Objectives: Various existing devices to measure the motion of mastication have their own deficiencies, such as large scale, heavy load, inaccuracy and etc. Those devices do not seem to be so popular in dentistry despite the increasing importance of early detection and medical treatment for abnormal mastication. A very simple, cheap and accurate mechanical device to measure the motion of mastication has been developed. 

Methods: The proposed sensor is mechanical and serial link type device of 6 degrees of freedom to measure mastication. To make it lighter, links are made of aluminum pipes of 6 mm in diameters. Angular displacements of all the 6 joints are geared up in 4 times with spur gears that are directly connected to ultra-micro encoders. Each encoder is 7.5ƒ³ x l0.5 mm in size. 5 grams in weight and of 360 pulses/rev has been used in fundamental frequency quadrupled. The root of the device is firmly connected to a frame attached to a headgear; the probe would be attached to the lower incisal point by some adhesive. And we examined the accuracy of positions and attitudes of the probe calculated from measured data.

Results: Accuracies on three dimensional incisal point positions were confirmed to be within 0.3 mm, and attitude accuracies were attained within 0.3 degrees in Euler angle.

Conclusion: A simple mechanical link type device to measure mastication motion has been developed. Mastication motion is complicated and has 6 degrees of freedom. Measurement of the motion isn't so popular. It is performed with quite a large device or without sufficient accuracy. In modern society, a simple and reliable mastication motion measurement device is increasingly recognized to be of importance. This device had high accuracy and its weighs only 90 grams and gives almost no load to examinees.

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