## 3 RE Process as \"Game Changer\": Clinical Applications
### Diagnosis
#### 3.1.3 Skeletal and Soft-Tissue Facial Asymmetry  
The evaluation of facial symmetry has been conducted in the past with anthropometric measurements, however, this approach has been criticized due to unreliable identification of landmarks, questionable validity of the symmetry plane, and lack of precision [20; 21]. In this regard, RE techniques allow for a more predictable and reliable way to assess facial symmetry using landmark-independent methods, which take into account all available facial points detected with FS and allow a full-face analysis [19]. With RE, analysis of asymmetry consists of generating a mirrored model from the original model using an anatomical mirroring plane as reference (Figure 8).  
This sophisticated reverse engineering software system allows us to evaluate the morphological symmetry of any anatomical structure, evaluate any progress in treatment, or monitor growth. The 3D facial anatomy (Facial scan), 3D bone structures (CBCT), and denot-alveolar and palatal anatomy (Intra-oral scan) can be mirrored and then superimposed in order to evaluate the distances between the surfaces of the superimposed anatomical structures. Such distances, expressed as Euclidean differences or root mean squared (RMS) differences, quantitatively represent the anatomical differences/changes that have occurred. The mirroring process is performed after identifying the anatomical plane that acts as a reference for the models' speculation. Afterward, the models are registered with \"Best-fit alignment\" algorithm, and a surface analysis is performed and visualized with a color map that highlights the differences between both anatomical sides (right-to-left or left-to-right) [22]. Figure 9 shows the changes in palatal morphology and dimension occurring in a 7-year-old female presenting transverse maxillary deficiency and anterior open bite before treatment using IOS acquisition, thus avoiding X-ray exposure.  
Figure 7: Registration of IOS and FS into free-source software (BlueSkyPlan v 4.9.4) for simultaneous assessment of dento-alveolar and soft-tissue parameters. (**A**), Separated intraoral upper and lower scans; (**B**), upper and lower arches with bite registration; (**C**), facial scan; (**D**), facial scan and intraoral scans matched.  
Figure 8: Example of computer-assisted analysis of facial asymmetry using reverse engineering 3-Matic software (Materialise, Leuven, Belgium). (**A**), Facial scan; (**B**), definition of the mirroring plane; (**C**,**D**), mirrored facial scans to assess asymmetry.  
Figure 9: Example of computer-assisted analysis of maxillary asymmetry using reverse engineering software. In this 7-year-old girl, there was a significant improvement of maxillary symmetry (blue-colored and red-colored areas) after treatment with maxillary expander. (**A**), Pre-treatment frontal view; (**B**), pre-treatment occlusal view; (**C**), pre-treatment deviation analysis between original maxillary scan and mirrored scan; (**D**), post-treatment frontal view, (**E**), post-treatment occlusal view; (**F**), post-treatment deviation analysis between original maxillary scan and mirrored scan.