Tooth Replacements: Bridges and Crowns
Tooth loss can have a profound effect on your health and well-being. Even though diseases leading to tooth loss are largely preventable, 46 percent of Americans ages 65 and older have lost six or more teeth, and 20 percent have lost all of their natural teeth due to decay or gum disease.
Research shows that it takes 20 well-placed teeth to preserve your normal chewing function. As the number of teeth decreases, the quality of a person’s diet drops. Missing teeth can also make speaking difficult and can make you self-conscious about your appearance. In addition, an empty space in the dental arch destabilizes the teeth that remain. The consequences can be tooth shifting, bone loss, and bite problems.
Although nothing can truly take the place of healthy natural teeth, several replacement options are available. They can improve your functioning and your appearance, as well as help you preserve surrounding teeth. One such option is fixed prostheses, or crowns and bridges.
There are many different kinds of fixed prostheses. Typically, a single crown is used to restore one damaged tooth, while a bridge can be substituted for one or more missing teeth.
Dentists use a crown, also called a cap, to repair a tooth that’s been broken by injury, undergone root canal therapy, or been so seriously weakened by cavities that it’s in danger of falling apart. Crowns also are used as anchors for a fixed bridge; the bridge is attached to crowns placed on the two adjoining teeth.
A crown fits over the entire tooth and is constructed to mimic the natural shape of your own tooth. The crown is made in a laboratory based on impressions your dentist takes of your teeth. One trend is to use CAD/CAM (computer-aided design/computer-aided manufacturing) technology to create crowns, bridges, and implants. The computer is used to scan the tooth and create a three-dimensional image of it. From that image, a restoration is created in a milling chamber that is part of the equipment.
Crowns on molars are often made of cast gold, another metal, or porcelain fused to metal because these materials can withstand the most chewing pressure. Crowns for front teeth are primarily made with tooth-colored material, typically ceramic, for aesthetic reasons.
To place the crown, your dentist removes the enamel from the tooth and grinds the dentin into a peglike shape. Then he or she cements the artificial crown onto this. It will take at least two visits before your dentist installs the final crown. Between visits, your dentist will put a temporary crown in place.
Bridges come in several variations, as follows.
Fixed partial denture (fixed bridge). This consists of artificial teeth, called pontics, fused to a metal frame. Fixed bridges are usually made of metal, such as gold alloy, or porcelain that’s fused on metal. The frame is anchored with cement to an abutment at either end. Abutments can be either implants or healthy teeth that have been covered by crowns. The more teeth being replaced, the more natural teeth or implants you will need to use as abutments on either side to give the bridge the necessary support. This ensures that the bridge remains stable under the pressure of chewing.
Cantilever (extension) bridge. Sometimes a bridge is anchored only at one end. This technique lets you avoid having to trim and cap one of the healthy adjacent teeth to use as an abutment. An extension bridge carries a higher risk of failure, especially on back teeth where most of the chewing takes place. Therefore, it’s rarely used in this position. It’s best suited for replacing teeth in the front portion of the mouth where there is not enough space to install an implant that could be used as an abutment.
Resin-bonded (Maryland ) bridge. With this type of bridge, the surrounding teeth don’t have to be capped. Instead, the dentist attaches the bridge by gluing thin metal strips to the backs of adjacent teeth with a resin adhesive. To help the adhesive attach, the dentist prepares the tooth surfaces with acid. If the abutting tooth is a molar, the bridge is attached by metal onlays that are cemented into it. The primary disadvantage to this type of bridge is that the bonding can loosen over time.
Source: Dental Health for Adults: A Guide to Protecting Your Teeth and Gums. Copyright © by Harvard University. All rights reserved.