With Recent Advancements Harmonizing Strength and Esthetics, CAD/CAM Is No Longer a Compromise
Computer-aided design/computer-aided manufacturing (CAD/CAM) has become the most common fabrication technique for crowns. Currently, the "holy grail" for an all-ceramic CAD/CAM material would be one that could replicate the esthetics and translucency of natural teeth while maximizing the properties of strength for high-stress applications in a conservative crown dimension.
In an attempt to achieve this ultimate goal, manufacturers seem to be pursuing two different approaches. The first approach involves recognizing the esthetic potential of glass ceramics and modifying them to significantly improve their strength properties. Materials such as lithium disilicate (eg, IPS e.max, Ivoclar Vivadent; Obsidian, Glidewell) and zirconia reinforced lithium silicate (eg, Celtra Duo, Dentply Sirona; Vita Suprinity, Vita) are reported to have flexural strengths approaching 400 to 500 MPa with very good esthetic results. The second approach involves recognizing the high strength properties of zirconia and modifying it to significantly improve its esthetic potential. Full contour zirconia materials were initially introduced with very high flexural strengths that exceeded 1,000 MPa; however, they were more opaque and resulted in compromised esthetics. Subsequently, newer "translucent zirconia" or "anterior zirconia" materials have been introduced that offer improved translucency with somewhat lower flexural strengths on the order of 650 to 750 MPa.
Chairside CAD/CAM systems have consistently focused on the delivery of single appointment procedures using a variety of materials, including glass ceramics, hybrid ceramics, and composite materials. After milling, these materials require minimal time for processing. Although they still demonstrate very good clinical outcomes and longevity, they lack the higher strength properties that many clinicians prefer. Higher strength CAD/CAM materials require additional post-milling fabrication steps; however, innovations in design software, milling algorithms, and zirconia sintering ovens have significantly reduced the processing times of these materials to make them viable alternatives for single appointment procedures as well.
Dennis J. Fasbinder, DDS, is a clinical professor in the Department of Cariology, Restorative Sciences, and Endodontics at the University of Michigan School of Dentistry where he also directs the Computerized Dentistry Unit, a leader in education and research for chairside CAD/CAM systems and digital impression systems that has published clinical research projects on all new chairside CAD/CAM materials introduced since 2000. Board certified in general dentistry by the American Board of General Dentistry, Fasbinder has delivered advanced education courses on digital dentistry for more than 20 years and is a frequent speaker on ceramic-based dentistry and digital dental systems at meetings and conferences. He also maintains a part-time private practice in Ann Arbor, Michigan.
