Gastric acid challenge of lithium disilicate-reinforced glass-ceramics and zirconia-reinforced lithium silicate glass-ceramic after polishing and glazing-impact on surface properties

Objectives To investigate the impact of simulated gastric acid on the surface properties of lithium disilicate-reinforced glass-ceramics and zirconia-reinforced lithium silicate glass-ceramic after certain polishing and glazing procedures. Materials and methods Four different types of square-shaped specimens (10x10x2 mm(3), n=13) were manufactured: lithium disilicate-reinforced glass-ceramic milled and polished (LDS-P); milled, polished, and glazed (LDS-PG); milled, glazed, and no polishing (LDS-G); and milled and polished zirconia-reinforced lithium silicate glass-ceramic (ZR-LS). Specimens were immersed in hydrochloride acid (HCl 0.06 M, pH 1.2) to simulate gastric acid irritation and stored in the acid for 96 h in 37 degrees C. Specimen weight, surface gloss, Vickers surface microhardness and surface roughness (R-a, R-q, with optical profilometer), and surface roughness on nanometer level (S-q, S-al, S-q/S-al, S-dr, S-ds with atomic force microscope) were measured before and after the acid immersion. Results ZR-LS specimens lost significantly more weight after acid immersion (p=0.001), also surface microhardness of ZR-LS was significantly reduced (p=0.001). LDS-G and LDS-PG showed significantly lower surface roughness (S-a, S-q) values compared to LDS-P before (p <= 0.99) and after (p <= 0.99) acid immersion and ZR-LS after acid immersion (p <= 0.99). Conclusions Gastric acid challenge affects the surface properties of lithium disilicate-reinforced glass-ceramic and zirconia-reinforced lithium silicate glass-ceramic. Glazing layer provides lower surface roughness, and the glazed surface tends to smoothen after the gastric acid challenge.