Multilayer Pre-Shaded Zirconia
White Dental Zirconia Blanks
DENTAL ZIRCONIA SPECIFICATIONS
Material Properties of Zirconia
The zirconia (zirconium dioxide or ZrO2) used in dental labs is chosen for its physical toughness, structural strength, chemically inert nature, and wear resistant properties.
Zirconia is a ceramic material derived from bonding an atom of the metal zirconium with two atoms of oxygen. Raw zirconia is then stabilized into a crystalline structure with yttria or other oxides such as magnesia, calcia, alumina, or ceria to imbue it with the toughness necessary for dental applications. Due to the chemical inertia of dental zirconia, it doesn’t corrode, discolor, or inhibit cell growth over time, making it the natural choice for dental purposes.
Zirconia for Dental Use
Dental zirconia blanks, often referred to as zirconia discs or pucks, can be milled into crowns, bridges, and sometimes into zirconia implants. Zirconia dental crowns and bridges have several advantages over other materials typically used in crowns:
Aesthetically pleasing and natural looking
Naturally tough material with high fracture and chipping resistance
Long lasting and wear resistant
Biocompatible, will not corrode or discolor the gingiva at the margin
High radiopacity, which makes it easier to inspect in X-Ray captures
As a result of these advantages, some labs and dentists will also choose to make zirconia implants as well as the crowns. For most patients, and by extension business owners, this is costly and offers marginal value over using titanium while suffering from a large compromise in strength.
Of course, zirconia is not the absolute best material for every purpose and patient. Zirconia is not quite as strong as a PFM (porcelain-fused-to-metal) or gold crown and it is not quite as natural looking as an E-MAX crown.
However, zirconia crowns are more than strong enough for regular use and most patients and doctors find that it is more likely to wear away your natural teeth than it is to structurally fail on its own. It is also less expensive than using E-MAX and PFM crowns while compromising minimally on aesthetics and strength. For general dental use zirconia is the most well-rounded material.
Pre-Shaded Zirconia & Multilayer Zirconia
To elevate consistency with production and eliminate some of the human error mimicking natural tooth shades, many dental labs use multilayer zirconia, which comes pre-shaded from most manufacturers in A1-D4 tooth shades. Multilayer discs typically contain between 4 to 6 layers, with the cervical portion consisting of a more opaque, darker shade and the incisal part consisting of a more translucent, lighter shade. Not only are the resulting crowns more of more consistent quality, but the pre-shaded multilayer units become far easier to produce, saving on time and labor. Should the unit require more detailed spot shading, such as nearer the incisal edge, stain (usually a solution of the A1 or B1 shade) can be applied as necessary.
Though some of the more premium zirconia blanks provide a combination of high translucency, high strength, and accurate shading, there is generally a trade-off between strength and translucency. I.e. a disc with a higher megapascal rating will usually have a lower transparency rating and vice versa. Finding discs with good strength, translucency, fine grain, and color is not impossible, but the trade-off comes in the form of a higher price, as these pre-shaded zirconia discs are manufactured with Tosoh or another reputable zirconium oxide powder.
Since teeth are not just one uniform color throughout the same tooth, much less one uniform color from patient to patient, zirconia also comes in various configurations to cater to the dental industry. Natural teeth generally follow a gradient from darker shade dentin to a lighter shade occlusal surface, so a crown made from bleach-white zirconia blanks needs to undergo hand staining by to give it a natural appearance. Staining is typically applied using an A1 or B1 tooth shade in multiple stages in order to achieve a gradient that mimics organically occurring coloration. However, since this process is done by hand, uneven dyeing and awkward shade transitions can render an originally unshaded white crown useless and require a remake.