Bilateral post-stimulus electromyographic complexes in human masseter muscles after stimulation of periodontal mechanoreceptors of bi- and unilaterally-innervated teeth.

These complexes (PSECs) were studied in full-wave rectified and averaged EMG in 13 subjects, who jaw-clenched at a controlled level. The PSECs were elicited by mechanical and electrical stimulation of receptors or their afferents in the unilaterally- and bilaterally-innervated periodontium of the upper first premolars and an upper central incisor. To exclude any contribution from acoustic receptors, subjects were exposed to high-intensity noise during mechanical stimulation. Comparison of peak amplitude and area from PSEC waves in normalized EMG amplitude-time plots suggests extensive crossing of the midline by periodontal afferent information. The small variation in latency of the first inhibitory wave on the two sides suggests that there are no additional synapses in the crossed pathway. Latency differences and wave incidence on the two sides of the later inhibitory and excitatory periods varied markedly between subjects suggesting that influences from higher centres affect masseteric motoneurones. In five subjects stimulation of periodontal receptors around different teeth resulted in different PSEC wave sequences.