DC/TMD Axis II Instruments and Their Association with MRI-Based Structural Classification of the Temporomandibular Joint and Oral Function in Female Patients with Malocclusion: A Cross-Sectional Study

Abstract

Background/Objectives: Few studies have examined the associations of the Oral Behaviors Checklist (OBC) and the Jaw Functional Limitation Scale (JFLS) of the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) Axis II with magnetic resonance imaging (MRI)-based structural characterization of the temporomandibular joint, and most have analyzed these instruments only at the scale level. We examined these associations in female patients with malocclusion in a sample that was selected without symptom-based screening and independently selected under the eligibility criteria of the present study. Methods: In this cross-sectional study, 240 female patients with malocclusion who had undergone TMJ MRI irrespective of symptoms were classified according to MRI findings into four groups: an osteoarthritis (OA) group characterized by degenerative osseous changes in the mandibular condyle, bilateral disc displacement (BDD), unilateral disc displacement (UDD), and Osseous Change/Disc Displacement negative (OC/DD (−)) groups (n = 39, 89, 53, and 59, respectively). Individual items, scale scores, and five oral function parameters were compared using the Kruskal–Wallis test followed by Dunn’s post hoc test, as appropriate. The OBC total score and the JFLS score were the primary outcomes, whereas item-level and oral function analyses were exploratory. The JFLS was analyzed as a continuous variable; for the OBC, a total score ≥ 25 defined a high oral behavior score, and odds ratios (ORs) were estimated using logistic regression. A prespecified ordered trend was evaluated using the Jonckheere–Terpstra test. Results: The OBC total score differed significantly among the four groups (p = 0.033), whereas the four-group comparison of the JFLS score did not reach statistical significance (p = 0.052). The prespecified ordered-trend test was significant for both the OBC total score and the JFLS score (p = 0.011 and p = 0.016, respectively); however, inspection of the group-specific estimates indicated that these trends were driven mainly by the OA group rather than by a graded increase across all four categories. Compared with the OC/DD (−) group, the OA group had higher odds of a high oral behavior score (OR = 2.72, 95% confidence interval [CI] 1.11–6.70), whereas the UDD and BDD groups did not differ from the OC/DD (−) group. In exploratory analyses, awake clenching (p = 0.011), chewing hard bread (p = 0.047), chewing soft food (p = 0.036), and occlusal contact area (p = 0.045) differed significantly; awake clenching was significantly higher in the OA group than in both the OC/DD (−) and UDD groups, whereas chewing hard bread, chewing soft food, and occlusal contact area differed significantly only between the OA and OC/DD (−) groups. Conclusions: The OBC total score was higher in patients with MRI-defined degenerative osseous changes in the mandibular condyle, whereas no statistically significant differences were detected between either disc displacement group and the OC/DD (−) group. Item-level differences were derived from exploratory analyses that were not adjusted for multiple testing and should be regarded as hypothesis-generating. These cross-sectional findings suggest an association between degenerative osseous change in the TMJ and Axis II measures, but do not establish a graded relationship across structural categories or a temporal or causal relationship.