Introduction

Temporomandibular disorder (TMD) is defined as a set of pathological clinical conditions involving the masticatory muscles, the temporomandibular joint (TMJ), or both, and the associated structures (Okeson, 1996). It is often associated with chronic headaches and cervical pain, and may be accompanied by some degree of physical or psychological disability in patients (Ballegaard, Thede-Schmidt-Hansen, Svensson, & Jensen, 2008; Sharma, Gupta, Pal, & Jurel, 2011; Plesh, Noonan, Buchwald, Goldberg, & Afari, 2012)

TMD affects about 31% for adults/elderly and 11% for children/adolescents (Valesan et al., 2021), and is more prevalent in females (Bueno, Pereira, Pattussi, Grossi, & Grossi, 2018). Its etiology is complex and multifactorial, and includes factors such as micro and macro trauma, emotional stress, sources of deep pain stimulation, and muscle hyperactivity, among others (Dworkin & Massoth, 1994; Lee, Yeung, Wong, & McMillan, 2008; Sharma et al., 2011). It manifests mainly as pain in the TMJ region and in masticatory muscles, fatigue, limitation of or deviations in mandibular movements, joint noises and locking of the jaw (Okeson, 1996).

In addition to the physical signs and symptoms of TMD, there is a strong association between the degree of TMD-related pain and the presence of psychological changes (Dworkin & Massoth, 1994; Felício, Faria, Silva, Aquino, & Junqueira, 2004). These associated comorbidities may facilitate the chronification of pathological processes, thus worsening the prognosis (Manfredini, Winocur, Ahlberg, Guarda-Nardini, & Lobbezoo, 2010), and may be related to the process of central sensitization, leading to an increase in the perception of this pain(Arendt-Nielsen et al., 2018; Nazeri et al., 2018)

The most reliable diagnostic protocol used for TMD was RDC/TMD (Diagnostic Criteria for Research in Temporomandibular Disorder) until the year 2018, when DC/TMD (Diagnostic Criteria for Temporomandibular Disorder) (Dworkin & LeResche, 1992; Schiffman et al., 2014) was being the substitute gradually. These protocols proposes a double diagnosis, divided by axis. Axis I refers to the diagnosis of TMD (physical axis), and Axis II to the psychological state and inability to feel pain. Together, they provide a comprehensive and consistent evaluation.

The objective of this study was to determine whether there was an association between the variables of Axis I (myofascial pain, disc displacement and other joint conditions) and Axis II (disability related to chronic pain, depression and somatization) of the RDC/TMD in a population in southern Brazil. The hypothesis was that the variables of Axis II were positively associated with the diagnosis of TMD of Axis I.

Materials and methods

This cross-sectional observational study was approved by the research ethics committee Federal University of Santa Maria (UFSM) under number CAAE 4728.9415.0.000.5346. The study evaluated the clinical records of all the individuals seeking treatment in the TMD Extension Program of the dentistry course UFSM, from March 2015 to December 2018.

The inclusion criteria were patients over 18 years of age, who presented with any of the diagnostic conditions of Axis I of the RDC/TMD (myofascial pain, disc displacement or any joint condition). A total of 349 individuals sought treatment in the period under study. Of these, 74 met the exclusion criteria, because they had a history of facial and/or mandibular trauma (26), neuropathic pain, such as trigeminal neuralgia (5), were under 18 years of age (13), or did not fill out the questionnaires correctly (30), leaving a sample of 275 individuals.

For muscle palpation and TMJ examination during RDC/TMD clinical evaluation (axis I), calibration of the applied force was performed using the Force One Algometer (Wagner, FDIX model, USA). Axis II reveals the psychosocial condition and functional impairment of the patient that leads to the following diagnoses: chronic pain-related disability measured according to RDC/TMD, using the Graded Chronic Pain Scale (GCPS) (Von Korff, Dworkin, & LeResche, 1990; Dworkin & LeResche, 1992; Von Korff, Ormel, Keefe, & Dworkin,1992) (categorizing diagnoses as no pain, low disability, or high disability), depression and somatization, using the Symptom Checklist 90-R (SCL-90-R), SCL-DEP and SCL-SOM, respectively (categorizing patients as normal, moderate, or severe) (Dworkin & LeResche, 1992; Schmitz et al., 2000).

