Anatomy of a tooth

The part of the tooth visible above the gum line, known as the crown, is covered with a hard, whitish material called enamel. Enamel is a nonliving substance composed of calcium and phosphorous. It's the hardest substance in the body, so it's ideal for biting, chewing, and resisting decay.

The enamel ends at the tooth neck (also called the cervix), where the root (the largest portion of the tooth) begins (see Figure 2). A tooth has one to three roots, depending on its size and the amount of chewing pressure it has to endure. The root of the tooth is covered with a thin layer of pale yellow bonelike material called cementum. Because cementum is softer than enamel, it's more vulnerable to decay if the gum line recedes enough to expose it.

Figure 2: A look inside your teeth A look inside your teeth When you look at one of your teeth, the portion that you see is the crown. The root lies below the gum line and is embedded in bone. The crown is covered in enamel, a hard and strong whitish material. The root is covered with cementum, a bonelike material that is more vulnerable than enamel. Dentin is found inside the tooth. It protects the pulp, the soft core of the tooth that houses blood vessels and nerves.

Inside the tooth are two other types of dental tissue: dentin and pulp. Dentin is harder than cementum but softer than enamel. It constitutes the largest portion of the tooth.

At the core of the tooth is a chamber extending from the crown into the root. Inside this chamber is the pulp, the only part of the tooth not hardened with calcium deposits. It consists of loose connective tissue laced with blood vessels that bring nourishment to the dentin. A network of nerves that runs through the pulp communicates pain when the pulp is damaged or infected. The nerves also respond to heat, cold, electricity, and some chemicals.

The teeth are secured by the periodontal ligaments, bands of fibrous tissue that connect the cementum to the bone.

Jawbone destruction and bisphosphonates

Scientists are investigating a possible connection between the death of bone tissue (osteonecrosis) of the jaw and medications known as bisphosphonates. Bisphosphonates are commonly used to treat and prevent osteoporosis and to treat bone pain in cancer patients. Thus far, no clear cause-and-effect relationship has been established, and scientists are unsure why some patients develop osteonecrosis of the jaw. But there are good reasons to suspect that bisphosphonates play a role.

Cases in which people taking bisphosphonates experienced osteonecrosis first began surfacing in 2003. The vast majority of cases — about 94% — have involved cancer patients receiving intravenous drugs such as pamidronate (Aredia), clodronate (Bonefos), and zoledronic acid (Zometa). But this side effect also has been reported, with much lower frequency, in patients taking oral bisphosphonates such as alendronate (Fosamax), risedronate (Actonel), and ibandronate (Boniva) for osteoporosis.

How common is this problem? Small studies have found that about 10% of patients with multiple myeloma (cancer of the plasma cells) treated with bisphosphonates are affected, as are nearly as many breast cancer patients who took these medications. Meanwhile, the American Dental Association has estimated that there will be about seven cases per year of osteonecrosis for every million people taking oral bisphosphonates.

Many of the reported cases occurred after dental surgery to treat infections, such as getting a tooth pulled. Before you start taking a bisphosphonate, it's a good idea to have a dental exam and complete any necessary extractions or implants. If you are already taking a bisphosphonate, tell your dentist so she or he can consider it in planning your treatment. Also, be aware of the symptoms of osteonecrosis, which include pain, swelling, or infection of the gums or jaw; gums that aren't healing; loose teeth; and numbness in the jaw.

Diabetes

One of the most thoroughly researched topics in this arena is the relationship between gum disease and diabetes. Diabetes is thought to affect gum health in two ways. First, diabetes can cause circulatory damage, narrowing the arteries and restricting blood flow to the tissues, including the gums. As a result, periodontal tissue and bone become more susceptible to infection. In addition, diabetes can encourage the growth of oral bacteria. High blood sugar translates into increased levels of sugar in oral fluids. This allows the bacteria responsible for periodontal disease to thrive.

Diabetes can also lead to oral infections, such as thrush, as well as to dry mouth, which can hasten cavity development. Often, dry mouth is an early sign of undetected diabetes.

Researchers are also probing the possibility that periodontal disease may be a factor contributing to diabetes, not just a complication of it. One theory is that the inflammation in periodontal disease may increase resistance to insulin, which, in turn, makes it difficult to control blood sugar. However, more study is needed to clarify the relationship between these two diseases.

Several small studies suggest that periodontal therapy, such as deep cleaning, can improve blood sugar control. Researchers are also evaluating whether supplementing deep cleanings with oral antibiotics can help reduce blood sugar levels in diabetic patients.

While researchers haven't established that periodontal disease contributes to diabetes, brushing and flossing regularly and having routine dental cleanings makes sense for many reasons.

Heart disease

Does having gum disease put you at greater risk for heart disease? And, by extension, would averting gum disease actually reduce your chances for developing heart disease? Those questions have been — and continue to be — heavily researched. But a definitive answer hasn't been found yet, because studies have turned up conflicting results.

Numerous studies have suggested links between chronic gum infection and heart disease. According to the American Academy of Periodontology, people with gum disease are almost twice as likely to have heart disease as those without it. A 2006 study found that people under age 60 with a certain amount of alveolar bone loss from gum disease were at greater risk for heart disease. Two studies linked the bacteria of periodontal disease to heart problems. The first, a 2005 study in Circulation, found that older adults who had higher proportions of four gum disease–causing bacteria also had thicker carotid arteries, which is a predictor of stroke and heart attack. The second study, published in 2006, found that people with acute coronary syndrome — which encompasses a variety of heart problems ranging from unstable angina to heart attack — had higher levels of oral bacteria.

How might gum disease influence heart health? One possibility is that oral bacteria enter the bloodstream and attach to fatty plaques on artery walls, contributing to the formation of blood clots. Another is that inflammation from infectious agents damages artery walls and leads to the formation of plaques. The 2006 Journal of Periodontology study supports the idea that inflammation plays a role. This study showed that oral bacteria provoked an inflammatory response that elevated levels of white blood cells and C-reactive protein, both of which are linked to cardiovascular disease.

