[Relationships between tooth loss and electromyographic activities of masticatory muscles]

For purpose of evaluating the characteristic of electromyographic activities of masticatory muscles with front or molar tooth loss, electromyographic activities of masticatory muscles and mandibular movements during tooth tapping and gum chewing were investigated in each group of tooth loss, and were compared with those of control group. The results were as follows. 1. In reference to the group with front tooth loss, 1) On tooth tapping, each S.D. of the time parameters of electromyographic activities of jaw closing muscles especially masseter and posterior temporalis was small, and that of jaw opening muscle was large. 2) On gum chewing, offset of jaw closing muscles' activities especially masseter and anterior temporalis were delayed. 3) On both tooth tapping and gum chewing, there was no difference in mandibular movements from control group. 2. In reference to the group with molar tooth loss, 1) On both tooth tapping and gum chewing, each S.D. of the time parameters of electromyographic activities of jaw closing muscles was large. 2) On tooth tapping, S.D. of opening ratio was large. 3) On gum chewing, both S.D. of chewing cycle and opening ratio were large.