# 3D Soft-Tissue Prediction Methodologies for Orthognathic Surgery--A Literature Review
## 3 Results
### Prediction Methodologies
#### 3.2.3 Works Based on Other 3D Software
The null hypothesis they started from was that the mean difference in absolute distance between the predicted surface generated by the software and the real 3D facial surface measured at eight anatomical regions did not exceed 3 mm. Pre- and post-operative CBCT for each patients were imported into 3 dMDvultus and hard tissue and soft tissue were separately segmented and saved in STL (standard triangulation language) format. A template of actual surgical changes was produced using a CAD/CAM software (VRMesh, VirtualGrid, Seattle, WA, USA). Post-operative hard and soft tissue linked together were aligned to the anterior cranial base of pre-operative hard tissue of the same patient. Regions of maxilla and mandible of post-operative models were saved as STL file and imported into 3 dMDvultus to generate a template of the actual maxilla-mandibular complex aligned in the same 3D space as the pre-operative image. Using the same software, a LFI osteotomy was simulated for the pre-operative hard tissue. The resulting soft-tissue prediction was exported as an STL file for the analysis. The predicted model and the real surgical result were imported as mesh in VRMesh; the differences between the two models were rendered as a color map, which showed the overall accuracy of the software. After the analysis on the overall surface, the accuracy was evaluated subdividing the mesh into anatomical regions: chin, lower lip, upper lip, nose, right and left nares, right and left paranasal areas. From the analysis of the results, the authors concluded that since the distances between software-generatedsurfaces and real facial surfaces were lower than 3 mm, 3 dMDvultus 3D soft-tissue predictions were acceptable for clinical use in LFI osteotomy. MSM seemed to correctly predict the positions of lip and chin, while improvements should be made for nasal and paranasal regions [33]. In the prospective study by [PERSON] et al., 16 patients with open bite dentofacial-dysmorphosis and underwent orthognathic surgery (surgery first) were analyzed. The surgery was planned using conventional sketches as a new software developed by the authors, SOTIRIOS planning software. A conventional pre-surgical planning was carried out using three sides X-rays and, in addition, a CT scan was performed before and 6 months after surgery. A constrained fitting approach using statistical shape modeling (SSM) technique to generate the patient-specific data was used in combination with the anatomical landmarks to compute the patient specific model. A quantitative comparison of the soft tissue prediction and post-operative data was made showing a mean error of 1.46 mm \(\pm\) 1.53 mm. Authors concluded that the SOTIRIOS planning software was quite accurate and enabled the surgeon to predict the soft tissue outcome [34]. A comparison between Dolphin 3D, ProPlan CMF and an in-house probabilistic finite element (PFEM) [6] was carried out by [PERSON] et al. [35]. The retrospective study included seven patients who underwent LFI maxillary advancement. From CBCT taken preoperatively, 3D models of bone and soft tissue were constructed. On the base of the advancement and rotation movements measured on the post-operative images, a virtual Le Fort I osteotomy was performed and three different soft tissue predictions were realized with the three softwares. Firstly, the three predictions were compared with the pre-operative model to evaluate differences. After that, the three predictions were compared with the real post-operative outcome, to assess which was the most predictive model. As the patients involved underwent a LFI maxillary advancement, the areas of interest for the comparison with post-operative situation were the upper lip and the paranasal regions. From the outcomes analysis, it resulted that the prediction generated by Dolphin 3D was affected by a general under-prediction of paranasal displacements, while both ProPlan CMF and the PFEM model were characterized by an over-prediction of displacements involving chelion regions.