Shaping outcomes using two Ni-Ti rotary instruments in simulated canals.

AIM: The aim of this study was to compare the shaping ability of Mtwo and ProTaper instruments in simulated curved root canals in resin blocks. METHODS: The study was carried out using 40 simulated canals in resin blocks, all of which had the same canal diameter (0.70 mm>D>0.20 mm), length (16 mm), and angle of curvature (40 degrees). These 40 canals were divided into 2 groups of 20 specimens. Both before and after instrumentation, all the resin specimens were photographed, and all the canals examined were measured at 4 different points of reference. Using a computer image analysis program, the photographs of corresponding sections were superimposed on one another. In this way we sought to evaluate the shaping ability of these 2 systems in relation to specific portions of the root canal, also with regard to maintenance of original canal curvature. The results were analysed using Student's t-test. RESULTS: Both rotary systems were found to respect the original root canal curvature, particularly in the areas most at risk of modification, namely the outer aspect of the curve in the apical third of the canal. The Mtwo instruments caused less transportation of the apex than the ProTaper instruments, but this difference was not statistically significant (P>0.05). CONCLUSION: According to the results of this study, both these instruments respected the original canal curvature, particularly in the areas at most risk of modification, and they also showed good shaping ability in curved canals, with minimum transportation of the apex.

Bond strength to deep coronal dentin: effect of bonding strategies.

AIM: The aim of this study was to evaluate bond strength at the composite-adhesive-deep dentin interface following pre-treatment with sodium hypochlorite using 4 different types of enamel-dentin adhesive and a composite for the core. METHODS: From 60 healthy human molars, cylindrical samples (3 mm high) were obtained using a special slow-speed saw. Cavities with 2-5-mm diameters were made in all the samples. Samples were assigned to 8 groups, 4 groups were designated as experimental groups and were irrigated with NaOCl and the other 4 groups designated as control groups were irrigated with distilled water. Adhesive systems were applied to the samples and then restored using a core build-up composite. Samples were subjected to shear stress test using an electronic dynamometer. RESULTS: The data were analyzed using one-way ANOVA and the Tukey test (P<0.05). The results, in terms of bond strength, demonstrate that the two-step self-etch adhesive systems generate a stronger bond than the other systems considered in the study (P<0.05). The results also show that pre-treatment with hypochlorite does not seem to influence the bond strength of self-etch adhesive systems. CONCLUSIONS: This in vitro study demonstrates that there exist differences in bond strength between self-etch and etch & rinse adhesive systems on deep dentin pretreated with sodium hypochlorite to simulate endodontic treatment.