Method: Extracted sound human molars were ground flat oclusally, exposing superficial dentin. The two-step total-etch adhesive Adper Single Bond 2/3M ESPE (SB1) and the three-step total-etch adhesive Adper Scotchbond Multi-Uso Plus/3M ESPE (SP) were used as follows: 1) as manufacturers' instructions; 2) etching with 37% H3PO4 (15s) followed by 2% chlorhexidine (120 s); 3) etching with 0.1 M EDTA (60s); 4) etching with 0.1 M EDTA 37% followed by 2% chlorhexidine (120 s). Resin composite build-ups (Filtek Z350XT/3M ESPE) were constructed incrementally. After storage in water for 24 h, bonded specimens were sectioned into beams of 1.0 mm2 cross-sectional area. Beams were tested to failure in an EMIC machine (1 mm/min). MTBS data were analyzed by Kruskal-Wallis and Dunn´s multiple comparisons tests (p<0.05).
Result: The highest bond strength values were attained after 37% H3PO4 etching. Chlorhexidine application did not interfere with bond strength, irrespective of the adhesive system used. Etching with EDTA resulted in lower bond strength results, mainly when associated with chlorhexidine.
Conclusion: When bonding with both total-etch ethanol-based adhesive systems, 37% H3PO4 etching yielded the highest MTBS results. Pre-treatment with chlorhexidine solution only reduced MTBS to dentin when used in association with EDTA.