The importance of lip muscle activity in determining the position of the anterior teeth in deep bite

Introduction. Low-strength forces of the soft tissues are closely related to the stomatognathic system morphology. The muscles of the lips have a significant influence on the position of the front teeth. The goals of our research were to: 1. Examine the electromyographic activity of the circular muscle of the lips in Class I and Class II division 2 patients with incisor retrusion in the position of physiological rest and centric occlusion at maximum voluntary muscle contraction; 2. Examine the existence of a correlation between the electromyographic activity of the lip muscles and the position of the incisors in the examined groups. Material and Methods. The action potentials of the circular muscle of the lips were registered at different positions of the lower jaw. Intramuscular coaxial electrodes were placed according to the Greenfield scheme. Measurements were performed bilaterally, summed up with ten muscle levels, in 100 patients aged 8 - 12 years; 30 patients were in the control group with neutroclusion, i.e. Class I and 70 patients in the study group with Class II division 2, according to Angle. Results. The results are given in microvolts as average cumulative voltage of action potential amplitudes, which were used to determine changes in the orbicular muscle activity. After statistical analysis of the obtained data, it was concluded that the bioelectrical activity of the examined muscles at all measured positions was lower in patients with distoclusion, except for the lower lip in patients with Class II division 2, where this activity was significantly higher. Conclusion. The results of the study show that the determined changes in the action potentials of the circular muscles of the lips in subjects with distoclusion indicate a cause-and-effect relationship between muscle function and occlusion. A significantly increased activity of the lower lip in deep bite can be considered responsible for the steep position of the upper incisors.