Morphologic evidence of muscle influence on dental arch width.

Tests on hypotheses to explain changes in arch width during correction of distoclusion with the activator appliance used in this study showed that statistically significant increases occurred in both maxillary and mandibular arch widths during treatment. The increase was substantially larger in the maxilla than in the mandible. The arch width showed no statistically significant decrease after completion of treatment. The activator designed for this study affected orofacial muscle balance. The findings suggest that there were changes in the influence of tongue and cheek muscles on the maxilla. Available experimental as well as clinical data support the assumption that the tongue had taken a higher and more anterior position in the palatal area and that the tension of the cheek muscles was reduced relative to the posterior part of the maxillary dental arch.