Color Aspect of Monolithic Zirconia Restorations: A Review of the Literature

Abstract

Monolithic zirconia restoration is an acceptable treatment option in restorative dentistry and a developing trend in esthetic dentistry. Digital dentistry has simplified fabrication of monolithic zirconia restorations. Zirconia ceramic has introduced an opportunity to achieve both esthetic and mechanical requirements for restorations. This is rarely found for a ceramic in dentistry. Monolithic zirconia restorations represent an acceptable durability, comparable to metal-ceramic restorations, while they are superior to metal-ceramic restorations esthetically; however, difficulties to gain an optimal shade reproduction and a color match with monolithic zirconia restorations still remain. The color of these restorations may be influenced by manufacturing processes, laboratory procedures, and clinical factors. Manufacturing processes determine basic optical properties of zirconia ceramics. Different laboratory procedures may create optical changes in zirconia ceramics. Also clinical factors such as dental background, cement, and zirconia restoration features may affect the resulting color. This literature review aimed to discuss potent factors in the color of monolithic zirconia restorations. An electronic search of the PubMed/Google Scholar database was performed to find related English-language articles published between January 1, 2000, and October 31, 2017. The key terms of background, cement, ceramic, color, esthetics, shade, spectrophotometry, thickness, translucency, and zirconia were used both individually and simultaneously. Also, a manual search was conducted, and five classic articles of color science were added. Thus 192 articles were included. In the last decade, shade reproduction of monolithic zirconia restorations has been highly regarded; however, further improvements are required in the manufacturing process to produce tooth-like zirconia ceramics. An esthetic guideline named background-cement-ceramic color harmony was suggested in this study; however, more clinical practice guidelines should be established for monolithic zirconia restorations on esthetics, and therefore, more studies are required.

Effect of glazing on translucency, color, and surface roughness of monolithic zirconia materials

“…This can be explained by the higher content of Yttria (Y 2 O 3 ) (6.5‐8%) in comparison with the other materials tested (Katana, Cercon, Vita YZ) (Yttria content 4‐6%), which favors the formation of cubic phase in addition to tetragonal phase in the composition of zirconia. Cubic phase increases the translucency by avoiding the high scattering and birefringence of light that is characteristic for the tetragonal zirconia …”

Optical properties of currently used zirconia‐based esthetic restorations fabricated with different techniques

“…Although it is necessary to veneer zirconia surfaces to improve the esthetic values of restorations, such bilayer systems have several major drawbacks, such as chipping . The obvious way to overcome these drawbacks is to replace the core and the veneer bilayer with a monolithic zirconia (MZ) . Currently, producing full‐contour restorations using MZ has become more common as it has some advantages, such as a reduced material thickness, fast fabrication, and reduced chipping .…”

Changes in Optical Characteristics and Surface Topography of CAD/CAM Materials after Bleaching Applications: An AFM Evaluation

“…The disadvantages of composite resin as polymerization shrinkage, porosities, inhomogeneity, and lack of color stability have been reported as most challenging problems . Conventional and milled ceramic restorations have also shortcomings such as lack of proper esthetics because of their monochromatic appearance, brittleness, and susceptibility to chipping fracture . To overcome these disadvantages and to combine the advantageous properties of composite resin and ceramic, CAD/CAM materials like resin nano‐ceramic and polymer‐infiltrated ceramic network materials have been fabricated .…”