The relationship between curve of Spee modification and changes in temporomandibular joint parameters: a CBCT-based study

The Curve of Spee (COS) is a critical aspect of occlusal anatomy that influences dental alignment and masticatory function. This study aims to evaluate whether COS modifications correlate with temporomandibular joint (TMJ) parameter changes following clear aligner therapy, and compare TMJ adaptations between patients with different initial COS depths. 50 adult patients with skeletal Class I and Class II malocclusions that underwent clear aligner orthodontic treatment were identified and divided into two groups based on their initial curve of Spee (COS) measurement. Group1: COS < 2 mm, and Group2: COS ≥ 2 mm. Pre- and post-treatment cone-beam computed tomography (CBCT) scans were used to construct three-dimensional digital models and evaluate TMJ parameters for accurate measurements. Statistically significant changes were found in posterior joint space (PJS) for Group 1 (p = 0.033) and condylar length (CL) for Group 2 (p = 0.006). Independent samples t-test revealed significant differences in CL change scores (p = 0.024) between the two groups. There is a significant association between COS modification and PJS changes (p = 0.043), suggesting that COS modification influences posterior joint space. Clear aligner therapy induces distinct TMJ adaptations depending on initial COS depth: mild COS cases (< 2 mm) exhibit posterior joint space reduction, indicating condylar positional adaptation, while deep COS cases (≥ 2 mm) demonstrate condylar lengthening, suggesting osseous remodeling. However, changes in TMJ parameters remain within physiological limits.