The aim of this study was to investigate the effects of temporomandibular joint dysfunction (TMJD) on pain, quality of life and psychological status.

A total of one hundred twenty people participated in the study, sixty with TMJD symptoms (according to the Research Diagnostic Criteria for Temporomandibular Disorders) and sixty without TMJD symptoms. The severity of temporomandibular joint (TMJ) pain and headache was assessed using a visual analog scale (VAS), pain threshold using an algometer, anxiety and depression levels with the Hospital Anxiety and Depression Scale (HADS), and the quality of life level was assessed by Short Form-36 (SF-36).

Treatment of TMJD with appropriate therapies and psychological support techniques may reduce TMJD symptoms and improve patients' quality of life and psychological status.

Temporomandibular joint dysfunction (TMJD) occurs as a result of the impaired functioning of the structures of the masticatory system. This disruption affects the chewing muscles, temporomandibular joint (TMJ), and related structures around the joint. TMJD can produce signs and symptoms, including pain in the TMJ and chewing muscles, restricted mouth opening, and articular sounds such as clicking and/or crepitus. Other symptoms include TMJ pain, limitation in joint movements, difficulty in chewing, jaw locking (trismus), lateral deviation of the jaw, tenderness in the TMJ and chewing muscles, tinnitus and pain, dizziness, and head and neck pain.

However, to the best of the investigator's knowledge, no previous studies have examined the relationship between quality of life, pain, and psychological status in individuals with TMJD. This study was designed to investigate whether a relationship between pain, quality of life, and psychological status in individuals with TMJD and asymptomatic individuals without TMJD.

One hundred twenty individuals were included in this study performed between March and July 2017 at the Gazi University and Ankara Yıldırım Beyazıt University Dentistry Faculties, Turkey. The research was designed as a controlled, observational, cross-sectional study. Sixty of the 165 individuals presenting with TMJD symptoms were diagnosed with TMJD by a specialist dentist, and those meeting the inclusion criteria were enrolled in the first group. Sixty individuals who met the inclusion criteria out of 143 individuals who did not exhibit TMJD symptoms were enrolled in the second group. These two groups were established based on clinical and radiological examination results. TMJD was diagnosed by professional and experienced dentists using the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD). RDC/TMD has been described as the gold standard physical examination method in the clinical diagnosis of TMD.

Individuals agreeing to take part in the study were included after signing informed consent forms. Ethical committee permission was granted by the Ankara Yıldırım Beyazıt University Social and Humanities Ethics Committee (date: 02.08.2016, no: 356).

Individuals who were able to understand and speak Turkish and cooperate, and aged 17 years or older were included in the study.

Inclusion criteria for Group 1 were articular sounds in the form of clicks or crepitation from the TMJ during mouth opening or chewing, sensitivity and pain in the TMJ at palpation, no treatment for the TMJ in the previous six months, and presence of TMJD symptoms for at least three months. Inclusion criteria for Group 2, maximum mouth opening exceeding 30 mm, absence of articular sounds such as TMJ click or crepitation during mouth opening and closing and/or chewing activity, and absence of tenderness and pain in the TMJ and chewing muscles at palpation.

Exclusion criteria for Group 1 were the absence of at least one of the TMJD symptoms, absence of diagnosis of TMJD and the presence of a history of tumor, cervical discopathy, orthopedic and rheumatic pathologies, head, neck and/or jaw surgery and pregnancy.

Exclusion criteria for Group 2 were the presence of at least one of the symptoms of TMJD, the presence of a history of tumor, cervical discopathy, orthopedic and rheumatic pathologies, head, neck and/or jaw surgery, and pregnancy.

G * Power (V.3.1.9.2, Germany) software was used to calculate the sample size. Analyses were performed to investigate significant differences in the pressure pain threshold (PTT), quality of life, and psychological evaluation results between the groups (α = 0.05 and β = 0.20). The analysis showed that at least 19 individuals in each group and at least 38 individuals in total would be sufficient.

Socio-demographic (age, sex, height, weight, educational status) and clinical data (history of bruxism, dominant side, side of the problem, duration of symptoms, dominant chewing side, sleeping position, tinnitus/pain, chewing difficulty, and parafunctional oral habits status) of individuals meeting the inclusion criteria were recorded onto an evaluation form.

Individuals in both groups were asked to mark TMJ pain and headache on a 10 cm straight line using a visual analog scale (VAS), and the results were recorded in cm. Patients were asked about pain in bilateral resting and mobile positions of the TMJ. On the VAS scale, "0" indicates no pain, and "10" the most severe pain possible.

