Can Zirconia Crowns Crack
Dental crowns are restorations used to cover compromised teeth. Should a tooth crack, fracture, or break, a dental crown can be used to restore the tooth.
Zirconia is a popular material used in the fabrication of dental crowns because of its strength and durability. With proper oral hygiene, care, and routine visits to the dentist, zirconia dental crowns can last 10 or more years. Despite their strength, it is possible for zirconia crowns to fracture. This article will examine some of the typical causes of zirconia crown fractures.
Tooth Preparations
This is likely the most important and predominant issue when it comes to zirconia crown fractures. In dental school, virtually all dentists learn the proper crown preparation requirements. But if the impressions of tooth preparations that dentists are sending to laboratories were reviewed, it would be clear there is a significant issue. Many preparations fail to adhere to the known characteristics needed to provide sufficient strength, retention, and long-term resistance to wear.
In some cases, labs are spacing the crown occlusal surfaces 0.5mm out of contact so that the crown does not have to be adjusted. This is entirely too much and places stress on the adjacent tooth until the crowned and opposing teeth extrude. Optimally, crowns should have perfect occlusion, but this is not likely. They should only have a few microns of space out of occlusion so that rapid tooth extrusion occurs in a few days or weeks. Rarely are these characteristics seen and while some cases may not allow for optimal preparation, most of the time optimum prep is feasible.
Quality of Zirconia Used in Fabrication
Another culprit of zirconia crown cracking is the quality of the material used. The original form of zirconia, 3Y zirconia (3% yttrium oxide content), has tremendous strength and a property known as transformation toughening (prevents crack propagation). These qualities have made 3Y zirconia virtually indestructible. Over 10 years, studies on 3Y zirconia crowns by the Clinicians Report Foundation have detailed almost no failures.
However, some new zirconia brands, that market as providing better esthetics, have been modified with formulations that are not as strong and have little or no transformation toughening. Because these formulas are not as strong, they are more prone to cracking or chipping. Patients are encouraged to inquire of their lab technician as to the type of zirconia they use. If they do not know answer to that question, patients should find another laboratory that does know what they use. To be safe, it is advisable to seek zirconia crowns that rely on the original 3Y formulation until sufficient evidence is available regarding the efficacy of new brands of zirconia.
Dental Education
A cracked zirconia crown could also stem from an error the dentist made when placing it. Unfortunately, the clinical experience and education levels of some new dentists is insufficient. Some new practitioners graduate with minimal education and limited clinical experience. As such, many years of practice and ongoing continuing education will be needed until they are clinically competent.