Three-Dimensional Facial Changes in Correlation with Sagittal Jaw Movements in Skeletal Class Iii Patients

Objectives: The decision which orthognathic procedure is the best for a good aesthetic result is not always straightforward. The aim of our prospective study was to verify whether facial changes occur within those regions not directly affected by movements of the underlying bones and to evaluate the postoperative 3D facial changes in correlation with sagittal jaw movements in skeletal Class III (SCIII) patients.

Methods: In 84 SCIII patients; one piece Le Fort I advancement only (N=18), set back of mandible only (N=38) or both procedures (N=28) were performed. Post-operative soft tissue changes were registered as regional best-fits on the areas of the foreheads and orbits on optical 3D scans, whilst lateral cephalograms were superimposed to assess sagittal jaw movements. We modelled soft tissue changes by linear regression with maxillary (point A) and mandibulary (point B) sagittal movements as predictors. The shell to shell differences were measured and the average distances between the observed regions were calculated.

Results: We found the highest values of regression coefficients for the sagittal jaw movements within the regions of the upper and lower lips. These values were around 0.5, which meant that for each mm of maxillary advancement and mandibulary set-back, the soft tissue moved for 0.5mm. In side regions of the face the regression coefficients were between 0.1 and 0.3. According to expectations, those changes were greatest in the regions where the underlying bones had been moved but, regardless of the operation performed, changes were found over the whole face.

Conclusions: Facial soft tissue changes due to bone movements were smaller as we expected. Changes of the nose, cheek and upper lip regions in the BSSO group, in the lower lip and chin region in Le Fort I group confirmed the concept of the facial soft tissue mask acting as one unit.