DEFINITION:

A dental crown is placed on the top of a tooth, and covers it to reconstruct its shape, size, strength, and improve its appearance. Once cemented, it resembles a cap in the shape of a tooth, covering completely the portion of the tooth above the gum line.

There are three types of crowns:

•Gold crowns. These are very resistant to the chewing forces, fracture rarely, and does not wear to the opposite teeth. They last the longest, though their gold colour can be a disadvantage. Gold crowns would be a good choice for a molar in the back.

•Porcelain fused to metal. These crowns are more esthetic because they can resemble a lot a natural tooth. The metal strengthens the tooth, but the porcelain can get fractured.

•Porcelain. These are the most esthetic crowns, as their appearance and colour match the natural teeth. They are less solid, though there are some new varieties of resistant porcelain that are offered. They are therefore recommended for anterior teeth.

The preparation of a crown requires two visits. The first visit, based on the examination of the x rays, allows the dentist to determine if a root canal is needed before putting a crown on it. The root canal allows a support to make the crown more solid, in cases where the tooth is very destroyed by the cavity. If a root canal is not necessary, a filling can be used to reconstruct the tooth and create a better support. An impression of the tooth is taken and sent to the laboratory for the creation of the crown. In the meantime, a temporary crown is placed until the next appointment. Two or three weeks later, the second visit implies the cementation of the permanent crown, and the removal of the temporary one.

A crown can last between five to twenty years, depending on oral hygiene, maintenance and habits.

APPLICATIONS:

Crowns are mainly used to:

•Protect a weakened tooth (i.e. after a severe cavity, filling or fracture) from breaking, or to keep intact a cracked tooth.

•Restore an severely worn or already broken tooth.

•Cover a malformed or severely discoloured tooth.

•Cover a dental implant.

SOURCES:     Wikipedia, the free encyclopedia (www.wikipedia.org).

                            WebMD, better information, better health (www.webmd.com).