This study compared the depth of irrigation of periodontal pockets achieved by a cannula subgingival irrigator tip and a standard oral irrigator tip. They were tested on periodontally involved teeth recommended for extraction from 17 patients. Before extraction, reference grooves were made circumferentially in each study tooth at the level of the gingival margin. In one group of 5 patients (29 teeth), a cannula was inserted halfway into the pocket at the facial, mesiofacial, distofacial, lingual, mesiolingual and distolingual surfaces and the surface irrigated for 5 s at 5 psi with a solution of plaque-staining dye from an oral irrigator. A 2nd group of 7 patients (29 teeth) was tested similarly with a standard irrigating tip at 80 psi. A 3rd (control) group of 5 patients (26 teeth) rinsed with the dye solution. Teeth were then extracted. The distance on each tooth from the reference notch to the apical extent of the stained plaque, and also to the coronal limit of the connective tissue attachment, was measured at 4 sites (mesial, distal, buccal, lingual) under a dissecting microscope to determine the extent of dye penetration. Mean linear penetration for the control group was only 0.1 mm. Irrigation with the cannula tip penetrated farther into both the medium (3.5-6 mm) and the deep (greater than 6 mm) periodontal pockets (p less than 0.01) than did irrigation with the standard tip.(ABSTRACT TRUNCATED AT 250 WORDS)