# 3D Soft-Tissue Prediction Methodologies for Orthognathic Surgery--A Literature Review
## 3 Results
### Prediction Methodologies
#### 3.2.2 Works Based on Maximim Software (3D)
Their analysis showed that for the entire face the mean absolute 90 th percentile error was less than 2 mm (clinically acceptable); the least accuracy resulted in the region of the lower lip, while the most accurate prediction involved the sub nasal region. A possible explanation suggested by authors for labial inaccuracies was the difficulty to replicate labial position during different image acquisition. The conclusion drawn by authors on the basis of this analysis was that the soft-tissue prediction produced by Maximim software was clinically acceptable both for the whole face and for restricted regions, but the limitation was the fact that patients considered in the study underwent a single type of surgery instead of combined operations. In the analysis by [PERSON] et al., 13 non-syndromatic adults with a midline deviation of the chin point not less than 2.0 mm underwent Le Fort I or bimaxillary osteotomies (BSSO) to correct facial asymmetry. The accuracy of an innovative concept for the soft-tissue changes prediction was evaluated. The segmentation of the 3D model was performed to identify the following regions: upper lip, lower lip, chin area, right and left paranasal regions, nose and right and left cheeks. To evaluate the prediction reliability, the surface distances between predicted and actual post-operative positions were measured. Particularly, mean (signed) and mean absolute distances were calculated on 3D meshes for each region. Through a directional analysis, the accuracy of the prediction of soft-tissue changes was evaluated. The results showed that the distances between the predicted and the actual post-operative soft tissue models were less than 2.0 mm in all regions. In details, a general tendency to the under prediction was found in the area of the cheek and of the chin (medio-laterally). An over-prediction of changes was found at the inferior border of the mandible (bilaterally) [24]. [PERSON], et al. realized a retrospective study with the purpose of giving an objective quantification of accuracy of the Maximim virtual planning method, through the comparison between planned and actual movements in jaw osteotomy. They started from the assumption that a simple superimposition of simulation and cephalometry results did not allow to define a correlation between positional error and surgical movements. Indeed, a slight positional error could be insignificant talking about large movements, but could be unacceptable dealing with small displacements. A 3D planning was performed, and virtual frontal and lateral cephalometries of pre-operative and simulated surgery were extracted; those were compared to define the predicted movements of the jaw in reference to cranial bones. All surgeries have been planned by the same surgeons using Maximim software, with digital intermediate splints to guide osteotomies. Cephalometric analysis has been performed with Dolphin. To evaluate the accuracy, the mean linear difference between planned and actual movements was considered. Measurement of the differences between planned and actual movements were deemed accurate. As reported by authors, most of the clinical studies validating the virtual surgical planningset to 2 mm the criterion for the prediction success, with a success rate slightly lower than 100%. In this study, some significant differences with other works were found; first, differences between planned and achieved anterior facial heights were found (\(p\) = 0.033). This discrepancy was relevant (\(p\) = 0.042) in patients that did not undergo genioplasty, while it was not significant in patients who underwent this surgery (0.235). This error is probably due to the approximation of the soft tissue model, which does not allow the management of the vertical dimension. Presumably, genioplasty compensate the error on facial eight.