A crown, also known as a cap, is a dental restoration that covers all or most of a particular tooth.
There are several reasons crowns are recommended. A crown is commonly necessary when natural tooth material (enamel and dentin- the inner layer) has been damaged by decay. A second reason why crowns are fabricated is when a tooth as been fractured by trauma. Sometimes a tooth that has a large filling and it has occurred that the large filling has decay- it can be impractical or impossible to restore this tooth with a still larger filling- so a crown will be recommended. Still another reason crowns may be necessary and that is for esthetic reasons. Perhaps the teeth are not in good alignment and crowns will give the appearance of straighter teeth. Finally, crowns are useful to improve the appearance by replacing older stained or dark fillings.
All crowns require the shape of the natural tooth to be altered. It is required to make the underlying tooth somewhat smaller in every dimension to accommodate the new material that comprises the new crown. Occasionally, the tooth to be treated will need a special service just prior to starting the crown called a “build-up.” This refers to a special quick setting material that is used to repair the decay or missing portion of the tooth and is bonded to the tooth. This gives the new crown more material upon which to hold. The more structure or taller the tooth the better the new crown will hold on to the tooth.
Crowns usually take two dental appointments. In the first dental visit local anesthetic is used so the patient is always comfortable, the tooth is reshaped as conservatively as possible, a mould or impression of the altered tooth is made and a custom temporary crown is made and cemented to the tooth being treated. Temporary dental cement is used to allow us to remove the temporary crown easily. On the second and final visit, the temporary crown is removed, usually without the need for local anesthetic, and the new crown is tried in for fit, adjusted for the fit and bite as necessary and after approval by the patient cemented in place for long term use.
Today there are various types of dental crowns in use. Most common are porcelain or ceramic crowns. These custom made crowns are designed to match the color of the neighboring teeth. Some porcelain crowns are porcelain crowns with a gold alloy underneath the ceramic. Other porcelain crowns have no metal whatsoever and this lends itself to a very natural appearance. Finally some crowns are entirely metal – gold crowns (either white or yellow gold). These crowns are the strongest and are commonly used in the teeth far back in the mouth where esthetics is not too important but maximum strength is most important. Modern porcelain crowns have been developed to be very strong and are improving with new techniques all of the time.
The care of a dental crown is just like any other tooth. It is important to keep dental plaque off of the crown – that is keep the food off of the crown long term- because the tooth at the edge of the crown is still susceptible to decay. No crown will last forever, so the cleaner the crown the longer it will last. With regard to porcelain it is important to remember that porcelain is like glass. Porcelain crowns can break. Consequently one should not bite or chew on very hard substances like chicken bones, rib bones, peach pits, ice and so forth. With proper care well made crowns can last many years.
David Silberman DDS FAGD
General, Cosmetic Dentistry and Orthodontics, for Adults and Children