[Experimental studies on adaptation of mandibular masticatory movements to given laterally shifted intercuspal position].

When, the intercuspal position is newly established during reconstruction of maxillomandibular relationship, understanding the process of adaptation for the laterally shifted eccentric intercuspal position is very significant for problems involving maxillo-mandibular registration and diagnosis of occlusion, which has very important meaning for clarifying the neuromuscular control system for mandibular movement. In this studies, changes in clinical symptoms and masticatory movements were observed longitudinally when the laterally shifted intercuspal positions were newly established. Conditions for selecting four subjects were that they wore suitable overlay maxillary dentures connected to abutment teeth and that their mandibular dentition were natural and included good fixed restoration. Experimentally prepared overlay dentures were identical to those worn by subjects except that they included a structure of lateral shift of artificial dentition positioning to given newly laterally shifted intercuspal position. The condition of lateral shift of the intercuspal positions are established by the protrusion of the condyle on one side, amounts of lateral shift of the intercuspal positions were 0, 0.5, 1 and 2mm. From immediately after until a week after insertion of the experimental denture, observations were made to determine clinical symptoms and alterations in the chewing strokes on the frontal plane and in the rhythm of chewing movements. At first, the experimental denture with no lateral shift was inserted into the subject's mouth. Next, this was replaced by the experimental denture with a lateral shift of 1mm, and then this was replaced with a denture with a lateral shift of 2mm. When clinical obstruction was encountered, during this process this was replaced by one with a lateral shift of 0.5mm. Analysis of data of mandibular movement obtained was performed by means of a personal computer system. Results 1. Individual difference was observed in the process of adapting to laterally shifted intercuspal positions. One subject adapted adequately to a shift of 2mm, another to a shift of 1mm; and still another to a shift of 0.5mm. One subject failed to adapt adequately to a shift of 0.5mm. 2. When the laterally shifted intercuspal position was newly established, subject complained of a slightly high feeling in occlusion on the direction opposite to the lateral shift, occlusal sounds, and glide from the initial contact positions to the intercuspal position. All subjects, however, found it difficult to indicate the amount or direction of lateral shift; and there was no obstruction to intentional mastication under these conditions.(ABSTRACT TRUNCATED AT 400 WORDS)