1997 Volume 17 Issue 2 Pages 136-153
Methods : Oral movement trajectories were studied by monitoring orofacial movements during mastication to obtain basic data on masticatory capability. Eleven dentulous young adults chewed a color-developing chewing gum that becomes redder as it is chewed, with the intensity of the red color serving as an indicator of masticatory capability. Light-emitting markers that were recorded as reflective points with clear outlines when illuminated with infrared strobe lights provided trajectory data for the monitoring of orofacial movements at the following reference points : the modiolus (Mo), menton (Me) and incisal point (IP), which was represented by a point on a wire extending from the lower incisor teeth to outside of the mouth.
The subjects' facial markers were located and automatically tracked while chewing using six video cameras from six different perspectives, and the video data were collected using a datastation (VICON 370 Datastation, Oxford Metorics Ltd.). After every 20 masticatory strokes, the color of the chewing gum was assessed using a Chroma Meter (CR-300, Minolta Co.) with respect to degree of redness or a* value, which is one of the coordinates in the L*a*b* color evaluation system. The same piece of chewing gum was continuously chewed for a total of 100 strokes. Digitally recorded video data at the start of the first period (1F) and at the end of each period (1L-5L) were analyzed using a workstation (VICON 370 software), and three-dimensional (3D) maker trajectories were reconstructed. The results of photogrammetric measurements were analyzed using a 3D analyzer (Movias 3D, nac Co.) with reference to the following parameters : total length of the trajectory from start to finish (TL), distance between the start and finish of the trajectory (SL), TL to SL ratio (T/S), volume of the rectangular solid encompassing the entire trajectory (cubic range [Cub]), and the mean of the 3D angles created by differences in the direction of the preceding and subsequent trajectories for each measured time (TH).
Results : The time required for one chewing cycle and closing phase decreased geadually from 1F to 5L. Similarly, the Cub and TL of the occluding phase in both the IP and Me also gradually decreased, while the TH of the IP and Me increased. In the closing phase of the Mo, the Cub, SL, and velocity on the working side were greater than on the nonworking side, However, the T/S and TH on the working side were smaller than on the nonworking side. These findings indicate that as mastication proceeds, the range of orofacial movements in the closing phase becomes narrower and that all trajectories become smoother.
