Patient Adherence to Splint Therapy and Counselling Programmes in Temporomandibular Disorders: Development and Validation of a New Questionnaire

BACKGROUND: Adherence to conservative treatments is essential for optimal outcomes in temporomandibular disorder (TMD) patients, yet validated tools for measuring adherence are lacking. PURPOSE: This study aimed to develop and validate a bilingual (Arabic-English) questionnaire to comprehensively assess adherence among TMD patients. STUDY DESIGN, SETTING, SAMPLE: A cross-sectional, observational, five-phase design was conducted at the Oral and Maxillofacial Surgery Department, Faculty of Dentistry, Mansoura University (Egypt). The study included a pilot sample of 60 TMD patients and a psychometric evaluation sample of 300 patients. EXPOSURE: The exposure was adherence behaviour, measured by a newly developed 50-item, 11-domain adherence questionnaire. MAIN OUTCOME VARIABLE(S): The primary outcomes were psychometric properties of the questionnaire, including content validity, internal consistency, test-retest reliability and construct validity. COVARIATES: Patient language version (Arabic or English) was considered to examine potential influences on questionnaire performance. ANALYSES: Content validity was assessed using Item-Content Validity Index (I-CVI) and Content Validity Ratio (CVR). Reliability was evaluated with Cronbach's α and intra-class correlation coefficient (ICC). Construct validity was examined with exploratory factor analysis (EFA). RESULTS: The final 50-item, 11-domain questionnaire demonstrated strong content validity. Internal consistency was acceptable for both Arabic (Cronbach's α = 0.70) and English (α = 0.68) versions. Test-retest reliability was good (ICC = 0.762-0.898; p < 0.001). EFA confirmed 11 domains, accounting for 61.5% of variance in Arabic and 64.73% in English. CONCLUSIONS AND RELEVANCE: The Badawy and Haggag Adherence Questionnaire for TMD demonstrated strong validity and reliability across Arabic and English versions. It provides a robust clinical and research tool for assessing adherence to conservative TMD management, enabling clinicians to identify non-adherence and design tailored interventions to improve outcomes. TRIAL REGISTRATION: ClinicalTrials.gov ID NCT07045441. The trial was first posted on 22 June 2025, and the most recent update was posted on 30 June 2025. Retrospectively registered.