It is a known fact that forces of small magnitude derived from the soft tissue are closely related with skeleton morphology. Orbicular muscles of mouth have an important impact on the position of frontal teeth. The goal of our research was as follows: 1. To examine electromyographic activity of the orbicular muscles of mouth in patients with neutral occlusion (class I) and distal occlusion joined with incisor retrusion (class 11/2 malocclusion) in the position of physiologic rest and central occlusion during maximal voluntary contraction 2. To examine possible correlation between electromyographic activity of the orbicular muscles of mouth and incisor position in the mentioned groups of patients. Action potentials of the orbicular muscle of mouth were registered at different positions of mandibule. We used intramuscular coaxial electrodes positioned according to Greenfield scheme. The measurement was done on both sides, summed up with ten muscle levels, in 100 patients aged 8 to 12, and one control group with 30 patients with neutral occlusion (class I) and another control group of 70 patients with class 11/2 malocclusion. Results are given in micro volts as average cumulative voltage of action potential amplitudes, which were used to determine changes in the orbicular muscle activity. After statistical analysis of the results, the conclusion is that bioelectric activity of the examined muscles at all measured positions was less significant in patients with distal occlusion, except for lower lip in class 11/2, where this activity was significantly higher. The conclusion is that confirmed changes in action potential of the orbicular muscles of mouth in patients with distal occlusion imply cause -and-effect relationship between muscle function and occlusion. Significantly higher activity of lower lip in malocclusion classll/2 can be considered responsible for angled position of upper incisors. .
