossa.