A crown, often referred to as a "cap", is a tooth restoration that fits over an entire tooth (the area above the gumline, that is). Crowns are usually placed on teeth which are badly broken down or weakened. Crowns are also almost always placed on teeth that have undergoneroot canal therapy. Most crowns done today are either all-porcelain, or porcelain fused to a metal substructure to add strength. Invariably, the cosmetic results are excellent, especially using the exceptional materials now available.
In order to fit a crown over an existing tooth, the tooth must be prepared by reshaping it into a form which will allow the crown to be seated onto the tooth. This typically involves shaving down most of the enamel covering of the tooth under local anesthetic. Once the tooth is reshaped, an impression is taken from which a plaster model of the tooth will be made for use in the dental laboratory. A temporary crown will then be cemented onto the tooth, to remain in place until the permanent crown or crowns are completed by the laboratory.
Crowns typically require two to three weeks of lab time. Once ready, your temporary crown is removed, and the permanent one cemented in place, after checking for correct shade and fit.
Often a tooth or teeth will be missing between other teeth. This gap can be filled with a permanent functional replacement tooth by using the teeth on either side of the space as a means of support. This type of restoration is called a bridge. A bridge is composed of crowns placed on the teeth adjacent to the gap, connected by an artificial tooth or teeth which replace the missing ones. The crowns which support the bridge are called abutments. The replacement teeth which are connected to the crowns are called pontics. Bridges are permanently cemented in place, and, even though the teeth are connected, they appear to be separate and distinct.
Bridges are often confused with partial dentures. Partials, however, are removable and usually grip the supporting teeth with visible metal clasps.
Bridges have been the standard treatment for replacement of one or two missing teeth for several decades. They tend to be highly predictable in longevity (often last a lifetime), and even for front teeth are excellent esthetically. The chief drawback is that the abutment teeth must be prepared for crowns, which often involves shaving down a virgin tooth which would not otherwise need a crown. Fortunately, this is more of a theoretical and psychological disadvantage than an actual one, and before the introduction of dental implants, also unavoidable. Now that the success rate of implants is so high, however, many patients choose implants over bridges. In many instances this is a choice based on personal preference, as the cost is usually comparable for a bridge vs. an implant supported crown.
The procedure for making a bridge is almost exactly the same as that for crowns, except for the time factor involved. The reason for this is that usually two teeth must be prepared for crowns instead of one.
Note: Most bridges are done in order to replace only one or two missing teeth, but bridges can also be made to replace multiple missing teeth in certain circumstances.