The influence of jaw position and antagonistic tooth relations on the appearance of a short-latency excitatory reflex in the human masseter muscles following mechanical tooth stimulation.

Post-stimulus electromyographic complexes (PSEC) were elicited by standardized tapping of a central upper incisor in 12 subjects during isometric voluntary biting in two positions, the incisor edge-to-edge (IEE) or the maximal occlusion (MO). In IEE a short latency excitatory peak (P wave) was present in the PSEC; this was absent in MO. By superimposing the rough EMG sweeps without full-wave rectification, it appeared that this P wave was brought about by synchronous masseter motor-unit firing.