Electromyographic indices, orofacial myofunctional status and temporomandibular disorders severity: A correlation study

Abstract

This study examined whether there is an association between surface electromyography (EMG) of masticatory muscles, orofacial myofunction status and temporomandibular disorder (TMD) severity scores.

Forty-two women with TMD (mean 30 years, SD 8) and 18 healthy women (mean 26 years, SD 6) were examined. According to the Research Diagnostic Criteria for TMD (RDC/TMD), all patients had myogenous disorders plus disk displacements with reduction. Surface EMG of masseter and temporal muscles was performed during maximum teeth clenching either on cotton rolls or in intercuspal position. Standardized EMG indices were obtained. Validated protocols were used to determine the perception severity of TMD and to assess orofacial myofunctional status.

TMD patients showed more asymmetry between right and left muscle pairs, and more unbalanced contractile activities of contralateral masseter and temporal muscles (p < 0.05, t-test), worse orofacial myofunction status and higher TMD severity scores (p < 0.05, Mann–Whitney test) than healthy subjects. Spearman coefficient revealed significant correlations between EMG indices, orofacial myofunctional status and TMD severity (p < 0.05).

In conclusion, these methods will provide useful information for TMD diagnosis and future therapeutic planning.

Introduction

The stomatognathic system performs many physiologic functions, such as mastication, speech, suction, deglutition, which generate mechanical forces that are dissipated by the skeletal tissues associated with the temporomandibular joint (TMJs) (Hinton and Carlsson, 1997). In all these functions, coordinated by the central nervous system and under the influence of peripheral inputs, there are mandibular motor requests and, at the same time, movements of the tongue, hyoid, soft palate, lips and other structures, involving several muscle groups (Douglas et al., 2010).

A relatively common problem of the stomatognathic system is the temporomandibular disorder (TMD); approximately 7–15% of the adult population is affected, with higher prevalence in women at reproductive ages. TMD is usually defined as a collective term embracing several clinical problems that involve the masticatory muscles, the TMJ and the associated structures. The most frequent complaints reported by subjects with TMD are pain in the TMJ and/or masticatory muscles, TMJ sound and difficulty to chew (Cooper and Kleinberg, 2007, Kurita et al., 2001, Lim et al., 2010, Michelotti and Iodice, 2010).

Due to the multiplicity of factors that may cause or contribute to TMD manifestation or worsening, multiple treatments have been employed, although the pathophysiology is not fully understood and the mechanisms of action of the treatments may be not clear (Cairns et al., 2010, Michelotti and Iodice, 2010).

The classic dental and skeletal etiologic theories of TMD have been challenged and refuted by studies conducted around the world (Klasser and Greene, 2009), and the relationship between malocclusion and TMJ is still far from being clearly understood (Michelotti and Iodice, 2010). The new approaches show a less restrictive understanding of TMD, and there is great interest in the relationship between oral motor function and TMD (Ardizone et al., 2010, Douglas et al., 2010, Koutris et al., 2009, Lobbezzo et al., 2006, Peck et al., 2008).

In normal conditions, the stomatognathic system shows neuromuscular harmony. Harmony may be disrupted, and alterations/dysfunctions of the appearance, posture and/or mobility of the lips, tongue, mandible and cheeks may occur. A collective label for these alterations is orofacial myofunctional disorders (OMDs) (Felício and Ferreira, 2008).

OMDs may disequilibrate TMJ function (Gelb and Bernstein, 1983), or may be a consequence of TMD since the nociceptive stimuli may generate compensatory muscle behaviors (Bianchini et al., 2008, Casanova-Rosado et al., 2006). For instance, pain may influence the characteristics of masticatory sensory–motor system (Koutris et al., 2009), and TMJ pain, especially when long-standing, is associated with marked functional impairment (Bakke and Hansdottir, 2008).

So, together with pain relief, the goals of TMD treatments should include function improvement (Michelotti and Iodice, 2010), reestablishing the possibility to chew (Kurita et al., 2001), swallow, and speak without pain and without exacerbating the problem (Felício et al., 2010). Otherwise, deterioration can progress into a self-perpetuating chronic condition with increasing dysfunction and pain (Cooper and Kleinberg, 2007). Nevertheless, there is a scarcity of studies about the relationship between TMD and OMD.

For this purpose, clinical and instrumental examinations should allow to discriminate subjects with and without TMD, but also to provide data about the orofacial myofunctional status and neuromuscular impairments that influence the global quality of life. A better therapeutic intervention may thus be planned. Therefore, the detection of relationships between the various diagnostic tools is one of the fundamental steps for the assessment of their validity and clinical performance.

Accordingly, we selected three assessment protocols for the present study:

• Surface electromyography (sEMG), according to Ferrario et al. (2000).

• ProTMDmulti-Part II, a questionnaire validated to determine the perception severity of TMD (Felício et al., 2009).

• Orofacial Myofunctional Evaluation with Scores Protocol (OMES Protocol) that provides information about the components and functions of the stomatognathic system (Felício and Ferreira, 2008, Felício et al., 2010).

The purposes of this study were to assess the characteristics of the stomatognathic system in a group of patients with TMD as compared to those of normal subjects, and to examine the relationship between the data obtained by sEMG of masticatory muscle, those gained by orofacial myofunction assessment, and the TMD severity scores, for future clinical use.