Comparison of 3D Computer-assisted Virtual Planning and Articulated Model Planning for Bimaxillary Orthognathic Surgery
Materials and methods: Surgical records for this retrospective study were gathered for ten patients who previously underwent bimaxillary orthognathic surgery at our institution. Standard records included intra- and extraoral photos, cone beam computed tomogram (CBCT), and two-dimensional virtual treatment objective using Dolphin Imaging®. Also, two sets of dental models were mounted on a semi-adjustable articulator using a facebow transfer and centric relation (CR) record obtained by the principle investigator. A standard mounting protocol was used that ensured accurate capture of the occlusal plane angle. Model surgery was performed for surgical splint fabrication. Subsequent to surgery, the cut and uncut models were remounted on the same articulator to create a new CR record, and an intermediate and final splint for each case. These records were made using polyvinylsiloxane bite registration material. Maxilla-first surgery was always performed. The 3D changes in the molar, canine and incisor positions for the maxilla and mandible were measured using an Erickson model block. The principle investigator performed all measurements. All relevant records were then sent to MedCAD® for virtual planning. CBCT data, dental models and the CR record were used to create a 3D composite model. Clinical photos and measurements were provided for model orientation. FreeForm Modeling® and Dolphin Imaging® software were used to perform virtual surgery per MedCAD’s routine protocol. The intermediate and final splints were used to position the maxillary and mandibular models into their new positions. GeoMagic Studio®software was used for this registration. The final registered models were imported into Dolphin and autorotation was performed appropriately to make the vertical incisor change coincident with the vertical change in the articulated model surgery. 3D changes were measured for comparison with articulated model moves. The same engineer performed all modeling and was blinded to the articulated model moves.
Methods of data analysis: The maximum difference, mean difference and standard error between the two methods were calculated in three dimensions.
Results: The surgical movements in the anteroposterior dimension ranged from 3.5 mm to 8.3 mm at the maxillary incisor and -4.0 mm to 12.0 mm at the mandibular incisor. The vertical movement at the maxillary incisor ranged from -2.4 mm to 2.0 mm. The maximum differences between the two methods in the anteroposterior, vertical and transverse dimensions were 1.2 mm, 1.6 mm, 0.9 mm respectively for both jaws. The mean differences and standard errors between the two methods for anteroposterior, vertical and transverse dimensions in the maxillary arch were 0.4 mm (0.04), 0.3 mm (0.04) and 0.3 mm (0.04) respectively. The mean differences and standard errors for anteroposterior, vertical and transverse dimensions in the mandibular arch were 0.4 mm (0.05), 0.5 mm (0.08) and 0.4 mm (0.05) respectively.
Conclusions: The overall difference in 3D dental movements between the articulated model and virtual planning methods was minimal and clinically insignificant. Computer-assisted virtual planning with MedCAD’s current protocol seems like a reasonable alternative for planning surgical movements.
References:
- Xia J, Ip HH, Samman N, et al: Computer-assisted three-dimensional surgical planning and simulation: 3D virtual osteotomy. Int J Oral Maxillofac Surg, 2000. 29(1): 11-7.
- Swennen GR, Mollemans W, Schutyser F: Three-dimensional treatment planning of orthognathic surgery in the era of virtual imaging. J Oral Maxillofac Surg, 2009. 67(10): 2080-92.