Abstract
The aim of this study was to develop a method to measure the range of the mandible during the occlusal phase of mastication. The mandibular movement of one healthy male subject (age 25 yrs), with normal occlusion, was measured with an opto-electronic motion analysis system (TRIMET, Tokyo shizaisha, Tokyo, Japan) . This system is able to measure mandibular motion with six degrees of freedom, and has a sampling frequency of 100 Hz. The subject was initially instructed to perform mandibular excursive movements, with tooth contact, on 4 occasions each lasting 30 seconds. Thus 12, 000 positions of the mandible were obtained. From this a three-dimensional curved mesh diagram of mandibular excursion was constructed for the mandibular incisal point which extended 15 mm anteriorly, 13 mm posteriorly (x axis), and 14 mm to the left and to the right (y axis), with intercuspal position at the origin with the resolution of 0.1 mm. To determine the supero-inferior position (z axis) of this mesh, the 12, 000 mandibular positions were. searched and, if two or more z values corresponded to a single x-y coordinate, the z value closest to the horizontal plane was chosen. In addition, this curvilinear mesh diagram could be constructed for any mandibular landmark. A masticatory cycle (for chewing gum) from the subject was compared to this mesh diagram. Coincidence between this cycle and the mesh indicated occlusal contact during mastication, and for this subject contact was observed for a distance of 3.8 mm (opening phase: 3.4 mm; closing phase: 0.4 mm) .
The curved mesh diagram of mandibular excursion enabled visualization of excursive movements of any point on the mandible, and is useful in examining and understanding the mandibular function.
