Alteration of the functional condition of the mandible during clinical treatment

Free mandibular movements and their neuromuscular guidance were measured wi th an ultrasonic device and analyzed with computer software developed by th e authors. In all patients examined, we found maxillarly- and mandibularly- fixed axes which maintain a constant distance. This guidance system is name d a neuromuscularly-determined dimeric link chain. The position of the mand ible is defined by the 2 rotational angles (mu, alpha) around the axes of t he dimeric link chain. This dimeric link chain of free movements normally functions according to t he principle of least action. The angular velocities around the 2 axes show a constant ratio during the different segments of motion. In the mu-alpha- diagrams, the segments of movements of the mandible are represented by stra ight lines, the shortest path between 2 positions. Individual cases and sta tistical data show that the structure of mandibular movements of patients w ith skeletal mandibular retrognathism combined with dental class-II-relatio nship without craniomandibular pain significantly differs from the structur e in patients with neutral alignment. Mandibular retrognathism and class-II -relationship are accompanied by marked coordination disturbances of rotati ons around the maxillary and mandibular neuromuscular axes. Following orthodontic-surgical treatment that restored ideal alignment of t he occlusal, articular, and skeletal structures, the patients examined show ed a similar pattern in the structure of mandibular movements to that of pa tients with neutral skeletal and dental relationships. Thus, combined orthodontic-surgical treatment leads to measurable functiona l harmonization not only of the skeletal and dental structures, but also of the neuromuscular guidance system.