The irrigant's ability to penetrate in areas not affected by the instruments during root canal preparation is essential for debridement and disinfection of the root canal system. The goals of this study will be to evaluate the penetration into dentinal tubules of different sodium hypochlorite (NaOCl) irrigants with or without surfactant (part 1) and the effect of passive ultrasonic irrigation in this penetration (part 2). In Part 1, the middle third of the roots of 32 bovine incisors will be instrumented, stained with crystal violet and sectioned longitudinally. The specimens will be assigned to 6 groups (n = 10) and will be immersed in the following endodontic irrigating for 20 minutes: Chlor-Extra (5,8% NaOCl + surfactant; Vista Dental Products, Racine, WI, USA), 5.8% NaOCl, 2.5% NaOCl + 0.2% cetrimide, 2.5% NaOCl, ChlorCid V (3% NaOCl in gel form - Ultradent, South Jordan, UT, USA), ChlorCid (3% NaOCl in solution form - Ultradent). The analysis of the penetration of NaOCl into dentin will be performed by measuring the depth of crystal violet stain that will be bleached using a steromicroscope under x40 magnification. In part 2 of the study, 24 bovine incisors with roots standard in 15 mm will be instrumented and stained with crystal violet. The roots will be assigned to 2 groups (n = 10) according to the protocol used for final irrigation: G1 - 2.5% NaOCl irrigation with passive ultrasonic irrigation and G2 - 2.5% NaOCl without passive ultrasonic irrigation. The irrigation period in the two groups will be 2 minutes. The roots will be longitudinally sectioned and analysis of NaOCl penetration into dentin will be performed by measuring the depth of crystal violet bleached using a stereomicroscope under x40 magnification in the three thirds of root canal. Statistical analysis will be determined based on the distribution and homoscedasticity of the data using a significance level of 5% for part 1 and part 2 of the study.
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