Soporte Oclusal y Actividad Muscular

Acta Odontologica Scandinavica, 2009; 67: 187Á192

ORIGINAL ARTICLE

Influence of changing occlusal support on jaw-closing muscle electromyographic activity in healthy men and women

MEI-QING WANG1, JIAN-JUN HE1, KELUN WANG2,3 & PETER SVENSSON4
Department of Oral Anatomy and Physiology and TMD, School of Stomatology, Fourth Military Medical University, Xi’an China, 2Center forSensory-Motor Interaction, Aalborg University, Aalborg Øst, Denmark, 3Department of Oral and Maxillofacial Surgery, Aalborg Hospital, Aalborg, Denmark and 4Department of Clinical Oral Physiology, School of Dentistry, University of Aarhus, Denmark
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Abstract Objectives. To test whether changes inocclusal support differentially modulate masseter and anterior temporalis muscle electromyographic (EMG) activity during controlled maximal voluntary clenching. Material and methods. Forty-seven healthy subjects (32 M and 15 F, 22.991.3 years) were recruited. Cotton-rolls were used to modify the occlusal contact relations and were positioned on the right, left, or both sides, and either in the molar orpremolar regions, i.e. six different occlusal combinations. Surface EMG activity was recorded bilaterally from the masseter and anterior temporalis area and normalized with respect to maximal voluntary clenching in the intercuspal position. Analysis of variance and the paired t-test were used to test the data. Results. Normalized EMG activity was influenced by changes in cotton-roll modifiedocclusal support, and there were differences between muscles (pB0.001). In general, EMG activity decreased in both muscles when occlusal support was moved from the molar to the premolar region. When occlusal support was moved from bilateral to unilateral contacts, EMG activity in the balancing-side anterior temporalis muscle and in bilateral masseter muscles decreased. Unilateral clenching on themolars, but not on the premolars, was associated with lower EMG activity in the balancing-side masseter and always associated with lower EMG activity in the balancing-side anterior temporalis compared to the working side (pB0.05). Conclusions. Masseter and anterior temporalis muscles respond differently to changes in occlusal support, which may have implications for stability of the mandible duringintense clenching.

Key Words: Dental occlusion, electromyography, jaw-closing muscles, mandibular position, trigeminal neurophysiology

Introduction Clinical experience and controlled studies support the notion that mandibular stability in the closing position depends on the mechanical support offered by the occlusion. Baba et al. [1] reported that clenching on the 1st premolars on both sideswithout any molar support causes a larger upward movement of the mandible in the posterior region compared to clenching on the 2nd molars. They also reported that clenching on unilateral occlusal stops causes a larger upward movement on the contralateral side of the mandible. Kozawa et al. [2] found that losing more posterior teeth causes greater displacement of the condyle and a lower level of biteforce. This kind of larger upward movement of the mandible and greater displacement of the condyle during clenching

implies instability of the mandible, which is obviously associated with occlusal support. Occlusal stability keeps the muscles fit and enables the masticatory system to meet its functional demands [3]. The masseter muscle generates the highest activity assessed byelectromyography (EMG) during isometric contractions in the maximum intercuspation position (ICP). If stability of the mandible is not supported by the occlusion, the jaw-closing muscles will contribute to the stabilization and reduce the magnitude of the EMG activity to avoid damage to the structures involved in the compensatory stabilization [4]. In a recent study, Hosoda et al. [5] suggested that the...