Simultaneous Noxious Stimulation of the Human Anterior Temporalis and Masseter Muscles. Part II: Effects on Jaw Muscle Electromyographic Activity.

AIMS: To test the hypotheses that, in comparison to control, the effects of simultaneous noxious stimulation of the right masseter and anterior temporalis muscles on jaw muscle activity (1) vary with the task; (2) are different between different agonist or antagonist muscles involved in a task; and (3) are correlated with mood or pain-related cognition scores. METHODS: In 15 asymptomatic participants, recordings were made of jaw movement and electromyographic (EMG) activity of the right digastric and bilateral masseter and anterior temporalis muscles during standardized open/close and free and standardized chewing tasks. The tasks were repeated in three blocks: block 1 (baseline), block 2 (during simultaneous infusion of 5% hypertonic or 0.9% isotonic saline infusion into the right masseter and anterior temporalis muscles), and block 3 (infusion sequence reversed). The Depression, Anxiety and Stress Scales questionnaire was completed prior to the experiment, and the Pain Catastrophizing Scale was completed before and after the experiment. Linear mixed-effects model analysis compared root mean square (RMS) EMG activity under baseline, hypertonic saline, and isotonic saline (control), and Spearman correlations between RMS and psychologic scores were calculated. P < .05 was considered significant. RESULTS: The significant effects of pain on the activity of a jaw muscle varied with the task, were different between different agonist and antagonist muscles in a task, and were significantly correlated with some of the psychologic scores. Qualitatively, the effects noted in a particular muscle could be different between different participants. CONCLUSION: Simultaneous noxious masseter and anterior temporalis stimulation results in changes in jaw muscle activity that can vary with the task, the muscle, the participant, and some psychologic variables.

Simultaneous Noxious Stimulation of the Human Anterior Temporalis and Masseter Muscles. Part I: Effects on Jaw Movements.

AIMS: To test the hypotheses that, in comparison to control (isotonic saline), simultaneous noxious stimulation (hypertonic saline) of the masseter and anterior temporalis muscles would result in (1) reductions in amplitude and velocity of jaw movements during standardized open/close jaw movements and during free and standardized chewing and (2) changes in amplitude and velocity of jaw movements that relate to higher levels of negative mood or pain-related thoughts. METHODS: Standardized open/close and free and standardized chewing were recorded in 15 asymptomatic participants in three blocks: block 1 (baseline), block 2 (during 5% hypertonic or 0.9% isotonic saline infusion into the right masseter and anterior temporalis muscles simultaneously), and block 3 (infusion sequence reversed). The Depression, Anxiety, and Stress Scale (DASS-21) and the Pain Catastrophizing Scale (PCS) were completed by the participants before the experiment, and the PCS was completed after the experiment. The amplitude and velocity of opening and closing movements for each task were compared between blocks (repeated-measures analysis of variance). Spearman rank correlation coefficient was used to explore correlations. Statistical significance was considered to be P < .05. RESULTS: In comparison to isotonic saline control, hypertonic saline resulted in significantly smaller opening and closing amplitudes and lower velocity during closing in free chewing, but no significant effects in the open/close task or standardized chewing. There were significant correlations between PCS scores and amplitude or velocity during isotonic saline and baseline, but not hypertonic saline. CONCLUSION: The pain-related reduction in amplitude and/or velocity of free chewing is consistent with the Pain Adaptation Model, but the absence of effects on the open/close task and standardized chewing is not. The few significant correlations between psychologic variables and jaw movement may reflect the low scores.

The Effects of Experimental Temporalis Muscle Pain on Jaw Muscle Electromyographic Activity During Jaw Movements and Relationships with Some Psychological Variables.

AIMS: To determine if the effects of experimental temporalis muscle pain on jaw muscle activity vary with the jaw task performed, jaw displacement magnitude, participant being studied, and with psychological measures. METHODS: Jaw movement was tracked, and electromyographic (EMG) activity was recorded from the masseter and anterior temporalis and digastric muscles in 14 asymptomatic participants during standardized opening/closing jaw movement, free chewing, and standardized chewing tasks. Tasks were repeated in three blocks: Block 1 (baseline), Block 2 (during 5% hypertonic or 0.9% isotonic saline infusion into the anterior temporalis), and Block 3 (during infusion of the opposite solution). Participants also completed the Depression, Anxiety, and Stress Scales 21 (DASS 21), the Fear of Pain Questionnaire (FPQ III), the Pain Self-Efficacy Questionnaire (PSEQ), and the Pain Catastrophizing Scale (PCS). Analyses involved linear mixed-model analysis and Pearson correlations. P < .05 was considered statistically significant. RESULTS: The presence of a significant difference in jaw muscle EMG activity between hypertonic and isotonic saline infusions varied between tasks and between jaw muscle agonists and antagonists, but not in displacement magnitude. There were qualitative differences between participants in the effects of infusion on EMG activity. During hypertonic saline infusion, significant positive correlations were noted between jaw-closing EMG activity and anxiety, fear of medical pain, and PCS scores. CONCLUSION: Noxious stimulation of the temporalis muscle results in changes in jaw muscle activity, which can vary with the task, the muscle, the participant, and some psychological variables.