Tooth replacements: Bridges, dentures, and implants

Tooth loss can have a profound effect on your health and well-being. Even though diseases leading to tooth loss are largely preventable, 45% of Americans age 65 and over have lost six or more teeth, and 20% 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.

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Fixed prostheses (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.

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Crowns

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 are also 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 (Figure 6). The crown is made in a laboratory based on impressions your dentist takes of your teeth. A new 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 peg-like 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.

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Bridges

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.

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Removable prostheses (dentures)

In certain situations, removable prostheses (either partial or full dentures) may be the best option for regaining at least some level of oral functioning. However, they are usually the treatment of last resort because they can be uncomfortable. If they aren't made properly and checked regularly, they may accelerate bone loss in the jaws.

There are several risks associated with full dentures. Once all the teeth are gone, the supporting alveolar bone reabsorbs into the body. The pressure from the dentures often hastens this process. As the bone disappears, the position of the dentures shifts, causing the teeth to meet unevenly and making chewing difficult. In addition, the dentures exert considerable pressure on underlying nerves, which are now unprotected. This can make chewing extremely painful. Even partial dentures can stress the alveolar bone. Partial dentures and overdentures may also lead to irritation and sores in the mouth. In addition, bacteria can collect around the dentures, increasing the risk for oral infections and root decay in any remaining teeth.

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Partial dentures

This prosthesis is recommended if you need to replace several teeth in a row or your remaining teeth are not strong enough to support a fixed bridge. Removable partial dentures consist of acrylic or ceramic artificial teeth embedded in a gum-colored plastic base that is form-fitted to the underlying mouth tissues. Inside the prosthesis is a framework of light, noncorroding metal that makes it strong and stiff.

Partial dentures are usually attached to your adjacent teeth by clasps that hook around the outside of the teeth. Precision attachments are a stable and more aesthetically pleasing alternative. These devices require placing crowns or inlays with vertical grooves on abutting teeth. The denture is fitted with matching ridges that dovetail with the grooves. The connecting mechanism is nearly invisible when it's in place.

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Full dentures

Full dentures are generally reserved for elderly people who've lost all their natural teeth and whose health or finances preclude implants or implant-based fixed appliances.

Full dentures consist of a pink acrylic base holding a complete arch of teeth. On an upper denture, the base conforms to the dental ridge at the front of the mouth and extends over the palate. On the lower jaw, the base is constructed in a horseshoe shape to leave room for the tongue. More than one in three people have difficulty tolerating lower dentures because of the size, shape, or position of their tongues.

Full dentures are sometimes difficult to keep in place. The lower denture is especially difficult to manage. Adherence of the upper denture depends on surface tension between the base and underlying oral mucosa. On the lower jaw, the denture is kept in position by pressure from your cheeks and tongue. Because dentures can tolerate less chewing force than natural teeth, many people find two matching dentures easier to use than a single one. In some cases this may mean having some good teeth extracted in order to have a matching set.

Immediate dentures. Traditionally, all remaining teeth had to be pulled and the mouth left to heal before dentures could be placed. But you and your dentist can now opt to place immediate dentures the same day your teeth are removed. The obvious advantage of this technique is that you don't have to go toothless while the dentures are being fitted. In addition, the tooth sockets actually heal more comfortably when the denture base covers them. However, as your mouth tissues adjust, the dentures must be refitted or a new set made. This usually happens within a few months of receiving the dentures.

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Overdentures

Overdentures are a variation on full dentures. If you have a few remaining teeth, their roots may offer enough support to sustain anchoring devices that can be used to support the dentures. One of the primary advantages of this technique is that it preserves the roots, thereby preventing loss of the alveolar bone that supports the dentures. Overdentures also provide a more natural chewing sensation than traditional complete dentures.

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Dental implants

The ideal dental prosthesis would be a replacement system that looks and functions like natural teeth, is durable, does not damage existing structures, and doesn't cause unwanted side effects. Many dentists are optimistic that the latest generation of implant technology will fulfill these goals.

An implant starts with a titanium metal screw that is surgically inserted into the alveolar bone of the upper or lower jaw where a natural tooth has been lost. The screw acts as a substitute for a natural tooth root, forming the base for a replacement. A dentist can place implants alone or in combination. They can serve as individual replacement teeth or as abutments for fixed bridges, or as anchors for full or partial removable dentures.

Implants had been used for decades with mixed success. The materials and techniques were less than ideal until a breakthrough occurred in the late 1960s, when researchers explored the use of titanium. They discovered that bone would grow directly into the surface of a titanium implant and create a bond so firm that the implant could not be dislodged. This osseointegration was something that didn't happen with implants made of other materials. These devices became known as osseointegrated implants.

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Placing implants

Traditional implant placement is a multi-step process (see Figure 7). First, the dentist carries out any necessary extractions and waits four to eight weeks for the tissue to heal. (Dentists sometimes waited as much as a year for healing to occur.) If there is not enough bone left to support a replacement, the dentist may need to perform a bone graft, which requires more healing before the implant can be done. Then the dentist places the implants deep enough so he or she can suture the gum tissue over them, and they are left to heal for three to six months without any teeth attached. This approach, called "unloaded" healing, reflects the belief that observing a long waiting period before burdening the implant with the stress of replacement teeth is essential to osseointegration. At the end of this healing period, a second surgery is performed to uncover the implants and to attach metal posts (called abutment cylinders) that protrude above the gums. The individual then waits another two to four weeks for the gum tissue to heal before the replacement teeth are installed.

