What is a crown?
A crown is a hollow cap that fits over a tooth, giving it strength and/or improving its appearance. The supporting tooth has to be reduced in size to make room for the crown. Crowns may be made from a variety of materials.
Crowns are indicated for teeth, which are too extensively decayed, heavily filled or damaged for treatment by other means.
The tooth to be crowned may require root filling or rebuilding with a “build-up core” material before the dentist drills the tooth to a “peg” shape for the crown. Tooth preparation for a crown is normally done under a local anaesthetic and takes approximately 15 to 45 minutes per tooth. It should be painless. The dentist then takes an impression of the prepared tooth/teeth, which is sent to a dental laboratory where the crown is made by technicians. A temporary crown is then fitted to maintain the appearance, and keep the tooth comfortable and in the correct position until the permanent crown can be fitted.
The quality of the final crown depends both on the skill of the dentist and the technician. At the fitting visit, the temporary crown is removed and the new crown tried in, to assess that it has an adequate appearance, fit, shape, and that the bite or occlusion is correct. The crown is finally cemented with a dental cement.
A well made crown or bridge, in a situation where the overall dental outlook is favourable, should last for 10 or more years.
Sometimes the supporting tooth under a crown decays – this is more likely when the crown does not fit tightly to the underlying tooth. Some crowns come off repeatedly, even shortly after being fitted. In these circumstances the reason for the failure may be a poorly fitting crown, or a crown shape or bite which is not right for that tooth. In those circumstances a replacement crown will be required.
A bridge is a restoration which replaces a missing tooth with a fixed solution. There are many different designs of bridges, but the most common is a fixed bridge, which is made by placing crowns on the teeth either side of the space, and then joining the crowns together by placing a solid crown in the space to replace the missing tooth. Because this type of bridge uses joined crowns, cleaning the teeth in the area will be more difficult. A well-designed bridge should allow effective daily cleaning.
Just like crowns, a bridge must fit the supporting teeth tightly – if not, then cleaning the bridge will be difficult and the teeth supporting the bridge may decay or get gum disease. Sometimes a bridge will come off repeatedly. This may be due to a variety of factors but the size, shape, and relationship to opposing teeth should be considered as possible problems as well as the way the bridge fits on the supporting teeth.