Masticatory muscle right-left differences in controls and hemifacial microsomia patients.

One aim of this study was to assess right-left differences in the volume of masticatory muscles in controls so as to be able to distinguish between normal variations and pathological differences. The other aim was to compare the masticatory muscle volume of the nonaffected side of hemifacial microsomia patients with the smaller side of controls so as to test the compensation hypothesis. The study group consisted of 39 children with hemifacial microsomia and the control group of 52 children. Computed tomography scans were made using a Philips Tomoscan 350 and a Pro Speed S Fast Spiral General Electric scanner. The normal right-left differences in volume of the masticatory muscle of the controls, calculated as a percentage of the total, demonstrated small mean differences of 2.57% to 2.88% (SD:1.98-2.74). For hemifacial microsomia patients, the relative difference was about 10 times the difference for controls. For controls, the averages of the right-left differences (%) were all below the generally accepted SEM of 4%. Testing the compensation hypothesis of all effects, only the age effect was multivariately significant (P < 0.001). No overcompensation of the masticatory muscles of the nonaffected side of hemifacial microsomia patients could be demonstrated.