[The alterations of occlusal sounds, jaw opening movement and electromyography depend on occlusal interference]

Before crown prosthetese are set on the prepared teeth, occlusal adjustments are normally necessary. Previous studies suggested that the tolerance of occlusal interference is less than 30 microns and that the occlusal sensibility of tooth must be smaller than 30 microns. The purpose of this study was to investigate the possibility of measuring small amounts of occlusal interference by using the occlusal examinations of occlusal sounds, jaw movement and muscle activity. Fifteen subjects participated in this study. They had healthy oral tissue and TMJ. The occlusal interferences were made from platinum foil (25 microns/layer). For 200 microns thickness, 100 microns thickness and 50 microns thickness, multiple-thickness (8, 4 and 2 layers) platinum foils were used. For 25 microns thickness, simple platinum foil was used. And for 15 microns thickness, rolled platinum foil was used. Each occlusal interference was applied on 3 or 6 of the subject in order from the thickest to the thinnest one. For the measuring of occlusal sounds, accelerometers were attached to the skin of each orbital point. For the measuring of jaw movement, a mandibular kinegiograph K-5R (Mio.tronics Co.) was used. Surface electrodes were used for the measurement of muscle activities of masseteres and anterior tempolar muscles. The measurements were performed regularly after the subjects were instructed to start tooth tapping at the speed of three times a second. The results were as follows. 1. When any occlusal interference was put on 3 or 6, both the peak to peak value of occlusal sounds were reduced and the duration of the sounds were increased compared to cases with normal dentition. The duration of the jaw tooth tapping movement and the peak to peak value of muscle activity for tooth tapping didn't show any tendency of change when occlusal interferences were used. However, the duration of muscle activity preceding the onset occlusal sound indicated increasing. 2. When the amount of occlusal interference was reduced, the peak to peak value of occlusal sounds was increased and the duration shortened. The increased or decreased time of the jaw tooth tapping movement depended on the amount of occlusal interference. 3. These findings suggest that the peak to peak value and the duration of occlusal sounds, the duration of the jaw tooth tapping movement, and the duration of muscle activity preceding the onset occlusal sound are useful data for objective assessments of occlusal contacts.