Dental bleaching with violet LED: Effects on dentin color change, resin-dentin bond strength, hybrid layer nanohardness and dentinal collagen biostability.

BACKGROUND: The purpose of this study was to investigate the effect of a novel dental bleaching technique with Violet LED on enamel color change, bond strength and hybrid layer nanomechanical properties in resin-dentin restoration, and dentin biostability. METHODS: A total of 125 bovine incisors were distributed into a control group, violet LED group (LED), and 35 % peroxide hydrogen bleaching gel (BLG) groups (n = 15). Three 45-minute sessions were performed for both bleaching procedures every week. Enamel color change (ΔE, ΔL, and Δb) was determined after every bleaching session. After color analysis, dentin was exposed for the resin-dentin bond strength analysis using microtensile test and evaluation of the nanomechanical properties at the hybrid layer (nanohardness). While half of the specimens were tested immediately, the remaining were evaluated after 10,000 thermal cycles (TC). Thirty additional teeth were used to investigate dentin ultimate tensile strength (UTS) after the bleaching treatments. UTS was evaluated before and after an enzymatic challenge. Two-way repeated measures ANOVA and Tukey's post-test were used for the statistical analysis (α = 0.05). RESULTS: Enamel bleaching effect was observed in the LED and BLG groups with significant alterations in the ΔE, ΔL, and Δb in the BLG group. No difference was observed in the resin-dentin bond strength among the groups (p > 0.05), however, TC negatively affected the bond strength values for all the groups. Nanomechanical properties ​​remained unchanged when comparing immediate and after TC results (p > 0.05). Bleaching with BLG reduced significantly the dentin UTS, while all groups showed major decrease in UTS after the enzymatic challenge. CONCLUSIONS: Although violet LED was able to promote a bleaching effect, less color changes was observed when compared to BLG. None of the bleaching techniques effected the resin-bond strength or the nanomechanics of the hybrid layer. Violet LED did negatively effect dentin biostability as observed for BLG and it may promote less changes to the organic content of dentin.

Influence of Cement Type and Relining Procedure on Push-Out Bond Strength of Fiber Posts after Cyclic Loading.

PURPOSE: The aim of this study was to evaluate the influence of cement type and relining procedure on push-out bond strength of fiber posts (FPs) after cyclic loading. MATERIALS AND METHODS: Forty bovine incisor roots were divided into four groups: group 1, FP luting with RelyX Unicem; group 2, FP relined with resin composite (FPC) luting with RelyX Unicem; group 3, FP luting with RelyX ARC; group 4, FPC luting with RelyX ARC. Afterwards, half the specimens were exposed to 250,000 cycles in a controlled chewing simulator. With the other half of the specimens in each group, the push-out test was performed 24 hours after FP luting (immediate groups). All roots were sectioned transversely, producing 1-mm-thick slices, and the push-out test was performed. Statistical analysis was performed using ANOVA and the Tukey test for post hoc comparisons (α = 0.05). RESULTS: FPC had higher bond strengths than FP (p < 0.05). RelyX Unicem showed higher bond strength than RelyX ARC (p < 0.05). Cyclic loading did not significantly affect the bond strength value (p > 0.05). CONCLUSION: The relining procedure and the cement type are important factors for the bond strength of FPs to root dentin.

Evaluation of antimicrobial effectiveness and dentine mechanical properties after use of chemical and natural auxiliary irrigants.

OBJECTIVE: To evaluate the effect of GSE, NaOCl, CHX and QMix as an antimicrobial agents against Enterococcus faecalis and their influence on flexural and ultimate tensile strength of root canal dentine. METHODS: Root canals were divided into five groups (n=10) according to the substances used: 2.5% NaOCl, 2% CHX, 6.5% GSE, Qmix and control group (distilled water) (DW). Final irrigation was done with 17% EDTA in all groups, except when DW was used. The number of colony-forming units was used to evaluate the antimicrobial activity. Dentine beams were used to assess the flexural strength after treatment with substances as described before (n=10). The UTS was evaluated after the treatment of root dentine hourglass shape sections with the same substances (n=30). RESULTS: The lowest bacteria contamination was observed for CHX and GSE, while NaOCl and QMix showed an intermediate antimicrobial activity (p>0.05). NaOCl and QMix significantly reduced the mechanical properties of dentine (flexural strength and UTS) (p<0.05) and no statistical difference was found among CHX, GSE and DW (p>0.05). CONCLUSION: CHX and GSE were more effective than NaOCl and QMix against E. faecalis. Furthermore, they did not harm dentine mechanical properties as observed for NaOCl and QMix. CLINICAL SIGNIFICANCE: The use of GSE can be recommended for endodontic procedures since it has good antimicrobial activity and does not interfere in the mechanical properties of dentine; similarly to CHX.