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Abstract
This study compares the effect of clenching and grinding on masseter and sternocleidomastoid electromyographic (EMG) activity during different jaw posture tasks in the sagittal plane. The study included 34 healthy subjects with natural dentition, Class I bilateral molar Angle relationship, and absence of posterior occlusal contacts during mandibular protrusion. An inclusion criterion was that subjects had to be free of signs and symptoms of any dysfunction of the masticatory system. Bipolar surface electrodes were located on the right masseter and sternocleidomastoid muscles. EMG activity was recorded while the subjects were in standing position, during the following jaw posture tasks: A. maximal clenching in the intercuspal position; B. grinding from intercuspal position to edge-to-edge protrusive contact position; C. maximal clenching in the edge-to-edge protrusive contact position; D. grinding from edge-to-edge protrusive contact position to intercuspal position; E. grinding from retrusive contact position to intercuspal position. EMG activities in tasks B, C, D, and E were significantly lower than in task A in both muscles (mixed model with unstructured covariance matrix). EMG activity among tasks B, C, D, and E did not show significant differences in both muscles, except between tasks D and E in the masseter muscle. A higher effect was observed on the masseter than on the sternocleidomastoid muscle to avoid excessive muscular activity during clenching and grinding. The EMG patterns observed could be of clinical importance in the presence of parafunctional habits, i.e., clenching and/or grinding.
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Notes on contributors
Macarena Venegas
Dr. Macarena Venegas received her D.D.S. degree in 2000 from the University of Concepción, Chile, a masters of oral rehabilitation in 2008 from the Andrés Bello University, Chile, and a diploma in fixed prosthesis from the University of Chile. She is a staff member of the Dental School of Diego Portales University. She devotes her professional time to work in oral rehabilitation in several private health institutions and in private practice.
José Valdivia
Dr. José Valdivia received his D.D.S. degree in 1981 from the University of Chile. He is master and specialist in oral rehabilitation and osseointegrated implants. Dr. Valdivia is a professor and chief of integral adult clinics at Andrés Bello University, Chile and also directs the masters program in odontology and the Brånemark Osseointegration Chilean Center. He is an active member of the American Osseointegrated Academy Center and a fellow of the International College of Dentists.
María Javiera Fresno
Dr. Maria Javiera Fresno received her D.D.S. degree in 1988 from the University of Chile and a master of oral rehabilitation in 2006 from the Andrés Bello University, Chile. She is a member of the Oral Rehabilitation Department of the same university and an academic of the Faculty of Odontology, University of Chile. She is currently a staff member of the Oral Physiology Laboratory, Biomedical Sciences Institute, Faculty of Medicine, University of Chile. She devotes her professional time to work in oral rehabilitation in private practice.
Rodolfo Miralles
Dr. Rodolfo Miralles received his D.D.S. degree in 1975 from the University of Chile. He is a professor and chief of the Oral Physiology Laboratory, Biomedical Sciences Institute, Faculty of Medicine, University of Chile. Dr. Miralles is a member of the International Association for Dental Research and an associate editor of the Chilean Odontology Journal.
Mario Felipe Gutiérrez
Dr. Mario F. Gutiérrez received his D.D.S. degree in 2007 from the University of Chile. He is ad-honorem academic of the Restorative Department of the Faculty of Odontology, University of Chile. Dr. Gutiérrez is currently a staff member of the Oral Physiology Laboratory, Biomedical Sciences Institute, Faculty of Medicine, University of Chile. He devotes his professional time to work in oral rehabilitation in several private health institutions and in private practice.
Saúl Valenzuela
Dr. Saúl Valenzuela received his D.D.S. degree in 1990 from the University of Chile. He is a staff member of the Prosthetics Department, Faculty of Odontology, University of Chile. Dr. Valenzuela is currently a staff member of the Oral Physiology Laboratory, Biomedical Sciences Institute, Faculty of Medicine, University of Chile. He devotes his professional time to work in oral rehabilitation in several private health instutions and in private practice.
Aler Fuentes
Dr. Aler Fuentes received his D.D.S. degree in 2006 from the University of Talca, Chile. He is an academic of the Faculty of Odontology, University of Chile. Dr. Fuentes is currently a staff member of the Oral Physiology Laboratory, Biomedical Sciences Institute, Faculty of Medicine, University of Chile. He devotes his professional time to work in oral rehabilitation in several private health instutions and in private practice.