Effectiveness of different final irrigant activation protocols on smear layer removal in curved canals

A final flush with chelating agents and antiseptic irrigating solutions is needed to remove the smear layer. The improvement of these protocols is possible by using specific delivery and agitation techniques. This study examined the effect of different final irrigation regimens and methods of activation on smear layer removal in curved canals after root canal instrumentation.

Mesial root canals of 50 extracted mandibular molars were prepared using ProTaper rotary files (Dentsply Maillefer, Ballaigues, Switzerland) and 3% NaOCl. Teeth were then allocated to two control groups and four experimental groups (n = 10) for final irrigation as follows: no-activation group (final rinse with a 27-gauge needle and 17% EDTA/3% NaOCl), manual-dynamic activation group (final rinse 17% EDTA/3% NaOCl + gutta-percha agitation), automated-dynamic activation group (final rinse 17% EDTA/3% NaOCl + RinsEndo [Dürr Dental GmbH & Co KG, Bietigheim-Bissingen, Germany]), and sonic-activation group (final rinse 17% EDTA/3% NaOCl + Endoactivator [Advanced Endodontics, Santa Barbara, CA]). All mesial roots were split with a new approach to allow visualization of every third of the canal, particularly the apical third. The samples were prepared for scanning electron microscopic observation to assess the smear layer removal. Blind scoring was performed by two calibrated observers using a five-score scale. The differences in smear layer scores between the experimental groups were analyzed with the Kruskal-Wallis test and the Mann-Whitney U test. The level of significance was set at p = 0.05.

Very high levels of root canal cleanliness (< or = score 3) were found for each test group with activation. For the middle and apical third, the no-activation group was significantly less effective than the three other activation groups (p < 0.05). The manual-dynamic activation group (final rinse 17%EDTA/3%NaOCl + gutta-percha agitation) and the sonic-activation group (final rinse 17%EDTA/3%NaOCl + Endoactivator) showed significantly better smear layer removal (p < 0.05) in comparison with the other test groups in the apical third.

Root canal cleanliness benefits from solutions activation (especially sonic activation and manual-dynamic activation) in comparison with no activation during the final irrigation regimen.