## 4 Discussion
### NSRME vs. SARME  
Through releasing the osseous centers of resistance, SARME is thought to reduce the physiologic burden placed upon the periodontium. After releasing the circummaximillary sutures, the force necessary to create palatal expansion should be less than that produced in NSRME. The prediction of a successful rapid maxillary expansion is influenced by suture bone density and the fracture resistance increasing with age (<25 years vs. >25 years [45]. Thus, this surgical intervention will allow the maxillary halves to separate transversely without major disadvantages in younger individuals (<25 years) [45], with less buccal migration of the teeth, and reduce the occurrence of REC and/or DEH in patients with thin periodontal phenotypes [42; 46]. Multiple studies have shown that both NSRME and SARME are individually associated with REC primarily located at posterior teeth and between central incisors [7; 19; 21; 28; 26; 41; 47]; however, only two studies within this review included both NSRME and SARME study arms directly comparing the two groups with similar average ages [28; 41]. Moreover, these studies reported that the incidence and amount of REC in posterior maxillary teeth were significantly greater for NSRME (8.4%, 1.2 mm) as compared to SARME (3.6%, 0.5 mm). Such findings were corroborated by the aggregation of reported changes in the CCH among the included studies, showing an increased magnitude of mucogingival deformities among NSRME-treated patients [29; 37; 38; 40; 41; 43]. [PERSON] and colleagues showed that REC that developed on posterior teeth during SARME persisted 1 year after appliance removal; however, no defects greater than 3 mm were observed [7]. Additionally, mild papillary REC affecting maxillary central incisors following SARME has been reported [48; 49]. Observations from the present review suggest that SARME is associated with a lesser incidence of soft tissue deficiencies when compared to NSRME. The current literature supports the idea that orthodontic treatment, with or without palatal expansion, may be associated with an immediate decrease in buccal alveolar bone dimensions that is alleviated over time. [PERSON] and [PERSON] showed a decrease in alveolar bone height immediately after orthodontic treatment [50]; however, [PERSON] and [PERSON] showed that there is no difference in bone levels among orthodontically treated and untreated individuals 10 years after the completion of orthodontic treatment [51]. It is not clear whether specific orthodontic treatment modalities are more strongly associated with alveolar bone loss than others [52]. [PERSON] and colleagues found that among patients undergoing SARME, those who were treated with PMD experienced less BBW reduction as compared to those without this additional procedure [38]. However, our  
Figure 2: Assessment of quality and risk of bias of human non-randomized studies. results were unable to find a significant difference of the change in BBH, BBW, DEH or fenestrations between SARME and NSRME-treated patients. The variability in measurement techniques and patient response to treatment may contribute to the inconsistent results found across the included studies. Ultimately, there is insufficient data to differentiate the effects of SARME and NSRME on CAL, PD, and KTW due to the lack of controlled clinical trials reporting these outcomes. No significant differences were found in the amount of transverse dental expansion achieved via SARME and NSRME. Among SARME study-arms, average gains in dental arch width ranged from 3.6 to 9.8 mm at the first premolars, and 3.1 to 9.8 mm at the first molars [7; 18; 28; 35; 37; 38; 39; 41; 43]. The amount of expansion achieved in NSRME study-arms ranged from 3.3 to 6.0 mm at the first premolars, and 3.1 to 9.3 mm at the first molars [27; 28; 33; 40; 41]. Studies directly compared NSRME and SARME found no statistically significant differences between the amount of dental expansion in either modality [28; 41].