A dental crown is a custom-made cap placed over a damaged tooth to restore its size, shape, and strength, protecting the compromised natural structure underneath. While early crowns made entirely of porcelain were susceptible to fracture, modern dental material science has significantly advanced the durability of these restorations. Contemporary porcelain crowns, often made of sophisticated ceramic compounds, are engineered to withstand the considerable forces of biting and chewing. Whether a porcelain crown will break depends more on its specific material composition and the forces it encounters rather than inherent fragility.
Understanding Porcelain Crown Composition
The term “porcelain crown” often refers broadly to any ceramic restoration, encompassing a range of materials with vastly different strengths. Traditional all-ceramic crowns, sometimes called feldspathic porcelain, are highly aesthetic, providing a natural translucency that closely mimics real tooth enamel. This material offers a lower flexural strength, around 100 megapascals (MPa), making it suitable primarily for front teeth that experience less biting pressure.
Porcelain-Fused-to-Metal (PFM) crowns represent a hybrid approach, using a metal alloy base for structural support with a layer of porcelain baked over it for aesthetics. The underlying metal frame increases durability, making PFM crowns reliable for back teeth, but the porcelain layer can still chip, and the metal substructure may show as a dark line at the gumline. Modern all-ceramic options, like Lithium Disilicate (e.max), have emerged as popular choices with a much higher flexural strength, often reaching 400–500 MPa.
Zirconia is another ceramic material that offers exceptional strength, with some monolithic versions reaching over 1,100 MPa, making them extremely resistant to fracture. Although some zirconia crowns are layered with traditional porcelain for improved aesthetics, monolithic versions are strong enough to withstand the heaviest bite forces, often surpassing the strength of PFM crowns. The inherent strength of a “porcelain” crown is directly proportional to the specific ceramic or ceramic-metal hybrid chosen by the dentist and lab technician.
Factors Leading to Structural Failure
When a porcelain crown fails, it is usually the result of excessive force or underlying structural problems, not a defect in the material. The most common cause of structural failure is mechanical stress, such as direct trauma or the sustained pressure from bruxism (unconscious clenching or grinding of teeth). Biting down on inappropriate objects, like ice, hard candy, or using teeth to open packaging, generates forces that exceed the crown’s fracture resistance, leading to cracks or chips.
Another category of failure relates to the fit and preparation of the tooth before the crown is seated. If the crown is not seated precisely or there are marginal gaps, chewing forces can concentrate stress at these weak points, initiating a crack. Improper bite alignment can also place uneven pressure on the crown, causing it to wear down prematurely or fracture.
Biological issues affecting the underlying tooth structure are major contributors to crown failure. Decay can still develop beneath the crown margin if oral hygiene is insufficient, compromising the natural tooth support. If decay progresses, the reduced tooth structure can no longer bear the load, leading to the crown loosening or the remaining tooth fracturing. The cement bond holding the crown in place can also weaken over time, causing the restoration to become loose and susceptible to dislodgement.
Maximizing Crown Longevity Through Care
Patients play a significant role in the long-term success of their porcelain crowns, which typically last 10 to 15 years or more with proper maintenance. Maintaining diligent oral hygiene is necessary to prevent recurrent decay, which starts at the crown margins near the gum line. Brushing twice daily with fluoride toothpaste and flossing around the crowned tooth helps remove plaque and bacteria, protecting the underlying tooth structure.
Lifestyle modifications are necessary to protect the crown from damaging mechanical forces. Patients should avoid biting or chewing on extremely hard foods, such as ice cubes, unpopped popcorn kernels, or hard candies, which can cause the ceramic to chip or fracture. Sticky or chewy items like caramel can also stress the cement bond, potentially leading to the crown becoming loose.
For individuals diagnosed with bruxism, wearing a custom-fitted nightguard is a highly effective protective measure. This device acts as a cushion, absorbing the intense forces generated during nighttime grinding and preventing wear or fracture of the porcelain. Regular dental check-ups and professional cleanings are also important. These appointments allow the dentist to evaluate the integrity of the crown margins, check the underlying tooth structure via X-rays, and address potential issues like cement failure or minor chipping.