If you have a chipped, broken or decayed tooth, a dental crown can repair the damage and restore functionality. A crown protects the remaining natural tooth from further damage, and helps to align the bite. A tooth crown isn’t made from a single metal; it’s actually a combination of metal alloys. These are blends of different pure metallic elements that combine to produce a material with superior properties than any of the pure materials could have on their own.
The crown itself can be made from several different materials. Some are ‘composite resin’, made of plastic type materials colour-matched to the natural teeth. Others are’monolithic’, milled from a single block on a CAD/CAM machine.
Porcelain
Porcelain crowns are tooth-shaped caps that cover, fit and restore the part of damaged teeth above the gum line. They have a translucent quality that mimics the color and depth of natural teeth, making them aesthetically appealing. In addition, porcelain crowns are biocompatible and resistant to staining.
They are a popular choice for front teeth since they look the most like real teeth and don’t affect the function of your existing natural teeth. They are also a safe option for people who have metal allergies, as they do not contain any toxic elements.
Some porcelain crowns are fused to a base metal for strength. They may not have the same aesthetically pleasing appearance as crowns made of 100% porcelain. However, porcelain fused to metal crowns do offer a more durable solution for molars and back teeth. They can be fabricated in the dentist’s office using the Cerec or Sirona CAD milling machines. This process is faster and less expensive than traditional crown fabrication.
Zirconia
Zirconia is one of the most popular materials used in dental operatories today, often replacing older porcelain-fused-to-metal crowns. It is highly durable, resistant to bruxism, and has superior strength over traditional porcelains. Zirconia is also biocompatible and chemically inert, making it an excellent choice for patients with metal allergies.
Zirconia crowns are available in a variety of shades that closely match natural teeth. In addition, they can be fabricated to cover discolored preps with minimal tooth reduction and meet patient demands for high-quality restorations.
Layered zirconia has a translucent and opalescent appearance, while monolithic zirconia has a more opaque look that is ideal for posterior crowns. The latter option also has a higher fracture resistance compared to traditional ceramics, so it is better suited for molars that undergo more bite force.
Base Metals
A popular choice for out-of-sight molars, these types of crowns are durable and require minimal enamel removal during the preparation stage. They also withstand chewing forces well and last longer than porcelain alternatives. Their only drawback is their metallic colour, but if this isn’t a concern for you then a metal crown may be an excellent option.
These crowns are created through a process known as milling, where the solid block of metal is custom-cut to create the desired shape with the help of a computerised machine and CAD software. Feldspathic porcelain is then layered over the core to provide a more translucent, natural appearance. This type of crown can be either bonded directly to the natural tooth surface or layered over a pre-built Zirconia core (such as Procera or Empress).
Alloys
Metal crowns are a strong and durable option for back teeth and can withstand biting and chewing forces. They bond well to the tooth and don’t wear down adjacent teeth as they do with some other crown materials.
However, they are not as translucent (transmitting light) as porcelain or zirconia, and they can have a metallic appearance. Additionally, they tend to be more expensive than other crown types.
To make a metal crown, we first create an investment mould of the prepared tooth. A wax pattern is attached to this mould and the mould is then placed in a furnace or oven. The wax melts, flows out and is replaced with molten metal which is then poured into the mould cavity to form the core of the crown. The molten metal is usually base metal alloys such as nickel, cobalt or chromium and may contain gold as well. The crown is then finished with a porcelain cap which resembles the tooth’s natural colour.