A dental crown is a tooth-shaped cap placed over a damaged tooth to restore its structure, size, shape, and overall appearance. This restoration is used when a tooth has suffered significant damage from decay, fracture, or wear that a simple filling cannot repair. The crown fully encases the visible portion of the tooth above the gumline. Understanding the different types available is important because the choice of crown affects the tooth’s function, durability, and aesthetics for many years.
Crowns Based on Material Composition
Full metal crowns, often made from gold alloys or non-precious base metal alloys like nickel-chromium, offer maximum durability and strength. These crowns are highly resistant to wear and fracture, making them an excellent choice for posterior teeth where chewing forces are highest and visibility is low. They require the least amount of healthy tooth structure to be removed during preparation.
Porcelain Fused to Metal (PFM) crowns represent a hybrid solution, combining the strength of a metal substructure with the tooth-colored aesthetics of a porcelain overlay. This design provides a good balance of fracture resistance for back teeth and a natural appearance for visible areas of the mouth. However, the metal core can sometimes cause a thin, dark line to become visible at the gumline, especially if the gums recede over time.
All-ceramic or all-porcelain crowns are valued for their superior aesthetics, as they perfectly mimic the translucent quality of natural tooth enamel. These metal-free restorations are the preferred choice for front teeth where cosmetic outcomes are paramount. One common type is Lithium Disilicate, often branded as E-Max, which is a glass-ceramic material offering excellent light transmission.
Zirconia crowns are a newer category of ceramic known for exceptional strength, rivaling that of metal. This material is a highly durable ceramic oxide that is ideal for patients with heavy biting forces or bruxism. Modern translucent zirconia materials have significantly closed the aesthetic gap, making them a versatile option for restorations in both the anterior and posterior regions of the mouth.
Crowns for Coverage and Replacement
Full coverage crowns are the most common type, entirely covering the prepared tooth structure above the gumline to provide maximum protection and reinforcement. This solution is necessary when a tooth has extensive structural damage, such as a large fracture or severe decay.
Partial crowns, often referred to as inlays or onlays, are a more conservative restorative option used when a sufficient amount of healthy tooth structure remains. An inlay fits within the cusps of the tooth, similar to a traditional filling but fabricated outside the mouth. An onlay is slightly larger, extending over and protecting one or more of the tooth’s cusps from fracturing under chewing pressure.
A temporary crown is a short-term, provisional restoration, typically made from an acrylic resin. Its purpose is to protect the tooth preparation from sensitivity and shifting while the permanent crown is being fabricated in a dental laboratory. Temporary crowns are held in place with a weaker, temporary cement for easy removal at the final appointment.
Implant crowns are distinct because they are designed to replace a missing tooth rather than cap a natural one. Instead of being cemented onto a prepared tooth, an implant crown is secured onto a titanium post, or abutment, which is itself anchored directly into the jawbone. This design creates a standalone replacement that functions like a natural tooth from the root up.
Factors Guiding Crown Selection
The location of the tooth is a primary consideration, dictating the necessary trade-off between aesthetics and mechanical strength. Front teeth, or incisors, prioritize a lifelike appearance, making highly translucent materials like Lithium Disilicate the standard choice. Back teeth, or molars, must withstand the heavy vertical chewing forces, favoring the fracture resistance of Zirconia or metal alloys.
Patient habits and the severity of their bite force also influence the material selection, particularly for individuals who grind or clench their teeth. Stronger materials, such as monolithic zirconia, are recommended in these cases to resist chipping and wear. Cost and expected longevity are also practical factors, as some materials, like gold alloys, may have a higher initial cost but potentially offer a longer lifespan than other options.
Health considerations, including sensitivities or allergies, must be taken into account before placing a crown that contains metal. Patients with a known nickel allergy, for example, should select a metal-free option such as an all-ceramic or Zirconia crown. The condition of the gum tissue around the tooth also affects the visibility of the crown’s margin, influencing the choice of a metal-free restoration to prevent a visible dark shadow.