Method:
Three materials were tested: 1) a reinforced zinc oxide-eugenol cement (IRM ® Powder Zinc Oxide Eugenol, Dentsply, Konstanz, Germany), 2) a high copper amalgam with spherical particles (Ventura Finest ®, Madespa SA, Toledo, Spain) and, 3) a nanohybrid composite (EvoCeram Tetric ®, Ivoclar Vivadent AG, Schaan, Liechtenstein). 6 specimens of each of the three materials were used on this study (N = 18). Each material was inserted into silicone molds with circular cavities of 10 mm x 2 mm. 3 specimens of each material were randomly assigned into whitening or control group, for a total of 6 groups. On the whitening groups, the specimens were exposed to a 10% carbamide peroxide gel (Opalescence ® PF 10%, Ultradent, South Jordan, UT, USA) for 14 consecutive days, 6 hours per day. On the control groups, the specimens were exposed to distilled water. After 14 days all specimens were prepared and observed under a scanning electron microscope (Hitachi S-450®). Microphotographs from representative areas of each specimen were taken at magnifications of 33x, 250x, 500x and 1000x.
Result:
All the specimens of the groups exposed to carbamide peroxide revealed an irregular surface, with increased surface porosity and numerous and relatively large cracks and pits. Specimens from the control groups showed regular and smooth surfaces, and although a few notches were visible, those are thought to be the result of the polishing procedures.
Conclusion:
The 10% carbamide peroxide gel seems to create a more irregular and porous surface of the materials tested – reinforced zinc oxide-eugenol cement, amalgam and composite – making that surface, possibly, more prone to staining.