OBJECTIVE: To compile the available evidence on the effectiveness of resin infiltration in masking demarcated opacities in permanent incisors with MIH and whether modifications to the treatment protocol impact the outcome. DATA SOURCES AND STUDY SELECTION: This review followed PRISMA2020 and was registered in PROSPERO (CRD42023414048). Searches were performed in MedLine, LILACS, BBO, Cochrane, Web of Science, Scopus, Embase, OpenGrey, and Google Scholar, by two independent reviewers. JBI and RoB2 were used to evaluate risk of bias. R software was used to perform meta-analyses. RESULTS: Eight uncontrolled, two non-randomized, and two RCTs evaluated 369 teeth in 6-31year-old participants. Six studies followed the standard resin infiltration protocol, while the others reported modifications. The meta-analysis estimated an overall proportion of total masking of 37 % (CI: 18-55). Modified protocols tended to achieve higher success rates (40 %
CI: 9-72) compared to standard protocols (30 %
CI: 17-44), though this difference was not statistically significant. The overall reduction in ΔE was 3.08 (CI: 0.74-5.42), with 1.54 (CI: 0.68-2.40) for standard protocols and 3.84 (CI: 0.80-6.89) for modified ones. Seven studies had moderate risk of bias, and three had high risk. The certainty of evidence was low due to heterogeneity (I² >
80 %) and imprecision concerns. CONCLUSION: Resin infiltration is effective in reducing the color difference between MIH opacity and normal enamel. The achievement of total masking was not significantly different between the standard and modified protocols. Heterogeneity and lack of controlled studies limit the certainty of evidence. CLINICAL SIGNIFICANCE: This review reinforces the effectiveness of resin infiltration in reducing the color difference between MIH opacity and normal enamel. Modifications in the protocol improved the infiltration but were not enough to be significantly superior. This review contributes to the understanding of peculiarities related to the microinvasive esthetic treatment of MIH.