The term "crown" can refer to either the natural crown which is part of a tooth or an artificial crown which is a dental restoration.

The natural crown of a tooth may be defined in two ways:

• Anatomical crown. The part of the tooth covered by enamel, which may be above or below the gumline.
  
  
• Clinical crown. The portion of the tooth visible inside the mouth and not covered by soft or hard tissue.

Different types of artificial crowns include:

• Full crown. An artificial crown that covers the entire natural crown.
  
  
• Jacket crown. A thin crown that covers large areas of the natural crown in the front teeth. It may not be strong enough for use in the back teeth, which endure greater levels of chewing stress and pressure.
  
  
• Dowel crown. A full crown that is anchored by a dowel pin that extends into the root canal of a tooth that has undergone a root canal treatment.
  
  
• Three-quarter crown. A crown that covers all of a natural crown except the front surface of the tooth, which remains natural for aesthetic purposes.
  
  
• Abutment crown. An artificial crown used to support a bridge or cover an implant.

Artificial crowns may also be classified by their materials:

• Gold alloys. Composed of a combination of gold, copper and other metals. These materials are strong and highly resistant to tarnishing, corrosion, fracture and wear. These materials do not tend to require as much removal of the underlying natural tooth material as other crown materials. They are compatible with the nearby teeth and are well tolerated by patients. However, many patients find the metallic gold color displeasing for teeth that are visible when talking, smiling or laughing.
  
  
• Base metal alloys. Composed of a combination of base metals (e.g., nickel, chromium). These materials have strength and resistance qualities similar to gold alloys. However, they have a metallic silver color that many patients do not like. They may also cause an allergic sensitivity or initial discomfort with hot and cold in some patients.
  
  
• Porcelain. May be composed of porcelain, ceramics or glasslike materials. These materials have a color and translucency that closely matches natural teeth. They are also highly resistant to wear. However, they may be prone to fracture and can wear down nearby teeth if the porcelain surface becomes rough. They may also require the removal of a larger amount of natural tooth than metal alloy crowns to support enough porcelain to produce a strong crown.
  
  
• Porcelain fused to metal (PFM). Composed of a porcelain crown bonded to a metal base. This combination is strong and durable and highly resistant to wear. However, it can wear down nearby teeth if the porcelain surface becomes rough. It may also cause an allergic sensitivity or initial discomfort with hot and cold in some patients. In addition, it may require the removal of a larger amount of natural tooth than metal alloy crowns to support the combined metal and porcelain.
  
  
• Composite resin. Composed of a type of composite plastic similar to the material used in tooth-colored fillings. This material tends to be relatively inexpensive and looks like natural teeth. However, it may stain more readily than porcelain and is not as strong or durable as porcelain.