A Review of Temporomandibular Disorder and an Analysis of Mandibular Motion
This study quantified mandibular motion of asymptomatic subjects upon jaw opening and closing. Five males, mean age of 28 years, agreed to participate; they showed no sign or symptom of temporomandibular disorder (TMD) on clinical examination or by anamnestic history. Mandibular motion for each subject was measured with a tracking system and software utilizing the Screw Displacement Axis (SDA), which is a mathematical approach to analyzing and quantifying the movement of an object in three dimensions. Rotation and translation were calculated, as well as two- and three-dimensional charting of condylar path and sagittal condylar intercepts. Furthermore, analyses examined error propagation, change in error amplitude with varying test conditions, and a comparison between theoretical and experimental data. The mean maximum roation around the screw displacement axes was 25.0o (sd=4.0o). Mean translation along the screw displacement axes was 2.3 mm (sd = 0.68 mm). The SDA intersection plots showed that the paths of motion for all subjects were posterior and inferior to the candyle. During opening, paths start nearer to the condyle and travel inferiorly and anteriorly. Jaw closing followed the reverse path (superior and posterior) with the final position approximating the area of the initial axis. Mean SDA intercepts with the sagittal plane of the condyle were positioned posterior and inferior of the selected center of the condyle. SDA position and orientation parameters were inversely related to the rotational increment. As rotational increments approached 5o, there was little change in the uncertainty values, indicating that data should be processed at increments of at least 4o to 5o. Coordinate data obtained with the tracking systemn displayed an error that was not present when the targets were stationary, nor did its amplitude change with a change in velocity. These observations led to the idea that the error associated with the tracking system relied purely on target position. The only way to counter this system error was to raise the rotational increments in data processing and find an area in the sensor's viewing field that produces the least error. The closest the targets could be brought to the camera while maintaining a viewing area large enough to test jaw motion was in the range of 150-200 mm from the senor. The experimental data obtained from the SDA intercepts at 10oiterations showed a path similar to theoretical expectations. The screw displacement axis method does have limitations. If only translational motion occurs, the SDA is undefinded. The SDA method is also very prone to measurement error. At low rotational increments, large error of the SDA parameters can be encourntered due to small measurement inaccuracies. However, small rotational increments are necessary to reliably approximate the continuous movement through a series of finite calculations. A balance is threfore required between these two opposing error sources.
TMJ, TMD (temporomandibular disorder), Joint Motion, Screw Displacement Axis (SDA), Medicine and Health Sciences
University of Tennessee Health Science Center
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