esin-modified glass–ionomer cement, the surface microhardness increased31 or remained stable41 after treatment with 10% CP. The elevated surface microhardness of resin-modified glass–ionomer cement was thought to be related to erosion of bleaching agents. By contrast, when utilizing a higher concentrated bleaching regimes (15% CP and 35% HP), a significant decrease in the surface microhardness of resin-modified glass–ionomer cement was reported.