tooth decay

Can you name the most common disease in the world today? It isn’t cancer, heart disease or influenza. Throughout every continent, across every demographic and age bracket, the most prevalent disease is tooth decay. While it’s not generally life-threatening, tooth decay can lead to lost time on the job or at school, impose a financial burden on families and significantly affect a person’s quality of life.

The traditional (and still effective) model for treating cavities is simply to “drill and fill”—that is, to remove the decayed area of the tooth and replace the lost structure with a filling. But over the past few decades, a growing body of research has given us a new understanding of the true nature of the tooth decay process and opened up new avenues for the management of this disease.

At one time or another, almost everyone has heard how tooth decay gets started: Sugars in the diet feed harmful bacteria in the mouth; those bacteria release acids, which cause tiny pits to form in the surfaces of teeth; the pits in turn shelter more bacteria and in a short time a cavity (a small hole in the enamel) develops, requiring treatment. Reducing the number of bacteria by brushing and flossing regularly is one way to fight tooth decay. Another way is limiting or eliminating excess sugar in the diet.

Yet despite good efforts, many people have recurrent problems with decay. In fact, two people could have a similar diet and oral hygiene routine…but one routinely develops cavities while the other never does. We might think the “cavity-prone” individual just has bad luck (or bad habits). However, research points to several factors that can drastically increase your risk of getting cavities—as well as the steps we can take to manage that risk.

Got Saliva?

The first risk factor is saliva—or more precisely, the lack of it. Normally, the salivary glands release about two liters of saliva into the mouth every day. This helps maintain a neutral acid-base balance, which corresponds to a pH of 7 (the exact middle of the pH scale; the strongest acids are pH 1, while the strongest bases are pH 14). Saliva is nature’s way of protecting the teeth—and that protection is needed because the process of digestion begins in the mouth. Whenever you eat, tiny particles of food are broken down on the surfaces of teeth and small amounts of acid are released. The chemical substances in saliva keep the pH of the mouth from tilting too much toward the acidic, which can break down tooth enamel.

But many people don’t produce enough saliva—a condition called xerostomia or “dry mouth.” In some people, increasing age slows saliva production. Others experience dry mouth as a result of taking certain medications. According to the Mayo Clinic, some 70% of all Americans (including both adults and children) take at least one prescription drug daily; about half take two or more. Dry mouth is a common side effect of many medications. Regardless of the cause, the lack of sufficient saliva can have serious consequences for the teeth. Enamel, the tooth’s outer coating, is the hardest substance in the body. But when teeth are subjected to a pH of 5.5 (moderately acidic), the enamel starts to dissolve, seriously weakening the tooth’s structure.

The Role of Diet

Diet is the second major risk factor for tooth decay. Americans consume on average around 23 teaspoons of sugar every day, and some 51 pounds of high-fructose corn syrup every year. Sweetened beverages make a major contribution to excess sugars in the diet of adults and children, and are helping to drive an epidemic of obesity. Whether consumed in food or drink, sugar is metabolized (processed) by oral bacteria, some of which release acids as an end product. Those acids are the direct cause of cavities.

But the effect of diet comes not just from what you eat; when you eat also makes a big difference. As you eat or drink, the pH in your mouth drops (becomes more acidic). But in about 30 minutes, thanks to the action of saliva and helpful bacteria, the mouth returns to a neutral state. If you eat too frequently, however—grazing throughout the day and constantly sipping sugary drinks—the normal process of recovery to a normal pH doesn’t have enough time to occur.

Your Biofilm: Good Bugs, Bad Bugs

The surfaces in your mouth are coated with a thin film of proteins, fluids, biochemical substances and microorganisms called a biofilm. This environment hosts both beneficial and harmful bacteria, which exist in a dynamic balance. The makeup of an individual’s biofilm plays a major role in susceptibility to tooth decay. In a healthy mouth, excess acids are neutralized and harmful bacteria are kept in check by helpful ones. But when the biofilm is continually pushed toward an acidic state, problems can start. The helpful bacteria (which we formerly considered “good bugs”) must adapt to the changed environment or die; their metabolism shifts, becoming more like the acid-loving bacteria (“bad bugs”)—much to the detriment of your teeth.

