Objective: To investigate the relationship between centric relation-maximum intercuspation (CR-MI) discrepancy and temporomandibular joint dysfunction (TMD) in pre-treated orthodontic patients.
Material and methods: The study involved an experimental group of 107 pre-treated orthodontic patients with signs and symptoms of TMD aged 18-32 years, and a control group of 70 students with no signs and symptoms of TMD aged 20-30 years. The psychological condition of subjects was evaluated using two standard questionnaires, and a clinical examination performed to assess masticatory musculature and temporomandibular joint (TMJ) function, and to establish the presence or absence of TMD. Helkimo indices, the anamnestic dysfunction index (Ai) and the clinical dysfunction index (Di), were determined. Dental casts were mounted on a semi-adjustable articulator in CR using a CR bite record taken by bilateral manipulation and verified by load testing and face bow records. Differences in condylar position between CR and MI in the three planes of space were determined using the condyle position indicator.
Results: A positive CR-MI discrepancy, defined as a discrepancy exceeding 1 mm in the vertical or horizontal planes or 0.5 mm in the transverse plane, was found in 72.9% of the experimental and 11.4% of the control group. Comparison of the groups showed a significant difference (χ² = 22.67, P < 0.001). CR-MI discrepancy was significantly correlated with Di and Ai in all subjects (P < 0.01).
Conclusions: There was CR-MI discrepancy in most of the pre-treated patients with signs and symptoms of TMD. This discrepancy may be a contributory factor to the development of TMD in these patients.