Dental Crowns, Inlays, and Br... Health Article

Definition

Dental crowns, inlays, and bridges are prosthetic devices that replace missing teeth or part of a tooth. They are made of metal, porcelain, and resin, or a combination of these materials.

Purpose

Bridges, crowns, and inlays are created to restore a tooth's appearance, structure, or function. Inlays and crowns are intended to repair damage to individual teeth. They replace tooth structure lost by decay or injury, protect the part of the tooth that remains, and restore the tooth's shape and function. Bridges fill in a space in the jaw left by a missing tooth or teeth. They protect the shape of the mouth and restore function of the teeth and jaw.

Precautions

Some patients are allergic to the medications used for local anesthesia in dental restorations. In addition, many people are afraid of dental work. Most dentists in practice today can help patients with this specific fear.

Crowns

The crown of a tooth is the portion that is covered by enamel. A restorative crown replaces this outer part to protect and strengthen the tooth. This protection becomes necessary when a tooth cracks, has its entire structure weakened by decay, or becomes brittle after a root canal. Crowns can also cover dental implants or abutment (adjacent) teeth when fitting a bridge.

Crowns are also used to cover discolored or otherwise aesthetically displeasing teeth. Cosmetic dentistry does not use crowns as much as it once did, since crowns, though aesthetically pleasing, require more radical dental techniques. Dentists are opting for more conservative methods such as bleaching, bonding, or veneers to improve the aesthetic appearance of teeth.

The dentist first removes the decayed portion of the tooth. The tooth is then prepared for a crown. It may be tapered on the outside edges to a peg, reinforced with a cast metal core, or rebuilt with both a cast metal core and a post. An impression of the prepared tooth and the teeth next to it is made. A retraction cord is placed around the tooth in order to get the impression medium under the gum where the crown will be fitted.

The dental technician will create a new crown, using a cast made from this impression. The technique the technician uses is called lost wax casting. A wax model is made of the crown. Another mold is made around the wax model and both are fired in a kiln. The wax melts, leaving an opening into which a restorative material can be poured. The crown may be made of gold or stainless steel alone, metal with a veneer of tooth-colored porcelain or resin, or of porcelain or resin alone. The finished crown is then placed over the prepared tooth, adjusted, and cemented into place.

When a tooth has had a root canal and the root has been filled, the tooth may not be strong. Post crowns are used in these cases. The tooth is leveled at the gum line and a stainless steel or gold post is fitted into the root canal. This post can then receive the new crown and hold it in place.

For other patients, it may be necessary to implant the crown. In this case, a steel post is embedded in the patient's jawbone. It is left in place until the bone adheres to the post. The post is exposed and the crown is made and fitted.

New computerized techniques are making the restoration process faster and more comfortable. Chairside Economical Restoration of Esthetic Ceramics (CEREC) uses a computer system to allow the dentist to create ceramic crowns, inlays, and onlays, in one sitting. The tooth is prepared as usual but impressions are made digitally, using a hand-held camera. These photographs are converted to three-dimensional images on the computer screen, thus eliminating the need to take a physical impression of the patient's teeth. The dentists uses special 3D CAD/CAM software to design the crown. A milling system attached to the CEREC machine is able to make a ceramic crown in 10-15 minutes.

Crowns can last 5-15 years or more, if they are well taken care of.