Abstract
Aims: To determine if the composite resin restoration need to be replaced after power bleaching atdifferent times.Materials and methods: Three composite resins (a flowable, a conventional andceramic composite) were used for this study. Transparent discs with 2mm thickness with a hole of5mm diameter were used for the production of composite samples, six samples were made for eachtype of composite with a total of 18 samples were used. The bleaching procedure was followed on thetop surface of each sample. For each sample a newly fresh material were mixed (lase peroxide sensygel) and applied over the prepared sample. Bleaching took place for 15, 30 and 45 minutes according tothe manufacturer instructions. For the microhardness measurements, a Vickers microhardness tester(Wolpert, Germany) was used, with a 200g load. Five microhardness measurements were obtained onthe top surface of each sample on the following time periods: before bleaching, after 15 min., after 30min. and after 45 min. of bleaching. Data were analyzed using T-test, a value of p≤0.05 was consideredsignificant followed by the analysis of variance (ANOVA). Results: The results showed a significantincrease in the microhardness of all the three types of composite resins after bleaching with a differenttime when compared to the control.Conclusion The bleaching agent that was tested has a significantincrease of the microhardness of the composite resins and there is no sufficient reason to indicate thereplacement of restorations.
