Abstract
The purpose of this study is to investigate the effect of occlusal condition upon the excitatory reflex response of the motor unit of the temporal muscle on the balancing side induced by the mechanical stimulation provided to the maxillary canine on the working side, in reference to the lateral movement from the working side to the intercuspal position in the final stage of jaw-closing phase during human masticatory movement.
6 subjects with canine in normal overjet and 2 subjects with cross-bite canine were chosen. Then, the responses of the temporal muscle induced by the mechanical stimulation provided to the maxillary canines on the working side in such different conditions were compared.
The mechanical stimulation, linguo-labially and labio-lingually directed pressure, was provided to the canines to stimulate the periodontal ligament and the range of the pressure applied was 100-800gf. The activity of the motor unit which spontaneously discharged were selectively delivered by needle electrode from the anterior part of the temporal muscle on the balancing side. While the canine was being stimulated, the mandibular position was kept to the lateral side approximately 2mm by using incisal point as reference point without occluding. This mandibular position measured by MKG was visually feedbacked by the subjects.
The results were as follows:
In the normal overjet, the excitatory response of the contralateral temporal muscle to linguo-labially directed pressure on the maxillary canine on the working side was observed. Although the similar tendency of the response to the labio-lingually directed pressure was observed, the response was less than that of to the linguo-labially directed pressure.
On the contrary, the cross-bite canine had different response pattern from the canines in normal overjet. The excitatory response to the labio-lingually directed pressure was observed, while there were no responses to the linguo-labially directed pressure. According to these obtained results, the temporal muscle showed the different responses, when the pressure of the same direction was provided to the tooth in the different occlusal condition. Hence, it suggested that the reflex response from the maxillary canine on the working side to the contralateral temporal muscle depended upon the occlusal condition of the canine, and the various response patterns of the temporal muscle possibly reflected the occlusal conditions.
