Analysis of denture mobility of complete dentures with numerical simulation and intraoral experiments.

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The purpose of this study was 1) to assemble and verify a system to measure the three-dimensional (3-D) movement of the upper and lower complete denture and the movement of the mandible simultaneously, and 2) to analyze a relation between denture movements and the path of closure of the mandible during functions. A 3-D motion capture system with four infrared TV cameras was used. It recognizes a number of targets with infrared rays reflecting membrane. Twelve targets were prepared for each subject. Three of them were attached to a rim of eyeglasses for the calibration of head movements, three of them were placed on each upper and lower denture, and remains were on a metal frame attached to the mandible. Then, the direction and range of dentures and mandibular movements were calculated from loca of each three targets. The relation between lower dentures and the mandibular movements was analyzed with the change of the inner product of normal vectors of denture occlusal planes and mandibular planes. The mandibular movements could be c1assified into two types. One (79.9%) was the type of normal stroke (the path of closure was on ipsilateral side of mastication : IS) and the other (20.1%) was reversed (the path of closure was on contralateral side : CS). The results are followed : This system could measure the denture mobility within 0.3 mm errors. Upper dentures tended to move toward the nonworking side in a case of IS, and toward the working side in a case of CS.The lower dentures tended to move and incline toward mastication side. The mobility of upper dentures had a correlation to the mandibular movement regardless of working side or nonworking side, and lower dentures had a tendency to move toward the working side.