To evaluate by scanning electron microscopy (SEM), the effects of external tooth whitening on the surface ultramorphology of two different types of resin-composite.
Method:
Eighteen (N=18) specimens were assigned to six groups using two different resin-composites: 1) a nanohybrid resin-composite (Tetric EvoCeram®, Ivoclar Vivadent AG, Schaan, Liechtenstein) and 2) a nanofill resin-composite (Filtek Supreme XT®, 3M ESPE, St. Paul, MN, USA); and three different whitening protocols: 1) 10% carbamide peroxide (CP), 2) 22% CP and, 3) control group. For each group, the resin-composite was placed into a silicon mold (10x2mm) and light-cured through a glass plate. After polishing procedures, the specimens of each composite were randomly divided among the six groups. For the whitening groups, the gel was applied (10% and 22% White Dental Beauty®, Optident, West Yorkshire, UK) for a period of 14 days, 6h per day. For the control groups the specimens were exposed to distilled water only. All specimens were stored in an incubator (37°C, 14d) and then prepared and observed by SEM (Hitachi S-450®). It was also measured the hydrogenionic potencial (pH) of the PC gels used.
Result: The SEM analysis of both resin-composites of the whitening groups showed superficial cracks and numerous pores, highlighting a real separation between the resin matrix and the composite fillers, regardless of the gel concentration. These changes were more notorious on the nanohybrid composite. 10% and 22% PC gels have a pH value of 6.71 and 7.42, respectively.
Conclusion:
The 10% and 22% PC led to changes on the surface of both resin-composites. These alterations are more pronounced on the nanohybrid composite, regardless of the concentrations used, which may yield a decrease on the resin-composite properties.