Validity and reliability of the Turkish version of the 8-item jaw functional limitation scale

Considering that temporomandibular disorder (TMD) can negatively affect individuals' general health and quality of life by limiting orofacial functions, it is important to evaluate jaw-related functional limitations in TMD. This study aimed to investigate the psychometric properties of the Turkish version of the 8-item Jaw Functional Limitation Scale (JFLS-8-TR) in Turkish-speaking TMD patients.

A total of 162 patients with TMD and 114 individuals without TMD participated in the study. Face and content validity were assessed. To confirm the construct validity of the JFLS-8-TR, structural (with confirmatory factor analysis (CFA)), convergent (with pain severity and maximum mouth opening (MMO), Oral Health Impact Profile (OHIP-14), Fonseca Anamnestic Index (FAI) and the Turkish version of the 20-item JFLS (JFLS-20-TR)) and known-group validity were analyzed. Cronbach's alpha and intraclass correlation coefficient (ICC) were calculated to examine internal consistency and test-retest reliability.

Both content and face validity were met. The acceptable model fit indices based on CFA confirmed the structural validity of the JFLS-8-TR. Robust associations between the JFLS-8-TR score and pain intensity (r = 0.92), MMO (r = -0.87) and scores on the FAI (r = 0.89), OHIP-14 (r = 0.86) and JFLS-20-TR (r = 0.96) supported the convergent validity (p < 0.05). The JFLS-8-TR was able to discriminate between individuals with and without TMD, indicating that it has known-group validity (p < 0.05). The internal consistency (Cronbach's alpha = 0.91) and test-retest reliability (ICC = 0.93) of the JFLS-8-TR were excellent.

The JFLS-8-TR is a valid, reliable and useful instrument for a more practical assessment of functional limitations in the masticatory system in Turkish-speaking TMD patients.