Effect of bleaching agents on the flexural strength of bovine dentin.

The aim of this study was to evaluate the effect of bleaching on the flexural strength of bovine dentin, using bleaching agents containing calcium (Whiteness HP Blue and Whiteness Class) and not containing calcium (Whiteness HP and Whiteness Perfect). Sixty bovine incisor tooth slices were obtained and divided into fve experimental groups (n = 12), such as G1, untreated control group; G2, Whiteness HP Max [35% hydrogen peroxide (HP)]; G3, Whiteness HP Blue (35% HP); G4, Whiteness Class (7.5% HP) and G5, Whiteness Perfect (22% carbamide peroxide). Samples were submitted to bleaching treatment according to the manufacturers' instructions. The control group remained in artificial saliva during bleaching. After bleaching, the enamel was removed and dentin specimens (7 mm length × 1.7 mm width × 0.5 mm thickness) were prepared. Samples were tested in a universal testing machine (EMIC). Data were analyzed by analysis variance (ANOVA) and Tukey's test. Differences between the groups were identified by ANOVA. The mean values (± standard deviation) for the experimental groups, such as (in MPa) G1 = 19.05 ± 2.68 a; G2 = 12.69 ± 4.52 b; G3 = 16.39 ± 3.74 ab; G4 = 14.90 ± 5.60 ab; and G5 = 12.71 ± 2.25 b. Groups with the same lowercase letter were significantly different from each other. The presence of calcium in bleaching agents appeared to influence the flexural strength of bovine dentin after bleaching treatment, for both office bleaching (35% HP) and home bleaching (7.5% HP).

Colour stability, staining and roughness of silorane after prolonged chemical challenges.

OBJECTIVES: To investigate the effect of prolonged chemical challenges on colour stability, staining susceptibility, and roughness of a silorane composite material when compared to methacrylate-based composites. METHODS: Initial colour and roughness were registered for specimens fabricated from methacrylate or silorane composites. Specimens were individually stored at 37°C in 0.02 N citric acid, 0.02 N phosphoric acid, 75% ethanol or distilled water for 7, 14, 21 and 180 days, when new measurements were performed. A staining test was performed after the chemical challenge by immersion in coffee during 3 weeks at 37°C. Colour changes were characterized using the CIEL a b colour system. Data were submitted to analysis of variance for repeated measures, two-way analysis of variance and Tukey's multiple comparison test (α=0.05). RESULTS: Colour changes on the methacrylate-based resins were considered acceptable (although significantly different) after immersion in water, citric acid, phosphoric acid or ethanol, but were unacceptable for the silorane composite immersed in ethanol for 180 days. The methacrylate-based resins stored in ethanol were significantly more stained by coffee than those stored in other media. The silorane composite demonstrated no staining, but increased roughness, when compared to the methacrylate-based resins. CONCLUSIONS: No effect of the immersion solution was noticed on roughness of the investigated materials. Ethanol influenced colour stability and staining susceptibility differently for the methacrylate-based and silorane composites. CLINICAL SIGNIFICANCE: The knowledge of how acids and solvents affect the properties of tooth-coloured restorative materials is one of the decision-making criteria for the selection of a restorative material.