Turkish cultural adaptation, validity and reliability of the jaw functional limitation scale

"Turkish Cultural Adaptation, Validity and Reliability of the Jaw Functional Limitation Scale", Trakya University, Institute of Health Science, Department of Orthopedic Physiotherapy and Rehabilitation, Master's Thesis, Edirne, 2025. Background and Aim: Temporomandibular joint dysfunction (TMD) can lead to restricted jaw function and negatively affect individuals' daily living activities. Accurate assessment of functional limitation is essential for diagnosis and treatment planning. The Jaw Functional Limitation Scale (JFLS) is a widely used instrument for this purpose; however, no culturally adapted Turkish version exists. The aim of this study was to provide the Turkish translation of the JFLS, to perform its cultural adaptation, and to evaluate its validity and reliability properties in patients with TMD. Material and Methods: The translation and cultural adaptation process was conducted according to the Beaton guidelines. A total of 100 adults diagnosed with TMD were included in the study. Construct validity was assessed using the Kaiser–Meyer–Olkin (KMO) test, Bartlett's test of sphericity, and Exploratory Factor Analysis. Convergent validity was examined using Spearman correlation analysis with the Mandibular Function Impairment Questionnaire (MFIQ). Reliability analyses included internal consistency assessed by Cronbach's alpha and test–retest reliability assessed by Intraclass Correlation Coefficient (ICC) in a subgroup of 30 participants with a two-week interval. Results: Exploratory factor analysis revealed a three-factor structure explaining 57.7% of the total variance. A strong positive correlation was found between total JFLS scores and MFIQ scores (r = 0.885; p < 0.001). The internal consistency of the scale was high, with a Cronbach's alpha coefficient of 0.915. The test–retest reliability was excellent, with an ICC value of 0.951 for the total score. Conclusion: The Turkish version of the JFLS is a valid and reliable instrument for assessing jaw functional limitation in individuals with TMJD. Its use may contribute to the standardization of clinical evaluations and enhance assessment procedures in clinical practice. Keywords: Masticatory system, temporomandibular dysfunction, questionnaire, reliability and validity, factor analysis.