Restorative Dental Materials

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Restorative Dental Materials

Definition

Restorative dental materials are substances that are used to repair, replace, or enhance a patient's teeth. These materials include metals, porcelains, and composite resins (often made from plastics).

Purpose

Restorative dental materials are used to create fillings, bridges, crowns, and inlays in order to restore a tooth's appearance, structure, or function.

Description

The end of the twentieth century witnessed a dramatic decline in dental caries and an increased interest in dental health and enhancement. Smaller cavities are being discovered in the general population and in children, with over half of those aged five to 17 having no tooth decay at all. At the other end of the spectrum, older Americans are retaining more and more of their natural teeth and are beginning to seek out dentists for restorative work.

Visits to prosthodontists (dentists who specialize in mouth reconstructions, such as crowns, fixed bridges, dentures, and implants) and cosmetic or esthetic dentists (those who repair and enhance teeth through whitening, veneer application, or attachment of permanent restorations) increased from the 1990s into the twenty-first century. An American Dental Association (ADA) survey in 2000 indicated that 84% of responding dentists reported offering some form of cosmetic services to their patients.

Dentists now have more tools with which to diagnose a patient's unique problems, and they are able to find more creative, conservative solutions for them. The dentistry of the 1970s provided limited options. A patient had a tooth filled or extracted, had teeth straightened with braces, or had a crown or bridge installed. Often, the crown cracked and had to be replaced, or the bridge that was fitted was a plastic tooth set in a maze of wires.

Thirty years later, dentists can whiten teeth, alter their shape, fill gaps between them, or build up a tooth that is cracked. Dentists can fill a cavity with a tooth-colored filling that appears invisible to the naked eye. They can replace a missing tooth with a porcelain bridge or a resin implant. Even crooked teeth can be greatly improved with veneers and bonding or invisible plastic braces.

Cosmetic dentists and prosthodontists create restorations in order to repair, replace, or enhance a patient's tooth or teeth.

Restoration types

All restorations perform one of three main functions. They repair, replace, or enhance. Among the types of restorations that repair are fillings. These are used to restore tooth damage that occurs as a result of dental caries (tooth decay). Metal amalgams or composite resins are used to fill cavities and restore the function and esthetics of a tooth. Inlays and crowns, used to repair damage to the teeth, replace tooth structure lost to decay or injury, protect what remains, and restore the tooth's shape and function. Inlays are more durable than amalgam fillings.

Crowns may be 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.

Bonding and contouring

Bonding is a low-cost alternative to crowns or veneers. A tooth-colored composite resin is molded over the tooth, exposed to a special light, and then polished. It is used to restore chipped or slightly ill-shaped teeth. It is less durable and subject to chipping. Bonding is also limited to areas of the mouth that do not experience strong chewing forces, such as the front teeth.

Contouring is done to correct the shape of a tooth. This is mainly an extractive procedure because small amounts of tooth enamel are removed. This technique can be combined with bonding or veneer application.

Restorations that replace

BRIDGES. Bridges fill in a gap left by missing teeth, preventing the remaining teeth from shifting and providing a more stable surface for chewing. Bridges consist of a metal framework and one or more artificial teeth anchored to adjacent teeth (abutment teeth). Sometimes, a two-implant bridge is required. It is then cemented into place.

IMPLANTS, DENTURES, AND PARTIAL DENTURES. Implants, dentures, and partial dentures also replace missing teeth. Individual artificial teeth may be implanted or inserted into the patient's jaw. Partial dentures are dental appliances that have more than one artificial tooth inserted into a metal framework. They are usually removable and can be designed for one or both sides of the mouth.

Restorations that enhance

Crowns are used less frequently to enhance stained or damaged teeth. Newer techniques, such as bleaching or veneer application, are less invasive, save more original tooth structure, and cost less than crowns.

Veneers are ultra-thin coatings used to close gaps between teeth or cover discolored teeth. They are also used to fill in spaces between teeth, repair broken or chipped teeth, and straighten out misshapen or crooked teeth.

Materials used in fillings

The dentist cleans out the decayed part of the tooth and fills the opening with an artificial material (a filling) to protect the tooth's structure and restore the beauty and utility of the tooth.

METALS The most common and strongest filling material is amalgam. It is a silver filling that is usually placed on the rear molars, which endure more stress during chewing. Amalgam fillings are strong and very resistant to wear, and are used for large, deep fillings. Amalgam has been in use since 1833. It is a mixture (an amalgam) of several metals, including liquid mercury (35% silver, 15% tin or tin and copper, 50% mercury, and a trace of zinc ). When it is prepared, it has a malleable consistency that can easily be shaped to fit the prepared tooth. It hardens to a durable metal.

Despite its durability, many dentists and patients avoid using amalgam fillings. They have found that amalgam has a tendency to expand with time. As a result, teeth become fractured from the inside and often split. Patients are not choosing amalgam, but this is strictly for aesthetic reasons. They darken over time and make teeth appear decayed. There has also been a question about the safety of amalgam since it contains mercury; the ADA has maintained that it is safe to use as a restorative material.

Gold fillings or inlays are created outside of the mouth by a dental technician, then cemented into place. They are also used to fill the back molars and are very durable. Like amalgam, however, they are not as aesthetically pleasing as tooth-colored fillings. Still, gold has been a good source for foundation materials for porcelain over metal crowns.

Alloys of palladium, nickel, or chromium are frequently used for inlays and overlays, as well as for some base material for porcelain over metal crowns. Palladium is the metal of choice for porcelain-to-metal reconstructions. It is strong and generates fewer allergic reactions. Low-fusing porcelain allows lab technicians to add onto existing restorations.

