Functional improvement of the mandibular neuromuscular guidance by orthodontic-surgical treatment.

The primary aim of the study was to reveal whether adult patients with skeletal mandibular retrognathism combined with a dental Class II relationship without craniomandibular pain show a characteristic pattern of free mandibular movements compared to patients with a Class I skeletal and dental morphology. The secondary aim was to investigate whether these characteristic structures are subject to change following combined orthodontic-surgical treatment. Free mandibular movements were measured with an ultrasound device and analyzed with computer software developed by the authors. In all patients examined, 2 maxillarily and mandibularly fixed axes were found. These axes have no direct relation to the temporomandibular joints, are positioned above and anterior to the joints and maintain a constant distance. This gear system is referred to as a neuromuscularly determined dimeric link chain. The position of the mandible is defined by the rotational angle mu and the inclination angle alpha around the axes of the dimeric link chain. This dimeric link chain of free movements of patients with Class I skeletal and dental relationship functions according to the principle of least action: The angular velocities around the 2 axes show a constant ratio within the different segments of motion, and in the mu-alpha diagrams the segments of mandibular movements are represented by straight lines, the shortest paths between 2 positions. Individual cases and statistical data show that the structure of mandibular movements of patients with skeletal mandibular retrognathism combines with a dental Class II relationship without craniomadibular pain differs significantly from that of patients with Class I alignment. Mandibular retrognathism and a Class II relationship are accompanied by marked coordination disturbances in the rotary movements around the maxillary and mandibular neuromuscular axes. Following orthodontic-surgical treatment to restore ideal alignment of the occlusal, articular, and skeletal structures, the patients showed a similar pattern in the structure of mandibular movements to that of patients with Class I sketal and dental relationships. Thus, combined orthodontic-surgical treatment leads to measurable functional hamonization not only of the skeletal and dental structures but also of the neuromuscular guidance system.