Effect of home bleaching on surface of zinc phosphate cement: A scanning electron microscopic study

The effect of home bleaching on surfaces of dental cements is controversial.

The aim of this study was to microscopically evaluate and compare the effect of different concentrations of carbamide peroxide (CP) home bleaching agents on the surface of zinc phosphate cement.

Forty 10 mm × 2 mm specimens of zinc phosphate cement were prepared following the manufacturer's directions. All specimens were immersed in artificial saliva at 37°C for 24 h. The specimens were equally divided into four groups (n = 10). One control group received no CP bleaching. Three experimental groups were exposed to 10%, 16%, and 22% of CP home bleaching agents. The bleaching agents were applied daily for 4 h for 14 days. Specimens were stored in artificial saliva at 37°C for 24 h and then examined under a scanning electron microscope. The surface micromorphology of the specimens was carefully evaluated and compared.

The zinc oxide particles in the specimens of the control group were tightly packed with well-defined plate-like crystals. When specimens were exposed to 10% CP gels, the particles became flat and irregular with few areas of eroded matrix. When 16% CP gel was used, the crystals became flatter and irregular with rounded edges. Bleaching with 22% CP gel showed little more erosion of the surface of the matrix of the cement. Fewer flat and irregular crystals were observed on the surface of the cement.

At-home bleaching using 10%, 16%, and 22% CP may be safely used in the presence of zinc phosphate-luted crown restorations without adverse effects.