Effects of different bleaching agent concentrations on surface roughness and microhardness of esthetic restorative materials

Abstract

Objectives

The study assessed the changes in surface roughness and microhardness of three esthetic restorative materials after bleaching with 10%, 20% and 35% carbamide peroxide (CP).

Methods

Standardized cylindrical specimens (n = 210) of 3 esthetic materials (nano composite resin (NC), resin modified glass ionomer (GI), feldspathic porcelain (FP) were fabricated (n = 70). They were divided into 3 groups (n = 20) and a control group (n = 10). Each group was bleached with different concentrations of CP. The specimens of group 1 and 2 (10% CP and 20% CP) were immersed in the bleaching gels for 6 h daily, while group 3 (35% CP) was immersed for 30 min weekly. The control group was stored in artificial saliva. After 21 days, the morphological changes of the specimens were investigated with surface texture analyzer, while the hardness was assessed by performing superficial microhardness analysis. The data were analyzed with one-way ANOVA, and Scheffe test at α = 0.05.

Results

No significant differences in roughness average (Ra) were recorded among the control group and 10% CP bleached groups of all tested restorative materials (NC (p = 0.1495), GI (p = 0.0761), FP (p = 0.2848)). However, there were significant differences in Ra among the control group, 20% CP, and 35% CP (p < 0.05). There were no significant differences in the microhardness of feldspathic porcelain (10% (p = 0.0786), 20% (p = 0.1041), and 35% (p = 0.2066). While nano composite resin and resin modified glass ionomer specimens were significantly affected by concentration of 20% and 35% CP (p < 0.05).

Conclusion

The effect of bleaching depends on the concentration of CP. The higher surface roughness was produced by 35% CP. Bleaching with different concentrations did not reduce the microhardness of the feldspathic porcelain. However, microhardness of nano composite resin and resin modified glass ionomer specimens was affected by 20% CP and 35% CP.