CROWN AND BRIDGE
Crowns are generally used on teeth that have been broken by trauma, or largely eaten down by decay. Crowns cover a large part or all of the external surface of the tooth. Some patients worry that it is necessary to cut the tooth down to the gum line to prepare a crown, but there is usually just a thin veneer (0.5 to 2.0 millimeters) of tooth that is reduced to make room for the coverage of the tooth.
The most commonly used crowns are metal, porcelain fused to metal, ceramic, and resin crowns. The metal crowns are usually an alloy of gold, silver and palladium. Cast stainless steel crowns were used a lot a few years ago, but nickel allergy has been a serious problem with this type of metal crown. A few labs in the U.S. make titanium crowns, but the fit is generally not as accurate as the noble metal crowns. Metal crowns have the obvious benefit of being stronger than any of the other types of crowns. A well prepared metal crown will often last twenty to thirty years, or longer. Their obvious disadvantage is that they are not the same color as teeth, so they are not esthetically acceptable in many areas of the mouth.
Porcelain fused to metal crowns are probably the next strongest, and usually have good esthetics, but the esthetics of the ceramic and resin crowns are a bit superior to the porcelain to metal crowns.
The teeth are generally prepared the first visit, with impressions being taken and temporary crowns being cemented. The second appointment is used for fitting, adjusting and cementing the crown. There are a great variety of cements and bonding agents used for different crowns.
BRIDGES (FIXED BRIDGES)
Bridges are generally made to replace missing teeth with a fixture that is not able to be removed from the mouth, but is cemented to existing teeth. The abutment teeth for the bridge are prepared as they would be for individual crowns. Bridges are usually made with metal crowns or porcelain fused to metal crowns as abutments. Some of the new ceramics and resins are being used occasionally for short span bridges without any metal under-structure.