PORCELAINS. Implants, partial dentures, dentures, crowns, and veneers are usually made from porcelain. Thin veneers made from porcelain are quite durable. All-porcelain products in the twenty-first century tend to fracture less often than those of the past. Some crowns and implants are made with porcelain-covered metals. They are extremely durable, but sometimes recede from the gums, exposing the metals. Porcelain-over-gold crowns often have a golden glow that is caused by the metal beneath. This glow creates a more aesthetically pleasing crown, but it is more expensive than a crown made of other materials.

When inlays are required for teeth exposed by a smile, 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 because metal fillings withstand the stress of grinding better.

COMPOSITE RESIN. Composite fillings, often called white fillings, are made of a plastic resin and finely ground glass. They must be applied to the tooth surface in thin layers. Dentists try to match the color of composites with neighboring teeth for a more natural look, making the fillings appear invisible. Composite resin fillings are often made smaller than amalgam fillings and require less tooth preparation, thereby saving more natural tooth surface.

The composite filling is bonded to the tooth so that the tooth becomes stronger than it was before. A composite filling is also less sensitive to temperature changes in the mouth, which can damage the tooth. Thus, there is less chance that the tooth will shatter because of the filling.

The major drawback of the composite resin filling is cost. The average cost is 1.5 to 2 times greater than the price of an amalgam filling. The composite resin filling can be stained by coffee and tea. Further, the large composite filling tends to wear out sooner than the large amalgam filling. However, the composite combined with porcelain is an excellent material for thin veneers. Finally, the light-cured composite's flexibility allows restorations to be repaired directly in the mouth. They are not abrasive and feel much like a natural tooth.

Operation

Crowns

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, rein-forced with a cast metal core, or rebuilt with both a cast metal core and a post. An impression is made of the prepared tooth and its adjacent teeth. A retraction cord is placed around the tooth to get the impression medium under the gum, where the crown will be fitted.

A new crown will be created by the dental technician, who will use 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 procedure and the root has been filled, the tooth may not be strong. In these cases, post crowns are used. 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.

Inlays

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.

When a restoration is cemented in place, the dentist and the dental assistant clean off all uncured restorative materials left on the tooth. Pumice or another mild abrasive is more effective in removing leftover materials than air or water spray, or even a roll of cotton.

Partial dentures, dentures, and implants

Partial dentures, dentures, implants, and veneers are created in much the same way as crowns and inlays. Teeth may already be absent, or they may need to be extracted. Impressions of the patient's mouth are taken and restorations are created from a variety of materials in a dental laboratory. The final product is fitted and/or cemented into place at the dentist's office. For a veneer, the tooth is etched and a strong bonding agent is applied. The veneer is then cemented to the tooth.

Bonding

For bonding, thin layers of enamel are removed. The bonding material is laid over the tooth and shaped. It is cured with a special light and then polished.

Maintenance

Restoration materials are durable. Composite and amalgam fillings can last seven to 10 years. They should be maintained with good oral hygiene and replaced as necessary. Some of the composite resins are sensitive to staining from coffee and tea. Amalgam fillings have a tendency to expand over time. As a result, teeth become fractured from the inside, and they often split. When a fracture occurs, a crown is needed. Unfortunately, amalgam fillings also darken over time and make teeth look as if they are decayed.

Cracks can occur in materials used for dentures and partial dentures, but far less frequently in older porcelain materials.

Composite resins are used to bond teeth, but they may not stand up to the patient who eats hard candy, popcorn kernels, or ice. They may require repair or touch-ups. Porcelain—a strong, translucent ceramic material—is used to make veneers, which can change the shape of teeth and fill in unsightly gaps. Porcelain veneers can become chipped or otherwise damaged, and may need to be replaced every five to 12 years.

Health care team roles

Dentists are assisted by dental assistants, who prepare patients for prosthodontic procedures. These usually involve taking x rays, making impressions of patients' teeth, making casts from the impressions, preparing restorative materials, and assisting the dentist in installing dental prosthetics or applying restorative materials. Cleaning and disinfecting of instruments and the treatment area are also the responsibility of the dental assistant. They take an active role in educating patients about the care and maintenance of their restorations, and instruct patients in proper aftercare, especially if there has been some invasive procedure (such as extraction or surgery). Dental assistants must be well trained in the preparation of dental materials and their applications, and must also have good communication skills, as they need to instruct patients and have the ability to reassure those who may be uncomfortable in a dentist's office.

In the laboratory, dental technicians are responsible for the creation of dental prosthetics. They must possess excellent manual dexterity and some creative skill. With recent advances in digital dentistry, the technician will require computer skills as well as manual ones.

KEY TERMS

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

Amalgam— A mixture of metals, primarily mercury and silver, used to make large, durable fillings. Also called silver fillings.

Composite filling— A resin material that is tooth colored and used to fill a tooth after decay has been removed. It is used most often in front teeth, but may be used in any tooth for aesthetic reasons.

Crown— A protective shell that fits over the tooth.

Denture— A dental prosthetic device consisting of a full set of teeth to fill the upper or lower jaw or both jaws. Also called false teeth.

Enamel— The hard outermost surface of a tooth.

Impression— An exact copy of the teeth and mouth using materials that will set sufficiently so that a more durable cast of the mouth can be made from plaster, dental stone, or other casting materials.

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

Onlay— A restoration like an inlay that wraps over the crown and sides of a tooth.

Partial dentures— A dental prosthetic of two or more teeth used to replace missing teeth.

Porcelain— A strong, translucent ceramic material.

Prosthodontist— A dentist who specializes in mouth reconstructions such as crowns, fixed bridges, dentures, and implants.

Restoration— Any prosthetic device or process used to replace or improve the structure or appearance of a tooth or teeth.

Resources

BOOKS

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