Effect of different fabrication processes and coloring on the properties of monolithic alumina

OBJECTIVES: To investigate the effect of different alumina fabrication techniques and sintering temperatures on the biaxial flexural strength. Also, to assess the resulting color of multiple metal salt solutions at different concentrations in monolithic alumina and its effect on the optical properties of the restoration. MATERIAL & METHOD: Forty disk-shape alumina specimens were divided into 4 groups (n=10) based on the fabrication process (slip cast or die press) and sintering temperature (1530°C or 1600°C). Biaxial flexural strength was calculated using universal testing machine at a crosshead speed rate of 0.5 mm/min until failure occurred. For the coloring part of the study, nine elements (Ba, Ce, Cr, Fe, Mn, Nd, Pr, Sm, Zn) were used to form metal-salt coloring solutions at a concentration of 0.1%, 1% and 5% wt. The solutions were then used to infuse 162 pre-sintered porous alumina disks that are either slip-casted (A1000) or die-pressed (CT3000). Color coordinates were recorded in CIE L*a*b* system using spectrophotometer. Color differences relative to the control (ΔE), translucency parameter (TP), contrast ratio (CR) and total transmission were calculated and analyzed using two-way analysis of variance (ANOVA) with Tukey post hoc test at α = 0.05. RESULTS: Slip cast group sintered at 1530°C had the highest flexural strength (479.14 MPa), but there was no significant difference between the four groups neither by fabrication process (p = 0.127) nor by sintering temperature (p = 0.276). Die press specimens colored with Ba at 0.1% and 1% showed significantly higher TP (2.65 and 2.49) and lowest CR (96.15 and 96.30) among the groups. There was a statistically significant effect on TP and CR when changing alumina powder on specimens colored by Ba, Ce, and Zn (p < 0.05). Changing the concentration of the coloring solution caused a significant effect on the optical properties of specimens colored by Ba, Nd, Cr, Mn. ΔE was significantly changed when changing alumina powder and coloring concentration for all ...