# 3D Soft-Tissue Prediction Methodologies for Orthognathic Surgery--A Literature Review
## 4 Discussion and Conclusions
Moreover, it requires plotting 79 landmarks on the CT volume (42 for the hard tissue and 37 for the soft tissue); the localization of such a large number of points seems to require too much time for a stable usage in clinical daily practice. Among the other considered software, SurgiCase_CMF was analyzed by [PERSON] et al. [29] and [PERSON] et al. [30]; they reported that the percentage of error was less than 2 mm for the majority of patients, but in both studies an important error in the areas of lips and chin was reported. [PERSON] et al., [PERSON] et al. and [PERSON] et al. used 3 dMDvultus to predict soft tissue changes; in general, they reported that its use on specific anatomical regions was more meaningful than on the full face [31; 32; 33]. Moreover, they reported an insufficient prediction accuracy particularly for the lower part of the face with errors exceeding 3 mm [32], and for nasal and paranasal regions [33]. Surprisingly, prediction results seemed to be reliable for lips and chin. The results reported for TIOPS showed significant inaccuracies in the predicted horizontal position of the lower lips and a relatively high variability of the predicted individual surgical outcome. The authors suggest care is needed when presenting the predicted image to patients before the operation [16; 41]. The SOTIRIOS planning software and the CASSOS program were found to be quite accurate [34] and able to give a clinically useful prediction of the soft-tissue profile change [17]. OrthoForecast software resulted as being in general an accurate tool for soft-tissue prediction; indeed, more than half of the involved evaluators assessed the predicted images to be very similar or similar to the actual post-operative images [15]. As a result of this review, it seems that Dolphin, CASSOS and OrthoForecast are the most accurate software in soft-tissue prediction. However, their reliability is not sufficient when further surgery is carried out and the complexity of the operation increases; moreover, they provide only partial information on the prediction, due to the lack of the third dimension. From this viewpoint, all articles agree on the potentiality of 3D methodologies. Maximlim produced clinically meaningful results, but its inaccuracy in specific facial areas (particularly in the lip region) led to the conclusion that further steps are needed to give surgeons a tool for predicting facial movements (including involuntary movements) that significantly supports the planning of the intervention in terms of aesthetic success. The comparison between 2D and 3D methodologies shows that the first reach better results in terms of accuracy and surgeon satisfaction. Consequently, the latter are still not able to meet medical needs. The analysis of these studies has led us to consider some issues that are still pending. Almost all of them report problems of reliability of the software or inaccuracy in specific areas; this shows that an ameliorative method would be necessary to improve prediction results. For this reason, it would be useful to clearly understand the way the existing software compute the tissue displacements. Moreover, it is important to notice that some of the considered software (Dolphin 3D) are not based purely on 3D methods, but they are an adaptation of a 2D algorithm to 3D data; the transfer of 2D data to a 3D representation may cause errors. This aspect affects both hard- and soft-tissue prediction, and it is more evident in soft tissue simulations, due to the complexity of its behavior (involuntary displacements). The tendency of surgeons to prefer conventional methods suggests that, despite the general positive opinion emerging from the studies, the reliability of automatic systems is not sufficient, since it has not significantly increased above the two-dimensional methods commonly used in clinical routine. Indeed, it seems to lack consistency between the results obtained with prediction software and practitioner satisfaction.