However, other research has failed to find a strong connection between gum disease and heart disease. A 2006 international Consensus Statement published in the journal Inside Dentistry found that the results of many studies have been inconsistent. In addition, a 2002 study concluded that the evidence supporting a cause-and-effect relationship between heart disease and chronic gum disease was weak.

Also unclear is whether treating advanced gum disease can reduce heart disease risk. Perhaps further study will clarify the relationship between the two diseases. In the meantime, practicing good oral hygiene and preventing gum disease will help you regardless of what future research turns up.

Pregnancy complications

Periodontal disease may increase a woman's risk of delivering a baby prematurely (before the 37th week of pregnancy). Premature babies are at greater risk for long-term health problems, and those who are born before their lungs have fully developed may not survive.

Researchers at the University of Alabama in Birmingham who followed a group of 1,300 pregnant women found that those who had periodontal disease between weeks 21 and 24 of their pregnancy were four to seven times more likely to give birth before 37 weeks. This study didn't examine whether treating gum disease during pregnancy could influence the outcome.

However, another study found that women with gum disease who were treated during their second trimester were less likely to give birth to low-weight or preterm infants than women who were not treated until after giving birth. Treatment included scaling and root planing, education on good oral hygiene, and the daily use of an antimicrobial mouth rinse. If gum disease worsens during the course of a pregnancy, there is evidence that the risk for premature birth rises.

According to the American Academy of Periodontology, the reason gum disease affects pregnancy is unclear, but some experts believe that gum disease may increase the levels of certain compounds that bring on labor.

Just as gum disease seems to have an impact on a pregnancy, pregnancy itself can influence the health of a woman's gums. Many pregnant women develop inflammation of the gums, known as pregnancy gingivitis. Their gums become swollen and red and may bleed easily. Usually, the condition subsides after they give birth. Experts believe that high levels of certain hormones, such as estrogen and progesterone, are to blame. While pregnancy gingivitis is common, studies have found that you may be able to avoid it by brushing and flossing daily and having your teeth cleaned regularly during your pregnancy.

Brushing up on toothbrush styles

The concept of mechanically cleaning the teeth has been around since ancient peoples chewed the frayed ends of aromatic twigs. The precursor to the plastic and nylon device we know in 2007 came on the scene in the 1930s. With hundreds of models to choose from, you may want to ask your dentist which style of toothbrush is right for you. Table 2 may also help you make your selection.

Manual vs. electric: Which is the better brush?

Electric toothbrushes have been widely touted, and indeed they can be effective when used consistently. However, you can achieve similar results with proper use of a manual toothbrush.

Electric brushes resemble the professional cleaning tools that your dentist uses. They use a variety of motions: back and forth, up and down, or rotation. One of the most widely used brushes, the Braun Oral-B 3D Excel, features a three-dimensional rotation pattern and a pressure sensor that stops the toothbrush from pulsating if you are brushing too forcefully. Sonicare, another popular brand of power toothbrush, relies on high-speed vibration (about 31,000 strokes per minute) of the individual bristles rather than movement of the toothbrush head. A variety of studies have been done comparing different power toothbrushes, and results have varied, with each toothbrush maker offering up studies showing that its product is more effective at removing plaque.

Similarly, studies comparing power brushes with manual ones have turned up conflicting evidence. According to an article published in the International Journal of Dental Hygiene, there is general agreement that power brushes are as safe as manual ones, but studies disagree on which type of brush removes plaque more effectively. This is due in large part to differences in the ways the studies were designed.

However, an analysis sifted through the existing information and found that one type of toothbrush was better at eliminating plaque than the rest. The Cochrane Collaboration, an independent nonprofit organization, evaluated randomized studies of toothbrushes done from 1966 to 2004. The researchers compared brushes' effectiveness at removing plaque, maintaining gum health, and removing stains, as well as their dependability and adverse effects. The power brushes were divided into seven groups based on how they worked.

What they found is that most of the power toothbrushes were no more effective than manual toothbrushes. Just one type of brush — the rotation oscillation design (where the brush heads rotate in one direction and then the other) — was consistently better at removing plaque and reducing gingivitis (gum inflammation) than a manual toothbrush. Examples of rotation oscillation brushes include the Braun Oral-B 3D and the Philips Jordan HP 735.

An electric toothbrush can be particularly helpful for people who have trouble reaching all corners of their mouth. For example, power brushes are useful for people with braces, parents brushing their young children's teeth, and individuals with mental or physical disabilities that impair dexterity. The thicker handle on power models is also a plus for some older patients and people with arthritis who have difficulty grasping the thinner shaft of a manual brush.

Your dentist may have good advice on which toothbrush is best for you. Consider bringing your toothbrush to your next dental visit so your dentist can examine it. While you're at it, demonstrate your brushing technique, so your dentist or hygienist can make sure you are brushing correctly.

Toothpaste: More than just mint

When it comes to plaque removal, it's your toothbrush that does most of the heavy lifting, but toothpaste contributes by removing stains and leaving your mouth fresher. Typically, commercial toothpastes are a concoction of abrasives, foaming agents, water, and binders, with flavor, color, and sweeteners added. They may also contain therapeutic agents such as fluoride or ingredients designed to combat tooth sensitivity. The main difference between gels and pastes is that gels contain more thickeners.

An important consideration when choosing toothpaste is its level of abrasiveness. Materials such as chalk, bicarbonate, and silicon or aluminum oxides remove external tooth stains. Polishers are included to restore the luster that abrasive materials dull. Although you want a toothpaste with enough abrasiveness to remove stains, high abrasive content and an incorrect brushing technique can lead to permanent tooth damage, particularly around the gum line. Abrasion can also wear away the fragile gum tissue, causing the gums to recede faster. If you don't smoke and have few stains, low-abrasive toothpaste is best for you. A standard test is used to determine the abrasiveness of toothpaste, and the result is a Relative Dentin Abrasivity (RDA) value. Unfortunately, the RDA values of different brands of toothpastes aren't readily available. Since the ADA only issues its seal of approval to toothpastes that are mild to moderately abrasive (250 RDA or less), choosing a toothpaste that carries the ADA seal is a simple way to ensure that your toothpaste isn't too harsh.

