Influence of Viscosity and Thickener on the Effects of Bleaching Gels.

OBJECTIVE: This study investigated the influence of the viscosity and kind of thickener of 35% hydrogen peroxide bleaching gels on the tooth (color change, demineralization of enamel, and permeation) and on the gel [reactive oxygen species (ROS), pH, and peroxide concentration]. METHODS AND MATERIALS: Two hundred forty specimens were divided into groups of bleaching gels with different thickeners (CAR, carbomer; ASE, alkali swellable emulsion; MSA, modified sulfonic acid polymer; SSP, semisynthetic polysaccharide; PAC, particulate colloids) in three viscosities (low: 50,000 cP; medium: 250,000 cP; high: 1,000,000 cP). Color change (ΔEab), demineralization of enamel by Knoop microhardness (KHN) reduction analysis, and peroxide permeation (PP) were analyzed in the specimens, while pH, peroxide concentration (PC), and ROS were evaluated in the gels. Data were analyzed by two-way ANOVA (α=0.05). RESULTS: The higher viscosity gels reduced ΔEab, PP, enamel softening, and ROS in relation to the lower viscosity gels. However, the drop in pH and PC were higher in the more viscous gels. Gels with MSA produced higher ΔEab compared with SSP and ASE. The PP was higher for PAC, and smaller for SSP and CAR. The KHN reduction was higher for CAR and smaller for PAC. The higher pH reduction was seen for ASE and CAR, and the smaller for SSP. The PC reduction was higher for SSP and smaller for CAR. More ROS were observed for MSA and fewer for ASE. CONCLUSIONS: Increased gel viscosity was associated with reduced color change, permeation, demineralization of enamel, and ROS, and led to increased peroxide decomposition and pH alteration during the treatment. The kind of thickener significantly interfered with the treatment effects.

Optical Property Stability of Light-Cured versus Precured CAD-CAM Composites.

Objective: The aim of this study was to evaluate the optical property changes after staining of precured (PC) and light-cured (LC) composites. Materials and Methods: Specimens were prepared using different LC composites (GrandioSO-Voco, Filtek Z350-3M/ESPE, Opallis-FGM, and Kalore-GC) and four PC blocks (Grandio Blocs-Voco, Lava Ultimate-3M ESPE, Brava Block-FGM, and Cerasmart-GC) from the same manufacturers (n = 20). Baseline color, gloss, translucency, and fluorescence were evaluated. The staining protocol was performed for 15 days, and the final optical properties were reevaluated. Results: The changes in each property were calculated (ΔGloss, ΔTranslucency, ΔFluorescency, ΔE ∗ 00). Data were analyzed by ANOVA and Tukey's test (α = 5%). Changes in all properties were observed after staining for all materials, with darkening and reduction of gloss, fluorescence, and translucency. Nonsignificant differences were observed between the light-cured and precured materials of the same manufacturer for ΔG and ΔT, but significant differences existed for ΔF and ΔE ∗ 00. For ΔF, the only significant differences were observed between Brava Block and Opallis (smaller). For ΔE ∗ 00, only the light-cured composites GrandioSO and Z350 showed significantly less change than the corresponding blocks. Precured composites were affected the same way as light-cured ones by the staining in relation to the reduction of gloss and translucency. Conclusion: A higher reduction in fluorescence was observed for only one brand of block and was similar for the others. The two brands of light-cured materials showed less staining, while for the others, the staining was similar. The effects of staining vary according to the composite formulation.