Objective
To compare the effect of two bleaching systems (bleaching gel and whitening strips) on the color change, roughness, and microhardness of enamel and two resin composites.
Material and methods
Two cavities were prepared on bovine enamel specimens (n = 16) and restored with two composites: a nano-hybrid [Herculite Ultra (HU)] and a micro-hybrid composite [TPH Spectra (TS)]. Baseline color (CIE L*a*b*), roughness (μm), and microhardness (kgf/mm
2
) were measured using a spectrophotometer, optical profilometer, and Vickers microhardness (VHN) tester, respectively. The specimens were stained with coffee for 14 days, and randomized into two bleaching groups: gel and strips (n = 8), then submitted to a 10-day bleaching/staining test. Color, roughness, and microhardness were re-measured. The outcomes were analyzed using two-way ANOVA and Fisher’s-PLSD test (α = 0.05).
Results
Gel significantly improved the color (ΔE 4.9–8.3) and increased the roughness (Ra 0.04–0.08 μm) of all substrates (p < 0.0001) compared to strips. Enamel color was significantly improved (ΔE 5.4–8.3) compared to that of HU (ΔE 2.6–4.9) and TS (ΔE 2.0–4.9) with either gels or strips. TS roughness (0.03–0.08 μm) was significantly higher than that of enamel (0.01–0.05 μm) and HU (0.02–0.04 μm). Enamel had significantly reduced microhardness compared to HU (p = 0.0144).
Conclusion
Gels produced the greatest color improvement and roughness compared to strips. Enamel had significant color improvement but had the greatest decrease in microhardness.
Clinical significance
There was unacceptable color change between enamel and the composites after the combined cyclic effects of staining and bleaching.
We compared a zinc-reinforced glass ionomer restorative material (ChemFil Rock) with three commercially available glass ionomer cements (GICs), namely, Fuji IX GP Extra, Ketac Molar Quick Aplicap, and EQUIA Fil, with respect to fracture toughness, microhardness, roughness, and abrasive wear. Fracture toughness (K IC ) was tested according to ISO 13586 (n = 10). Hardness, roughness, and abrasive wear were also tested (n = 9). Data were analyzed using the Wilcoxon rank-sum test with adjustment for multiple comparisons (α = 0.05). As compared with the other GICs ChemFil Rock exhibited a greater increase in surface roughness (P < 0.05) and lower microhardness (P < 0.01). The wear resistance of ChemFil Rock was comparable to that of the other GICs (P > 0.05). ChemFil Rock had significantly lower fracture toughness as compared with EQUIA Fil (P = 0.01) and significantly higher fracture toughness as compared with the other GICs (P < 0.02). In conclusion, as compared with the three other commercially available GICs, ChemFil Rock had intermediate fracture toughness, the lowest microhardness, and the greatest change in surface roughness. (J Oral Sci 56, 11-16, 2014)
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