Bond strength of resin composite to enamel submitted to at-home desensitizer and bleaching agents

Aim: This study evaluated the effect of a desensitizer agent (DES) during bleaching with 10% carbamide peroxide (CP) on enamel microshear bond strength (µSBS). Methods: Sixty bovine incisors were obtained and randomly distributed into groups (n=15): (C) Control: no desensitizing or bleaching, (DES) desensitizing gel application, (CP) bleaching with 10% CP and (CP/DES) bleaching with 10% CP combined with DES. Bleaching was performed for 6 h/day for 14 consecutive days. DES was applied for 8 h only on the 7th and 14th days of therapy. Specimens were stored in artificial saliva among the CP or DES applications and submitted to µSBS testing at three postrestoration times (n=5): 24 h, 7 days, and 14 days after bleaching using a universal testing machine. Failure modes were observed under a stereomicroscope. Data were analyzed by two-way ANOVA and Tukey's test (α=5%). Results: Immediately after bleaching (24 h), CP promoted lower µSBS than the C and DES groups (p<0.05) but with no differences from the CP/DES. µSBS increased in the DES, CP, and CP/DES groups (p<0.05) when bonding was performed for 7 or 14 days elapsed from bleaching. CP/DES exhibited the highest µSBS among the groups 14 days after bleaching (p<0.05). Cohesive failure in enamel was predominant in the CP groups, while adhesive failure was mostly observed for the other groups. Conclusion: The use of a desensitizer during at-home bleaching maintained the enamel immediate bond strength, and its application favored bonding when the restoration was delayed for 14 days

Effect of wetting agent coverage on the surface properties of resin composite submitted to brushing and staining cycles.

BACKGROUND: Wetting agents facilitate the composites handling, acting as a lubricant and decreasing their stickness to spatula. The effects of these materials on the properties of composites are not completely clear. This study aimed to evaluate Gloss, Color, Roughness and Microhardness of a composite (Filtek Z250 XT, 3M Oral Care) covered by a wetting agent (Modeling Resin, Bisco), submitted to brushing and staining cycles with red wine. MATERIAL AND METHODS: Cylinder-shaped samples (8 mm ø x 2 mm height) were divided into 4 groups, according to application of wetting agent and brushing cycles (n = 20). The composite was placed in the orifice of a polytetrafluoroethylene mold, received wetting agent coverage, and was light-cured. Gloss, Color, Roughness and Microhardness were evaluated in two times: after samples confection and after brushing + staining cycles. Data were submitted to one-way ANOVA and Tukey's test (ΔL, Δa, Δb and ΔE) and two-way repeated measures ANOVA and Bonferronis's test (gloss, roughness and microhardness). RESULTS: In general, the composite showed higher gloss values when added by the wetting agent. No statistical differences were observed regarding colors' groups. Roughness increased after brushing cycles, regardless of wetting agent application. The only group which presented decreased Microhardness after cycles was the group without wetting agent, only submitted to staining with red wine. CONCLUSIONS: The application of wetting agent on the composite did not interfere negatively with its properties of Gloss, Color, Roughness and Microhardness. Key words:Resin composite, wetting agent, surface properties, gloss, color, esthetic dentistry.

Decomposition Rate, pH, and Enamel Color Alteration of At-Home and In-Office Bleaching Agents.

This study evaluated the decomposition rate (DR), pH, enamel color alteration (DE) and whiteness index (DWI) promoted by at-home and in-office bleaching. Enamel surface was submitted to (n=10): at-home (10%, 15%, 20% carbamide peroxide - CP, 6% hydrogen peroxide -HP) and three 35% HP agents with light irradiation (LED, laser, and halogen) or no treatment (control). The DR and pH of agents were measured after 0, 2, 4, 6 and 8 h (at-home) or after 5, 15, 20, 30 and 40 min (in-office). Color parameters (L*, a*, b*, DE, DWI) were determined at baseline and after bleaching. DR, pH, L*, a*, b* data were analyzed by one-way (at-home) or two-way (in-office) repeated measures ANOVA and Tukey test. DE and DWI, by one-way (at-home) or two-way (in-office) ANOVA and Tukey test. DR of at-home agents was similar after 6 and 8 h (p>0.05), with pH close to neutral (6.5 to 6.9, CP) or acid 5.9 (6% HP). From 4 to 8 h, DE was higher for 15% and 20% CP compared with 10% CP (p<0.05). After 40 min, DR of 35% HP agents was similar and all exhibited significant DE in one application (p<0.05), regardless light irradiation. DWI indicated whitening effect with no differences among groups (p>0.05). One 35% HP showed alkaline pH, and the others, pH < 5.5. At-home agents could be applied for 2 h (15%, 20% CP, 6% HP) and 4 h (10% CP) and the in-office agents, up to 40 min in one application, without light.

Evaluation of home bleaching gel modified by different thickeners on the physical properties of enamel: An in situ study.

OBJECTIVE: This in situ study evaluated the influence of 10% carbamide peroxide (CP) in combination with different thickeners on physical characteristics of enamel. MATERIALS AND METHODS: Eighty-four bovine blocks of enamel and dentin (4 mm × 4 mm × 2.5 mm) were divided into seven groups (n = 12), fixed in palatal intraoral devices, and submitted to different treatments: CP + carbopol (FGM), CP + carbopol + glycerin (ultradent), CP + natrosol (experimental gel), carbopol, carbopol + glycerin, and natrosol, without treatment (control group). The physical properties tested were color (ΔE), roughness (Ra), and Knoop microhardness (KHN). STATISTICAL ANALYSIS USED: Data were submitted to ANOVA, Tukey's, and Dunnett's tests (α = 0.05). Results: all groups presented significant color variation, except carbopol. For microhardness, all bleached groups did not differ from control. Roughness increased in all bleached groups when compared to the control group, but CP + natrosol presented statistical lower results than CP + carbopol. CONCLUSION: Replacement of carbopol by natrosol caused less change on roughness surface, at the same time yielding an effective whitening result.