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Nocturnal Masseter EMG Activity of Healthy Subjects in a Natural Environment

Clinic for Masticatory Disorders and Complete Dentures, Center for Oral Medicine, Dental and Maxillo-Facial Surgery, University of Zurich, Plattenstrasse 11, CH-8028 Zurich, Switzerland

S.S. Salis Gross

Clinic for Masticatory Disorders and Complete Dentures, Center for Oral Medicine, Dental and Maxillo-Facial Surgery, University of Zurich, Plattenstrasse 11, CH-8028 Zurich, Switzerland

S. Palla

Clinic for Masticatory Disorders and Complete Dentures, Center for Oral Medicine, Dental and Maxillo-Facial Surgery, University of Zurich, Plattenstrasse 11, CH-8028 Zurich, Switzerland

Facial pain of patients with craniomandibular disorders might be caused by muscle overload. However, the activity of masticatory muscles of healthy individuals is still unknown. The aim of this study was therefore a first attempt to clarify this question by recording the masseter muscle activity of healthy subjects during sleep by means of portable recorders. The study was performed on 21 healthy subjects selected after telephone and questionnaire screenings and clinical examination from among randomly selected inhabitants of Zurich. The masseter EMG was recorded during seven nights in each subject's natural environment with the electrodes in reproducible position. The signal was analyzed for number, amplitude, and duration of contraction periods defined as signal portions above a threshold which could contain sub-threshold signal portions shorter than the standby time of 5 sec. The signal amplitude was expressed in percent of the amplitude recorded during maximum voluntary clenches (%MVC). An average of 71.9 ± 28.7 contraction episodes per night (men, 74.7 ± 30.1; women, 65.0 ± 23.8; p = 0.043), i.e., of 10.5 ± 3.8 per hour (men, 11.0 ± 4.0; women, 9.3 ± 3.0; p = 0.005), was found. The average mean amplitude was 26.2 ± 6.4 %MVC (men, 27.0 ± 6.8; women, 24.4 ± 4.5; p = 0.009). The duration of the episodes had a mode of 0.5 sec, and the group mean of the integral of the amplitude over time was 123.7 ± 157.9 %MVC (men, 138.9 ± 184.0; women, 85.9 ± 28.2; p = 0.005). Healthy subjects showed intermittent periods of masseter activity during sleep which, on average, were of rather low intensity and short duration.

Key Words: bruxism • electromyography • masseter muscle • nocturnal activity • sleep

Journal of Dental Research, Vol. 78, No. 8, 1436-1444 (1999)
DOI: 10.1177/00220345990780080901


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