Also, choose toothpaste with fluoride. This additive is instrumental in warding off tooth decay. Most brands on the market in 2007 contain fluoride. Another ingredient, triclosan, has long been used in European dental products to combat gingivitis, a form of periodontal disease. Colgate Total was the first FDA-approved brand of toothpaste in the United States to contain this antimicrobial agent.

Some toothpastes are designed to reduce hypersensitivity. The ADA has granted approval to several products formulated for this purpose. Some antisensitivity toothpastes contain fluoride as well.

Toothpaste companies have bombarded the marketplace with toothpastes that claim to whiten teeth. Most major brands have at least one such toothpaste. All toothpastes contain mild abrasives that help remove surface stains. However, "whitening" toothpastes that contain the ADA Seal of Acceptance also have chemical or polishing agents that provide added stain removal power. For more information on whitening products, see "Teeth whitening."

Proper brushing technique

Numerous toothbrushing techniques have been recommended over the years. All have similar goals — removing food, stimulating gums, and preventing plaque buildup. Some people may get better results with one method than another, depending on their particular dental conditions and oral anatomy. Your dentist can help you decide which method is best for you. In the meantime, here's a basic brushing plan that works for many people.

• Start on the outside surface of your top teeth, beginning with the furthermost molars on one side and working forward.

• Holding your brush horizontally, place the bristles against the gum line at a slight angle (about 45 degrees). Using a short, rolling stroke, gently brush down toward the chewing surfaces of the teeth.

• Repeat this motion at least five times before moving along the gum line, overlapping brushing sites slightly.

• Repeat the same procedure over the inner surfaces of the teeth.

• For the bottom teeth, repeat the steps above, brushing up from the gum line toward the chewing surfaces.

• To get behind the top and bottom front teeth, hold the brush vertically with the bristles pressing against the interior surface of the teeth. Move the tip of the brush up and down over the teeth and gums.

• To clean the chewing surfaces of the teeth, use short vibrating strokes pushing down slightly so that the bristles penetrate the grooves of the teeth.

• Brushing your tongue when you cleanse your teeth will cut down on the hordes of bacteria that congregate on the tongue's surface. It can also help banish bad breath. To brush your tongue, place your toothbrush as far back toward the throat as you can without gagging. Sweep the brush forward six to eight times. Or, if you prefer, you can use a flexible strip of plastic or stainless steel called a tongue scraper. Center the arch of the scraper on your tongue as far back as you can without gagging and pull it forward, pressing lightly.

• Finish up by brushing the roof of your mouth.

Flossing technique

Here's one method for flossing your teeth:

• Using a piece of floss about 18 inches long, wrap one end securely around the middle finger of one hand. Do the same with the other end and the other hand, leaving a length of several inches in between.

• Hold the floss taut with the thumb and forefinger of either hand, leaving about an inch exposed between the fingers.

• Gently slide the floss between two teeth using a seesaw motion, which flattens the floss. Avoid snapping the floss into the space between the teeth, as this could damage your gums.

• Curve the floss around the side of one tooth, forming a "C" shape, and rub the floss up and down to clean the tooth. Then curve the floss in the opposite direction and repeat the scraping action on the adjacent tooth.

• Remove the floss and repeat the procedure between the next pair of teeth. Unwrap more clean floss from around your fingers as needed.

Cosmetic rinses

These solutions, commonly called mouthwashes, have a pleasant taste and leave your mouth feeling fresher for a time, but they don't possess any lasting ability to fight tooth decay or gum disease. They are best used as a temporary antidote to bad breath in the same way that showering with deodorant soap can control body odor for a period of time.

Mouthwashes contain flavorings, an astringent to make the mouth tingle, and an active ingredient that temporarily kills off bacteria. Some products also contain zinc, which neutralizes odor-causing compounds produced by oral bacteria. Because many brands contain a high percentage of alcohol (as much as 18%–26%), they are potentially poisonous to young children.

Therapeutic rinses

These preparations contain medicinal ingredients. The most popular kinds contain fluoride for cavity prevention. Among these, the Oral-B Anti-Cavity Rinse and ACT for Kids have earned the ADA Seal of Acceptance. Dentists sometimes recommend fluoride rinses for people who are prone to cavities.

Other types of over-the-counter therapeutic rinses advertise plaque-fighting benefits. However, only a few, such as Listerine and various store-brand equivalents (often marketed with the words "antiseptic mouth rinse"), carry the ADA Seal of Acceptance for this purpose. Listerine has been used as an oral antiseptic for more than a century. Listerine's claims are supported by long-term studies demonstrating that rinsing twice a day with the product (or a generic equivalent) can reduce plaque buildup and gum inflammation by 34%.

By far, the most powerful chemical for controlling oral bacteria is a substance called chlorhexidine, which is available only with a prescription from your dentist. It's sold under the brand names of Peridex or PerioGard. Chlorhexidine is most often used before or after oral surgery and for treating periodontal disease. It's also helpful for people who cannot brush effectively — for instance, because of a hand injury. Long-term use of this substance may temporarily stain teeth, but the problem can be corrected with professional cleaning.

Eliminating bad breath

Fortunately, there's much you can do to battle bad breath. Here are some steps you can take:

• Brush and floss daily.

• Brush your tongue and use a tongue scraper if necessary.

• Rinse with plain water after meals if brushing isn't an option.

• Get regular professional checkups to catch and treat periodontal disease.

• Seek medical care for underlying health problems.

• Snack on sugar-free foods (such as carrots and celery) or chew gum sweetened with xylitol to clear away debris and keep saliva flowing.

• Use an over-the-counter mouthwash containing zinc. Your dentist may also prescribe a rinse with chlorhexidine. Be aware, though, that long-term use of this ingredient can stain teeth.

Exposure risk is low

Because exposure to high levels of radiation can cause skin burns, cancer, and birth defects, some people fear getting dental x-rays. Today, though, the risk from x-rays is relatively low, thanks to improvements in technology and better regulation of the process. For example, modern dental x-ray machines narrowly focus radiation beams so that only your teeth are exposed. Better technology can also create the image more quickly, reducing your radiation exposure.

