# 3D Soft-Tissue Prediction Methodologies for Orthognathic Surgery--A Literature Review
## 3 Results
### Prediction Methodologies
#### 3.2.1 Works Based on Traditional (2D) Methodologies
Landmarks located on structures not involved in the surgery were directly transposed from pre-operative to post-operative cephalogram to refine the superimposition process. The objective of an accurate superimposition of pre- and post-operative cephalograms was to construct a spreadsheet for landmarks movements to quantify changes of each point after operation; the position of points was defined in form of x and y. In accordance with the spreadsheet, a simulation of the treatment was produced, and the prediction tracings were obtained from actual post-operative changes amount. Actual post treatment tracings and prediction tracings were superimposed and differences have been measured again according to an x, y coordinate system. The mean differences between the predicted and the actual result were less than 1 mm in four of seven soft tissue measurements; predictions turn out to be more accurate for the sagittal plane than for the vertical one. The largest errors were reported for the lower lip region, in accordance with other studies considered by authors and investigating other software [11]. [PERSON] et al. studied the accuracy of digital prediction with respect to the actual post-operative outcome with Dolphin program. Patients with class II malocclusion were involved. Eighty Caucasian subjects treated with combined surgical and orthodontic treatment were considered. Cephalometric radiographs of pre- and post-operative were digitized; a time of at least one year from surgical to post-operative was required to rule out any effects of post-operative swelling. Digital tracings were performed with Dolphin imaging software and digital lateral cephalometric radiographs were traced at the same time to minimize the error variance; before tracing, Dolphin program was used to carry out the compensation for the effect of radiographic magnification. An x y coordinates system was constructed with the x axes corresponding to the horizontal Frankfort plane and the y-axes passing through Nasion and perpendicular to x-axes. On x-axes, vertical changes have been measured, while on y-axes authors evaluated horizontal changes. Dalberg formula was used in evaluating the reproducibility of measurements; with regard to the method error, it did not exceed 0.37\({}^{\circ}\) for angular measurements and 0.29 mm for linear measurements. Results of the statistical analysis were based on mean values found in each studied group. The analysis of the authors underlined that there were no significant differences between soft-tissue values at pre-operative (t1), post-operative (t2) and predicted (t3) stages. In both groups, surgeries have been more extensive than planned; facial convexity and the distance between the lips and the cranial base presented similar values between t2 and t3. The conclusion of the authors was that statistical differences in the considered measurements did not invalidate surgical prediction performed with the software, because forecasted changes were sufficiently close to of the surgical outcomes [12]. [PERSON] et al. followed the same approach of the previous article on two groups of patients; the former underwent Le Fort I without segmental surgery, while on the latter, in addition to LFI surgery, mandibular setback was performed with an SSRO. What came out from this study was that 12 months after the operation surgical reductions in mandibular length and angle were substantially greater than indicated by predictive cephalometric tracings. The analysis of dental and skeletal mandibular changes in anteroposterior and vertical directions revealed that the effect on the profile was greater than those of the maxilla; this is probably due to the fact that the mandible is a moving structure and the upper lip leans upon the lower lip. Maxilla advancements were performed for both groups according to the planning provided by Dolphin imaging software; in group two, mandibular setback was statistically overestimated by the software planning.