Development of a Three-Dimensional Shape Measurement System for Occlusal Surfaces Using a Laser Beam Section Method

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We investigated the measurement accuracy of a shape measurement equipment which was developed last year, and developed a system for a computerized analysis of occlusal contact.Measurement accuracy of shape measurement using Laser-beam-section method is known to depend on not only material of the object but shape of its surface point where the light spot is located. To clarify this interaction, We investigated how much curvature and the normal direction of the surface point reflect measurement eroor. As a test object, we used a plaster ball produced from the precise impression of bearing ball. Measurement error of each surface point data was evaluated by the difference between the distance from an estimated center of the ball and diameter of the ball. This test was carried out twice using two balls with different diameters about 3.1 and 1.5mm, yielding the results as follows : 1) there was no difference between the two test balls in the measurement error and 2) the error was less equal than 10 mum when the difference between the direction of normal vector and that of Laser beam was less equal than 50 degrees.The analyzing system consists of the following three subsystems : 1) an analytical system, 3) a display system and 4) a data-file management system. The obtained data are transferred to a mini-computer (MX5600, Mitsubishi Electric). The computer then carries out such takes as the elimination of unnecessary data,interpolation of missing data,computation of intercuspal distance between opposing teeth and recognition of contact area. The display system visualizes the shape data and the intercuspal distance date on CRT display.