The newest breakthrough is a digital device that saves images in electronic files rather than on film. These high-resolution pictures require as little as 10% of the amount of radiation needed to create a traditional x-ray image.

Still, as a precaution, your dentist should cover your body with a lead apron when taking x-rays of your teeth. This prevents up to 94% of the radiation from reaching your chest, abdomen, and reproductive organs. For most x-rays, you can also wear a lead collar to shield your thyroid gland.

How often you need dental x-rays depends on the state of your dental health. Adults with no oral health problems are advised to have x-rays every two to three years. People who are at high risk for cavities or have a history of advanced gum disease may need x-rays more frequently. If you change dentists or see a specialist, bring your x-rays with you, so your new dentist won't need to duplicate the existing films.

Guided imagery

You can take your mind off what's happening in your mouth by visualizing a pleasant, restful setting. Concentrate on sensory details — for example, the warmth of the sand, the gentle sound of water lapping against a shore, the bright blue of the sky. Allow yourself to be transported into the image you've created. Breathe deeply and slowly as you imagine this place. If other thoughts intrude, accept them and then try to return to the haven you've created. Practice guided imagery a few times before your next dental appointment, as practice makes it easier to conjure up a soothing scene.

Relaxation exercises

Relaxation techniques such as breath focus, progressive muscle relaxation, and mindfulness meditation can slow your heart rate and bring about a state of restfulness. You may want to explore different methods to see which works best for you. In the meantime, here are two simple relaxation exercises to try.

• Make yourself as comfortable as possible in the dental chair. With your eyes closed and your muscles relaxed, breathe in slowly and deeply. Choose a focus word such as "calm" or "peace" to repeat mentally as you exhale. Keep your mind as clear as possible. If thoughts intrude, return your concentration to your breathing and focus word.

• Place your hand just beneath your navel so you can feel the gentle rise and fall of your belly as you breathe. Breathe in. Pause for a count of three. Breathe out. Pause for a count of three. Continue to breathe this way for several minutes.

Hypnosis

For many people, hypnosis can take the place of all other forms of pain control during dental procedures. It can be used successfully in people who can't tolerate anesthesia because of health issues, as well as those who are afraid of the needles that deliver medication. Self-hypnosis may be a practical approach; a professional hypnotherapist can teach you the steps to follow to enter a hypnotic state.

The tooth decay process

Here's a look at how tooth decay progresses (see Figure 3).

1. Bacterial growth. Bacteria from the Streptococcus family are the main cause of decay. The most prevalent species in the plaque that forms on the teeth (supragingival plaque) is Streptococcus mutans. Other varieties of bacteria are also involved in the decay process, but to a lesser extent. Lactobacilli colonize the crevices on the crown, and Actinomyces are implicated in decay around exposed portions of the root.

2. Demineralization. Cavity-causing bacteria thrive on a steady supply of carbohydrates, especially sugars, coupled with poor oral hygiene that enables them to feed and grow without interference. When bacteria metabolize sugar, they produce acid. This acid dissolves the enamel surface of the teeth in a process called demineralization. Ordinarily, this erosion takes place slowly, giving the body time to replenish the enamel or remineralize. But when enough bacteria accumulate, they produce sufficient acid to dissolve the enamel faster than the body can rebuild it. Tiny pits mar the surface of the tooth, and cavities begin to take hold. It usually takes many months of alternating demineralization and remineralization for decay to develop.

3. First-stage decay. The earliest stage of decay appears as a white or brown area on a tooth. This "white spot" is discernible only to your dentist. Another clue that decay is occurring is a "shadow," or area of lesser density, on an x-ray image. If decay is caught at this stage, there's a good chance that it can be halted and reversed (see "Treatment for first-stage decay").

4. Cavity formation. Unchecked, the acid eventually penetrates the enamel, and a cavity forms. This process may take three or four years. Once this stage is reached, the tooth can no longer repair itself. Both the mineral crystals and living cells that constitute the dentin are vulnerable to cavities. The decay may also travel through the dentin and destroy parts of the tooth tissue still covered by sound enamel. At this point, your tooth may ache. It may also be sensitive to hot, cold, or sweet foods.

5. Pulpitis. Without intervention, the cavity grows, extending into the soft tissue of the pulp and causing an infection called pulpitis. The infected pulp tissue swells, but the harder dentin surrounding it prevents it from expanding. Ultimately the swollen tissue squeezes the blood vessels, the blood supply to the pulp is cut off, and the pulp dies. At this point, you'll probably experience severe pain.

6. Abscess and systemic disease. The infection can continue to spread to the root of the tooth, creating an inflamed pocket called an abscess. From there, it can travel into the surrounding tissue. Finally, the infection can enter the bloodstream, causing a system-wide infection that's potentially life-threatening.

Diagnosing tooth decay

Although any tooth surface is susceptible to decay, the most vulnerable spots are the uneven or hard-to-reach areas where bacteria can take refuge. Particularly prone to decay are the crevices (known as pits and fissures) on the surface of the crown, the points where adjacent teeth meet, and the exposed neck of the tooth at the gum line. Root decay is a growing problem, particularly among people over age 55 whose gums have receded as a result of periodontal disease.

Your dentist can often spot decay on the visible surfaces of the teeth, while cavities in unseen spots — such as in the pits and fissures or between teeth — generally show up as dark areas on x-rays. A traditional method of uncovering decay by probing for soft spots in the teeth with a sharp metal tool has fallen out of favor. Researchers began to suspect that this practice actually augmented the decay process by piercing areas of soft enamel and spreading bacteria from one tooth to another.

Still, finding cavities can be tricky. One of the biggest challenges facing the dental community is accurate detection of the more subtle manifestations of decay, including root cavities, active cavities under existing fillings, and areas of demineralization (known as incipient caries). To this end, researchers are testing several technologies. Some promising avenues include using fiber-optic light to visualize deep decay between teeth and using electrical current or laser energy to identify decreases in tooth density that signal demineralization.