Muscle sensitivity was measured using an algometer (Baseline® dolorimeter/algometer, Pain Diagnosis, and Treatment Inc., Great Neck, NY, USA). The algometer is pressed gradually to the area where the sensitivity is to be measured, and the measurement is terminated as soon as the subject experiences pain. The PPTs of the anterior part of the temporalis muscle, the TMJ lateral capsule, and the masseter muscle were measured in the present study. Measurements were performed three times at 30-second intervals on both right and left sides. The mean values of the three measurements were recorded. PPT is defined as the lowest pressure force required to be applied to the tissue for the pain to occur. Results are expressed as kg/cm2.

The Hospital Anxiety and Depression Scale (HADS) was used to measure participants' anxiety and depression levels. The HADS scale was developed by Zigmond and Snaith and contains 14, with two sub-scales, one of seven questions (odd numbers) measuring anxiety, and another of seven questions (even numbers) measuring depression. Aydemir et al. conducted the Turkish validity and reliability study of HADS. Each question is scored between 0 and 3. The lowest possible scores for the depression and anxiety subscales were 0, and the maximum possible scores were 21. Subjects' depression and anxiety status are evaluated as normal/no symptoms (0-7 points), borderline abnormal/suspicious (8-10 points), and abnormal/definite (11-21 points), depending on the scores obtained.

Short Form-36 (SF-36) was used to assess the quality of life. Ware et al. developed the SF-36 in 1987 to determine overall health-related life quality. The scale consists of 36 questions and evaluates life quality in the previous four weeks in eight subscales and two main components. The subscales are; Physical Function (PF), Role Difficulty-Physical (RP), Body Pain (BP), General Health (GH), Vitality (V), Social Function (SF), Role Difficulty-Emotional (RE), and Mental Health (MH), while the main components are Physical Component Score (PCS) and Mental Component Score (MCS). The eight subscales assess health from 0 to 100 points. "0" indicates that health-related quality of life is poor, and 100 indicates the best possible quality of life, so higher scores indicate better quality of life. SF-36 was translated into Turkish by Koçyiğit et al. and has been subjected to validity and reliability studies.

The distributions of continuous variables such as age, body mass index (BMI), and SF-36 scores were examined using the Shapiro-Wilk test and normality graphs. Mean ± standard deviation (mean ± sd) and median (min-max: minimum-maximum) were used to express all continuous variables, while results for categorical variables such as gender and occupation were expressed as percentages (%). The independent samples t-test and Mann-Whitney U test were applied to determine the distribution of continuous variables such as SF-36 and HADS scores between groups 1 and 2. The relationship between the scale scores and pain threshold and pain severity was analyzed using Pearson and Spearman correlation analysis. The consistency of responses to SF-36 and HADS was examined using Cronbach's alpha coefficient. Statistical significance was set at p <0.05. All statistical analyses and calculations were performed on IBM SPSS Statistics 21.0 software (IBM Corp. Released 2012. IBM SPSS Statistics for Windows, Armonk, NY: IBM Corp., USA).

Inclusion Criteria:

For Group 1 (group with TMJD):

• Patients diagnosed with TMJD
• Able to understand and speak Turkish and cooperate
• Aged 17 years or older and 65 years or younger
• Patients have articular sounds in the form of clicks or crepitation from the TMJ during mouth opening or chewing
• Sensitivity and pain in the TMJ at palpation
• Not receiving TMJ treatment in the past six months
• Presence of TMJD symptoms for at least three months For Group 2 (group without TMJD)
• Able to understand and speak Turkish and cooperate
• Aged 17 years or aged 17 years or older and 65 years or younger
• Maximum mouth opening 30 mm or more
• Absence of articular sounds such as TMJ click or crepitation during mouth opening and closing and/or chewing activity.
• Absence of tenderness and pain in the TMJ and chewing muscles at palpation

Exclusion Criteria:

For Group 1 (group with TMJD):

• Absence of at least one of the TMJD symptoms
• Presence of a history of tumor, cervical discopathy, orthopedic and rheumatic pathologies, head, neck and/or jaw surgery and pregnancy For Group 2 (group without TMJD)
• Presence of at least one of the symptoms of TMJD
• Presence of a history of tumor, cervical discopathy, orthopedic and rheumatic pathologies, head, neck and/or jaw surgery and pregnancy

Group 1 (60 patients, group with TMJD) consists of patients diagnosed with TMJD according to the Research Diagnostic Criteria for Temporomandibular Disorders by a specialist and experienced dentist in TMJD.

Group 2 (60 healthy individuals, group without TMJD) consists of individuals who are evaluated by a specialist and experienced dentist in TMJD and who do not show symptoms of TMJD.