A three-dimensional analysis of soft and hard tissue changes after a mandibular setback surgery

Area of Science:

• Oral and Maxillofacial Surgery
• Medical Imaging
• Biomechanical Analysis

Background:

• Mandibular setback surgery corrects skeletal Class III malocclusion.
• Accurate assessment of soft and hard tissue changes is crucial.
• Existing 2D cephalometric analysis has limitations in capturing complex 3D facial morphology.

Purpose of the Study:

• To develop and validate a novel three-dimensional (3D) registration and analysis method for evaluating soft and hard tissue changes after mandibular setback surgery.
• To compare 3D analysis findings with traditional 2D cephalometric data.
• To investigate the ratio of soft tissue movement to bone movement in different facial planes.

Main Methods:

• A 3D registration method was developed using cephalometric landmarks on pre- and post-operative CT scans.
• A universal 3D coordinate system and a coronal plane grid were established for standardized analysis.
• Bone and soft tissue changes were quantified by comparing coordinate values of intersected points between pre- and post-operative models.

Main Results:

• Facial surface changes extended beyond the mandible to the mouth corner region.
• Soft tissue changes at the mid-sagittal plane were 77-102% of bone changes (p<0.05).
• Other sagittal planes showed similar patterns with decreased soft tissue to bone movement ratios.

Conclusions:

• The proposed 3D analysis method accurately reflects soft and hard tissue changes after mandibular setback surgery.
• The findings align with established 2D cephalometric knowledge and clinical expectations.
• This 3D approach is potentially applicable to various oral, maxillofacial, and plastic surgeries.