Temporomandibular disorders (TMD) are a musculoskeletal disorder affecting the masticatory muscles, the temporomandibular joint (TMJ), and associated structures. Evidence suggests that TMD are commonly associated with other conditions of the head and neck region, including cervical spine disorders and headache. Presence of neck pain was shown to be associated with TMD 70% of the time [
Although the association of cervical spine disorders and TMD has been studied by different authors, it is far from being exhaustively explained [
Muscle tenderness in the cervical spine and jaw was shown to be associated with increased levels of jaw and neck disability. For example, one study by our team revealed a strong relationship between neck disability and jaw disability (
Muscle tenderness is the most common sign [
Although several studies have evaluated neck tenderness in subjects with TMD, none of these studies have evaluated the relationship between the level of tenderness and jaw dysfunction. Moreover, most studies that investigated muscle tenderness in subjects with TMD used palpation techniques, which are difficult to quantify and standardize [
There is a great interest on the knowledge for further relationship between stomatognathic system and cervical spine. If further relationship is established, new clinical strategies that target both regions should be considered and, therefore, the need of a multidisciplinary approach should be reinforced in the management of patients with alterations of the stomatognathic system, including TMD patients. In order to further investigate this relationship, the objective of this study was to determine the correlation among neck disability, jaw dysfunction, and muscle tenderness in subjects with chronic TMD. We hypothesized that the higher the level of neck disability, the higher the level of jaw dysfunction and the higher the level of muscle tenderness.
A convenience sample of 20 female subjects diagnosed with chronic TMD (at least 3-month duration) and 20 healthy female subjects participated in this cross-sectional study. Subjects were recruited from the TMD/Orofacial Pain Clinic at the University of Alberta and by using advertising around the university and on the local television news. Sample size calculation was based on bivariate correlation. Based on a moderated and conservative correlation (
Subjects with TMD were classified with either myogenous TMD (mainly muscle complaints) or mixed TMD (myogenous and arthrogenous) and presented concurrent neck disability. The subjects were excluded if they presented arthrogenic TMD only, a medical history of neurological, bone, or systemic diseases, cancer, acute pain or dental problems other than TMD, or a history of trauma or surgery to the upper quarter within the last year or if they had taken any pain medication or muscle relaxants less than 4 hours before the diagnostic session.
The healthy group included subjects with no pain or clinical pathology involving the masticatory system or cervical spine for at least one year prior to the start of the study. Exclusion criteria included previous surgery, neurological problems, any acute or chronic musculoskeletal injury, or any systemic diseases that could interfere with the procedure and taking any medication such as pain relieving drugs, muscle relaxants, or anti-inflammatory drugs.
After obtaining consent, all subjects were examined clinically using the research diagnostic criteria for temporomandibular disorders (RDC/TMD) [
This study was approved by the Ethics Review Board from the University of Alberta, where the study was conducted.
The “Limitations of Daily Functions in TMD Questionnaire” (LDF-TMDQ) was used to measure the jaw function of all the subjects in this study. The LDF-TMDQ is multidimensional and includes specific evaluations for TMD patients [
The NDI is a questionnaire designed to give information about how neck pain affects the ability of the subject to manage her everyday life [
The manual pressure algometer (force dial) was used to measure the muscle tenderness in both groups by one investigator, blinded to the subjects’ group allocation. Muscle tenderness was measured bilaterally in the following muscles: masseter (i.e., deep masseter, anterior, and inferior portions of the superficial masseter), temporalis (i.e., anterior temporalis, medial temporalis, and posterior temporalis), sternocleidomastoid, and upper trapezius (i.e., occipital region and half way between C7 and acromion) in a supine position for all muscles but trapezius muscle which was evaluated in seating [
The pressure pain threshold (PPT) was defined in this study as the point at which a sensation of pressure changed to pain. At this moment, the subject said “yes,” the algometer was immediately removed, and the PPT was noted [
PPT points evaluated (♦ temporalis muscle, ■ masseter muscle, ▲ sternocleidomastoid muscle, and
Pressure rates were decided based on previously studies that showed the most reliable rates to use on cervical and facial muscles [
Muscle tenderness data for all analyzed muscles, jaw, and neck disability levels were analyzed descriptively. A paired
Level of significance for all statistical analyses was set at
Mean age for TMD group was 31.05 (SD = 6.9) and for the healthy group was 32.3 (SD = 7.2). Thirteen subjects were classified as having mixed TMD and 7 were classified as having myogenic TMD. The range of neck disability ranged from 0 to 31 (no to severe disability) and the range of jaw dysfunction ranged from 10 to 50 (no to severe disability) among all subjects included in this study.
