Acid etching on an adherent substrate is a critical process to achieve successful adhesion between dental hard tissues (i.e., enamel or dentin) and restorative materials. Although the importance of phosphoric acid etching for dentin has been deemphasized due to the development of self-etch adhesives and self-adhesive resin cements, selective enamel etching with phosphoric acid is advocated to achieve better clinical performance with these self-etching materials. Since the biofilm coats all surfaces in the oral cavity, the dentin surface to be restored with the composite resin may also be coated for short or long periods. Surface prophylaxis with a rubber cup and pumice before acid etching led to significantly higher bond strength of the resin composite to the dentin than the rest of the test groups. However, it did not reach to the level of bond strength in the control group, which contained a biofilm-free dentin surface.