During the past decade, zirconia-based ceramics have been successfully introduced into the clinic to fabricate fixed dental prostheses (FDPs), along with a dental computer-aided/computer-aided manufacturing (CAD/CAM) system. In this article (1) development of dental ceramics, (2) the current status of dental CAD/CAM systems, (3) CAD/CAM and zirconia restoration, (4) bond between zirconia and veneering ceramics, (5) bond of zirconia with resin-based luting agents, (6) surface finish of zirconia restoration and antagonist enamel wear, and (7) clinical evaluation of zirconia restoration are reviewed. Yttria partially stabilized tetragonal zirconia polycrystalline (Y-TZP) showed better mechanical properties and superior resistance to fracture than other conventional dental ceramics. Furthermore, ceria-stabilized tetragonal zirconia polycrystalline and alumina nanocomposites (Ce-TZP/A) had the highest fracture toughness and had resistance to low-temperature aging degradation. Both zirconia-based ceramics have been clinically available as an alternative to the metal framework for fixed dental prostheses (FDPs). Marginal adaptation of zirconia-based FDPs is acceptable for clinical application. The most frequent clinical complication with zirconia-based FDPs was chipping of the veneering porcelain that was affected by many factors. The mechanism for the bonding between zirconia and veneering ceramics remains unknown. There was no clear evidence of chemical bonding and the bond strength between zirconia and porcelain was lower than that between metal and porcelain. There were two alternatives proposed that might avoid chipping of veneering porcelains. One was hybrid-structured FDPs comprising CAD/CAM-fabricated porcelain parts adhering to a CAD/CAM fabricated zirconia framework. Another option was full-contour zirconia FDPs using high translucent zirconia. Combined application of silica coating and/or silane coupler, and 10-methacryloyloxydecyl dihydrogen phosphate is currently one of the most reliable bonding systems for zirconia. Adhesive treatments could be applied to luting the restorations and fabricating hybrid-structured FDPs. Full-contour zirconia FDPs caused concern about the wear of antagonist enamel, because the hardness of Y-TZP was over double that of porcelain. However, this review demonstrates that highly polished zirconia yielded lower antagonist wear compared with porcelains. Polishing of zirconia is possible, but glazing is not recommended for the surface finish of zirconia. Clinical data since 2010 are included in this review. The zirconia frameworks rarely got damaged in many cases and complications often occurred in the veneering ceramic materials. Further clinical studies with larger sample sizes and longer follow-up periods are required to investigate the possible influencing factors of technical failures.

Two types of tetragonal zirconia polycrystals (TZP), a ceria-stabilized TZP/Al2O3 nanocomposite (CZA) and a conventional yttria-stabilized TZP (Y-TZP), were sandblasted with 70-μm alumina and 125-μm SiC powders, then partially annealed at 500-1200℃ for five minutes. Monoclinic ZrO2 content was determined by X-ray diffractometry and Raman spectroscopy. Biaxial flexure test was conducted on the specimens before and after the treatments. Monoclinic ZrO2 content and biaxial flexure strength increased after sandblasting, but decreased after heat treatment. However, in both cases, the strength of CZA was higher than that of Y-TZP. Raman spectroscopy showed that a compressive stress field was introduced on the sample surface after sandblasting. It was concluded that sandblasting induced tetragonal-to-monoclinic phase transformation and that the volume expansion associated with such a phase transformation gave rise to an increase in compressive stress on the surface of CZA. With the occurrence of such a strengthening mechanism in the microstructure, it was concluded that CZA was more susceptible to stress-induced transformation than Y-TZP.

A bi-axial flexure test (piston-on-three-balls), a four-point flexure test, and a diametral tensile test were used to measure the failure stress of four brittle dental materials: zinc phosphate cement, body porcelain, opaque porcelain, and visible light-cured resin composite. Furthermore, the fracture probability of the bi-axial test specimens was predicted from the results of the four-point flexure test, with use of statistical fracture theory. Bi-axial failure stresses calculated from an equation developed by Marshall (1980) exhibited no significant difference for zinc phosphate cement as a function of piston size, specimen thickness, presence or absence of a stress-distributing film, and loading rate. The four-point flexure strength values of zinc phosphate cement and opaque procelain were significantly lower (p less than 0.05) than the corresponding mean bi-axial strength values, while the mean four-point flexure strength values of body porcelain and resin composite were not significantly lower (p greater than 0.05) than the corresponding mean bi-axial strength values. The diametral tensile strength of all materials was significantly lower than the bi-axial flexure strength. The mean bi-axial flexure strengths of zinc phosphate cement and opaque porcelain were much higher than the theoretical values predicted from surface flaw theory, while the strength values for body porcelain and resin composite were comparable with those determined from the four-point flexure test. These results demonstrate that the strength of zinc phosphate cement depends not only upon the geometric factors, but also upon sample preparation conditions.

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The purpose of this investigation was to examine the effect of filler particle size and shape as well as filler content on light transmittance characteristics and color of experimental composite resins. A mixture of 30 mol％ Bis-GMA and 70 mol％ TEGDMA was prepared as a base monomer and to which a photoinitiator (camphorquinone) and a co-initiator (N,Ndimethylaminoethyl methacrylate) were added. Four different irregular-and spherical-shaped filler types with an average particle size of 1.9-11.1 μm were added to the mixture in three different filler contents of 20, 30, and 40 vol％. Light transmittance characteristics including light diffusion characteristics of the materials were evaluated. Color values and color differences among filler contents of the materials were also determined. Materials containing smaller and irregular-shaped fillers showed higher light transmittance and diffusion angle distribution with a sharper peak, as compared with those containing larger and spherical-shape fillers. It was also found that there was a significant correlation between the specific surface area of fillers and the color difference of the materials containing the fillers.Our results indicated that the shape of filler particles, as well as particle size and filler content, significantly affected the light transmittance characteristics-including light diffusion characteristics-and color of composite resins.