Role of Virtual Surgical Planning in Increased Predictability of Orthognathic Surgery

Success of orthognathic surgery depends not only on the technical aspects of the operation but to a larger extent on the formulation of a precise surgical plan, consistency and capability of achieving predictable, stable results. Traditionally, 2-dimensional cephalometry has been utilized for the planning and postoperative evaluation of orthognathic surgery. However, there are several limitations that are associated with traditional 2-dimensional cephalometry such as inability to measure many important parameters on plain cephalograms, and inability to measure post surgical surface volume difference of maxillofacial reconstruction.

This study conducted a retrospective evaluation of treatment outcomes by comparing single-jaw and double- jaw orthognathic surgery using superimpositioning of CT scans. Three dimensional (3D) imaging based planning systems enable the surgeon to establish necessary osteotomy planes preoperatively. The virtual surgical approach allows the clinician to assess different surgical scenarios. Of practical importance is the assessment of postsurgical outcomes to the planned outcome. Pre-surgical predictions may not necessarily reflect the actual surgical outcomes; therefore accuracy of our surgical outcomes needs to be assessed.

30 patients were selected as candidates for analysis who underwent orthognathic surgery at Case Western Reserve University, University Hospitals in Cleveland, Ohio between June 2009 and November 2014. Inclusion criteria were presence of pre-operative CBCT scans, virtual surgical planning, cad-cam splint fabrication, lefort I osteotomy and bilateral sagittal split osteotom, post operative CBCT scanning within 1 week post – surgery. Exclusion criteria were patients who required prosthetic joint replacement. 24 patients were selected for final analysis. Patients received a standard Orthognathic workup including alginate impressions, occlusion in centric relation, facebow analysis, photographs, and intraoral soft tissue measurements. Scanning was completed using CB Mercuary from Hitachi with 0.37 voxel size of 512 slices. Copy of stone models and photographs were uploaded to the medical modeling technicians. A virtual meeting was held to discuss surgical plan. Bite splints were fabricated by medical modeling and used perioperatively. Post-surgical imaging was obtained at one week follow up. Comparison was completed by superimposition of planned to actual CBCT using Dolphin software.

Outcome data was assessed by calculating mean distance difference (MDD) over A-point, maxillary left molar, maxillary right molar, B-point, and mandibular left molar. ANOVA model was used to calculate the difference between planned surgical outcomes to actual surgical outcome. A-point MDD was 1.75mm with SD=1.48. Maxillary left molar MDD was 2.04mm with SD=1.17. Upper right molar distance was 2.11mm with SD=1.29. B point MDD was 1.68mm with SD=1.40. Mandibular left molar MDD was 1.59mm with SD-0.87. ANOVA analysis found p=0.75.

Preliminary findings of the study reveal no statistically significant differences between virtually planned surgical treatments and the actual outcomes. Tucker et al have shown that differences of less than 2mm have been shown to be not clinically significant. Our mean differences ranged from 1.75 mm to 2.11 mm. We believe that successful reproduction of pre-surgical plans in the current study proves virtual surgical planning’s potential to increase predictability in orthognathic surgery. We assess that our post surgical outcome has variance in anticipated distance moved with Lefort I osteotomies and bilateral sagittal split osteotomies. By comparing our planned to our surgical outcome via superimposition of CBCT scans, we can reflect and learn how to modify surgical techniques to achieve the ideal plan.

 

1. Tucker, Scott, Lucia Helena Soares Cevidanes, Martin Styner, Hyungmin Kim, Mauricio Reyes, William Proffit, and Timothy Turvey. "Comparison of Actual Surgical Outcomes and 3-Dimensional Surgical Simulations." Journal of Oral and Maxillofacial Surgery (2010): 2412-421.
2. Swennen, Gwen R.j., Wouter Mollemans, and Filip Schutyser. "Three-Dimensional Treatment Planning of Orthognathic Surgery in the Era of Virtual Imaging." Journal of Oral and Maxillofacial Surgery (2009): 2080-092. Web. 13 Mar. 2015.