Activity of the masticatory muscles and occlusal contacts in young adults with and without orthodontic treatment.

BACKGROUND Symmetry evaluation of the craniofacial complex generally involves models of mandibular movement and masticatory muscle activity, especially during the development of the craniofacial complex. The aim of this screening study was to detect differences in the asymmetry and activity indices and in the occlusal contact distribution in groups with and without orthodontic treatment, and between the sexes in the healthy population. MATERIAL AND METHOD This screening study involved the participation of 149 Caucasian (F = 101, M = 48) 18-year-old volunteers, of whom 77 had received orthodontic treatment (Group I) and 72 had not (Group II). All participants underwent sEMG recording with an eight-channel electromyograph (Bio EMG III). A T-Scan III device was used to analyze the occlusal contact points. We measured the voltage of the right and left temporalis anterior (RTA, LTA) and of the right and left masseter muscles (RMM, LMM). On the basis of the Naeije study, we calculated the Asymmetry and Activity indices (AsI, AcI). RESULTS No significant differences were found in the asymmetry or activity indices, or in the occlusal contact distribution of young adult subjects with or without orthodontic treatment. There were two findings in the females. First (p = 0.04), a higher voltage (131.12 μV) was recorded in the right temporalis anterior muscle in female group, compared to 119.65 μV in the male group. Secondly (p = 0.002), the activity index showed a predominance of the temporalis anterior (AcI = 10.52). In the males, the activity index showed a predominance of the masseter muscles (AcI =-1.22). CONCLUSIONS The null hypothesis was supported, as we found that no significant differences were observed in occlusal contact, asymmetry, or activity indices between healthy young adults with or without orthodontic treatment. However, there do exist significant differences in the activity index between genders.