Comparing the strength of a modern dental crown to a natural tooth is complex, as it involves contrasting a biological composite with an engineered ceramic. Dental crowns are restorations designed to cover a damaged tooth, restoring its shape, strength, and function. The material’s strength is crucial for withstanding the tremendous biting forces of the human jaw.
The Inherent Strength of Natural Tooth Structure
The natural tooth is a layered biological composite designed for both hardness and flexibility. The outermost layer, enamel, is the hardest substance in the human body, consisting of about 96% mineral content. This high mineral content gives enamel its exceptional hardness and resistance to wear, making it capable of enduring the friction of chewing.
The enamel is relatively brittle, but it is supported by the underlying dentin, which is a softer and more flexible tissue. Dentin is composed of about 70% mineral, providing a shock-absorbing cushion. This layered structure, where the hard enamel is bonded to the more resilient dentin, works together to prevent catastrophic fracture under load.
Composition of Modern Dental Crown Materials
The term “porcelain crown” is largely outdated, as modern dentistry relies on sophisticated engineered ceramics that far surpass traditional porcelain in strength. Two dominant materials today are Lithium Disilicate (Emax) and Zirconia (zirconium dioxide).
Lithium disilicate is a glass-ceramic known for its superior translucency and lifelike appearance, making it a preferred choice for front teeth. It offers a flexural strength of approximately 400 megapascals (MPa), a significant improvement over older ceramics.
Zirconia, sometimes called “ceramic steel,” is a high-strength polycrystalline ceramic. It is processed under high heat, called sintering, which creates an extremely dense, crystalline structure. This gives zirconia exceptional mechanical properties, including flexural strength that can range from 900 MPa to over 1200 MPa. The highest strength versions are often reserved for posterior teeth that must withstand the heaviest biting forces.
Comparing Fracture Resistance and Durability
The strength of modern crowns, particularly monolithic zirconia, often exceeds the compressive strength of healthy natural enamel, which is typically around 400 MPa. Zirconia crowns have higher compressive strength and greater resistance to fracture than natural teeth, making them highly suitable for patients who clench or grind their teeth.
However, the comparison is complex because natural teeth rarely fail due to compression alone. Their structure is compromised by decay, cracks, or large fillings before a crown is needed. The crown’s primary function is to act as a protective cap, preventing the catastrophic failure of the remaining, compromised tooth structure.
While the engineered ceramic of a crown may be stronger than the natural tooth’s enamel, crowns can fail differently, often through chipping of the surface or by the underlying tooth decaying at the crown’s margin. Overall, a well-placed modern crown, especially one made from high-strength zirconia, is typically more resistant to fracture than the compromised tooth it is protecting.