What's in Your Mouth?
To understand what happens when your teeth decay, it's helpful to know what's in your mouth naturally. Here are a few of the elements:

Saliva ? Your mouth and teeth are constantly bathed in saliva. We never give much thought to our spit, but this fluid is remarkable for what it does to help protect our oral health. Saliva keeps teeth and other parts of your mouth moist and washes away bits of food. Saliva contains minerals that strengthen teeth. It includes buffering agents. They reduce the levels of acid that can decay teeth. Saliva also protects against some viruses and bacteria.

Plaque ? Plaque is a soft, gooey substance that sticks to the teeth a bit like jam sticks to a spoon. Like the slime that clings to the bottom of a swimming pool, plaque is a type of biofilm. It contains large numbers of closely packed bacteria, components taken from saliva, and bits of food. Also in the mix are bacterial byproducts and white blood cells. Plaque grows when bacteria attach to the tooth and begin to multiply. Plaque starts forming right after a tooth is cleaned. Within an hour, there's enough to measure. As time goes on, the plaque thickens. Within two to six hours, the plaque teems with bacteria that can cause cavities and periodontal (gum) disease.

Calculus ? If left alone long enough, plaque absorbs minerals from saliva. These minerals form crystals and harden into calculus. Then new plaque forms on top of existing calculus. This new layer can also become hard.

Bacteria ? We have many types of bacteria in our mouths. Some bacteria are good; they help control destructive bacteria. When it comes to decay, Streptococcus mutans and Lactobacilli are the bacteria that cause the most damage to teeth.

How Your Teeth Decay
The bacteria in your mouth need food to live and multiply. When you eat sugary foods, or even starches such as rice, the bacteria use them as food, too. The bacteria then produce acids that can dissolve tooth enamel (outer layer of the tooth).

It's not just candy and ice cream we're talking about. All carbohydrate foods eventually break down into simple sugars. Some of this process begins in the mouth.

Foods that break down into simple sugars in the mouth are called fermentable carbohydrates. These include the obvious sugary foods, such as cookies, cakes, soft drinks and candy. But they also include pretzels, crackers, bananas, potato chips and breakfast cereals.

Bacteria in your mouth turn the sugars in these foods into acids. These acids begin to dissolve the mineral crystals in teeth. The more times you eat each day, the more times your teeth are exposed to an acid attack.

This attack can lead to tooth decay, also known as dental caries or cavities. First, the acid begins to dissolve calcium and phosphate crystals inside a tooth. A white spot may appear on the enamel in this weakened area. But the loss of minerals develops beneath the surface of the enamel. The surface may still be smooth.

At this stage, the tooth can be repaired with the help of fluoride, proteins and minerals (calcium and phosphate) in the saliva. The saliva also helps reduce the acid levels from bacteria that attack the tooth.

Once the decay breaks through the enamel to cause a cavity, the damage is permanent. A dentist must clean out the decay and fill the cavity. Left untreated, the decay will get worse. It can destroy a tooth all the way through the enamel, through the inside dentin layer and down to the pulp or nerve of the tooth. That's why it is important to treat caries at a very early stage, when the process can be reversed.

Types of Decay
Young children can get a type of decay called baby bottle tooth decay or early childhood caries. It destroys enamel quickly. This type of decay is common in children who are put to sleep with a bottle of milk or juice. The bottle exposes the teeth constantly to carbohydrates through the night. Bacteria can grow rapidly and produce acid that decays teeth.

Decay can become worse if the parent does not clean the child's teeth. It can eat through enamel and leave a large cavity in a matter of months.

In older adults, the exposed roots of teeth can develop cavities. This is called root caries. Older adults are more likely to have receding gums caused by years of hard brushing or periodontal disease. They also are more likely to have dry mouth (xerostomia). The decrease in saliva results in less protection of the teeth. This increases the risk of decay. Many common medicines can cause dry mouth. Be sure to ask the doctor or pharmacist if any of your medicines cause dry mouth.

Decay can form beneath fillings or other tooth repairs, such as crowns. Sometimes bacteria and bits of food can slip between the tooth and a filling or crown. This can happen if the filling cracks or pulls away from the tooth, leaving a gap.

Preventing Cavities
Do you or your family members get cavities often? Dental research has found out that certain factors can affect your risk of tooth decay. These factors include:

The current number of decayed or filled teeth
Your fluoride exposure, including fluoride in drinking water, toothpaste and rinses, and fluoride treatments in the dental office
Parents or siblings with dental decay
How well you take care of your teeth
The amount of saliva and the balance of minerals, enzymes and buffering agents it contains
How often and what types of foods you eat (especially fermentable carbohydrates)
Ask your dentist about the best ways to reduce your risks and limit dental decay.

To prevent your teeth from decaying, you can do three things:

Strengthen your teeth's defenses with fluoride, sealants and agents that contain calcium and phosphate ions.
Have your dentist or dental hygienist place sealants on your back teeth.
Reduce the number of bacteria in your mouth.
Fluoride penetrates into teeth. It strengthens them by replacing minerals that acid has removed. The benefits of fluoride to teeth were first discovered in the 1930s. Dentists started to notice that people who drank water that naturally contained fluoride had less tooth decay. In 1945, communities started to add fluoride to water supplies. Adding fluoride to water systems has been the most successful cavity prevention method to date.

In the early 1960s, fluoride also began to be added to toothpaste. This also had a major impact on cavity prevention. Now almost all toothpastes contain fluoride. Everyone should brush with a fluoride toothpaste every day. Dental offices sometimes recommend higher levels of fluoride in toothpastes, gels and mouth rinses for both children and adults.

Sealants are protective coatings placed over the tops of the back teeth ? molars. They block bacteria and acids from sticking in the tiny grooves on the chewing surfaces of these teeth. Sealants can be placed in adults and children. Children can have sealants placed on their permanent molars once they come in, around age 6. Sometimes they are also used on primary (baby) molars. Dentists can put sealants on molars with signs of early decay, as long as the decay hasn't broken through the enamel.

You can never get rid of all the bacteria in your mouth. But you can take steps to control and disrupt the bacteria so they don't attack your teeth:

Brush twice a day.
Floss daily.
Reduce the number of times each day that you consume fermentable carbohydrates.
Some mouthwashes reduce bacteria in your mouth. This can help prevent decay. Chewing sugarless gums, especially those with xylitol, can help reduce the number of bacteria that cause cavities and increase the flow of saliva.

Most importantly, visit your dentist regularly. Then the dentist can find any decay early, when it can be treated and reversed.