Relationship between measured value of bite force measurement devices and amplitude of masseteric electromyogram waveform: comparison of different bite force measurement systems

Purpose: This study aimed to investigate the relationship between amplitude of masseteric electromyogram (EMG) and measured values of T-scan system (TS) which can measure dynamic occlusal force but whose measured values are not expressed in a specific unit of force, and the relationship bet ween the masseteric EMG amplitude and bite force value expressed in Newton units measured using the Dental Prescale (PS). Methods: A total of 18 healthy participants were included. EMG and bite force were measured simultaneously as the participants’ jaws occluded at 10 levels of strength, including the maximum voluntary contraction force. Measurements were taken twice on different days. EMG electrodes were attached to the masseter muscle region on the main masticatory side and maintained for TS and PS measurements on the same day. Regarding EMG measurements, the maximum amplitude of each waveform was measured. Regression analysis was performed with the measured values for TS and PS as objective variables and EMG amplitudes as explanatory variables. In addition, the ratio of the regression coefficients for TS and PS (TS/PS) was calculated. Results: Both PS value and EMG amplitudes and TS value and EMG amplitudes showed a linear and significant correlation. The average correlation coefficients of PS and EMG values measured first and second were 0.91 and 0.88, respectively. Those for TS measured first and second were 0.90 and 0.85, respectively. For both PS and TS, no significant difference（PS：P=0.20，TS：P=0.35）was observed in the regression coefficients of the measured occlusal force values and EMG amplitudes between the 1st and 2nd measurements. However, considerable variabilities were observed both between days and between participants. A significant correlation was found between the regression coefficient of the occlusal force measured using PS and the EMG amplitude between the 1st and 2nd measurements. However no significant correlation was found in the TS measurements. The median values of the ratio of regression coefficients (TS/PS) for all participants in the 1st and 2nd measurements were 5.67 and 6.84, respectively. Although there was no significant difference（P=0.37） between the 1st and 2nd measurements, variability was observed between the days. In addition, the variations among participants were large. Conclusion: The measurement values using TS and PS correlated with the EMG amplitude. The finding suggests the possibility of linking the occlusal force displays of the TS an d PS via electromyogram amplitude values. However, the ratio of regression coefficients between measurement values using PS and EMG amplitudes and TS and EMG amplitudes in the linear regression equations was not constant owing to large inter-individual variations and day-to-day variabilities. It is suggested that it is necessary to improve the analysis methods and parameters that link the occlusal force displays of the TS and PS