A Study of Occlusal Contact and Asymmetry Index of Masseter and Temporal Muscles in Patients with Mandibular Prognathism

Abstract

Occlusal contact was assessed and the action potentials of the masseter and temporal muscles were measured in patients with the skeletal mandibular prognathism and in healthy controls. Occlusal contact (by processing the image taken with Silicone Black) was assessed by the and image method. The action potentials of the masseter and temporal muscles were measured using a K6- I Diagnostic System The data was converted to an asymmetry index as proposed by Naei j et al., which represents the asymmetry levels of the number of contact points when biting with mild or moderate force. The asymmetry of the masseter and temporal muscles when clenching with and without cotton wadding between the teeth was also assessed using the same index. The relationship between the number of contact points and the action potentials of the muscles was analyzed using iso-probability ellipses, which had a 95% reliability.
The results were as follows:
1. Asymmetry index of the number of contact points was greater in the mandibular prognathism group than in the control group.
2. In the prognathism group, the asymmetry index of the number of contact points was less marked when biting with moderate force than when biting with mild force.
3. The muscular action potentials of patients with mandibular prognathism were not always higher on the side of the mouth with the larger number of contact points.
4. In the prognathism group, the action potentials of the temporal muscles tended to be more asymmetric than those of the masseter muscles.
5. In the prognathism group, the asymmetry of action potentials of the temporal muscles was less marked when clenching on cotton wadding.