Purpose: The purpose of this study is to assess the marginal adaptation of cavities restored with a three-step etch-and-rinse adhesive, OptiBond FL (OFL) under different application protocols.

Materials and methods: Twenty-four class V cavities were prepared with half of the margins located in enamel and half in dentin. Cavities were restored with OFL and a microhybrid resin composite (Clearfil AP-X). Three groups (n = 8) that differed in the etching technique were tested with thermomechanical loading, and specimens were subjected to quantitative marginal analysis before and after loading. Micromorphology of etching patters on enamel and dentin were observed with SEM. Data was evaluated with Kruskal-Wallis and Bonferroni post hoc test.

Results: Significantly lower percent CM (46.9 ± 19.5) were found after loading on enamel in group 3 compared to group 1 (96.5 ± 5.1) and group 2 (93.1 ± 8.1). However, no significant differences (p = 0.30) were observed on dentin margins.

Conclusions: Etching enamel with phosphoric acid but avoiding etching dentin before the application of OFL, optimal marginal adaptation could be obtained, evidencing a self-etching primer effect.

Clinical relevance: A reliable adhesive interface was attained with the application of the three-step etch-and-rinse OFL adhesive with a selective enamel etching, representing an advantage on restoring deep cavities.