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The Effect of Smear Layer Removal on Endodontic Outcomes
Introduction: A layer of organic and inorganic debris referred to as the smear layer is produced during mechanical instrumentation of the root canal system. The combination of ethylene-diamine-tetraacetic-acid (EDTA) and sodium hypochlorite (NaOCl) has been shown to effectively remove the smear layer. To date, no prospective controlled in vivo studies have been published examining the effect of smear layer removal on endodontic outcomes in permanent teeth. Objective: This randomized, prospective, double-blinded clinical trial compared the endodontic outcomes of teeth where the smear layer was either removed or left intact. A secondary analysis assessed the influence of covariate factors on healing. Methods: Subjects meeting study inclusion criteria were randomly assigned to one of two irrigation groups. Root canals were instrumented in a standardized manner followed by a final irrigation of either 1ml of 17% EDTA or 1ml of 0.9% sterile saline. Clinical and radiographic evaluations were completed no earlier than 12- months posttreatment to assess outcomes. A modified periapical index (PAI) score (1-5) was used for radiographic analysis. Data were analyzed using Fishers exact test (a < 0.05). Results: For this interim analysis of 243 subjects, no significant difference in outcome was found between groups (p = 0.57). Pre-operative necrosis (p = 0.01) and a pre-operative apical lesion (p < 0.0001) were the only covariates found to affect healing rates. Conclusions: Within the limitations of this in-vivo clinical study, removal of the smear layer did not affect endodontic outcomes.
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