Although certain cases still demand this conservative protocol, advances in implantation techniques mean that the treatment can often be done successfully in fewer steps over a shorter period. Keep in mind, though, that not every patient is a candidate for these speedier procedures and, in many cases, a dentist cannot choose a particular approach in advance because he or she isn't able to fully assess the situation until the problem teeth are removed.

Some of the newer options available to implant candidates are

one-stage placement, in which implants and abutments are placed in a single surgery

immediate implants, in which the implants are inserted right after tooth extraction

shorter healing times before installing the teeth (six to eight weeks instead of three to six months over all)

immediate loading, a less common procedure in which teeth are attached to implants immediately after surgery.

Implant surgery is a complex process, and successful osseointegration demands certain conditions. The implant material must be titanium. The dentist must use a careful surgical technique, drilling slowly and irrigating copiously to avoid overheating that can damage the bone. The implant must be placed firmly into the alveolar bone so that it remains stable (bone won't heal on a mobile implant), and there must be no infection in the implant site.

Given these requirements, the dentist performing the procedure must carefully evaluate the oral status of each patient to determine which option has the best chance of success. Your dentist will select a procedure based on a number of factors, including where the affected tooth is, the type of problem being treated, how much bone there is to support the implant, and the health of that bone. Your dentist will also consider his or her level of experience with a particular procedure.

Technology is also helping with the creation of replacement teeth. CAD/CAM technology (computer-aided design/computer-aided manufacturing) is being used by more and more dentists.

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Are implants right for you?

Implants aren't a good option for children and adolescents, because their jawbones are still growing. For adults, though, age doesn't matter. Adults of any age may be good candidates for implants, depending on several factors.

For example, certain medical conditions can interfere with the success of implants. Treatments such as chemotherapy, radiation, and immunosuppression can hinder healing. In addition, people with conditions such as type 2 diabetes, bleeding disorders, immune deficiency, impaired cardiovascular function, or certain bone diseases are not good candidates for implants.

Having osteoporosis, a disease that causes bone loss, does not necessarily prevent a person from getting implants. Although bones elsewhere in the body may be damaged, the jawbone may not be affected to the degree that implants are impossible. If you have osteoporosis and are taking a bisphosphonate medication, ask your dentist whether this poses a problem. It appears that, rarely, bisphosphonates taken for osteoporosis can contribute to osteonecrosis, a condition in which jawbone is destroyed.

People who smoke more than 10 cigarettes a day may not have as much success with implants. Generally, smokers have a 5% to 10% lower long-term success rate than nonsmokers. If you are considering dental implants, it's wise to quit smoking.

If you have any oral diseases — such as mouth ulcers, active periodontal disease, decay, or pulp problems — your dentist should treat them before placing dental implants. Implants may not be suitable for individuals who aren't motivated to maintain their oral health or who have conditions that interfere with their ability to care for an implant over time.

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Bone grafts and implants

In the past,having an alveolar bone that wasn't wide or high enough also made dental implants impossible. That's no longer the case, thanks to significant advances in techniques to regenerate or replace missing jawbone. Newer augmentation or grafting procedures enable a dentist to add bone to areas that are deficient.

One example is the "sinus lift" procedure, in which the thin bone at the bottom of the maxillary sinuses in the back of the upper jaw is augmented with additional bone, typically from another part of the body. This process nets enough bone to support the placement of dental implants.

Bone grafting can be done at the same time the implant is placed, provided there is enough bone to stabilize the device. If there is too little bone to guarantee that the implant can be placed firmly, the process is done in steps. The bone grafting is performed first, and the new bone is allowed to heal for several months before the implant placement. The length of healing time needed after bone grafting depends primarily on the type of grafting material used.

The surgeon can choose from a variety of materials and techniques. One option is to take bone from another place in the patient's mouth, such as the back of the lower jaw or the chin. These sources are used when relatively small amounts of bone are needed. For larger amounts, the surgeon must look to sites outside the mouth, such as the hip, shin, ribs, or skull. Someone who has worn dentures for many years and has lost most of his or her alveolar bone would need this type of larger graft. Other sources for replacement bone include allografts (human cadaver bone), xenografts (animal tissue), or synthetic products.

Generally, overall success rates are very good for the bone grafts themselves, as well as for implants placed in bone grafts. The surgeon's expertise with the particular technique seems to be more important than the choice of material or technique.

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Complications of implants

The success rate for modern implants is very good. Data from long-term clinical trials have shown success rates of more than 95% at the end of 5 years and 90% after 10 years.

Implants fail for two major reasons. First, if the bone does not adhere to the titanium screw, the implant will come loose and must be removed. This failure can be caused by trauma during the surgery, infection, or the installation of replacement teeth before the bone has completely healed around the implant base. The second major source of problems is infection that occurs in the gum tissue surrounding the implant. Such an infection can usually be cleared up with antibiotics.

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Caring for implants

Keeping plaque levels to a minimum is just as crucial to the health of your implants as it is for your natural teeth. Following these steps will help you avoid problems:

Brush daily.

Use specially designed interproximal brushes (see "Types of dental floss and cleaning devices") for cleaning between the implants.

Use end-tufted brushes for cleaning around the implant neck at the gum line.

Use an antimicrobial mouth rinse, such as chlorhexidine, as prescribed by your dentist.

See your dentist every three to six months for a professional cleaning and checkup.

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Review Date: 2007-04-01

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