After the RDC/TMD was applied, diagnostics were obtained (Axis I and II) and the patients were invited to undergo the treatment recommended by the TMD extension program at the university (UFSM). Complementary exams such as computed tomography or magnetic resonance imaging were requested when a more accurate diagnosis was needed in cases of clinical doubt.

The data were tabulated and analyzed using the STATA 14 program (Stata Corporation, College Station, TX, USA). First, a descriptive analysis was performed to present the clinical, demographic and socioeconomic characteristics of the sample. The association between the variables of Axis I (myofascial pain, disc displacement and joint conditions) and Axis II (degrees of chronic pain-related disability, depression and somatization) was evaluated using Fischer's Exact Test, at a 5% significance level.

Results

Regarding demographic and socioeconomic characteristics of the sample, 73.82% of the patients were female, 85.35% were caucasian, 51.29% were unemployed, 56.30% were single, and 52.07% received until 3 Brazilian minimum wage (Table 1). The average age of the patients evaluated were 34.32 years (SD = 14.73).

In the data analysis of Axis I variables, 65.65% of the patients presented with myofascial pain, 33.33%, with some type of disc displacement and 45.38%, with some joint condition. Analyzing Axis II, 84.56% of the sample had some degree of chronic pain-related disability, 49.04% had some degree of depression, and 52.31%, with some degree of somatization (Table 1).

Chronic pain-related disability, regardless of its intensity, was observed in most of the patients, and demonstrated a statistically significant association with myofascial pain and joint conditions (arthralgia, osteoarthritis and osteoarthrosis) (Table 2). The degrees of depression and somatization were also associated with myofascial pain and joint conditions (Tables 3 and 4).

Discussion

The results of the present study show a positive association between variables of Axis II (chronic pain-related disability, depression and somatization) and TMD of subtypes myofascial pain and joint conditions. The exception was disc displacement, which was not associated to Axis II variables, so the study hypothesis was partially accepted.

The sample was composed of a significantly larger number of female than male patients, similar to the comparative numbers found in the literature (Bueno et al., 2018). Some of the reasons why women prevailed over men is that women are more sensitive not only to pain, but also to depression and anxiety; moreover, they experience hormonal changes, and are more concerned about health, hence, seek treatment more often than men (Von Korff et al., 1990; Nazeri et al, 2018). According to Brazilian National Institute of Geography and Statistics, in 45% of Brazilian households, those who head and support the family are exclusively women, who accumulate roles as caretakers and educators, which probably generates physical and mental overload in this part of the population. The average age of the patients evaluated were 34.32 years (SD = 14.73), which is similar to the age range found in other studies (Nazeri et al., 2018).

RDC/TMD was used as a diagnostic tool in this research to observe the data of a given population in a standardized manner that allows it to be compared with different populations in other regions of the world (Manfredini, Landi, Di Poggio, Dell’osso, & Bosco, 2003; Vedolin, Lobato, Conti, & Lauris, 2009; Arendt-Nielsen et al., 2018). The most current diagnostic method, the DC/TMD (Schiffman et al., 2014), was validated for use in Portuguese only in August 2019. The migration to DC/TMD, which presents some modifications that facilitate logistics for the dentist, such as the report of familiar pain and muscle palpation only of the TMJ, masseter and temporalis muscles, should occur naturally, but does not invalidate the results of this study.

The biobehavioral screening instruments of the RDC/TMD Axis II were evaluated herein. The variables of chronic pain-related disabilityand of depression are clinically relevant and have acceptable psychometric properties. Thus, they are valid and useful as instruments to identify high degrees of suffering, pain and disability in patients with different diagnoses of TMD (Ohrbach et al., 2010). Axis I and II are complementary, and are meant to offer the professional or researcher a more complete diagnosis of the patient, taking into account all physical and psycho-emotional aspects that may interfere with the patient's ability to deal with pain, especially in chronic conditions, such as the case of most TMD patients.

