Three-dimensional surgical simulation improves the planning for correction of facial prognathism and asymmetry: A qualitative and quantitative study

Abstract

Traditional planning method for orthognathic surgery has limitations of cephalometric analysis, especially for patients with asymmetry. The aim of this study was to assess surgical plan modification after 3-demensional (3D) simulation. The procedures were to perform traditional surgical planning, construction of 3D model for the initial surgical plan (P1), 3D model of altered surgical plan after simulation (P2), comparison between P1 and P2 models, surgical execution, and postoperative validation using superimposition and root-mean-square difference (RMSD) between postoperative 3D image and P2 simulation model. Surgical plan was modified after 3D simulation in 93% of the cases. Absolute linear changes of landmarks in mediolateral direction (x-axis) were significant and between 1.11 to 1.62 mm. The pitch, yaw, and roll rotation as well as ramus inclination correction also showed significant changes after the 3D planning. Yaw rotation of the maxillomandibular complex (1.88 ± 0.32°) and change of ramus inclination (3.37 ± 3.21°) were most frequently performed for correction of the facial asymmetry. Errors between the postsurgical image and 3D simulation were acceptable, with RMSD 0.63 ± 0.25 mm for the maxilla and 0.85 ± 0.41 mm for the mandible. The information from this study could be used to augment the clinical planning and surgical execution when a conventional approach is applied.

Figure 1. The Pie chart showing the percentage of patients with different numbers of parameter change.

Figure 2. The frequency of parameter changes in the patients.

Figure 3. Outcome of patient satisfaction at least 6 months after the orthognathic surgery for correction of prognathism and facial asymmetry.

Figure 4

The discrepancy of superimposition of models was represented in the color-coded visualization and presented in terms of RMSD value (a). Initial registration of virtual planning and postoperative CBCT model (b). The RMSD distribution and statistics (c). The discrepancy of superimposition of virtual surgery and postsurgical images in maxilla, mandible and maxilla-mandibular complex segments. The blue color indicated the no deviation on both surfaces, other colors showed different degree of deviation.

Figure 5. Flow chart of this study procedure.

Figure 6. Angular measurement of yaw, roll, pitch rotation and ramus inclination on 3D model.

Frontal view (a), Oblique view (b) and Basal view (c) (dashed line shows the yaw rotation after modification). Pitch rotation is the angle between lateral occlusal plane to FH plane. Roll rotation is the angle formed by FH plane and bimaxillary first molar line. Yaw rotation is the angle between sagittal plane and midpalatal suture. Frontal ramus inclination is the angle between FH plane and line from lateral condyle point to lateral gonion point.