Crowns

Crowns may be indicated when a tooth is heavily filled, broken down or requires protection (e.g. after a root filling) They may restore the shape, function and appearance of a tooth. The tooth may firstly require rebuilding with a filling material (this is called a core) before preparation to reduce both height and width. An impression is taken for the laboratory to work on. A provisional crown is then made and fitted in the surgery to protect the tooth while the crown is being made. A second appointment, usually 2 weeks later, is required to remove the provisional crown and fit the final crown.

There are a variety of crowns available:


• Porcelain bonded to precious metal
  

  These comprise of metal sub frames with porcelain fused to the surface, they gives high strength coupled with natural appearance. They have a long track record for reliability, although metal can sometimes be a problem at the front of the mouth if the gums recede, giving rise to a visible dark line.

• All Porcelain
  

  An example of a porcelain crown is a zirconia crown which comprises of a zirconium oxide sub frame with porcelain fused to the surface. Porcelain provides ultimate natural appearance with no metal, it is very strong, but relatively new, so has a shorter track record.

• Gold
  

  Gold crowns provide a good fit to the tooth and may be useful at the back of the mouth if the tooth is very short. This is the most durable crown, but due to its appearance, can be limited to use on back teeth. These have an excellent long track record.

• Fixed
  

  One or more teeth need to be prepared in the same way as for a crown. The supporting teeth need to be sufficiently strong and firm. In addition, it may be undesirable to use a tooth with no previous dental treatment, as the preparation would result in the extensive removal of healthy tooth substance. The resulting bridge is very durable and is unlikely to come off unless a problem develops in one of the supporting teeth. Materials may be porcelain bonded to precious metal or for shorter spans, zirconia all porcelain.

• Adhesive
  

  Also known as a Maryland bridge, these rely on a thin metal wing to glue the tooth onto the back of an adjacent tooth. The beauty of adhesive bridges is that only minimal preparation is required, often not even requiring a local anaesthetic. The supporting tooth needs to be sound, firm and have minimal or no fillings. The glue used is incredibly strong, but occasionally these bridges may come off and require re fixing. This however, needs to balance against the advantages of the minimal preparation and tooth preservation.