Abstract
[Purpose] In electromyographic (EMG) examination of sleep bruxism (SB), the relative value against the burst at maximum voluntary contraction (MVC), i.e., %MVC value, is usually applied to standardize obtained data of EMG muscular activity. In this study, we investigated the correlation between %MVC value of SB bursts and maximum bite force that is exerted in an awake state to clarify their relationship.
[Methods] Twenty-nine sleep bruxers participated in this study. Polysomnography (PSG) including masseteric EMG with audio-video recordings was carried out, and SB bursts were classified into 4 categories:a burst judged as a true SB (SBB), one or two consecutive phasic bursts (POE), bursts originating in other movements (OMB) and bursts during transient awake periods after onset of sleep. The average of %MVC values of each category and %MVC value of the maximum burst in each category were calculated and designated as “average-%MVC” and “max-%MVC”, respectively. Maximum bite force during a awake period was measured using Dental Prescale®.
[Results] The smaller maximum bite force was, the larger was average-%MVC, and a significant negative correlation was found between maximum bite force and average-%MVC in SBB, POE, OMB, WB, and total bursts including all categories. The same tendency was found in max-%MVC, and there were significant negative correlations in SBB, POE, OMB, and total bursts.
[Conclusions] For assessment of SB based on %MVC values in an SB EMG examination, there is a possibility that bite force is assessed as being higher than the actual force in cases with less maximum bite force and assessed as being lower than the actual force in cases with stronger maximum bite force. We need to take these characteristics into consideration when interpreting EMG results expressed using %MVC values.
