Dental Crowns, Inlays, and Bridges

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.

Description

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 to 15 minutes.

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

Bridges

Bridges are restorations that fill in a gap caused by missing teeth. They prevent the remaining teeth from shifting and provide a more stable surface for chewing. If the gap is not filled, the other teeth shift, affecting the patient's bite (occlusion), which sometimes produces pain in the jaw joint. As the teeth move and become crooked, they also become more difficult to keep clean. The risk of tooth decay and gum disease increases, also increasing the likelihood that additional teeth will be lost. A bridge is inserted to prevent this risk.

Bridges are appliances consisting of a metal framework and one or more artificial teeth (pontics) anchored to adjacent teeth. The abutment teeth carry the pressure when the patient chews food. Bridges can be removable or fixed (permanent). Removable bridges are attached to the abutment teeth by wires or precision attachments. Fixed bridges are attached to permanent crowns placed on abutment teeth. There are two types of fixed bridges—the crown-and-bridge design and the Maryland Bridge. A Maryland Bridge does not have crowns on it. The backs of the abutment teeth are reduced slightly and small wing-like appendages on the bridge are cemented to the back of the abutment teeth.

When the adjacent teeth are not strong enough to support a bridge, a two-implant bridge is required. This type of bridge takes longer for the permanent bridge to be fitted because of the necessity for the gums to heal. Posts are surgically implanted into the patient's bone and the gum closed. It takes several weeks for the bone to attach to the posts. The posts are re-exposed and the bridge is made to fit. It is then cemented in place.

Inlays

An inlay resembles a filling in that it fills the space remaining after the decayed portion of a tooth has been removed. The difference is that an inlay is shaped outside the patient's mouth and then cemented into place. After the decay is removed and the cavity walls are shaped, the dentist makes a wax pattern of the space. A mold is cast from the wax pattern. An inlay is made from this mold and sealed into the tooth with dental cement.

Inlays and their counterparts, onlays, are conservative alternatives to crowns. They don't require as much tooth preparation and often are more durable than amalgam fillings. Inlays cover the grooves on the surface of the molar. Onlays wrap over the tooth, covering more of its surface.

Inlays used to be made entirely of gold for its durability. New inlay alloys of palladium, nickel, or chromium are frequently used. Metals have been the dentist's choice for inlays in molars. When inlays are required for teeth that will be seen when a patient smiles, tooth-colored composites and porcelains are used. Reinforced porcelain and Lucite porcelain are durable but still may not be suitable for patients who grind their teeth. Composites are also used in fillings.

Preparation

Before a restoration is placed in the mouth, the dentist removes all traces of decay or damage and shapes the remaining tooth structure for the restoration. When bridges or crowns are necessary, the tooth or teeth that are to receive the crowns are shaped into posts or pegs. Temporary crowns and bridges are installed until the permanent restoration is delivered by the laboratory.

Aftercare

Temporary crowns or bridges must stay in place until the permanent restorations have been fitted to the patient's mouth. Dentists and dental assistants should educate the patient about ways to keep the temporary in place; for example, avoid hard foods, gum and other sticky or chewy foods. If possible, the dental assistant and dentist should encourage the patient to avoid eating foods on the side of the mouth where the temporary is. Also, the patient should be reminded to call immediately if the temporary is loosened so that it can be re-cemented.

There can be some gum swelling or discomfort when a crown or bridge is fitted. If a bridge implant was completed, there is naturally some discomfort from the surgery. The dentist can recommend medications or oral rinses to mitigate the discomfort.

Patients may also experience sensitivity to cold foods or drinks for a few weeks after a crown, bridge, or inlay is in place.

Patients should be urged to maintain normal oral hygiene while they wear a temporary and after the crown or bridge is in place. Specialty brushes and floss threaders may be used to remove plaque and food from around crowns and bridges.

The patient should see the dentist for an adjustment if there is any discomfort or irritation resulting from a restoration. Otherwise, the patient should see the dentist at least twice a year for an oral examination.

Complications

Restoration procedures typically require local anesthesia. Some people may have allergic reactions to the medication. A very small number of people are allergic to one or more of the metals used in a dental restoration. In most cases, the dentist can use another material.

Results

A well-made restoration should feel comfortable and last a relatively long time with proper care. Artificial dental restorations only approximate the original tooth, however. It is better, therefore, to prevent the need for restorative dental work than to replace teeth. Restorations are expensive, may require many appointments, and still need careful cleaning and attention.

Health care team roles

The dentist is crucial in diagnosing a patient's particular dental needs and determining the correct remedy. The dentist will prepare a patient's teeth for restorative work. Often, this requires a great deal of skill and structural knowledge, because the dentist must remove enough tooth material for the restoration to fit and yet leave enough architecture within the tooth in order to stabilize the restoration.

The dental technician prepares the restoration so that it will fit the prepared tooth and fit in with the rest of the patient's mouth structure. The technician is part scientist and part artist in order to craft natural looking teeth that match the others in a patient's mouth.

The dental assistant prepares the patient and the patient's teeth for the dentist to do what is necessary to determine what restoration is best suited for this particular patient. The dental assistant takes impressions of the patient's teeth and gums and makes plaster-type casts to aid the dentist in diagnosis and the dental technician in creating life-like restorations that fit comfortably in the patient's mouth.

KEY TERMS

Abutment tooth— A crowned tooth that stabilizes a bridge or partial denture.

Bridge— An appliance of one or more artificial teeth anchored by crowns on the adjacent teeth.

CAD/CAM— A computer-aided design and manufacturing package.

Complete denture— A full set of upper or lower teeth, mounted in a plastic base. Dentures are also called false teeth.

Crown— A protective shell that fits over the tooth.

Dental caries— A disease of the teeth in which microorganisms convert sugar in the mouth to acid that erodes the tooth.

Enamel— The hard outermost surface of a tooth.

Inlay— A filling that is made outside of the tooth and then cemented into place.

Occlusion— The way upper and lower teeth fit together during biting and chewing.

Pontic— An artificial tooth.

Pulp— The soft innermost layer of a tooth that contains its blood vessels and nerves.

Resources

BOOKS

Shillingburg, Herbert T., Jr., Sumiya Hobo, and Lowell D. Whitsett. Fundamentals of Fixed Prosthodontics. Chicago: Quintessence Pub. Co, 1997.

PERIODICALS

Doyle, Audrey. "Digital Dentistry." Computer Graphics World 23 (October 2000): 50.

"Technology Triggering Brighter Smiles." USA Today 129, no. 2666 (November 2000): 7.

ORGANIZATIONS

Academy of General Dentistry. Suite 1200, 211 East Chicago Avenue, Chicago, IL 60611. (312) 440-4300. 〈http://www.agd.org〉.

American Dental Association. 211 East Chicago Avenue, Chicago, IL 60611. (312) 440-2500. 〈http://www.ada.org〉.

OTHER

"Inlays & Onlays: What's the Difference?" Dentistry Online. April 9, 2001. 〈http://www.dentistryonline.com/cons/articles/view_document.cfm?Article_JD=490〉.