Analysis of the smear layer generated by different activation systems: an in vitro study



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Clinical Oral Investigations





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Objectives: To evaluate via scanning electron microscopy the amount of smear layer generated during the use of sonic and ultrasonic activation systems with standardized short-term intentional contacts with the canal walls. Methodology: Seventy single-root human teeth were randomly assigned to 2 control (n = 5 each): NC (negative control), PC (positive control) and four experimental groups (n = 15 each): NC (negative control), PC (positive control), G1 (passive ultrasonic irrigation with Irrisafe), G2 (ultrasonic irrigation with EndoUltra), G3 (sonic irrigation with Endoactivator), G4 (sonic irrigation with Eddy). Samples were instrumented with ProTaper Next®. An irrigation protocol with sodium hypochlorite (NaOCl) and ethylenediaminetetraacetic acid (EDTA) was followed for both PC and the experimental groups. Standardized intentional contacts were made in the mesial walls during 5 s at WL − 2 mm in all experimental groups. Two calibrated evaluators scored the smear layer generated with an ordinal scale by scanning electron microscopy. The weighted kappa coefficient (Kw) was calculated to determine the inter-observer agreement. Post-consensus ordinal data were analyzed using the ordinal (linear) chi-square test. Results: When the agitation file is in contact with dentine walls, Irrisafe® significantly generated the least amount of smear layer in the coronal third (p < 0.05). Both in the middle and apical third, activation with Irrisafe® also showed statistically significant better results than Eddy™ and EndoUltra®. Endoactivator® showed significant better results than EndoUltra® and Eddy™ in the apical third (p < 0.05). Conclusions: Irrisafe generated the least amount of smear layer in the entire canal and similar to Endoactivator in the apical third when the agitation file is in contact with dentine walls. Clinical relevance: The smear layer is generated during activation. It is common to apply irrigation protocols where after the removal of the smear layer using chelants, a final rinse and activation is carried out but there are no previous studies analyzing the possible creation of a new smear layer with this final activation.