“Plaque” is another name for a thick layer of biofilm on your teeth. Brushing and flossing can remove it—but when it is allowed to build up and harden, it is called dental calculus or tartar. Unlike plaque, tartar can’t be removed by brushing or flossing, and it’s an ideal home for the bacteria that cause oral health problems. Scientists used to think that just two kinds of bacteria, Streptococcus mutans and some Lactobacillus species, were responsible for tooth decay. But with improved methods of genetic identification, we now know that about 40% of adults and children in the US with serious tooth decay don’t even have Streptococcus mutans in their mouths. This finding changed our understanding of the tooth decay process: Instead of a disease caused by particular “bad” bacteria, we now think of it as a disease of the biofilm driven by a prevalence of acid (low pH).

Genetic Factors

The final major risk factor for decay is genetics. There are some 40 to 50 genes that play a role in your risk for developing cavities. Some affect anatomy or physiology: how your teeth are formed or how much saliva you produce. Others may have a behavioral impact: for example, whether or not you have a craving for sugar—a “sweet tooth.” While the overall influence of genetic factors on cavities is thought to be about 9%, for some it may have a big effect. Genetic variation can explain why individuals with the same diet, environment and oral hygiene habits have a very different outcome with respect to cavities.

What’s Your Risk?

When your dentist discovers a cavity, the standard solution is to remove the decay using a dental drill and replace the lost tooth structure with a filling material. This is an effective treatment, but it doesn’t change the reason why the cavity developed—and it doesn’t keep you from getting more. That’s where an evaluation of your particular risk for developing cavities (also called dental caries) can help. It could be that you’re taking a medication that inhibits saliva production; maybe your biofilm is being pushed out of balance; perhaps your diet is a contributing factor. Caries risk assessment is aimed at pinpointing an individual’s specific risk factors.

Once, caries risk assessment (if done at all) was mainly handled by dental staff. Today, it’s easier and more productive for people to begin by filling out a short form, answering questions like: “What medications do you take?” “Do you often snack between meals?” “Do you notice plaque on your teeth between brushings?” The answers not only help pinpoint issues that may make you more susceptible to cavities, they can also provide a great starting point for discussion with your dentist about your overall oral health. Your dental professionals can also perform testing on your mouth chemistry and even do an assessment of your biofilm, which can give specific information about your risks.

Does the system really work? Years of research, including a recent large study in the San Francisco Bay Area, demonstrate that it does. In fact, caries risk assessment is now the standard of practice taught in every accredited dental school in the United States. And while it isn’t yet a routine part of all dental checkups, the practice is becoming more and more widespread.

What You Can Do to Control Cavities

Once you know the risk factors, can you do anything about them? Generally, the answer is yes. One positive step is to use a fluoride toothpaste and/or mouth rinse with a higher (more basic) pH. This can help maintain healthier (less acidic) conditions in your mouth and promote a healthier oral environment.

Fluoride itself is highly beneficial to your teeth: It is readily incorporated into your tooth structure, and it actually reduces the process of demineralization (erosion of tooth enamel) caused by acids. When used as directed, fluoride toothpastes and mouth rinses are safe and proven ways to reduce the incidence of cavities—as are the small amounts of fluoride added to some municipal water systems. Xylitol is another ingredient of toothpastes and rinses that can help fight cavities. It is thought to interfere with the metabolism of acid-loving bacteria, and studies show some evidence of its therapeutic benefits.

Changing your diet can also be a big help. Reducing excess sugar and limiting your consumption of food and drinks (not including water) to around mealtimes is a good way to help keep your biofilm in a healthy state. If a caries risk assessment points to other issues—dry mouth from medications, for example—making positive changes in the way you eat can be even more important.

Despite our growing knowledge about it, tooth decay is likely to remain a common disease in the near future. However, we have seen that it’s quite possible for an individual to reduce the risk of decay, and even become cavity-free. With a better understanding of how the oral biofilm mediates the disease—and how it is driven by acidic pH levels—we can assess each person’s risk for tooth decay and tailor a plan to counter it. As more people understand the benefits of caries risk assessment, we have reason to hope it will become a more routine part of dental care.

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