To systematically review the existing literature comparing mini-implant assisted rapid palatal expansion (MARPE) and conventional rapid palatal expansion (RPE) regarding the effect on the buccal alveolar bone thickness (BT) and marginal bone level (BL).
PubMed/MEDLINE, Scopus, Web of Science, The Cochrane Library, Virtual Health Library, Embase, Ovid, Livivo, CINAHL, the Portal de Periódicos da CAPES, Scholar Google and SIGLE were searched up to January 2020. Risk of bias (RoB) assessments were performed using the Cochrane Collaboration and ROBINS-I tools. Fixed effects meta-analysis of standardized mean differences (SMD) was implemented to assess the pooled estimates for the BT outcome. The analyses were performed adopting a significance level of 5%. A narrative synthesis was performed to summarize the results on the BL. The GRADE tool was used to assess the quality of the evidence.
Three randomized clinical trials and one retrospective study were included. Only one study was rated as with low RoB, while the others were scored as with moderate to serious RoB. Limited evidence indicated that patients using conventional RPE had a greater loss of the BT compared to patients using MARPE (SMD=0.55; 95% CI: 0.29-0.80; p<0.0001). Subgroup analyses showed that differences were significant in both premolars' regions, right (SMD=0.75; 95% CI: 0.24-1.25; p=0.004) and left (SMD=1.05; 95% CI: 0.52-1.57; p<0.0001); and these were not significant for the molars' regions (p>0.05) (Low quality of evidence).
Limited amount of selected papers, methodological issues that could lead to bias, and high clinical heterogeneity among the studies. Due to the statistical model applied for the quantitative synthesis of the results, no generalization to any other population is recommended.
Limited evidence suggests that MARPE could decrease the loss of the buccal alveolar bone when compared to conventional RPE.

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