## 1 Introduction  
Orthognathic surgery (OS) is usually performed to improve functional and esthetic parameters by repositioning the maxilla, mandible and/or the symbiosis, particularly among patients that have either passed the pubertal growth spurt or may be unsuitable for orthodontic camouflage [1]. Surgical interventions such as LeFort and sagittal split osteotomies are often performed in conjunction to orthodontic tooth movement (OTM), particularly in patients with severe craniofacial deformities to produce a functional and stable occlusal outcome [2, 3]. Following OS, orthodontic therapy (OT) using fixed appliances is conventionally performed to attain the desired tooth movement [4, 5]. Clear aligner therapy (CAT) emerged as a potential therapeutic approach to induce OTM and treat dental malocclusions over two decades ago. These are removable appliances that can produce clinically acceptable orthodontic outcomes (OO) that are comparable to clinically satisfactory outcomes achieved using fixed OT [6, 7]. With advancements in clinical orthodontics and related research, CAT has been shown to be an effective approach for the correction of not only mild to moderate but severe malocclusions [8], and it can also be used successfully after OS to attain OTM [9; 10; 11; 12; 13]. However, according to [PERSON] et al. [13] esthetic outcomes in terms of occlusion are superior with fixed OT in contrast to CAT after OS. [PERSON] et al. [14] also concluded that OT in adults using CAT is associated with worse esthetic outcomes in contrast to OT performed using fixed appliances.  
Postoperative facial swelling (FS) after OS is a common yet significant concern as it can cause discomfort, hinder oral intake, affect speech and prolong the recovery period [9; 10; 11; 12; 13]. However, there is a paucity of research specifically comparing the impact of CAT and fixed OT on postoperative FS following OS. [PERSON] et al. [10] used three-dimensional (3D) subtraction imaging to compare the volume of FS after OS in patients undergoing CAT (\(n=11\) patients) and fixed OT (\(n=11\) patients). In this study [10], OS interventions comprised LeFort-1 osteotomy (L1O), genioplasty and bilateral sagittal split osteotomy (BSSO). The results showed that patients undergoing CAT displayed a significantly smaller volume of FS compared with individuals undergoing fixed OT at a one-week follow-up [10]. The authors concluded that in the short term (up to the first post-operative week), FS is less in patients undergoing CAT than those undergoing fixed OT [10]. On the other hand, in a retrospective chart review and 3D morphometric study, [PERSON] et al. [12] showed no significant difference in FS among patients that either underwent CAT or fixed OT 6 months after OS. The authors suggested CAT can be used as an alternative to fixed OT after OS [12]. It is, however, pertinent to mention that the studies by [PERSON] et al. [10] and [PERSON] et al. [12] were based on the supposition that peri-operative OT with CAT causes less post-operative FS than fixed OT; however, a scientific justification in this regard remained unclarified in these studies [10; 12]. A systematic review of studies comparing FS and OO of CAT and fixed OT after OS is not yet reported in indexed databases.  
With this background, the purpose of this systematic review was to assess the postoperative FS and OO attained with CAT and fixed OT after OS.