A comparison of centric relation with maximum intercuspation based on quantitative electromyography.

The study concerned the nature of the alterations, if any, in muscle activity demonstrable when the mandible shifts from maximum intercuspation into its most retruded physiological relation (i.e. centric relation). An integrator-averager was used to determine micro V average amplitude from masseter and temporal muscles in two maxillo-mandibular positions, centric relation and maximum intercuspation, and three modes, first contact occlusion, chewing and swallowing. Vertical reference marks on the cuspids were used to quantitate horizontal deviation from maximum intercuspation to centric relation. Data were obtained from twelve subjects and analysed for variance. Results demonstrated a significant increase in micro V in all centric relation positions. Statistics yielded an F value of 5.88258 with a probability of 0.005. Results suggest critical limitations in reliance on centric relation as a reference position during clinical therapy.