Treatment for first-stage decay

If the start of a cavity is caught early enough — while it's still an area of demineralization or a "white spot" — the tooth may be able to repair itself. The goal is to arrest the decay so that the natural remineralization cycle can take hold and repair the tooth. You and your dentist may be able to encourage this process. Following are some of the techniques your dentist might use at this stage.

Fluoride application. Fluoride applied to the teeth in the form of a gel or varnish can boost remineralization. Most promising are the thick, lacquer-like varnishes that adhere to the tooth surface for about 12 hours. Your dentist may paint your teeth with this substance at your twice-yearly checkup.

Chlorhexidine treatment. Applying a gel or varnish containing this powerful antiseptic agent can reduce the level of Streptococcus mutans in your mouth, slowing the demineralization process.

Sealant application. Your dentist may apply a liquid plastic coating, which is usually hardened with UV light, to the biting surfaces of the molars to create a physical barrier against bacteria. Because 90% of decay among children occurs on these surfaces, the best time to apply sealants is shortly after the tooth first erupts. However, sealants can help at any point, even after there is evidence of decay. Applied correctly, sealants can last for several years.

Treatment for cavities

Once the decay has penetrated the surface of the enamel and a cavity has formed, the emphasis shifts from prevention to restoration. The tooth cannot repair itself; instead, your dentist must correct the damage. If the damage extends into the dentin (but has not yet reached the pulp) and the tooth is stable, repair usually means cleaning out the area and filling the cavity.

After numbing the area, your dentist will clean away the decayed enamel using a high-speed rotary drill, an air-abrasive device, or a laser system. He or she may also use a slower drill or manual scooping tool to remove damaged dentin. Once the decayed portion is removed, your dentist will cut the hole into a shape that enables the filling to adhere securely and gives the rest of the tooth the most support.

The next steps depend on the size of the hole to be filled and the material to be used. In some cases, the dentist will coat the inside of the hole with a lining material that prevents tooth sensitivity, seals against leakage, and helps the filling material adhere. This step is often taken for large or deep cavities. When tooth-colored fillings (composites) are used, the dentist must etch the interior of the prepared cavity with acid to ensure that the filling material adheres to the enamel.

Silver amalgam restorations are generally completed in one visit with no other preparatory steps. Other types may take more than one visit to complete. Inlays (which fit into the tooth) and onlays (which fill the tooth and cover part of the biting surface) must be specially made to match the size and shape of the area being filled. These restorations, which are usually reserved for larger cavities, may take two or three visits to complete.

Materials used for fillings

You and your dentist should consider several factors when choosing a filling material. These include the size and location of the filling, the health of the surrounding teeth, the chewing force the affected tooth must endure, the number of visits necessary to make the repair, the cost of the procedure, and the appearance of the completed restoration. Table 4 describes the materials commonly used to repair damaged teeth and summarizes their benefits and drawbacks.

Silver amalgam, the most common filling material, has been used for more than 150 years, but it continues to be controversial. The source of the concern is fear that mercury, a component of amalgam, may promote conditions such as Alzheimer's disease, multiple sclerosis, and autism. Amalgam fillings release mercury vapor not only when they are placed in and removed from the teeth, but also during chewing.

Over the years, a variety of health organizations have examined the medical literature to determine whether silver amalgam is safe. To date, no scientific studies have demonstrated that it is harmful. As a result, organizations such as the FDA, American Dental Association, World Health Organization, National Institutes of Health, CDC, and U.S. Public Health Service have, at one point or another, stated that amalgam is safe for all but the few individuals who are allergic to the material and that banning it would eliminate an important filling option for many people.

These organizations periodically revisit the topic, however, a FDA reassessment made headlines when an advisory panel to that agency declared that more study on the safety of silver amalgam was needed. After reviewing studies on amalgam from 1997 to 2006, the FDA drafted a report that reiterated that amalgam is safe for nearly all people. But in September 2006, the advisory panel that reviewed this report said there were too many uncertainties to make that claim. The panel concluded that while there's no evidence that silver amalgam causes health problems in most people, more information is needed on how it might affect certain groups, particularly pregnant women, children, and people who are sensitive to mercury.

Nearly all the data on silver amalgam safety come from studies of adults (in many cases, people who worked in places where mercury is present in sizable quantities, like dental offices). In fact, the first randomized trials in children appeared only in April 2006. These two studies, published in the Journal of the American Medical Association, found that children whose cavities were filled with silver amalgam had no health problems as a result. Each study involved more than 500 children, who randomly received either amalgam or composite fillings. One study tested the children over several years on memory, attention, physical coordination, and speed of nerve conduction; the other study tested IQ. Researchers found no difference in test scores between the children with amalgam fillings and those with composite fillings. They did find, however, that the children with the amalgam fillings had slightly higher levels of mercury in their urine.

While these studies are reassuring, more information is still needed. In the meantime, should pregnant women and children avoid amalgam fillings? The FDA advisory panel said there wasn't enough information available to answer this question. Some other countries take a precautionary approach, avoiding the use of amalgam in pregnant women or restricting it even further.

The debate about amalgam has prompted some dental professionals to substitute more expensive restorations for intact silver fillings for all patients. But there is no evidence that removing your amalgam fillings will benefit your health.

Most amalgam fillings wear out in 10 years or less and need to be replaced. At that time, you and your dentist should discuss which restoration material is best for your dental needs.

How gum disease develops

Periodontal disease gets its foothold when plaque forms in the sulcus, a shallow trough at the point where the gum meets the tooth. Without proper cleaning, plaque can build up here like leaves in a gutter. Successive layers of bacteria prevent oxygen from reaching the innermost recesses of the sulcus. This enables the anaerobic bacteria to prosper. Thus, these pockets at the margins of the gum become a fertile breeding ground for the bacteria (see Figure 4).

Figure 4: The progression of gum disease The progression of gum disease Gum disease develops when decay spreads to the tissues that support the teeth. Healthy gums (A) are firm, embracing the teeth tightly. But without proper cleaning, plaque can build up where the gum tissue meets the tooth. As plaque accumulates, the gum tissue pulls away from the tooth, creating a tiny pocket. The gums become inflamed, a condition called gingivitis (B). Gingivitis sometimes progresses to more severe gum disease, known as periodontitis (C). Here, the pocket widens as the gum pulls back from the root of the tooth. The disease also destroys the periodontal ligament and bone, reaching the tooth socket. Eventually, the ligament and bone damage cause the tooth to become loose, and it may fall out.

