Cone-beam computed tomography evaluation on the changes in condylar long axis according to asymmetric setback in...

To determine whether the condylar rotation is affected by asymmetric setback in patients undergoing sagittal split ramus osteotomy.

Thirty patients who underwent bilateral sagittal split ramus osteotomy setback surgery were divided into the two groups, symmetric setback and asymmetric setback, according to the right/left difference of setback amount (<2.0, ≥2.0 mm). Condylar long axis changes were evaluated using the three-dimensional superimposition of before and immediately after surgery cone-beam computed tomography volume images. Evaluations were performed separately in lesser setback and greater setback side in patients undergoing asymmetric setback, whereas both side condyles were evaluated together in patients undergoing symmetric setback. Condylar axis changes on axial view were correlated with setback amount or right/left setback difference using Pearson correlation analysis.

In general, the condylar axis change occurred in a pattern of inward rotation. The condyles in patients undergoing symmetric setback showed 3.4° rotation in average. In case of asymmetric setback, the lesser setback side showed larger value (4.3°) than the greater setback side (2.3°) with a statistical significance. In the correlation analysis, setback amount showed no significant correlation with the condylar axis changes in both groups. However, correlation with right/left setback difference showed a positive correlation in lesser setback side of patients undergoing asymmetric setback.

The findings of this study indicate that large amount of setback alone does not contribute to the change in condylar long axis, but asymmetric setback might cause a change in condylar long axis, particularly on the lesser setback side.