The Reliability of the Bilateral Trigeminal Roots-motor Evoked Potentials as an Organic Normalization Factor: Symmetry or Not Symmetry?

Abstract

Background: In order to achieve a complete clinical evaluation of mastication, an in-depth neurophysiopathological assessment of masticatory muscles control is needed. Electromyography technique (EMG) is widely used for this purpose but failed to give convincing results. The aim of this work was to describe our quantitative objectivation of the motor control of the masticatory muscles and to verify the hypothesis to consider the bilateral Root Motor Evoked Potentials as an electrophysiological normalization factor. Methods: 25 healthy people (15 males, 10 females; mean age 29 years ± 5) with normal occlusion and no history of temporomandibular disorders and orofacial pain underwent a transcranical electrical stimulation that allowed a direct bilateral stimulation of the motor roots of the trigeminal motor system called bilateral Root Motor Evoked Potentials (b R-MEPs). The maximal Absolute Neural Evoked Energy, symmetry and synchrony properties of the resulting b R-MEPs were studied using measures like latency, amplitude and integrated area of the collected signal. An Artificial Neural Network computational model was used to estimate the correlation coefficient with the EMG values of each of both sides to predict the values from the right side by inputting values from the left side. Results: With regard to the descriptive statistical aspect the mean and SD values were for onset latency (1.96 msec ± 0.18 msec vs. 2.01 msec ± 0.21 msec), amplitude (5.76 mV ± 2.01 mV vs. 5.89 mV ± 2.51 mV) and integral area (11.09 mV/msec ± 4.45 mV/msec vs. 11.27 mV/msec ± 4.34 mV/msec) for right and left masseter muscle, respectively. The Kruskal-Wallis test shows not statistically significant difference between the medians (confidence level 95%) in fact the P-value was 0.33, 0.96 and 0.86 between sides for latency, amplitude and the EMG integral area, respectively for the b R-MEPs. The similarity between sides of the data sampled, studied in terms of mean squared error and correlation coefficients for latency (R 2 =0.955, SME=0,032) amplitude (R 2 =0.948, SME=0.162) and integrated area (R 2 =0.947, SME=0.212), indicates an organic symmetry of the trigeminal motor nervous system. Conclusion: These results show the high efficiency in terms of symmetry and stability of the b R-MEPs as a normalization factor.