What Makes Zirconia So Strong?
The strength of an ISO- and ADA-approved monolithic zirconia comes from its tetragonal crystalline properties. The biggest problem with a full-contour monolithic zirconia crown is the opaque appearance caused by structural defects that absorb light rather than allow it to pass through. It does not possess all of the translucent and refractory properties that would be desirable for natural, lifelike appearances. In other words, monolithic zirconia is great for implant abutments, fabricating non-metal bridge frameworks, hiding core build-ups, and restoring posterior teeth, butut it’s not so aesthetically pleasing for anterior restorations. How do you overcome this drawback?
Zirconia Now Looks Better Than Ever
More recently, manufacturers have developed translucent zirconia to improve appearances and allow for crowns that look great to be manufactured specifically for use in the anterior part of the mouth. By reducing the alumina content of the zirconia structure, adding stains and dyes, and using a multi-layered technique to fabricate crowns, manufacturers have helped to improve translucency. These modifications to the tetragonal structure are not without drawbacks. Whenever the composition of a chemical compound is altered, it changes the material’s other properties. In the case of zirconia, the strength of the material is slightly diminished by altering what makes it naturally opaque. Make sure to keep this tradeoff in mind when you are deciding what material is best for your patients.
How Long Will Zirconia Last?
Since zirconia has only been in use for about ten years, there are no long-term studies comparing its longevity to other tried-and-true materials such as gold or porcelain fused-to-metal (PFM).
Like gold or PFM crowns, zirconia crowns are strong only when they are of sufficient thickness. Lack of adequate tooth reduction will cause a less than desirable result and make it impossible for the dental laboratory technician to provide you with an aesthetic crown that will last for years. Gingival margins should be at a minimum of 0.6 mm deep. The axial walls of the preparation should be at least 1.0 mm in depth, and occlusal reduction of at least 1.5 mm should be anatomic, following the original tooth’s anatomy.