Comparison of the mechanical properties of translucent zirconia and lithium disilicate

Abstract

Statement of problem. Three mol% yttria‐stabilized tetragonal zirconia polycrystal (3Y‐TZP) possesses excellent mechanical properties but is relatively opaque. Five mol% yttria‐stabilized zirconia polycrystal (5Y‐ZP) offers improved translucency, but many of its clinical properties have not been compared with those of 3Y‐TZP and lithium disilicate. Purpose. The purpose of this in vitro study was to compare the flexural strength, translucency parameter, bond strength, and enamel and material wear of 5Y‐ZP (Katana UTML) with 3Y‐TZP (Katana HT) and lithium disilicate (e.max CAD). Material and methods. Flexural strength bars were sectioned (n=10, 25×4×2 mm), sintered or crystallized, polished, and fractured at 1 mm/min. Translucency specimens (1 mm thick) were fabricated (n=10). Their L*a*b* values were measured against a black‐and‐white background with a spectrophotometer, and &Dgr;E00 was calculated. Zirconia bond strength specimens were airborne‐particle abraded with 50 &mgr;m alumina followed by the application of a 10‐methacryloxydecyl dihydrogen phosphate–containing primer (Clearfil Ceramic Primer). Lithium disilicate bond strength specimens were etched with 5% hydrofluoric acid followed by application of a silane‐containing primer (Clearfil Ceramic Primer). A Tygon tube filled with resin cement (Panavia SA) was fixed to the surface of the ceramics and light‐polymerized. After 1 day or 150 days of water storage, the resin cement was debonded in a macroshear test (n=10). The cusps of extracted human molars were isolated and mounted into the University of Alabama at Birmingham wear‐testing device. Wear testing was performed with a 20‐N load for 300 000 cycles in 33% glycerin. The volumetric wear of polished zirconia, lithium disilicate, and enamel were measured along with the wear of the opposing enamel cusps using a noncontact profilometer (n=8). The data were compared by ANOVA and Tukey‐Kramer analysis (&agr;=.05). Results. No statistical difference was seen between the bond strengths (P=.155) or the opposing enamel wear (P=.533) of different ceramics. A statistically significant difference was seen between the flexural strength (P<.001), translucency parameter (P<.001), and wear (P<.001) of the materials. The flexural strength values (MPa) were 1194 ±111 (Katana HT), 688 ±159 (Katana UTML), and 450 ±53 (e.max LT). The translucency parameter values were 6.96 ±0.53 (Katana HT), 8.30 ±0.24 (Katana UTML), 9.28 ±0.36 (e.max LT), and 12.64 ±0.48 (e.max HT). Bond strength values (MPa) at 1 and 150 days were 34.22 ±5.14 and 28.37 ±6.03 (Katana HT), 35.04 ±5.69 and 25.03 ±6.44 (Katana UTML), and 35.50 ±3.45 and 22.32 ±3.45 (e.max LT). Material and enamel wear (mm3) were 0 and 0.24 ±0.19 (Katana HT), 0 and 0.23 ±0.09 (Katana UTML), 0.28 ±0.13 and 0.31 ±0.10 (e.max CAD), and 0.09 ±0.03 and 0.31 ±0.14 (enamel). Conclusions. 5Y‐TZP has a flexural strength and translucency parameter between those of 3Y‐TZP and lithium disilicate. Both the short‐term and long‐term bond strength of 5Y‐ZP and 3Y‐TZP was shown to be similar to lithium disilicate. 5Y‐ZP demonstrated no measurable material wear and opposing enamel wear similar to that of all the other materials tested.