This study investigated the effect of airborne particle abrasion on the exposed dentin surfaces of 40 extracted teeth. A Siroflow abrasion unit was used to treat four groups of ten specimens that were subjected to 5, 10, 20, and 40 seconds of abrasion respectively. Statistical analysis (Spearman Rank Order) showed a significant difference between all groups (P{.05) but not within groups (P}.05). Scanning electron micrographs showed smear layer removal as an immediate effect of air polishing. Application times of longer than 5 seconds showed obstruction of dentinal tubule openings, possibly a result of abrasive powder residue. It was concluded that airborne particle abrasion removes the smear layer, and the amount of dentin removed corresponded to the time of application.