Comparison of Different Bleaching Treatments Effect on Micro Hardness of Four Different Aged Composites

In this study, four different types of composite samples were aged then exposed to 16% carbamide peroxide and 40% hydrogen peroxide, and the results were compared to a control group..
The aim of this study was to investigate variations of micro hardness in types of composite materials after bleaching treatments and comparison of hardness in types of composites..
From each composite, (Z100, Z250, Z350, P90) 36 composite discs were prepared with dimensions of up to 3 × 8. The samples went through the aging process for four weeks, and then they were placed in a thermocycling device for 5000 cycles. The composite samples were divided to duodenary three subgroups and each subgroup was exposed to different bleaching treatments including: 1. untreated control group, 2% - 35% hydrogen peroxide (Office B.) and 3% - 16% carbamide peroxide (Home B.). After 14 days of treatment, micro hardness of composite samples (Vikers) was evaluated. The obtained data were analyzed via Analysis of Variance (ANOVA) and Tukey tests and significance level was determined as 0.05..
The mean values of VHN after home bleaching treatment in composite Z100 (163.0), Z250 (100.4), Z350 (116.7) and P90 (80.0) were different from non-treated group including Z100 (146.8), Z250 (84.0), Z350 (110.4) and P90 (76.8), yet this difference was not significant. While in the after office bleaching treatment, the results of mean value were as follows, Z100 (163.0), Z250 (100.4), Z350 (116.7), P90 (80.0) Z100 and Z350; a significant increase in hardness was seen in both groups..
Aged composite bleaching leads to an increase or no change in microhardness compared to the control group that depends on the type of restorative material and bleaching agent. Meanwhile, in the composite examined in this study, the highest rate of microhardness was related to composite Z100 and subsequently Z350 and the lowest rate was related to both composites Z250 and P90..