Toxins released by the bacteria inflame the surrounding tissue. Meanwhile, the surface of the plaque hardens into tartar, which further irritates the gums. When inflammation becomes apparent, dentists say you have gingivitis.

Your immune system responds to the bacterial activity by sending a legion of antibodies to the site. How well the antibodies combat the bacteria depends on several factors, including the type and number of bacteria present as well as your ability to fight off disease. As periodontal disease advances, enzymes your body releases as a by-product of the immune response begin attacking the gum tissue itself.

The connective tissue attaching the tooth to the gum is the first structure to be destroyed. The detached gum then pulls back from the root of the tooth, deepening the gingival pocket and leaving the exposed portion of the tooth root vulnerable to cavity-causing bacteria.

Next the disease attacks the underlying periodontal ligament. The diagnosis officially switches from gingivitis to periodontitis when the destruction reaches the tooth socket in the alveolar bone. As the periodontal ligament continues to break down and more bone is lost, the tooth loosens in its socket. Eventually, it may fall out.

Occasionally, deep pockets close up at the top, walling off the pus in a bubble of inflamed gum tissue called an abscess. The swelling and inflammation often loosen adjacent teeth and hasten the destruction of the surrounding alveolar bone.

Dentists gauge the severity of periodontal disease by how fast it degenerates from one stage to the next and how well the person responds to treatment. Inflammation doesn't always progress to periodontitis. How and why the transformation takes place is still a subject of speculation. According to the American Academy of Periodontology, 30% of the population may have a genetic predisposition to gum disease. This tendency makes them six times more likely to succumb to periodontitis, despite their best oral hygiene efforts.

Gingivitis

Gingivitis, the earliest manifestation of gum disease, can cause redness, swelling, bleeding, and sometimes tenderness of the gums. Inflammation is usually limited to the surface tissue. If the inflammation is very mild, your dentist may detect it even before you notice any discomfort.

Gingivitis usually results from poor oral hygiene. With no brushing at all, a previously healthy mouth will begin to show evidence of gingivitis in less than three weeks. Some factors can make gum disease more likely or accelerate its pace. These include

• hormonal changes associated with puberty, pregnancy, or menopause

• certain medications for epilepsy, heart disease, and other chronic conditions

• poor nutrition

• poorly fitting braces, dentures, or restorations

• smoking

• diabetes

• HIV infection.

Gingivitis is almost always correctable when it's caught early. The first step is a thorough professional cleaning to remove plaque and tartar from the sulcus. This treatment, along with better brushing and flossing habits, usually does the trick.

Several rare forms of gingivitis are brought on by factors other than plaque accumulation. These forms of the disease include

• acute necrotizing ulcerative gingivitis, also called trench mouth or Vincent's infection

• desquamative gingivitis, a rare form targeting primarily postmenopausal women

• gingivostomatosis, painful ulcers on the gums and oral mucosa caused by the herpes simplex virus

• pericoronitis, the inflammation of the gum around an impacted wisdom tooth.

Periodontitis

Left untreated, gingivitis can progress into periodontitis. The gingival pockets deepen, inflammation increases, and the tissues that support the teeth deteriorate. While periodontitis always begins with gingivitis, not all cases of untreated gingivitis develop into periodontitis.

Periodontitis can start as early as adolescence, but it's more common after age 30. Although periodontitis tends to worsen with age, it doesn't always pro-gress in a linear fashion. Researchers believe that short episodes of intense disease activity are followed by periods of remission. Periodontitis appears to come and go randomly at different sites in the mouth. The disease doesn't actually disappear; it merely subsides for a while or reactivates in another area.

Periodontitis comes in several forms, with chronic adult periodontitis being the most common. One relatively rare type of adult periodontitis advances very rapidly and often doesn't respond to treatment. Two other forms of periodontitis — prepubertal and juvenile — affect children and teenagers. These variations tend to be linked to a systemic disorder or a family history of periodontal disease.

Diagnosing gum disease

Your dentist can calculate the extent of your periodontal disease using a series of measurements, laboratory tests, and x-rays.

Gingival bleeding index. Your dentist scores the severity of the disease based on how easily the gum bleeds when the sulcus is prodded gently.

X-rays. X-rays can reveal bone disintegration and track the level of bone loss over time.

Pocket probing. The dentist measures the depth of the gingival pockets with tiny rulers or electronic devices. The results range from 1–3 millimeters (less than one-eighth inch) for healthy gums to more than 7 millimeters (about one-quarter inch) for advanced periodontitis.

Bacterial tests. This kind of testing identifies the types of bacteria in the plaque and helps pinpoint areas of active disease.

Host response tests. These tests detect markers in blood, saliva, or gingival fluid that indicate areas where the disease is active. Scientists are trying to develop forms of the test that can identify people who are at greater risk for periodontitis.

Treating gingivitis and periodontitis

When treating gum disease, the goal is to eliminate plaque, reduce bacterial activity, and protect the teeth from further damage. The specific therapies your dentist recommends will depend on your particular circumstances. Most treatment, however, involves some or all of the following procedures.

Scaling and root planing (debridement). Your dentist or hygienist removes accumulated plaque and tartar above and below the gum line with either a manual scaler or an ultrasonic instrument. This is known as scaling or deep scaling. Depending on the circumstances, he or she may also scoop damaged tissue out of the bottom of the gum pockets to spur the healing process (a procedure called curettage). The final step — root planing — smooths the root surface so that the gum tissue can reattach more easily. These procedures are usually performed under local anesthesia.

Surgery. Occasionally with moderate to advanced disease, the periodontist must surgically remove the degenerated gum tissue and reduce the depth of the pocket before the tooth root can be properly cleaned. Surgery (see below) is recommended only in cases where it will prevent the loss of the tooth and when more conservative measures have failed to stop the progression of the disease.

