BACKGROUND Glycine powder air polishing (GPAP) has been shown to be significantly more effective in reducing the subgingival cultivable microflora in shallow periodontal pockets compared to curets and is safe when applied directly to root surfaces. The purpose of this study was to assess the subgingival debridement efficacy of GPAP in periodontal pockets with various depths. METHODS In each of 60 patients with severe periodontitis, one tooth with a probing depth (PD) > or =6 mm was randomly assigned to one of the following interventions: GPAP performed in teeth instrumented 3 months earlier (I); GPAP performed in previously non-instrumented teeth (NI); or no treatment (control). GPAP was performed for 5 seconds per surface. After extraction, teeth were stained with 0.5% toluidine blue, and subgingival debridement efficacy was assessed. RESULTS Overall, median debridement depth was 2.00 mm in I teeth and 1.86 mm in NI teeth, and the median debrided root surface was 49.24% and 45.64%, respectively. In anatomic PDs (APDs) of 2 to 3 mm, relative debridement depth (debridement depth/APD) ranged from 65% to 80% and 60% to 75% in I and NI teeth, respectively; the corresponding values for debrided root surface were 60% to 70% and 50% to 60%. In control teeth, virtually all subgingival root surfaces were stained. Clinical PD measurements were a median of 1.05 mm deeper than APD. CONCLUSIONS GPAP for 5 seconds per surface is effective in removing most of the subgingival biofilm in periodontal pockets with an APD < or =3 mm.