PH-Cycling Effects on Mechanical and Optical Properties of Veneering Ceramics.

Objectives: To evaluate changes in flexural strength and translucency of veneering ceramics for glass-ceramic, and zirconia copings by exposing them to various ph cycling.
Methods: Disc-shaped specimens (Φ14 x 1 mm) of Vita PM9 (feldspar), IPS InLine PoM (leucite-containing), and IPS e.max Zirpress (nano-fluorapatite) were fabricated using the lost-wax method while IPS e.max Ceram (nano-fluorapatite) were prepared using the enameling technique. The top and bottom surfaces of the disc specimens were polished to a 1-μm finish. Half of specimens were subjected to pH cycling by alternating the samples between solutions of pH 2 and pH 10, 3 days at a time, for 60 days. All samples had the CIEL*a*b* coordinates measured over a black and white background for translucency calculations (TP). Flexural strength of both groups was measured using the piston-on-three-balls test. Data was analyzed using ANOVA and T-tests.
Results: After pH cycling, a significant deterioration in both flexural strength and translucency were observed for e.max Ceram, prepared by the enameling technique, due to localized elemental dissolution, leading to the formation of large flaws both on the surface and in the bulk. e.max ZirPress showed no change in translucency and flexural strength. Lastly, an increase in flexural strength was seen for PoM and PM9 specimens subjected to pH cycling relative to their baseline counterparts.
Conclusions: Glass ceramics are susceptible to surface degradation and corrosion, which affects their physical and optical properties. However, the susceptibility to corrosion is determined by the material’s microstructure and fabrication technique.