Crowns are indicated in a variety of situations. Most commonly is when there is not enough solid healthy tooth structure to support a filling. For a filling to work there has to be at least one third of the chewing surface left. Any less than that will mean that the tooth will be prone to fracture as seen in the following picture:
The picture on the left shows a tooth after a large amalgam (silver) filling has been removed. The arrows point to fracture lines. As you can see the filling that was there occupied more than two thirds of the chewing surface of the tooth. Amalgam fillings have a tendency to cause fractures more readily than composite or white fillings. This is because silver fillings are metal and they expand and contract with hot and cold temperatures differently than natural teeth. However, any filling that is too large will tend to fracture teeth. If a fracture is caught early enough the tooth can either be fixed with a filling (if it is small enough) or with a crown. The process involves removing the fracture lines with a dental drill, filling the tooth with a “core” and then placing a crown or cap on top of it. Placing a crown will strengthen the tooth and prevent the fractures from getting larger. If the fracture isn’t fixed there is the possibility of the tooth breaking. Certain types of breaks can be painful if they involve the pulp (nerves and vessels of the tooth) and may be non-restorable. If the tooth is non-restorable the tooth would need to be extracted and plans for a bridge or implant would be needed... a much more expensive fix!
Other reasons for crowns are after having a root canal or for cosmetics. Root canals cause the tooth to become brittle due to the tooth being unable to receive the nutrients it needs with the vessels removed. In order to prevent the tooth from sustaining further damage a crown and core are placed. Cosmetic crowns are placed to improve the appearance of teeth, many times in the absence tooth disease. Most of the time they are made of highly esthetic ceramic and can be matched to your existing tooth color or any other color you may desire. Many times they are used to restore the natural form of your teeth following grinding or fracture or to make the teeth appear straighter or whiter.
Crowns have an average longevity of 5-7 years before they need to be replaced no matter what reason they are made for, cosmetic crowns are no exception. Again this is an average which is influenced by many factors. One of these factors is the clinical ability of the dentist while preparing your teeth. Another is the selection of materials. Metal crowns (gold) or porcelain fused to metal (porcelain shell on a metal base) crowns can generally be better adapted to the tooth but may be less esthetic than full ceramic crowns. If the margin of the crown (where the tooth and crown meet) is slightly open it can allow bacteria to get underneath and cause decay. A couple newer materials are showing some promise to bridge the gap between the benefits of metal and ceramic crowns. These crowns are made of lithium disilicate (a type of ceramic glass) or solid zirconia. Zirconia has very similar physical properties to that of gold with the esthetic properties of porcelain. They are beginning to become very popular for use in dentistry.
The final factor is your ability to keep the crown and tooth clean. No matter how well the crown is made or how good the dentist is, if you aren’t brushing and flossing the tooth religiously the crown will fail over time.
Porcealin Fused To Metal Crowns (PFM)
Solid Zirconia Crown (Bruxir)
Lithium Disilicate Crowns (EMax)
Full Gold Crown
Restorative Dentistry: Dental Crowns and Bridges
Dental Crowns or "Caps":
Bridges are indicated when one or more teeth are missing. They can be made of the same materials shown above. They are a good option for tooth replacement because they stabilize the area (preventing tipping) and restore your functional ability (allowing you to chew normally) Bridges are also glued in place. This means you don't have to take them out of your mout to care for them like removable dentures, which are another option for replacing teeth. For a bridge to work there needs to be a tooth on either end of the missing tooth space that acts as an abutment for the bridge to be glued to. If there is no back tooth the options are limited to removable partial dentures or implants. The following picture shows how bridges attach to your teeth: