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The aim of this study was to evaluate the effect of Er:YAG and Nd:YAG laser on radicular dentine permeability when using distilled and deionized water and 1% sodium hypochlorite as irrigating solutions. Thirty human maxillary canines obtained from laboratory stock and conserved in 0.1% thymol until use were divided randomly into six groups of five teeth each. The root canals were instrumented with K files and the step-back technique. The surgical diameter was achieved 4 files above the original anatomical diameter. Group I, the teeth were irrigated with distilled and deionized water; Group II, the teeth were irrigated with 1% sodium hypochlorite, Group II the teeth were irrigated with distilled and deionized water and then Er:YAG laser was applied with 140mJ, 15Hz, 300 pulses and 42J; group 4 the teeth were irrigated with 1% sodium hypochlorite and Er:YAG laser was applied in the same parameters as Group III, Group V, the teeth received irrigation with distilled and deionized water and Nd:YAG laser application with 150mJ, 15Hz, 2,25W and Group VI the teeth were irrigated with 1% sodium hypochlorite and Nd:YAG laser was applied with the same parameters as Group V. During laser application the teeth were always filled with irrigating solution. The fiber optic tip was introduced until the apex and the laser was activated. The tip was withdrawn gently with helicoidally movement from the apex until the pulp chamber. After preparation the teeth were immersed in 10% copper sulfate for 30 minutes, in vacuum for the first 5 minutes. The teeth were then placed in a 1% rubianic acid alcohol solution for the same periodsin solution and in vacuum as above. Upon completion of this reaction the teeth were sectioned transversally, in 150micrometers slices, and sanded, washed, dehydrated, cleared and mounted on glass slides for microscopic examination. The quantification of the penetration of copper ions was done by morphmetric analysis with a 400-point grid. The data was submitted to statistical analysis and shoed normality and hemocedacity of the sample, parametric analysis was applied. The Tukey test showed that the cervical and middle thirds were statistically similar (p>0.05) and greater than the apical third (p<0.05). The Scheffe test showed greater dentine permeability in root canals where water and Er:YAG laser were used and significant different from the other treatments (p<0.05). The use of 1% sodium hypochlorite with Nd:YAG laser, distilled and deionized water with Nd:YAG laser and the use of water, were statistically similar (p<0.05) and increased less dentine permeability when compared to other groups. The use of 1% sodium hypochlorite with and without Er:YAG laser application presented statistically similar permeability values (p>0.05) and positioned in an intermediate among the treatments.
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