The effect of a bleaching system on properties related to different ceramic surface textures

This study examined the effect of a manufacturer's proposed bleaching protocol on surface properties of a low-fusing ceramic.

Forty ultra low-fusing ceramic samples (Ducera LFC) were constructed for this study. Half the discs were autoglazed, and the other half were overglazed. The two main groups (autoglaze, overglaze) were further divided into subgroups of four. Group I: autoglazed (control group I), bleached autoglaze, diamond polished, diamond polished and bleached. The same division was applied to Group II: overglazed (control group II), bleached overglazed, diamond polished, diamond polished and bleached. The total number of subgroups was eight. Control groups I and II (n = 10) were both immersed in distilled water, which was changed daily for 1 week. The other six subgroups (n = 30) were subjected to the following protocol: 2-hour bleaching using carbamide peroxide 35%, followed by six 8-hour bleaching applications using 15% carbamide peroxide gel. Every two bleaching procedures were interrupted by a 10-hour fluoride gel application. At the end of each bleaching step, the treated specimens were washed under running water in readiness for the next application.

Bleaching did not significantly affect the surface roughness of the autoglazed group; however, it significantly increased the roughness of the overglazed ceramic, especially after polishing. Regarding whiteness, the overglazed group had significantly increased values compared to the autoglazed group. It appeared that bleaching whitened the overglazed specimens significantly, whereas polishing alone showed less whiteness. There appeared to be a strong inverse relation between the roughness and the whiteness of the autoglazed specimens as affected by the bleaching. On the other hand, a weak inverse relation was found between the roughness and whiteness of the overglazed specimens, as affected by the bleaching.

In-office bleaching with 35% carbamide peroxide, followed by home bleaching with 15% carbamide peroxide and a fluoride gel may affect the roughness and whiteness of overglazed and polished/overglazed Duceram LFC restorations. No significant change in roughness or whiteness was detected by this bleaching system on autoglazed Ducera LFC. Ceramic restorations should be protected before any bleaching for fear of altering their roughness and whiteness. Patients should be advised that their existing porcelain restorations may not match their natural teeth after bleaching.