Dental prostheses

Definition

Dental prostheses, artificially made devices resembling natural teeth, are used to replace missing or damaged teeth. These devices include inlays/onlays, crowns, bridges, dentures, partial dentures, and dental implants.

Purpose

Crowns and inlays/onlays 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, dentures, and partial dentures 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 constituents in local or general anesthesic agents. In addition, many people are afraid of dental work and therefore may experience stress-related symptoms, even fainting, while in the dental office. Most dentists can help patients with this specific fear. Also, the dentist and dental assistant will need to be aware of any pre-existing conditions in the patient's history, e.g. diabetes, high blood pressure , heart disease, hemophilia , or HIV/AIDS.

Description

Inlays/onlays

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 durability. New inlay alloys of palladium, nickel, or chromium are now frequently used. Metals are the dentists' choice for inlays in molars. When inlays are required for visible anterior teeth, tooth-colored composites and porcelains are used. Reinforced porcelain and Lucite porcelain are durable but may not be suitable for patients who grind their teeth. Composites are also used in fillings.

Crowns

A prosthetic crown replaces the outer portion of the tooth to protect and strengthen it. 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 can also cover discolored or otherwise aesthetically displeasing teeth. Cosmetic dentistry does not use crowns as much as it once did. Crowns, though aesthetically pleasing, require more radical dental techniques. Dentists are opting for more conservative methods such as bleaching, bonding, or veneers.

The dentist first removes the decay, and 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 desirable 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 accurate. Chairside Economical Restoration of Esthetic Ceramics (CEREC) uses a computer system that allows 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 3-D images on the computer screen, thus eliminating the need to take a physical impression of the patient's teeth. The dentist uses special 3-D 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.

Provided they are well taken care of, crowns can last 5–15 years or more.

Bridges

Bridges fill in the spaces 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 rises, increasing the likelihood that additional teeth will be lost. A bridge is inserted to prevent this from happening.

Bridges are made of a metal framework and one or more artificial teeth (pontics), which are 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. 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.

Implants

Dental implants are hard plastic or metal fixtures surgically embedded through the soft tissue into the jawbone that will act as artificial roots or anchors for a prosthetic tooth. Over time, bone will grow around these fixtures, firmly anchoring them. The implant posts are then surgically exposed and an artificial tooth is crafted and fitted over these anchors. Implants may also serve as stable abutments for bridges, partial dentures, or over-dentures. Dental implants may be the best choice for patients who have denture intolerance or who cannot chew food properly with other prostheses.

Partial dentures

A partial denture is similar to a bridge in that it fills a gap left by missing teeth. It is a removable dental appliance consisting of artificial teeth fitted onto a metal frame, which attaches to an abutment tooth or teeth, with a metal clasp or precision attachment. A partial denture is often used at the end of a row of natural teeth, where there is only one abutment tooth. The pressure exerted by chewing is shared by the abutment tooth and the soft tissues of the gum ridge beneath the appliance.

Complete dentures

Complete dentures may be worn when all of the top or bottom teeth have been lost. A complete denture consists of artificial teeth mounted in a plastic base molded to fit the remaining oral anatomy. It may or may not be held in place with a denture adhesive.

Removable implant supported over-denture

Some people cannot wear dentures because they cannot tolerate having a foreign substance in their mouths. Others simply can no longer wear dentures because of serious bone loss. In response to this denture intolerance, a removal implant supported over-denture may be the best solution. Implant anchors may be installed in either the upper or lower dental arch or both. Five or six implants are anchored into the bone of the upper arch and four or five are placed in the lower arch. Each group of jaw implants is connected by a stabilizing bar. A custom-made over-denture is placed over the bar by means of a silicone gasket, which holds the denture in place and provides a cushion between the denture and the implants. For patients with Parkinson's disease , telescopic attachments are added to the over-denture that have the ability to adjust to varying pressures within the mouth, allowing these patients to chew better.

Preparation

Before a restoration is placed in the mouth, the dentist removes all traces of decay or damage and shapes the remaining tooth structure to receive the restoration. Impressions are taken of the mouth and models are created from which the dental prostheses are made. When bridges or crowns are necessary, the tooth or teeth that are to receive the crowns are shaped into posts or pegs.

Prostheses are made up in a laboratory using a model of the tooth structure. 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 educate the patient about ways to keep the temporary in place, e.g. avoiding hard foods, gum, and other sticky or chewy foods. If possible, the dental assistant and dentist encourage the patient to avoid eating food on the side of the mouth where the temporary has been placed. Also, the patient is reminded to call immediately if the temporary is loosened so that it can be re-cemented.

There may be some gum swelling or discomfort when prostheses are fitted, or if surgery is performed. The dentist can recommend medications or oral rinses to reduce the discomfort.

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

Patients are urged to maintain normal oral hygiene while they wear a temporary, and after the actual the crown or bridgeis in place.

