This study evaluated the influence of chemo-mechanical or bur excavation methods on bond strength of dentin bonding agents, micromorphology of the treated-dentin surfaces, and the bonded interfaces. Smear layer-free surfaces were used as control. The methods of cavity preparation (chemo-mechanical and rotary burs) were used under specific parameters and four commercial dentin bonding agents (three two-step self-etching primers and one "etch-and-rinse" adhesive system) were applied to treated surfaces, according to manufacturers' instructions. Composite blocks were built on bonded surfaces and restored teeth were vertically, serially sectioned to obtain bonded slices for interfacial micromorphologic analysis or to produce beam specimens for micro-tensile bond testing. A clear difference of the preparation of dentin surfaces and formation of hybrid layer and resin tags are noted. The use of burs or chemo-mechanical methods did not affect the bond strength for etch-and-rinse system and for a self-etching primer with a very low pH (0.5). However, dentin surface preparations decreased the bond strength for the milder versions (pH of around 2) of self-etching adhesive systems. The manner of dentin preparation prior to bonding procedures can influence the effectiveness of some self-etching primers, which dissolve the smear layer and dentin surface only partially.