Chia-Ling Li, Ping-Ju Chen, Jui-Che Lin, Shu-Fen Chuang
Optical behaviors of zirconia ceramics are governed by composition and microstructure. Opaque zirconia, particularly at greater thickness, significantly impairs post-curing polymerization of resin cement.
BACKGROUND/PURPOSE: Adequate polymerization of resin luting cements is essential for durable bonding in zirconia restorations. However, variations in zirconia microstructure and composition may influence translucency and light transmittance, thereby affecting resin cement polymerization. This study aimed to investigate the optical properties of conventional and high-translucency zirconia ceramics and their effects on resin cement polymerization.
MATERIALS AND METHODS: Six zirconia ceramics were evaluated: CerconBase, CerconHT, and VitaHT (3Y-TZP); VitaST (4Y-PSZ); and CerconXT and VitaXT (5Y-PSZ). Disk specimens (0.5 and 1.0 mm thick) were fabricated and sintered. Grain size and elemental compositions were analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy, and phase composition was assessed by X-ray diffraction. Optical properties, including light transmittance, translucency parameter (TP), and contrast ratio (CR), were measured using a UV-NIR spectrophotometer. A light-curable resin cement (Variolink N base) was polymerized through zirconia disks, and surface microhardness was measured immediately and after 24 h.
RESULTS: Two 5Y-PSZ ceramics (CerconXT, VitaXT) exhibited the highest cubic-phase fractions (48.66-54.36%), and larger grain sizes, whereas 3Y-TZP showed finer grains. Light transmittance at 468 nm was lowest for CerconBase (15.52% and 10.33% at 0.5 and 1.0 mm, respectively), while other zirconia exhibited higher and comparable values (24.63-31.41%). TP and CR followed similar trends. Although immediate microhardness values were comparable, resin cement polymerized through 1.0-mm-thick CerconBase exhibited significantly lower microhardness after 24 h.
CONCLUSION: Optical behaviors of zirconia ceramics are governed by composition and microstructure. Opaque zirconia, particularly at greater thickness, significantly impairs post-curing polymerization of resin cement.