Effects of a 36% tooth bleaching gel on zinc phosphate cement.

Purpose: To assess the effect of a 36% hydrogen peroxide bleaching gel on the roughness, microhardness, indentation modulus, and micromorphology of zinc phosphate cement aged 24 h or 1 week, compared to cement not exposed to bleaching gel.

Methods: Dynamic indentation was performed for microhardness and indentation modulus. Contact profilometry was performed for surface roughness. Scanning electron microscopy assessed micromorphology. Means for microhardness, indentation modulus, and roughness were analyzed for differences among groups (No. 1 = 24 h/control; No. 2 = 24 h/treatment; No. 3 = 1 week/control; No. 4 = 1 week/treatment).

Results: Means (SD) for groups 1-4 respectively: Vickers Microhardness (HV): 34.2(8.7)a, 32.8(10.9)a, 24.8(5.0)b, 41.5(7.4)c; Indentation Modulus (EIT, GPa): 14.2(6.9)a,b, 10.6(3.6)a, 11.2(3.8)a, 14.7(2.8)b; and Surface Roughness (Ra, microns): 1.08(0.38)a, 1.21(0.55)a, 1.55(0.21)b, 1.52(0.29)b. Means labeled with the same superscript were not statistically significantly different. Scanning electron microscopy of groups 1 and 2 revealed similar details. Group 3 surfaces had plate-like crystals not present on the group 4 surfaces.

Conclusions: Bleaching gel exposure increased hardness and indentation modulus and caused limited changes in surface morphology, but the cement was not adversely affected by the bleaching protocol.