Surface properties of resin-modified glass-ionomers subjected to in-office bleaching agents

This study examined the influence of two in-office bleaching on surface roughness, topography and microhardness of RMGIs. Disc-shape samples of RMGIs (Ketac N100, Fuji II LC-Capsule, and Photac Fil Quick Aplicap) were prepared and polymerized by a LED light curing unit. Polished samples, were subjected to in-office bleaching agents, Opalescence Xtra Boost (OXB) and Pola Office (PO), for 3 consecutive applications of 15 min each. The surface roughness parameters (R-a and R-max, mu m) and Knoop hardness number (KHN, kg/mm(2)) were measured using contact profilometer and microhardness tester, respectively. The surface topography of the bleached surfaces was evaluated by SEM. Two-way ANOVA demonstrated high significant differences between the KHN, R-a and R-max values among the RMGIs and the bleaching agents evaluated as well as their interactions (p < 0.05). Pearson's correlation indicated mainly no significant correlation between KHN and R-a surface finish at each in-office agent for each RMGI (p > 0.05). Low R-a (0.193 mu m) and high KHN (49.34) values were presented in N100, whereas high R-a (0.916 mu m) and low KHN (31.54) were found in PFQ and FII, respectively, after bleaching with OXB. Surface properties are affected by the differences in material's composition, mainly fillers, and type of bleaching agent. High concentration of hydrogen peroxide from bleaching agent and type of RMGIs can influence the chemical softening of these restorations and their clinical durability.