Efficacy of Different Passive Ultrasonic Irrigation on Smear Layer Removal

Objectives: Passive ultrasonic irrigation (PUI) is a term that describes ultrasonic irrigation of the root canal without canal shaping. The purpose of this study was to compare the effect of continuous, intermittent passive PUI and active scrubbing of irrigants with endodontic files in removing smear layer of the dentin surface in root canals of primary teeth.

Methods: Forty single-rooted teeth were randomly divided into 4 test groups. The working lengths of all teeth were established by passing a #10 K-file to the apical foramen and then reducing the length by 0.5 mm. The roots were then fractured and prepared for SEM. Specimens were subjected to final irrigation with 17% EDTA followed by 2.5% NaOCl for 1 minute each using different activation methods: no activation (control), endodontic files with 2.5% NaOCl, continuous PUI with irrigant delivered at pulp chamber and intermittent PUI. Specimens were examined under SEM. Representative photomicrographs were evaluated and recorded and ranged from no smear layer, dentinal tubules open to heavy smear layer, outlines of dentinal tubules obliterated. The data were analyzed using the Kruskal-Wallis nonparametric ANOVA and nonparametric Tukey’s multiple range tests. 

Results: A significant difference was found using ANOVA when coronal thirds compared, middle thirds compared and when apical thirds are compared. A significant difference was found when thirds in each group were compared. A significant difference between group 1 and all other groups (p value <0.001) was found in the coronal third. There was no significant difference between any other groups at the coronal level.

Conclusions: Passive ultrasonic irrigation of the primary teeth root canals with and without instrumentation resulted in removal of the smear layer particularly with the use of continuous ultrasound for 60 seconds.