We examined the abrasiveness of glycine powders with particle diameters of 63 and 100 mum by measuring the depth and volume of defects produced during air polishing of human dentin. A total of 36 extracted human teeth were embedded in acrylic resin. The resin blocks were polished until the dentin surfaces were exposed. The nozzle of an air polisher was mounted 4 mm from the dentin surface, and the dentin surface was treated for 5 s at one of two angles of incidence (45 degrees or 90 degrees). Three materials were used in the polishing process: NaHCO(3) powder with a mean particle diameter of 100 microm (Handy Jet Powder), glycine powder with a mean particle diameter of 63 microm (Handy Jet Powder PMTC), and glycine powder with a mean particle diameter of 100 microm (Handy Jet Powder Recall). The defect depth at both angles was significantly deeper after treatment with Handy Jet Powder or Handy Jet Powder PMTC. The defect volume was the greatest with Handy Jet Powder, followed by Handy Jet Powder PMTC, and Handy Jet Powder Recall. The larger diameter glycine powder resulted in less damage to the dentin.