Objective: The purpose of this study was to investigate the effect of conditioners on smear layers produced by different bur types and rotational speeds and to study the interaction of subsequently applied primer and sealer with these conditioned surfaces. Method and materials: Smear layers were produced on human teeth immediately after extraction by burs rotating at approximately 6,000 rpm without water sprary and 400,000 rpm with water sprary. Gluma CPS etchant was applied for 15, 30, and 60 seconds, and a 20% phosphoric acid liquid (control) was applied for 30 seconds to smear layers. The specimens were prepared by critical point drying for scanning electron microscopic imaging within 24 hours. Additional specimens were prepared and treated with Gluma CPS primer and sealer, according to the manufacturer's instructions. Results: There were only small variations in the smear layer thicknesses with different bur types or speeds of rotation. Gluma CPS conditioner, applied for the recommended t imes, did not completely remove the smear layer. An altered smear layer, composed of a reaction product, remained on the dentinal surface. A zone of demineralization did occur, however, beneath the partially removed smear layer in both the 15- and 30-second specimens but was only partly filed by primer and sealer. Smear layers were completely removed by the 20% phosphoric acid liquid to expose a delicate collagen network. Conclusion: An understanding of the appropriate treatment for smear layers is crucialto the development of improved dent in bonding systems.