Condylar volume changes in class II division 2 cases treated with unlocking the mandible using clear aligners

Class II Division 2 malocclusion involves retroclined maxillary incisors and deep overbite, often accompanied by mandibular retrusion. "Unlocking" the mandible by proclining the maxillary incisors, correcting the deep bite, and expanding the maxillary arch has been used to treat this malocclusion. However, the impact of this treatment, using Invisalign® clear aligners, on condylar volume remains unclear. This study evaluates three-dimensional changes in condylar volume after using Invisalign® to unlock the mandible in Class II Division 2 growing patients.

Cone-beam computed tomography (CBCT) data were collected from 22 adolescent patients (11 in the treatment group; 11 in the control group) at T1 (pre-treatment) and T2 (1.5-2 years post-T1). Dolphin imaging software was used for cephalometric tracing, while 3D Slicer and ITK-SNAP software calculated condylar volume. Repeated measure ANOVA compared condylar volume changes, and Pearson's Correlation Coefficient assessed the relationship between condylar volume change and ANB angle in the treatment group.

Both groups showed significant condylar volume increases between T1 and T2 (treatment: P < 0.001, 127.45 ± 30.97, control: P = 0.015, 98.8 ± 36.31), with no significant difference between groups at T1 (P = 0.289, 89.19 ± 81.2) or T2 (P = 0.167, 117.9 ± 81.7). The change in ANB angle did not correlate with the condylar volume increase in the treatment group (Pearson's R = -0.15, P = 0.681).

Unlocking the mandible successfully corrected Class II Division 2 malocclusion, but condylar volume increases in both groups were likely due to normal growth rather than treatment. Condylar volume change was not correlated with malocclusion correction.