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 (10 × 10 × 2 mm, 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 °C. Specimen weight, surface gloss, Vickers surface microhardness and surface roughness (R , R , with optical profilometer), and surface roughness on nanometer level (S , S , S /S , S , S 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 , S ) 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. Clinical relevance: Surface finish of lithium disilicate–reinforced glass–ceramic and zirconia-reinforced lithium silicate glass–ceramic has a clear impact on material’s surface properties. Gastric acidic challenge changes surface properties but glazing seems to function as a protective barrier. Nevertheless, also glazing tends to smoothen after heavy gastric acid challenge. Glazing can be highly recommended to all glass–ceramic restorations but especially in patients with gastroesophageal reflux disease (GERD) and eating disorders like bulimia nervosa.