This study is a cross-sectional study. A total of 131 Korean patients (15 males, 116 females; mean age, 37.9 ± 14.7 years; age range 19–76 years) who visited the TMJ·Orofacial Pain Clinic at a tertiary medical center in from July 2019 to July 2020 were enrolled. Patients with a history of head and neck trauma within 12 months of study entry; autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, fibromyalgia, and ankylosing spondylitis; craniofacial anomalies, including cleft lip and palpate; neurodegenerative disorders; history of temporomandibular joint surgery; routine intake of antipsychotic drugs; and communication incapability were excluded. Patients who were associated with worker’s compensation such as private or public insurance were also excluded from the study owing to secondary gain.
All participants were interviewed and examined by a single TMD and orofacial pain specialist (JHK). The participants underwent an interview and a physical examination at baseline (T0) and six months after TMD management (T1). Assessments of both the roles that participants preferred to play, or had perceived themselves as playing during the decision-making process and the levels of health literacy of the participants were performed at T1.
The research protocol was reviewed and found to be in compliance with the Helsinki Declaration and was approved by the Institutional Review Board of the Ajou University Hospital (AJIRB-MED-SUR-19-261). Informed consents were obtained from all participants.
Diagnosis of the TMD and determination of the number of myofascial trigger points (TrPs)
TMD was diagnosed according to the Diagnostic Criteria for/TMD (DC/TMD) criteria . Clinical parameters, such as the extent of pain free opening and maximum unassisted opening, as well as the duration of TMD symptoms, including TMJ noise, difficulties in opening and/or closing the mouth, and pain in the jaw, temple and preauricular areas were evaluated. A visual analogue scale (VAS) and Global Chronic Pain Scale (GCPS) based on the DC/TMD axis II were applied to assess the subjective severity of the orofacial pain. Myofascial TrPs were bilaterally evaluated in the two masticatory muscles including the temporalis and masseter muscles. TrPs were determined in accordance with the criteria suggested by Simon and Travell . The parameters which were assessed by one TMD specialist (JHK) such as extent of pain free opening and maximum unassisted opening and number of active and latent TrPs in masticatory muscles were regarded as objective outcome variables. One examiner (JHK) repeated same procedures for determining extent of pain free opening and maximum unassisted opening and number of active and latent TrPs in masticatory muscles in 20 participants after 2 weeks and the data were compared using intraclass correlation coefficient (ICC) to assess the intra-examiner reliability. The ICC was 0.906 with statistical significance. The parameters which were determined by self-administered questionnaires such as VAS and GCPS scores were considered as subjective outcome variables.
To assess the confounding factors for TMD treatment, the Symptom Checklist-90-Revised (SCL-90-R)  was applied. The SCL-90-R is a tool designed to assess psychological conditions. The instrument consists of 90 questions and includes nine symptomatic dimensions, such as somatization (SOM), obsessive–compulsive (O–C), interpersonal sensitivity (I–S), depression (DEP), anxiety (ANX), hostility (HOS), phobic anxiety (PHOB), paranoid ideation (PAR), and psychoticism (PSY) and three global functioning indices, such as the global severity index, positive symptom distress index, and the positive symptom total. The T scores for the symptomatic dimensions were utilized.
Assessment of the participants’ roles in decision-making
The Control Preferences Scale (CPS) was used to evaluate the roles that participants preferred to play or had perceived themselves as playing in actual decision-making during the six months of TMD management . The CPS consists of five items that determine different roles in decision-making. Participants ranked ordered possible approaches of decision making from 1 (most active) to 5 (most passive). The perceived roles which participants had perceived during the decision-making were categorized in to 3 groups: active-A (CPS 1–2), collaborative-A (CPS 3), and passive-A (CPS 4–5) . The 5 different roles which participants preferred during the decision-making were also re-grouped into 3 groups that active-P (CPS 1–2), collaborative-P (CPS 3), and passive-P (CPS 4–5) . The evaluation of perceived and preferred role in decision-making were conducted at T1.
Measurement of health literacy
The Newest Vital Sign (NVS) was used to assess the participants’ levels of health literacy . The NVS health literacy test is based on a nutrition label from an ice cream container, and the overall score ranges from 0 to 6. Participates were categorized as having limited (NVS score of 0–2), potentially limited (NVS score of 3), and appropriate (NVS score of 4–6). The assessment of level of health literacy was performed at T1.
Management of TMD
The participants who performed stabilization splint therapy and physical therapy for six months to manage the orofacial pain and parafunctional habits for six months were included in the study. The participants who showed limited range of jaw movement owing to disc displacement, sustained pain around masticatory muscles or preauricular area despite of 2 weeks of treatments including medication and habit control, and pathologic bony changes on TMJ condyles were prescribed stabilization splint therapy. All participants were instructed to wear their stabilization splints every night for at least seven hours per day during the treatment period. All participants were instructed to control for TMD-related contributing factors including excessive parafunctional habits, masticatory muscle tension, and conduct routine physical therapy such as 6 × 6 exercises  and moist hot pack application. The stabilization splint which covered all of the maxillary teeth was fabricated in acrylic resin. Even uniform contact of the stabilization splint with the lower functional cusps was provided at premolar and molar teeth sites. Continuous wearing of stabilization splint more than seven hours per day was regarded as valid wearing and considered as compliant with stabilization splint therapy. All participants visited the clinic monthly for routine check-ups and confirmation of compliance.
Power analysis indicated that a total sample size of 131 participants in the F test with 3 groups and 2 times repetitions would provide a statistical power of 92.1% at a 0.05 significance level with an effect size of 0.25. Based on the Shapiro–Wilk normality test, the data were found to be normally distributed; therefore, parametric tests were applied.
To compare the differences of demographic characteristics and parameters related with TMD of the participants including age, sex distribution, body mass index (BMI), education level, and classification of TMD based on DC/TMD criteria, duration of TMD, amount of pain free opening and maximum unassisted opening, number of active and latent TrPs in masticatory muscles, GCPS, and VAS among three groups, Acitve A, Collaborate-A, and Passive-A, one-way analysis of variance (ANOVA) and chi-square test were applied for continuous and categorical variables, respectively. Chi-square test was used to determine statistical differences of levels of preferred and perceived level of decision-making role and educational level accordance with the levels of health literacy. To estimate the responses of differences of the subjective and objective TMD treatment outcomes in accordance with the perceived role in decision-making, two-way repeated measure ANOVA was applied.