Drug therapy. Short courses of oral antibiotics, as well as antibiotic and antiseptic medications applied directly to the gums, can reduce bacteria and inflammation. For example, the medication Periostat helps halt disease progression by blocking the enzyme that attacks tooth and gum tissue. In some cases of moderate disease, drug therapy along with regular debridement can avert the need for surgery.

Maintenance. After initial treatment, plaque levels must be kept low to avoid a resurgence of the disease. A good plan includes visiting the dentist or hygienist every three months, brushing and flossing without fail, and using an antimicrobial mouth rinse.

Types of gum surgery

If more conservative treatment measures don't solve the problem, your dentist will probably recommend gum surgery. The type of procedure used depends on the level of damage to your gum and bone tissue. Generally, your periodontist will perform these procedures in his or her office, using local anesthesia.

Curettage. The periodontist scoops out the infected gum tissue. This promotes healing.

Flap surgery. After making an incision in the side of the pocket, the periodontist folds back a flap of gum tissue. This procedure exposes the interior of the pocket, the tooth root, and the alveolar bone for cleaning. The periodontist removes the infected tissue and scales and planes the root. Finally, he or she stitches the flap back into position, closing up the gum pocket.

Tissue regeneration. During flap surgery, the periodontist inserts bioactive membranes or tissue-stimulating proteins under the gum. This promotes the regrowth of bone that's been damaged by gum disease.

Bone surgery. To reduce the chance of new pocket formation, the periodontist smooths irregularities on the bone's surface caused by degeneration.

Gum grafts. The periodontist grafts tissue from the roof or other areas of the mouth onto the gum, at the tooth line, to cover portions of the root that have been left exposed by a receding gum. This procedure is usually done to halt gum recession, cut down on tooth sensitivity, and improve appearance.

Bone grafts. The periodontist grafts new tissue onto areas where the alveolar bone has degenerated. The graft may consist of bone taken from another part of the mouth, bone from a donor, or synthetically manufactured material.

If several of your teeth need work, you may have to return a few times. After surgery, the periodontist will cover the affected gum with quick-drying protective putty so you can eat normally while it heals.

Hypersensitivity

Although tooth sensitivity is a hallmark of pulp injury, hypersensitivity does not in itself mean that the pulp is damaged. It's a signal that the dentin has been exposed, allowing sensations of heat, cold, and irritation to reach the tooth's nerves.

Tooth sensitivity diminishes naturally with age. To reduce sensitivity, you might try one of the many toothpastes made for sensitive teeth. The effects of these products accrue over time, so it may take several brushings before you feel any relief. Also, active ingredients vary from brand to brand, so if one brand isn't helpful, try another.

As an alternative, your dentist can apply a fluoride sealant to the crown of the tooth. The sealant covers the exposed dentin and should protect against pain. If the discomfort is extremely bothersome, your dentist may suggest that you apply the sealant to your teeth at home for several nights, using a specially made mouthpiece. If all else fails, root canal therapy can resolve the problem.

Pulpitis

Pulpitis is an umbrella term for all forms of pulp inflammation. The pulp may be irritated by decay in the nearby dentin or by periodontal disease. Often pulpitis is reversible. In some cases, a natural coating of dentin will form over the pulp to shield it from the irritant, and the nerve will recover without treatment.

In situations where the pulp cannot heal itself, pulpitis is classified as irreversible. A bacterial infection in the pulp usually kills the nerve. The infection then spreads through the dead tissue in the root canal (the channels in the root portion of the tooth containing the pulp) and passes through the opening at the end of the root into the surrounding tissues. A cavity then forms in the alveolar bone and fills with pus. This pocket of infection is called an abscess. The pressure from the swelling tissue and the mounting pus forces the tooth slightly upward. At this point, severe pain, fever, weakness, and facial swelling are almost always present. Root canal therapy or removing the tooth are the only ways to prevent the infection from invading other parts of the body.

Root canal therapy

In this procedure, an endodontist removes diseased pulp tissue and seals off the chamber to prevent further infection. The entire process — the root canal procedure itself and restoration of the tooth — takes two to three office visits to complete.

During the first visit, the endodontist injects a local anesthetic and isolates the tooth from the rest of the mouth with a thin sheet of rubber called a dam. The endodontist cuts a hole through the top of the tooth and removes the pulp material (see Figure 5); cleanses the root canal of bacteria, tooth fragments, and tissue; and then shapes the root canal. If the tooth has more than one root, the process is performed on all of them. The endodontist injects an antiseptic (and sometimes antibiotics) into the pulp chamber to kill remaining bacteria. Then he or she dries the root canal and places filling material (usually a rubber-like material called gutta-percha) in the chamber and root canals. Finally, he or she will place a temporary restoration in the access hole of the tooth. This completes the actual root canal portion of the therapy.

Figure 5: How root canal therapy is done How a root canal is done Root canal therapy is done to remove damaged pulp and prevent further infection. The procedure usually requires one or two office visits. At the start of the process, the dentist drills a hole to access the pulp (A). After cleansing the pulp chamber using special instruments and irrigation liquids, the dentist fills the pulp chamber and root canals with a permanent filling material known as gutta-percha (B). Then he or she places an amalgam or composite filling in the rest of the pulp chamber; this is sometimes called a "core buildup." Finally, the dentist restores the treated tooth, often with a crown.

While most endodontists will try to complete this procedure in just one visit, occasionally it requires two visits. The gutta-percha can be placed only if the root canal is dry and free of infection. If this isn't the case (for example, pus or blood may still be present), then the endodontist will delay this step. Instead, during the first visit, he or she will pack an antibiotic paste into the root canal and close the pulp chamber with a temporary filling. On the second visit, your endodontist will remove the temporary filling and fill the chamber and canal with gutta-percha to prevent the tooth from becoming infected again. He or she may also insert a plastic or metal post into the root canal to give the tooth extra support.

After the root canal treatment is complete, you will need to visit your restorative dentist so he or she can place a permanent restoration on the tooth. The material used for the restoration will depend on the size of the access hole as well as the type and location of the tooth. Your dentist may choose an amalgam or composite restoration, a crown, or both. Premolars and molars in particular should be crowned after root canal therapy to prevent the tooth from breaking.

