A Three-dimensional Analysis of Orofacial Masticatory Movements in an Edentulous Subject.

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  • 無歯顎者のそしゃく時の口腔・顔面運動経路の３次元解析

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Abstract

Oral movement trajectories in a denture wearer were studied to evaluate masticatory capability by monitoring orofacial movements during mastication of a color-developing chewing gum. The subject was an edentulous patient who had 4 dental implants of the mandible to anchor a mandibular overdenture.<BR>To monitor the orofacial movements, a cordless light-emitting target that was recorded as a shining point with a clear outline when illuminated by a cold spot light was developed. An image processor enabled the recording and autotracking of multiple reference points.<BR>The subject chewed a new color-developing chewing gum that, on mastication, indicates the patient's masticatory capability using the intensity of red.<BR>During 250 strokes of chewing, the subject's face markers were recorded on a video tape by two high-speed TV camaras from two different perspectives, i. e., frontal and lateral. At the end of every 50 strokes, the color of the chewing gum was assessed by a Chroma Meter (CR-300, Minolta Co.), with respect to the degree of redness or a* value. Thus, the same chewing gum was continuously chewed for a total of 250 strokes, with the a* value measured at the end of every 50 strokes in 5 stages.<BR>Then, the video tape recordings of the start of the first stage (1F) and the end of each stage (1L-5L) were reproduced on a high-speed video and fed into an image processor (Image Data, ID-8000). The movements of each marker were automatically tracked by the Image Data, after which the resulting data of the 3-dimensional coordinates were fed into a computer.<BR>The trajectory of each monitored point during the 4 sec of each stage was computed by a 3-D analyzer (Movias 3D) with reference to the following parameters: the total length from start to finish of the trajectory (TL); the distance between the start and finish of the trajectory (SL); the ratio of the TL to the SL (T/S); the volume of the rectangular solid encompassing the entire trajectory (the cubical range); and the mean of the 3-dimensional angles that were created by differences in the direction of the preceding and following trajectories at each measured time (TH).<BR>Our results revealed that the time needed for one chewing cycle reduced gradually from 1F to 5L. Similarly, the TL of the incisal point (IP) and the THs of both the IP and the modiolus (Mo) also gradually reduced. These findings indicated that as mastication proceeds, the range of mouth movement becomes narrower and all the trajectories become smoother.

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