Dental prostheses, especially partial and full dentures, may take several weeks to adjust to. Inserting and removing dentures and other removable appliances takes practice. Speaking clearly may be difficult at first, but this usually passes with continued usage. Eating may also feel awkward. The patient should begin by eating small pieces of soft foods. Very hard or sticky foods should be avoided. Care should also be taken when eating hot food or food with bones, since artificial prostheses may make the mouth less sensitive to hard objects and hot food.

Also, patients may experience a reduced sense of taste , since teeth act as taste sensors. Many patients will eat a lot of very spicy, salty, or sweet foods because they can taste them better. Since it is important to include a variety of foods in the diet so that proper nutritional needs are met, it may be necessary to adjust seasonings to counter the blandness patients may be experiencing.

Permanent prostheses should be cleaned as regularly as real teeth. Specialty brushes and floss threaders may be used to remove plaque and food from around crowns and bridges. Full or partial dentures should be removed and brushed daily with a specially designed brush and a denture cleaner or other mild soap. Optimally, full and partial dentures should be removed at night and soaked in a cleaning solution. This allows the soft tissues in the mouth to recover from the pressures of the prostheses. The solution will preserve the denture material, since it may shrink or warp if it dries out. At this time, patients should also clean their gums to increase blood circulation and maintain healthy bones and gums.

The patient should see the dentist for an adjustment if there is any discomfort or irritation resulting from a prosthesis. Otherwise, the patient should see the dentist at least twice a year for an oral examination. If the patient has had several teeth extracted before dentures were installed, these prostheses should be adjusted within the first six months after the dentures have been fitted. Patients should also expect to have their full dentures adjusted if they lose or gain ten pounds or more. Also, dentures may need to be relined or replaced every five to ten years.

Complications

Restoration procedures typically require local anesthesia . In some cases, the patient may require general anesthesia because the procedures involve gum surgery or the extraction of several teeth. Some people may have allergic reactions to either kind of anesthesia. A very small number of people are allergic to one or more of the metals or acrylics used in dental restorations. In most cases, the dentist can use another material.

Surgery is an invasive procedure. The risk of trauma or infection is always present, though it is often a minor risk. The patient may commonly experience swelling, nausea, pain, or bleeding. When these symptoms are prolonged or fever is present, there may be infection. Rarely, nerve disturbances or bone fractures may occur.

Some patients experience speech difficulties when they have dental prostheses, especially with full dentures or several implants. Usually, this occurs during the first weeks after they have been fitted with prostheses for the maxillary or upper jaw bone. Once patients adapt to the prostheses, this problem disappears.

Results

A well-made dental prosthesis should feel comfortable and last a relatively long time with proper care. Artificial dental restorations only approximate the original tooth, however. They will never feel as comfortable or function as well as natural teeth. It is better, therefore, to prevent the need for dental prostheses to replace teeth. They 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 dental prostheses. Often, this requires a great deal of skill and structural knowledge in order to remove enough tooth material for the prosthesis to fit, yet leave enough architecture within the tooth in order to stabilize the restoration.

The dental technician prepares the dental prosthesis so that it will fit the prepared tooth and be compatible with the rest of the patient's mouth structure. The technician is part scientist and part artist and is able to craft natural-looking teeth that match the patient's mouth and facial features.

The dental assistant prepares the patient and the patient's teeth for the dentist. The dental assistant takes impressions of the patient's teeth and gums and prepares study models to aid the dentist in diagnosis and the dental technician in creating life-like prostheses that function comfortably in the patient's mouth.

Resources

BOOKS

"Dentistry in Medicine: Dental Restorations and Appliances." In The Merck Manual of Diagnosis and Therapy, edited by Mark H. Beers, Robert Berkow, and Mark Burs. 17th ed. Rahway, NJ: Merck Research Laboratories, 1999.

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

PERIODICALS

Carter, Ann. "Denture Care." Clinical Reference Systems (Annual 2000): 467.

"Custom-Made Dentures Can Improve Chewing Ability." Health & Medicine Week (January 15, 2001): 23.

"Denture Wearers at Risk for Poor Nutrition." Tufts University Health & Nutrition Letter 18 (July 2000): 3.

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

"Technology Triggering Brighter Smiles." USA Today, v. 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

"Upper Jaw Implants." Dentistry Online. http://www.dentistryonline.com/cons/pated2/08_pr_uji1.html>. (May 1, 2001)

KEY TERMS

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

Anesthesia —A condition created by drugs that produces a loss of sensation, particularly pain. General anesthesia produces unconsciousness, a local anesthesic only results in localized numbness.

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

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 a prepared tooth in order to restore its function.

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

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

Onlay —A restoration that covers the upper surface of a tooth. It is bigger than a filling but smaller than a crown.

Pontic —An artificial tooth suspended between two prosthetic crowns to fill a space left by a missing tooth.

Janie F. Franz