Experimental Study of the Effects on Premature Contact involving Masticatory Activity

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Malocclusion and CMD (Craniomandibular Disorder) are occasionaly attributable to abnormal mandibular movement due to premature contact. The results of earlier studies revealed that a periodontal membrane reflection recurred from premature contact which affected the excitability of the masticatory muscle. Thereby revealing a relatively earlier formation of this reflection and its eventual disappearance. Then we examined the effects of the difference in stimulation with the loading pressure on the periodontal membrane.We studied 14 teeth consisting of bilateral upper and lower first molars, first pre-molars, canines, right upper and lower central incisors in adults who had no particular abnormalities in the teeth arrangement, occlusion and temporomandibular joint. We attempted to clarify the variation in masticatory muscular activities when 1 Kg of stimulation pressure was exerted from three different directions, buccal to lingual, lingual to buccal and to tooth axis for one second. We s … More et 3 different stimulation pressures for muscle activities, these being 5,10 and 15 Kg under clenched conditions.When stimulation pressure was given to the periodontal membrane at rest, an excitatory electric discharge from the muscle was induced in most cases. However, muscular electric discharge was inhibited when stimulation pressure was added at a 10 Kg clenching force condition. Both induction and inhibition were recognized when the clenching force was 5 Kg. When the clenching force was around 5 Kg it was conceivably a borderline for the excitatory reflection to switch over to an inhibitory reflection. It is considered that this reversal phenomenon adjusts the masticatory movement as follows : subjects would like to bite more strongly at the masticatory muscle is still weaker on mastication, and to inhibit the masticatory muscular excitation reflectively at the masticatory muscle is already strong enough when the stimulation pressure is added to the periodontal membrane.On the other hand, the direction of stimulation pressure concerning the periodontal membranous reflect showed an inhibitory reflection without causing an excitatory reflection when the stimulation pressure was loaded from the maxillolingual side. On the other hand, it was made clear that an excitatory reflection was recognized in the stimulation pressure from the lingual side when the mandibular teeth were involved, and there was a stimulant direction in the periodontal membrane.As a result of this study it was suggested the possibility that the information on periodontal membrane by stimulation pressure give variety to the excitability of mastication muscle and then exert a varid influence upon mandibular movement. Less