Influence of jaw clenching and tooth grinding on bilateral sternocleidomastoid EMG activity

Karen Rodríguez, Rodolfo Miralles*, Mario Felipe Gutiérrez, Hugo Santander, Aler Fuentes, María Javiera Fresno, Saúl Valenzuela

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


This study compares the effect of tooth clenching and grinding on sternocleidomastoid electromyographic (EMG) activity during different laterotrusive jaw posture tasks. The study included 28 healthy subjects with natural dentition and bilateral molar support, 14 with bilateral canine guidance and 14 with bilateral group function. Bipolar surface electrodes were located on the left and right sternocleidomastoid muscles. EMG activity was recorded during the following tasks: A. eccentric grinding from intercuspal position to the right lateral edge-to-edge contact position; B. clenching in right edge-to-edge lateral contact position; C. concentric grinding from right lateral edge-to-edge contact position to intercuspal position. On the working side, activity in the task C was significantly higher than in tasks A and B in subjects with canine guidance, whereas no significant differences were observed between tasks in subjects with group function. On the nonworking side, activity was significantly lower during task A than in tasks B and C, in both occlusal schemes (mixed model with unstructured covariance matrix). When comparing by side, EMG activity was significantly lower during task B on the working side than on the nonworking side. However, there were no significant differences during tasks A and C. The EMG activity was significantly lower with canine guidance than group function on the working side during tasks A, B, and C, and on the nonworking side during tasks B and C. These results could explain muscular symptoms in the sternocleidomastoid muscles if the subject is experiencing parafunctional habits while awake and/or during sleep that exceed the individual's adaptation capability.

Original languageEnglish
Pages (from-to)14-22
Number of pages9
JournalCranio - Journal of Craniomandibular Practice
Issue number1
StatePublished - Jan 2011


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