Radiographic analysis for jaw motion normalization.
Academic Article
Overview
abstract
PURPOSE: This study incorporated 3 objectives: 1 ) to evaluate the physical location of the center of rotation as determined by a custom mathematical algorithm, 2 ) to identify and compare the geometric center of the condylar head in radiographs with the calculated center of rotation, and 3 ) to determine whether a correlation exists between jaw motion characteristics and the mandibular geometry of the subject. MATERIALS AND METHODS: Lateral cephalometric radiographs of 9 subjects who underwent motion path analysis were obtained. The determined center of rotation of each mandible was calculated through a custom algorithm and recorded on the radiograph. Circular templates were used to determine the geometric center of the condyle for comparisons. Finally, measurements of 4 geometric jaw parameters were made and compared with motion characteristics to investigate whether mandibular geometry can be correlated to motion parameters. RESULTS: All calculated centers of rotation were found to lie in the condylar head of the mandible. The average difference between the calculated center of rotation and geometric center of the condylar head was 2.87 mm (SD, 1.69 mm). In addition, correlations were found linking the length of the mandibular rotational arm to the rotational and translational motions. However, there was no correlation found with the other geometric mandibular parameters. CONCLUSIONS: Analysis of mandibular motion allows for an accurate determination of the center of rotation. Previously identified characteristic motion exists in terms of primary rotation, followed by translation of the mandible with rotation. The magnitude of each phase differs between subjects. This study points to a natural mechanism of mandibular opening as the amount of rotation increased for longer rotational arms and amount of translation increased for shorter ones, serving to lessen the disparity in the opening amounts among individuals.
