Spear Resident Faculty Q&A: Zirconia Crowns

Dentists reach out to me all the time with questions about clinical techniques, material selection, and restorative protocols. And honestly? I get it. Sorting through stacks of studies to build a predictable, evidence-based approach is no small feat — especially when manufacturers insist their product is the answer and patients come in quoting social media as if it were the new ADA guidelines.

In this article, I’m addressing some of the most common questions I receive about the strength, durability, and long-term performance of zirconia crowns compared to traditional porcelain-fused-to-metal restorations. It’s a topic that sparks interest across the full spectrum of clinicians — and for good reason.

Can I tell a patient that a zirconia crown is stronger than a PFM crown?

Yes, a zirconia crown is stronger than PFM crowns!

Both high-strength (“Bruxzir-type”) and low-strength (translucent) zirconia are stronger than PFM crowns, at least relative to the porcelain. 

• High-strength zirconia: 1,000–1,200 megapascals
  • [1 megapascal ≈143 pounds per square inch] 
• Low-strength zirconia: 600–800 megapascals 
• Lithium disilicate (e.max): 400–500 megapascals, depending on if it’s bonded or cemented 
• Porcelain fused to metal: 80 megapascals 

A few disclaimers, though: First, these values are for compressive strength of the restorations; this does not relate to shear force, which would be weaker. 

And although zirconia restorations are stronger, that’s not to say that PFM crowns don’t work or aren’t strong themselves: By the nature of the metal underlying the layered porcelain, there is significant strength or resistance to crown fracture. The metal of the PFM crown is significantly stronger than the zirconia restoration. 

• If a zirconia crown fractures, it’s catastrophic — the crown must be replaced, because the tooth is exposed as a result of the fracture. 
• But if the porcelain of a PFM crown fractures, the crown may not require complete replacement because the underlying metal will continue to protect the tooth substrate from the oral cavity. 

The decision to use a zirconia or a PFM crown must be determined by reasons other than strength alone — for example, a PFM crown may be the restoration of choice to block out a dark tooth substrate for esthetic reasons. A ceramic restoration requires greater ceramic thickness to block the underlying dark tooth, and inadequate ceramic thickness may result in a low-value (grayish) appearance of the final restoration. 

Depending upon the outcome you’re trying to achieve — strength, appearance, longevity, etc. — the type of restorative material chosen must be able to achieve your goal. 

Can I tell the patient a zirconia crown will last longer than a PFM crown?

The answer to this partly relates to proper tooth preparation and the material’s strength. If the preparation depth is inadequate, a ceramic restoration may fail prematurely. Similarly, if the metal of a PFM crown is too thick, the fused layered porcelain could fracture prematurely as well. Proper planning and design, including adequate preparation, are key to long-term success and will significantly impact the lifespan of the restoration. 

The preparation margin is another significant key to success: The smoother and more refined the margins are, the better the crown adaptation and the longer the lifespan.  

Creating smooth, precise margins requires adequate magnification and proper use of the rotary burs during preparation. For proper vision and efficiency, the recommended minimal magnification is 4.5 power; below this, it’s difficult to achieve smooth and precise contours of the preparation. Use loupes or a microscope to provide adequate vision. 

Whether analog or digital impression techniques are applied, the key to restoration longevity is smooth, precise margins. Ideally, we want margins in the 25–50 micron range. 

Will zirconia crown wear the opposing teeth?

Yes and no! Our profession has long known that any unpolished ceramic — such as glass ceramic, lithium disilicate, or zirconia — is abrasive to opposing tooth structure. The literature contains many references to this, including one article from 1994¹ that discusses the importance of polishing porcelain, even glazed porcelain, to prevent attritional wear of the opposing teeth. 

Opposing tooth wear should be a major consideration when using any ceramic material. Proper polishing and adjustment are critical for restoration longevity and occlusal stability. Wear studies show that deterioration of opposing surfaces is linked to the frictional coefficient of materials. This is directly related and influenced by surface roughness: Two rough opposing surfaces will have higher frictional coefficients. Rough zirconia has a higher frictional coefficient against enamel than polished zirconia²; properly polished ceramic is also less damaging to the opposing tooth enamel. 

Virtually all restorations require occlusal adjustment to gain proper functional contact. Adjusting ceramics is a task that all dentists perform regularly. Care must be taken not to create flaws in the ceramic during the adjustment process. Surface and subsurface damage from grinding on ceramic is well-documented in the literature; References 3–5 can provide greater insight into the effects of ceramic and opposing tooth wear. 

How do we persuade patients that all-ceramic crowns like zirconia and e.max crowns are better than PFM crowns?

I believe we don’t need to persuade patients that one type of restoration is better than another! As dental restorative professionals, we should decide the best restorative solution based on the patient’s presented situation; that decision shouldn’t be up to them. 

As we discuss the considerations behind tooth preparation and appropriate materials with patients, this co-discovery helps them understand what’s best and allows them to be part of making the decision, but in the end, they’re trusting us to provide the best service and materials to correct and restore a given circumstance. 

Remember, restorative success isn’t solely about the type of crown or material used; it’s about designing the outcome to be achieved and selecting the appropriate services necessary to attain that outcome.  

Thanks for reaching out with your questions! I enjoy sharing my knowledge and experience with other dentists so they may improve their understanding and skills, and I’m happy to provide you further information if you wish. I hope our paths cross someday in person! 

References

1. Oh, W. S., DeLong, R., & Anusavice, K. J. (2002). Factors affecting enamel and ceramic wear: a literature review. The Journal of Prosthetic Dentistry, 87(4), 451-459.
2. Jagger, D. C., & Harrison, A. (1994). An in vitro investigation into the wear effects of unglazed, glazed, and polished porcelain on human enamel. The Journal of Prosthetic Dentistry, 72(3), 320-323.
3. Goo, C. L., Yap, A. U. J., Tan, K. B. C., & Fawzy, A. S. (2016). Effect of polishing systems on surface roughness and topography of monolithic zirconia. Operative Dentistry, 41(4), 417-423.
4. Song, X. F., Yin, L., Han, Y. G., & Wang, H. (2008). In vitro rapid intraoral adjustment of porcelain prostheses using a high-speed dental handpiece. Acta Biomaterialia, 4(2), 414-424.
5. Yip, K. H. K., Smales, R. J., & Kaidonis, J. A. (2004). Differential wear of teeth and restorative materials: clinical implications. International Journal of Prosthodontics, 17(3).