Zirconia basics

Feb. 1, 2006
Every year dental manufacturers bring at least a few new indirect restorative products to market, and dental laboratories are faced with the decision of whether or not to use these new materials.

Every year dental manufacturers bring at least a few new indirect restorative products to market, and dental laboratories are faced with the decision of whether or not to use these new materials. Many dentists tell me they also are confused about the dizzying array of restorations currently available. Their frustration comes from not knowing which restorative systems truly represent a step forward in terms of technology and esthetics, and which are simply “me too” products most likely created by the marketing department rather than the research and development department.

With this in mind, I would like to use this column to introduce a class of materials - zirconia oxide. I believe zirconia oxide is a step forward in terms of technology and esthetics, and is worthy of consideration as a single-crown material and for simple bridges.

Many dentists ask me when they should consider all-ceramic bridges. My honest answer is: when the patient requests it. Otherwise, I am much more confident using an esthetic PFM material, like Captek, to fabricate these bridges because of their increased strength and proven track record of success.

Zirconia is ideal for those who are sensitive to metal or simply prefer the esthetics of metal-free restorations. Its biocompatibility has been proven through the years in the medical field. In fact, zirconia has replaced metal as the material of choice in hip replacement surgeries. Zirconia can be used for both anterior and posterior crowns and bridges.

Zirconia is the strongest all-ceramic coping material available today. I don’t know of any contenders on the horizon. In breakage tests in the R&D department at Glidewell Labs, zirconia crowns and bridges easily outperform other all-ceramic restorations. But they still do not have the strength of a typical PFM. Whether this lower strength is clinically significant is a decision for you to make. I can share with you that, from the hundreds of zirconia crowns and bridges I have placed in all areas of the mouth, I have not had a zirconia coping break yet.

You have several choices when selecting a zirconia restoration for a patient. One of the first systems to hit the market was Cercon, which became commercially available for North American dental laboratories in 2002. I took the opportunity to test it by placing a Cercon bridge from tooth Nos. 17 to 20. Tooth Nos. 18 and 19 were both pontics. The patient was rough on his dentition. I thought this would be a good test for the material, replacing two missing molars with an all-ceramic bridge. I expected this bridge to fail but have been pleasantly surprised by how nice it looks almost four years later. This is when I began to see that zirconia does have strength that surpasses other all-ceramic materials.

About the same time, Nobel Biocare introduced zirconia to its Procera product line. Historically, Procera had been an aluminum oxide material, which was one of the first classes of cementable all-ceramic crowns. Aluminum oxide restorations comprise materials such as Procera, In-Ceram, and Wol-Ceram. Dentists ask me why they would want to use an aluminum oxide material when the stronger zirconia material is now available. I think it simply comes down to personal preference. If you work with a lab technician who creates beautiful Wol-Ceram restorations, and you are not experiencing any problems, then why switch? Try a zirconia restoration or two to see if you notice a difference. But I suggest not tampering with a successful system.

The next commercially available system is the Lavasystem from 3M ESPE. Because of its unique density, Lava’s zirconia oxide coping and bridge frameworks can withstand stresses many times greater than those that occur in patients’ mouths. It also can be fabricated thinner than most zirconia systems. In fact, Lava anterior copings can be fabricated as thin as 0.3 mm. This leads to greater translucency and, therefore, better esthetics. Also, PFM-like chamfer margins and conventional cementation make Lava an easy system with which to work.

At Glidewell Labs, the R&D department is working to process its own zirconia, Glidewell “CZ” or Clinical Zirconia. We process the zirconia powder at 21,000 psi into milling blanks. The ability to fabricate our blanks, combined with our proprietary scanning and milling systems, should allow us to add one more benefit to zirconia - affordability.

Dr. Michael DiTolla is the Director of Clinical Research and Education at Glidewell Laboratories in Newport Beach, Calif. He lectures nationwide on both restorative and cosmetic dentistry. He also teaches hands-on courses on digital photography and digital image-editing for the entire team. Dr. DiTolla has several clinical programs available on DVD through Glidewell. For more information on this article, or for more information on receiving a free copy of one of Dr. DiTolla’s clinical DVDs, e-mail him at [email protected].

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