Lithium disilicate ceramics were first introduced to the dental restorative market in 1988, before CAD/CAM technology for fabricating crowns was available or commonplace. At that time, the all-ceramic crowns were created using a pressure casting technique. By 2005, the process was changed to take advantage of the development of CAD/CAM technology in the dental lab industry. The same monolithic lithium dioxide was used but the technique changed from pressure casting to milling. Thus the IPS Emax that is used today in dental laboratories was born.
Emax is aesthetically pleasing and possesses the translucent and reflective properties that mimic and blend with neighboring natural teeth. The tooth preparation required for Emax is less aggressive than for zirconia or porcelain fused-to-metal (PFM) crowns. Cementation is achieved by both bonded and mechanical retention. The material can be used for full coverage crowns, inlays, onlays, and veneers and has an average lifespan of 10-15 years before fracturing.
CAD/CAM crowns made from zirconia dioxide were introduced to dentistry in 2010. Before being considered a crown material, zirconia dioxide was used for endodontic posts and dental implants. The material is incredibly strong, resistant to wear, and difficult to crack. Crown preparation involves a more aggressive reduction than required for Emax. Cementation is achieved via mechanical retention using a glass ionomer resin dental cement.
Zirconia does have one major drawback. In its true monolithic milled form, it is fairly opaque. So it hides tooth discoloration and large core build-ups well. But it lacks the translucent properties that make it appear truly natural and lifelike. The manufacturers have improved the appearance by developing a translucent version of zirconia that more closely mimics the translucence of natural teeth. Because zirconia crowns have been in use for a relatively limited time, there are no long-term longevity studies are available. In other words, no one has observed exactly how long a zirconia crown will last before it must be replaced.