Neuromuscular and skeletal adaptations following mandibular forward positioning induced by the Herbst appliance

The purpose of this study was to examine neuromuscular and skeletal adaptat ions to changes in sagittal jaw relationships induced by the Herbst applian ce. Six patients (age, 9 years and 5 months to 11 years and 2 months) with Angle Class II, division 1 malocclusions were studied longitudinally. The s tructural changes were determined by analyzing serial lateral cephalograms. Electromyographic recordings of specific masticatory muscles were used to evaluate neuromuscular adaptations. Similar cephalometric changes were obse rved in all patients. In all patients, lateral pterygoid muscle activity in creased inmmediately after insertion of the appliance, but the activity dec reased markedly after 4 to 6 months of treatment. In 4 of the 6 patients st udied, however, the condyles were located in a slightly more downward and f orward position. These findings indicate that the adaptation of muscular fu nction occurs within a relatively short period and precedes the compensator y morphological changes produced through functional appliance therapy. (Ang le Orthod 2000;70:000-000.).