Pulpotomy

In a pulpotomy, your dentist removes the damaged pulp from the crown portion of your tooth, but leaves the pulp that's in the root intact. This procedure is used primarily in children and young adults because it allows the root to continue to grow. However, it's suitable only if the inflammation is mild to moderate, and the tooth may still need root canal therapy at a later date.

Pulp capping

If decay has penetrated through the dentin, the dentist may try to save the pulp by coating it with a layer of medication and giving the tooth a chance to heal on its own before placing a permanent filling. This is called pulp capping.

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.

Figure 6: Fitting a crown Fitting a crown Crowns are often used to repair a broken tooth (A), a tooth that has been severely damaged by cavities, or one that's had root canal therapy. The dentist makes the crown from an impression of your teeth. Then, he or she removes the enamel from the damaged tooth and grinds the dentin down (B). The crown is then fitted over the remaining tooth and cemented into place (C).

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.

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.

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.

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.

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.

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.

Figure 7: Putting in an implant Putting in an implant The implant procedure begins with the dentist opening the gums and drilling a hole in the jaw where the tooth will be set (A). Then a titanium screw is set into the hole and the gum tissue is stitched around or over the healing cap (B). The area is allowed to heal for up to six months so that the bone can grow around the titanium screw. Then if necessary, another surgery is done to uncover the healing cap, which the dentist removes and replaces with an abutment (C). Finally, the custom-made crown, which is fabricated in the dental laboratory, is attached to the abutment (D). The new tooth is in place.

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.

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.

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.

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.

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.

Dentist-supervised bleaching

Your dentist can perform a bleaching process in the office or prescribe a procedure for you to do at home.

Chair-side bleaching. Your dentist begins a whitening treatment by applying a protective gel or rubber shield to your gums to protect them from the bleaching agent. Your dentist etches your teeth with an acid solution and then applies an oxidizing agent to the enamel. Your teeth are exposed to a bright light or a laser to hasten the lightening. It usually takes three to four sessions, each lasting about 30–60 minutes, to achieve the color you want. Chair-side bleaching can offer more uniform results than at-home bleaching methods. A newer technique, called power bleaching, uses a highly concentrated form of hydrogen peroxide as the lightening agent. It can deliver results in just one session. Your teeth will darken again within one to three years, and you may need to repeat the procedure. Costs vary, with some dentists charging between $100 and $250 a session and others charging a single fee of $250 to $400 per arch (upper or lower teeth).

Bleaching pulp-damaged teeth. When the pulp is dead or injured, a tooth will darken. To correct this problem, your dentist can rinse the pulp chamber with a bleaching agent while performing root canal therapy. If the stain persists or the tooth darkens after the root canal procedure is completed, your dentist can reopen the pulp chamber and fill it with bleach for several minutes under a heat light. This process may have to be repeated several times. Alternately, the dentist can fill the pulp chamber with bleaching solution and cover it with a temporary filling. In this case, you'll need to return after a few days to have the bleach removed and the tooth permanently sealed. Costs vary; some practices charge between $300 and $600 per tooth.

Home bleaching (dentist prescribed). To enable you to do the bleaching at home, your dentist makes a custom-fitted mouthpiece to hold the bleaching chemicals (carbamide peroxide or hydrogen peroxide). Then you spread the chemicals into the mouthpiece and put it on for the recommended period (between 30 minutes and several hours) each day for a week or two. Some users report tooth sensitivity during the treatment, but it usually subsides once the treatment is complete. This procedure generally costs between $250 and $400 per arch (upper or lower).

Over-the-counter bleaching kits

All of the following products contain some kind of peroxide as their active ingredient and, therefore, actually change the natural color of the teeth. The bleaching agents in these products usually aren't as strong as the chemicals found in the products administered by a dentist.

Whitening strips. Whitening strips are thin, flexible pieces of plastic applied directly onto the teeth. After the specified amount of time, usually 30 minutes either once or twice a day, the strips are peeled off the teeth. This process is repeated for between 5 and 14 days. In general, the strips designed for use over a shorter number of days contain a higher concentration of the peroxide ingredient than those intended to be worn over a longer number of days.

Gels. The main difference among the gels is how they are applied to the teeth. Some are applied with a small paintbrush, while others come in a pen-like applicator. Generally, the gel is applied before you go to bed and left on, and is used for about two weeks.

Combination gel and light. One whitening system, called Klear Action, involves three steps: You use an acid rinse, apply a whitening gel, and hold a special light up to your teeth for two minutes to "trigger" a whitening ingredient in the gel.

Whitening rinses. A whitening rinse from Listerine promises whiter teeth in 12 weeks. Simply rinse with the product for 60 seconds twice a day before brushing.

Which method is right for you?

Unfortunately, there is no simple answer. It isn't clear which bleaching method is the most effective. An analysis of studies that compared at-home whitening products (dentist dispensed and over-the-counter) with placebos and with each other found that whitening products are effective. The analysis, conducted by the independent Cochrane Collaborations, found differences among the products, primarily because of varying levels of the active ingredients. But they didn't recommend one product over another, because they found that most of the existing studies on whiteners were sponsored or conducted by the makers of whitening products and thus were not very reliable. The researchers concluded that more independent studies are needed. They also suggested that consumers be made more aware of side effects such as tooth sensitivity and gum irritation.

One advantage of over-the-counter bleaching methods is that they cost far less than techniques offered by dentists. On the other hand, as of 2007, none of the over-the-counter bleaching products carry the ADA Seal of Acceptance, while several bleaches used by dentists do carry the seal.

Some Internet companies sell materials to make a bleaching tray for use at home. However, according to the Academy of General Dentistry, trays can cause gagging, gum irritation, or damage to existing dental work if not properly fitted and supervised by a dentist.

There is not yet enough information to determine the long-term safety of whitening products. Therefore, they are not recommended for children under age 16, women who are pregnant or breast-feeding, people with sensitive teeth or an allergy to peroxide, or those with gum disease or worn tooth enamel.