The perpetuation of apical periodontitis due to failure of endodontic treatment requires, in most cases, the retreatment process. However, the anatomical complexity of the root canal system and the physical characteristics of the cements used can influence the effectiveness of removing the filling material. Therefore, the aim of this study is to evaluate, through confocal microscopy and computerized microtomography (micro-CT), the volume, in percentage, of remnants of two calcium silicate-based sealers in powder and liquid form, and two of the type ready for use, after procedure of retreatment of canals with the presence of isthmus in mesial roots of mandibular molars. A total of 100 human permanent teeth, corresponding to the mandibular molars, will be previously evaluated through micro-CT to confirm the presence of isthmus. After selecting the teeth, they will be inserted in a metal muffle to make 3 sections in the roots corresponding to 2, 4 and 6 mm from the apex. Then, the channels will be instrumented with R25 and the complementary Mtwo 35/04 system. Soon after, the samples will be randomized and distributed into 5 groups, 4 of them regarding to the calcium silicate-based sealers used in their respective fillings, which 2 of the groups will use the bioceramic sealers presented in powder and liquid, BioRoot RCS (n=20) and NeoMTA 2 (n=20), the other 2 groups will use the ones presented ready for use, the EndoSequence BC (n=20) and the Bio-C Sealer (n=20), also a control group will take place using the epoxy resin-based sealer cement AH Plus Jet (n=20). After one month of filling, the samples will be subjected to retreatment of the channels with R40 and XP-Endo Finisher files. The remnants of bioceramic cements will be analyzed through images obtained by computerized microtomography and confocal microscopy. The setting time test will also be performed involving the root canal sealers of this study, following the ISO standard and an additional test based on dentin moisture.The test to assess whether there is a statistical difference of the remnants between the cement groups and between the thirds of the root canals will be the one-way ANOVA. To verify the normality of the data, the Shapiro-Wilk test will be submitted and, to identify where the statistical difference between the groups is, Tukey's post hoc will be used, with a significance level of 5% (p <0.05).
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