Study design and participants
This research is a cross-sectional, comparative study conducted between September 2021 and January 2022 at a large urban hospital center (Shahid Beheshti hospital), Qom, Iran. The study protocols were designed according to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement.
We recruited a random sample of RA patients diagnosed with RA from the Shahid Beheshti hospital rheumatology clinic during the study period by expert attends of the rheumatology department. The inclusion criteria were age>18 years and consent for participation. We excluded RA patients with other rheumatologic, systemic or autoimmune diseases, active infection, inflammatory conditions, endocrine disorders or malignancies and pre-existing oral disorders unrelated to RA. The patients who had one of the mentioned conditions were excluded according to the consultation and evaluation by the second specialist. The control group was selected from a random sample of parents who visited the vaccination clinic of the same hospital to give their children routine vaccination shots. The controls were matched for gender and age ± two years.
The participants were examined and interviewed by one expert rheumatologist and one expert dentist for demographic (age, gender, education, employment status, marital status), medical history, and clinical data. The medical and clinical data included disease duration and severity, oral and dental examination, temporomandibular disease examination, oral health-related quality of life assessment, medication history and laboratory data. Informed consent was taken from all participants.
Diagnosing and severity assessment of RA
The patients were diagnosed with RA according to ACR/EULAR 2010 criteria for rheumatoid arthritis classification be an expert rheumatologist(12). We used DAS28 (13) score to label RA activity in patients to remission (DAS28 < 2.6), low (2.6 ≤ DAS28 < 3.2), moderate ( 3.2 ≤ DAS28 ≤ 5.1) and high (5.1< DAS28). DAS28 score was calculated using the "das-score" online calculator(14) based on four measures, including the number of tender joints, the number of swollen joints, the blood level of ESR(mm/hr) and visual analog scale (VAS) of patient's general health (mm).
Oral health-related quality of life assessment
We used Oral Health Impact Profile (OHIP-14) during interviews to assess the participants' oral health-related quality of life. The validated version of OHIP-14 consists of 14 items in seven dimensions: functional limitation, physical discomfort, psychological discomfort, physical disability, psychological disability, social disability, and handicap(15). The score for each item is recorded in the form of a Likert scale: 0(never), 1(hardly ever), 2(occasionally), 3(fairly often) and 4(very often). The OHIP-14 sum score is the sum of all items ranging from 0 to 56; The OHIP-14 extent score is the total number of questions that had scores 3 or 4(fairly often and very often) ranging from 0 to 12 (16). Higher scores of OHIP-14 represent a higher overall burden of oral health-related quality of life.
Oral health examination and temporomandibular joint disorders
One expert dentist and one rheumatologist examined and interviewed patients for dental health and temporomandibular disorders (TMD). The dental examination consisted of the number of decayed, missing and filled teeth represented as DMFT (sum of all three measures). The TMD was measured using a researcher-designed questionnaire with 13 items that demonstrate the patient's extent of discomfort (Supplementary Table 1). The questions are subject to different aspects of TMD, including clicks, discomfort, pain, limitation in movement, chewing, and swallowing. The questions are in the form of a Likert scale with scores of 0(never), 1(sometimes), 2(often) and 3(always). The total TMD score ranges from 0 to 52, and a higher score represents a higher extent of TMD.
Blood samples were taken during the last visit and were analyzed to determine the erythrocyte sedimentation rate (ESR), C- reactive protein (CRP), rheumatoid factor (RF), anti-CCP antibody.
The risk of bias for the clinical judgment was limited by the clinician's judgment according to ACR/EULAR system. Laboratory tests were also analyzed in an exclusive laboratory in Shahid Beheshti hospital. If participants had inconsistent clinical and paraclinical assessments, the participant was re-assessed for a second time, and the latter was reported.
Continuous variables were presented as mean ± standard deviation (SD), and categorical variables were described in frequency and percentage in the form of tables. Categorical variables were compared between groups using Fischer's Exact test. Preliminary analyses showed no outliers, as assessed by boxplot. The continuous variables were tested for normality using the Shapiro–Wilk's test; data that did not meet assumptions for parametric tests, including variables without normal distribution (Shapiro–Wilk's test (p < 0.05)) were compared between two independent groups with Mann-Whitney U test and between more than two groups with Kruskal-Wallis test.; the Man-Whitney U test assumption of equal distribution were tested by using Levene's test for equality of variances based on median and with an adjusted degree of freedom. To detect correlations between clinical and medical variables and disease activity (DAS-28 score) in RA patients, Spearman's rank correlation coefficient was applied with and without adjustment for DMFT. According to Cohen 1988, the effect size of correlations was interpreted as small (0.1– 0.3), medium (0.3–0.5) or large (> 0.5)(17). Statistical analysis was performed using SPSS, Version 26.0 (SPSS Inc., USA.).