# Effects of Surgically Assisted Rapid Palatal Expansion on Facial Soft Tissues: A Systematic Review
## 4 Discussion  
Several studies aimed at investigating the effect of various orthognathic procedures on the soft tissues. However, the available systematic reviews addressing this issue concluded that better designed studies are needed in order to draw definitive conclusions regarding the effect of the orthognathic procedures on the appearance of the face [32; 33; 34]. The present study agrees with this conclusion. The variability of the soft tissues' response to surgical procedures requires careful consideration during research protocol development. Predictor variables of the soft tissue changes after maxillary advancement can be categorized in relation to the surgery as presurgical, intrasurgical and postsurgical [34]. Presurgical variables may include soft tissue characteristics such as lip tone, length, and thickness. Intrasurgical variables may include the magnitude of the surgical trauma and the formation of edema or hematoma, surgical bone recontouring, magnitude and direction of maxillary movement, soft tissue manipulation techniques, and type of suture. Postoperative variables include magnitude of bone remodeling, relapse, healing, scarring and contraction, postsurgical infection, magnitude and direction of postoperative orthodontic movements, and hard and soft tissue stability [34]. These predictors may explain soft tissues changes after SARPE and should be controlled for either in the design of the study or in the statistical analysis; otherwise, they may bias the study results. Unfortunately, it is not possible to control all these factors in a randomized clinical trial (RCT). From the included studies, the RCT of [PERSON] et al. [17] used the presence of all anterior teeth as an inclusion criterion in their study. Absence of maxillary anterior teeth might bias the results decreasing lip support. The studies by [PERSON] et al. [25] and [PERSON] et al. [17] were the only ones to use the history of facial trauma as an exclusion criterion; facial trauma can alter the effect of SARPE on the facial soft tissues via its subsequent scarsing. No other potential predictors mentioned above were considered in the included studies. On the other hand, [PERSON] et al. [18] were the only authors to control for some of the above-mentioned variables in their analysis. They tested for 3D upper lip and cheek changes, controlling for age, gender, amount of expansion, and upper incisor inclination. They found that age and upper incisor inclination affected the upper lip, whereas the \begin{table}
\begin{tabular}{l l} \hline \hline
**Study** & **[PERSON] et al., 2013 [17]** \\ \hline Random sequence generation (selection bias) & Low \\ Allocation concealment (selection bias) & Unclear \\ Blinding of participants and personnel (performance bias) & Unclear \\ Blinding of outcome assessment (detection bias) & Unclear \\ Incomplete outcome data addressed (attrition bias) & Low \\ Selective reporting (reporting bias) & Low \\ Summary & Unclear \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Risk of bias of the randomized clinical trial. amount of total expansion affected the cheeks. Moreover, studies without control groups should at least control the amount of expansion in their analysis, since the reported facial soft tissue changes are additionally influenced by the orthodontic movements. This fact renders the pure SARPE effect impossible to quantify [23; 24; 25; 26; 27; 28; 29; 30]. Studies with treated controls may also benefit from controlling the total amount of surgical expansion for two reasons: primarily, because the latter could be a confounder as indicated by [PERSON] et al. [18], and secondarily, because it would be of clinical interest to quantify the expected facial soft tissue changes for the individual patient considering, among other things, the amount of expansion. On the other hand, as the number of variables increases, the required sample size also grows. Power analysis is a key component for planning prospective studies in the future. Both [PERSON] et al. and [PERSON] et al.