Shape Analysis of Stability following Skeletal Class III Surgery

OBJECTIVES: To localize and quantify surgical displacements and stability 1 year following surgical correction for Class III malocclusion, using superimpositions of 3D virtual surface models and shape correspondence methods. METHODS: 3D surface models of 17 Class III patients treated with two jaw surgery were built from Cone-Beam CT images taken pre-surgery, at splint removal and 1 year post-surgery. Surface models were superimposed through a fully automated voxel-wise method using the cranial base of the pre-surgery scan as reference. Shape correspondence was computed to quantify bone remodeling and stability of surgical correction. Measurements of longitudinal changes included 3D signed distances and vectors of bone changes obtained at each anatomic region of interest. Color maps were used to visualize rotational displacements and localize the regions of surface remodeling. RESULTS: Measurements of all surgical displacements revealed that the vectors of maxillary advancement were in average 5.56 +/-1.65 mm and the average chin position setback was 5.86 +/- 2.87mm. The findings 1 year post-surgery revealed stability of the maxillary advancement (average 4.89 +/- 1.28mm. but chin changes compared to pre-surgery were 3.99 +/- 1.28mm. Condylar changes at all time points were in average < 1mm, however variability in ramus displacements with surgery and post-surgical adaptations were >2mm for 9 patients and >4mm for 4 patients. CONCLUSIONS: These preliminary findings indicate that in two jaw surgery for Class III correction maxillary advancement is stable, but mandibular setback shows considerable individual variability in the stability of the correction 1 year post-surgery. Nearly half of the patients had >2mm forward displacement changes in chin position from splint removal to one year follow-up, and that even in two jaw surgery undesirable rotational movements are often observed at the mandibular ramus.

SUPPORT: NIDCR DE017727, DE018962, DE005215 and NCRR UL1RR025847.