The correlations (Spearman’s rho) between level of muscle tenderness and jaw dysfunction (LDF-TMDQ) as well as between level of muscle tenderness and neck disability (NDI) ranged from low to moderate correlations. Spearman’s rho ranged from 0.387 to 0.647 for muscle tenderness and jaw dysfunction and Spearman’s rho ranged from 0.319 to 0.554 for muscle tenderness and neck disability (Table
Correlation between muscle tenderness (PPTs) and neck disability and jaw dysfunction.
Spearman’s rho | |||
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Side | Muscle | Jaw dysfunction | Neck disability |
Right | Temporalis |
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Masseter |
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Sternocleidomastoid |
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Upper trapezius |
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Left | Temporalis |
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Masseter |
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Sternocleidomastoid |
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Upper trapezius |
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It was found that the correlation (Spearman’s rho) between jaw disability and neck disability was significantly high (
This study investigated the correlation among neck disability, jaw dysfunction, and muscle tenderness in subjects with and without chronic TMD.
The main results of this study were that jaw dysfunction and neck disability were strongly correlated, showing that changes in jaw dysfunction might be explained by changes in neck disability and vice versa. Also, the results showed that the higher the level of muscle tenderness in upper trapezius and temporalis muscles is, the higher the level of jaw and neck dysfunction the subject will have. These results add to the body of knowledge in this area providing new information regarding these associations. Furthermore, they corroborated the importance of looking at cervical spine and stomatognathic system as a functional entity when evaluating and treating subjects with TMD, neck pain, and muscle tenderness. Another study that is corroborated to this association was the study by Herpich and colleagues [
The discussion will focus on each of the results separately, as well as highlighting the strengths and limitations of this study.
Several studies examined the presence of signs and symptoms in the cervical area of patients suffering with TMD and they have been showing that the presence of tender points in the cervical area of TMD’s patients is quite common, which is in line with the findings of this study [
Muscle tenderness is only one factor among multiple factors that could contribute to maintaining or perpetuating a level of dysfunction in people with TMD either in the jaw or in the neck. Usually, jaw dysfunction and neck disability are both related to gender, psychological factors, and social factors. For example, studies have shown that the presence of muscle tenderness is more commonly found in women than in men suffering with signs and symptoms of TMD [
“Pain is a complex phenomenon influenced by both biologic and psycologic
The correlation (Spearman’s rho = 0.915) between jaw disability and neck disability was significantly high in this study. This means that the variance of jaw dysfunction is highly dependent on the neck disability (approximately 82%). Thus, subjects who had high levels of jaw disability (evaluated through the JDI) also presented with high levels of neck disability (evaluated through the NDI) and vice versa. Recently, the study by Armijo-Olivo and colleagues [
Disability is a complex concept, since it involves more than accounting for the individual signs and symptoms alone. It also includes the perception of the patient about his or her condition as an important factor [
The fact that jaw disability and neck disability are strongly related also shows that one has an effect on the other, which provides further information about the importance of assessing and treating both regions when evaluating chronic TMD patients. Assessment of the neck structures such as joints and muscles as well as the disability of patients with TMD could direct clinicians to include the cervical spine in their treatment approach. In addition, if patients with TMD have neck disability in addition to jaw disability, or vice versa, physical therapists and dentists should work together to manage these patients.
As strong correlation between jaw disability and neck disability does not indicate a cause and effect relationship, longitudinal studies where subjects with TMD are followed up to determine the appearance of neck disability are still necessary to determine any cause and effect connection.
This study showed that the higher the level of muscle tenderness, mainly in upper trapezius and temporalis muscles, the higher the level of jaw and neck disability. Therefore, when clinicians assess higher levels of muscle tenderness either in the jaw and/or in the neck regions, they should infer that this could be possibly related to higher levels of jaw and neck disability. This information will guide health professionals to consider new clinical strategies that focus on both masticatory and cervical regions to improve patients’ outcomes. Jaw dysfunction and neck disability were strongly correlated, showing that changes in jaw dysfunction might be explained by changes in neck disability and vice versa. This provides further information about the importance of assessing and treating both the jaw and neck regions as a complex system in TMD patients.
The convenience sample used increased the potential subject self-selection bias. It was difficult to recognize what characteristics were present in those who offer themselves as subjects, as compared with those who did not, and it was unclear how these attributes might have affected the ability to generalize the outcomes [
High levels of muscle tenderness were correlated with high levels of jaw and neck disabilities. Furthermore, jaw dysfunction and neck disability were strongly correlated, showing that changes in jaw dysfunction may be explained by changes in neck disability and vice versa in patients with TMD. This study has highlighted the importance of assessing TMD patients not only at the level of the jaw, but also including the neck region. Muscle tenderness, however, is only one aspect of the TMD. TMD is a complex problem and involves many factors such as gender, levels of anxiety and stress, and the level of socialization of the patient. Future studies investigating the association between neck and jaw should also include factors other than muscle tenderness which are still needed.
The authors declare that there is no conflict of interests regarding the publication of this paper.
This study was supported by the Queen Elizabeth II Scholarship from the University of Alberta.