Accuracy of Intentional Change of Frontal Ramal Inclination From Virtual to Actual Orthognathic Surgery Using Computer-Aided Design and Computer-Aided Manufacturing-Made Customized Metal Plates

Objective: To evaluate the accuracy of intentional change of the frontal ramal inclination (FRI) from virtual to actual orthognathic surgery. Materials and Methods: A total of 16 patients who underwent orthognathic surgery for correction of facial asymmetry and took cone-beam computed tomography 2 to 3 weeks before surgery (T-0) and 3 days after surgery (T-1A) were selected. After reorientation of cone-beam computed tomography, the digital imaging and communications in medicine data was converted to StereoLithography format for the merging with dental cast scan using R2GATE software (MegaGen Implant, Daegu, Republic of Korea). During virtual surgery using Geomagic Freeform Plus software (3D Systems, Rock Hill, SC), bilateral FRI discrepancy was corrected (T-1V) and 3D-printed surgical wafers and customized metal plates were manufactured using 3D printer (Meg-printer II, MegaGen Implant, Daegu, Republic of Korea) and computer numerical control milling machine (ARDEN, TPS Korea Ltd., Gwangju, Republic of Korea) accordingly. During surgery, FRI correction was done using surgical guide and customized plates. The difference between preoperative and virtually corrected FRI (Delta T-1V - T-0) and the difference between preoperative and actually surgically corrected FRI (Delta T-1A - T-0) were measured, and the achieved FRI correction in percentage ([Delta T-1A - T-0]/[Delta T-1V - T-0] x 100) was calculated. Results: The mean absolute value of virtual FRI correction (Delta T-1V - T-0) and actual FRI correction (Delta T-1A - T-0) were 3.0 degrees and 2.9 degrees, respectively (n = 32). In the increased (medial rotation) FRI group, mean virtual and actual correction amount were 3.2 degrees and 2.8 degrees (n = 17), whereas in the decreased (lateral rotation) group, mean virtual and actual correction amount were -2.7 degrees and -3.1 degrees, respectively (n = 15). No statistically significant difference between virtual and actual measurements were present in either group. The mean achievement rate was 102.8%. Tendency of undercorrection (91.2%) in the increased FRI group and overcorrection (116.0%) in the decreased FRI group were noted. Discussion: With virtual planning and computer-aided design and computer-aided manufacturing-made customized plates, it is possible to correct FRI during orthognathic surgery of patients with facial asymmetry.