Zirconia gradation and thermal expansion compatibility between infiltration glass and antimicrobial glass

This study evaluated an infiltration glass over zirconia in order to form a graded layer with thermal expansion coefficient compatibility and antimicrobial capacity. 210 discs of 3Y-TZP were polished and divided into groups: YZ sintered (Sintered), YZ glazed (Glaze), YZ + Ag 5% (Ag 5%), YZ + Ag 4% (Ag 4%), YZ glass infiltrated (INF.), YZ glass infiltrated + Ag 5% (INF. + Ag 5%) and YZ glass infiltrated + Ag 4% (INF. + Ag 4%). Analyzes of biaxial flexural strength, X-ray diffraction (XRD), EDS, translucency, scanning electron microscopy (SEM) and fractographic were performed. The biofilm was quantified by counting the colony forming units (CFU/mL) of S. mutans. Strength values (MPa), translucency and CFU data were analyzed by one-way ANOVA and Tukey's test (α = 0.05). Weibull analysis was performed to calculate the material's modulus (m) and characteristic strength (95% CI). Infiltrated zirconia glass (INF.: 1149.7; INF. + Ag 4%: 928.2; INF. + Ag 5%: 791.5), sintered (819.0) or glazed (790.8) showed higher flexural strength (MPa) than silver-doped soda-lime glass zirconia without infiltration glass (Ag 5%: 612.1; Ag 4%: 519.2). Diffractograms showed combeite crystals in INF. + Ag 4%/5%. EDS analysis of Ag 5% group showed the higher quantity of silver when compared to INF. + Ag 5% group. Silver-doped soda-lime glass did not affect the translucency, while infiltration glass decreased the values. SEM showed irregularities on the surface of the silver-doped soda-lime glass groups and a smooth surface on the glass and glaze groups. Fracture origin of all groups was in the glaze layer and silver-doped soda-lime glass, while it was inside the zirconia in the INF. group. Lowest colony growth was observed in the Ag 5%. Glass-infiltrated zirconia showed greater strength, while Ag 5% presented greater antimicrobial capacity. The application of silver-doped soda-lime glass did not influence zirconia translucency, while glass infiltration decreased it.