Longterm Stability Following Orthognathic Surgery for Class III Using CBCT

OBJECTIVES: To quantify surgical displacements and stability after 3 years following surgical correction for Class III malocclusion using superimpositions of 3D virtual surface models. METHODS: 3D surface models of 23 patients treated with two jaw surgery and 23 treated with maxillary advancement only were built from Cone-Beam CT images taken pre-surgery (T1), 1 year post-surgery (T2) and 3 years post-surgery (T3). Surface models were superimposed through an automated voxel-wise method using the cranial base of the pre-surgery scan as reference. Measurements for each of the anatomic regions of interest (condyle, ramus, chin and maxilla) were obtained using the CMF Application (University of Bern, Switzerland). The largest displacement for each of the anatomic regions was computed from T1-T2, T1-T3 and T2-T3 by using point-to-point distances and color-coding. RESULTS: The maxillary advancement observed at 1 year post-surgery remained stable 3 years post-surgery in both groups (mean changes T2-T3 less than 1mm). Long term follow up of maxillary advancement only showed that 17.4% of the subjects had postsurgical adaptations greater than 2mm in the maxilla and autorotation of the chin, and 4.34% of the subjects had unilateral remodeling of the posterior surface of the condyle greater than 2mm. Only 4.34% of the two jaw surgery subjects had long term postsurgical adaptations greater than 2mm in the maxilla. However, displacements and remodeling greater than 2mm were observed in the chin, mandibular rami and at least one of the condyles (right or left) for 21.74% of the subjects. CONCLUSION: Bone healing at the surgical sites after orthognathic surgery is generally thought to occur primarily during the first post-operative year, but skeletal modeling /remodeling /adaptation frequently continues after all post-surgical orthodontic treatment is complete. Supported by NIH DE017727, DE018962, DE005215.