[ effect of bleaching products on hardness of glass ionomer cements]

The use of bleaching agents for the sake of whitening teeth has extended for many years. On the other hand, due to the simultaneous presence of a series of tooth colored restorations and existence of few research studies on the effect of different whitening materials on the tooth restorations, the present study with the aim of determining the efficacy of carbamide peroxide on the hardness of Glass Ionomer cements had been emerged. Forty numbers of glass ionomer cylinders were prepared and preserved for 48 hours in 100% humidity and in the room temperature, then were divided into 4 groups each contained 10 samples. The bleaching gel 16% VARI-SHADE [Lochemco USA] was applied for groups I to IV as respectably o, 21, 42, 63 hours. Finally the microhardness of each sample group was measured by Vickers's machine. Microhardness mean was respectively 27.37 +/- 2.4, 25.98 +/- 2.7, 24.41 +/- 3.6 and 26.02 +/- 3.7 in group I to IV, and there was no significant difference between them. Vari-shade bleaching gel did not result to reduced microhardness of Vitremer glass-ionomer in the studied time

[Effect of plasma ARC and halogen lights on composite microhardness]

Together with the controversy which exists in the efficacy of new PAC light curing units, this study evaluated the irradiation effect of plasma ARC and halogen light curing units on the microhardness of three resin composites. In this experimental study, two light - curing units including Remecure CL 15 [PAC] [with the output of 1600 mW/cm[2]] and Arialux [QTH] [with the output of 710 mW/cm[2]] were used. Six specimens of three type of resin composite were prepared in a steel mold with 2mm thickness. The three composites were CeramX [Dentsply], Heliomolar [Vivadent] and Z100 [3M]. Curing time with Remecure was 5 seconds and with Arialux was as the composite manufacturer recommended. After 24 hours, vickers hardness measurements on top and bottom surfaces of each specimen were made and the bottom/top vickers hardness [B/T VHN] was determined. Microhardness of two surfaces in each group was compared by t, 2-way ANOVA and Tukey tests. For Ceramx composite two light curing units showed the same microhardness on the top and bottom surfaces. Heliomolar showed significantly lower values of microhardness on both surfaces and B/T VHN with Remecure. In Z100 specimens microhardness [on both surfaces] was lower with Remecure but B/T VHN was the same [P<0.05]. Except Heliomolar specimens which were cured by Remecure, B/T VHN was acceptable in all groups [more than 80%].The efficiency of Remecure unit in manufacturers' instruction time was equivalent or lower than conventional halogen light depending on the type of resin composite