The sample evaluated in the present study included patients with some TMD diagnosed by RDC/TMD Axis I. Of these, 49.04% presented an indicator of moderate to severe depression, 52.31% had moderate to severe somatization, and 84.56% had some degree of chronic pain-related disability, in accordance with other populations previously investigated (Lee et al., 2008; Rehm et al., 2019). Yap, Tan, Chua and Tan (2002) also found an association among patients with TMD with indicators of depression and a considerable degree of somatization(Yap et al., 2002). Rehm and collaborators (2019) compared the prevalence of depression and somatization in patients with TMD and healthy control patients, and found significantly higher levels of depression and somatization in these patients, compared with the control group subjects (Rehm et al., 2019). This relationship between worse psychological state of patients and diagnosis of myofascial pain is a common finding in the literature (Eversole, Stone, Matheson, & Kapla, 1985;McCreary, Clark, Merril, Flack, & Oakley, 1991; Dahlström, 1993; Manfredini, Bandettini di Poggio, Cantini, Dell’osso, & Bosco, 2004; Trivedi, 2004; Manfredini, Ahlberg, Winocur, Guarda-Nardini, & Lobbezoo, 2011; Miettinen, Lahti, & Sipilä, 2012; Kindler et al., 2012; Dıraçoǧlu, et al., 2016). It suggests that depression and anxiety can contribute to myofascial pain and migraine, by interacting with the pain modulating networks and lowering the threshold of pain or altering the perception of pain in patients suffering from anxiety or depression, albeit the exact mechanism is not yet clear (Sharma et al., 2011). Joint pain is a diagnosis also associated with depression, and it is thought that there is a relationship of mutual amplification, i.e., the greater the pain, the more severe the depression (Miettinen et al., 2012), a finding which is in line with those of this study.

Somatization, which is characterized by the physical expression of a psychological condition, and which usually manifests as pain (Trivedi, 2004; Miettinen et al., 2012) was evaluated by the presence of non-specific physical symptoms. In this study, most patients diagnosed with severe and moderate somatization presented with myofascial pain and other joint conditions, as found in previous studies in also Brazil and Singapure populations (Manfredini et al., 2003; Ohrbach et al., 2010).

Some of the strong points of this study include: 1) the large number of patients in the sample, 2) the use of the RDC/TMD, an internationally validated questionnaire, which allows comparisons to be made with other studies, and 3) the use of a reference center for performing TMD treatment, considered a large teaching center in the region.

The limitations include the use of a convenience sample, which requires caution so as not to extrapolate the results, and the transversal analysis, which cannot establish an effect-cause relationship. It is advisable that future research use random samples and longitudinal evaluations in order to obtain more robust conclusions.

Even though no cause-effect relationship can be established, a positive association was found between variables of Axis I and II of RDC/TMD. It seems advisable that patients should be encouraged to seek early professional help for the multidisciplinary approach therapy for better global healing. Cognitive-behavioral therapy has demonstrated important therapeutic effects on TMD (Rudy, Turk, Kubinski, & Zaki, 1995; Wright et al., 2004) and conventional treatment for pain relief may be limited in some these cases (Sheng, Liu, Wang, Cui, & Zhang, 2017). Patients who actively participate in their own healing process, through self-care, show improvement more quickly, altering their overall perception of pain (Pimentel, Bonotto, & Hilgenberg-Sydney, 2018).

Conclusion

It can be concluded that myofascial pain and joint conditions(variables of Axis I) present a positive association with chronic pain-related disability, depression, and somatization (variables of Axis II). The disc displacement diagnoses had no association with Axis II.

Acknowledgement

The authors would like to thank the UFSM for the opportunity to develop the research. In addition, we express our gratitude to the participants who have devoted time and effort in support of this research.

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Notas de autor

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