RESUMEN
0.05) 2. The mean electric activity of the masticatory muscles was found to have decreased during more clenching than resting, but there was no statistically significant difference because of individual difference of measuring values. (p>0.05) 3. The asymmetry index of masticatory muscles in asymmetric groups was significantly greater during clenching compared with controls. (p<0.05) In conclusion, no right-left difference of muscle activities was found in patients with facial asymmetry before orthognathic surgery and 4weeks afterwards. Not only muscular functioning but also many other factors, such as occlusion, temporomandibular joint disorder and trauma, probably affect facial asymmetry and will be analyzed in future studies. And we will need long term follow-up after orthognathic surgery.