Not all individuals respond the same way to functional appliance treatment. The magnitude of anteroposterior intermaxillary forces after insertion of the functional appliance displays a wide variation. It is still unknown if properties of the soft tissues may explain the variation of the treatment results. In a series of studies we investigated the masticatory muscle characteristics as a predictive variable in determining treatment effects of activators in Class II malocclusion children. We found that children with weaker masticatory muscles seem to show greater improvement in dental sagittal
relationship, possibly due to lower occlusal forces and less "occlusal friction" when shifting the bite.