How Teeth Decay

Tooth decay is a gradual process that starts from bacterial and acidic attacks on our teeth.

There are many types of bacteria in our mouths, some of which are actually good as they help control destructive bacteria. However, when it comes to decay, Streptococcus mutans and Lactobacilli are the bacteria that cause the most damage to teeth. Just like any other living organism, bacteria need food to live and multiply. When we eat sugary foods and other carbohydrates, the bacteria use them as food, too. The bacteria then produce acids that can dissolve tooth structure.

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 our mouths turn the sugars in these foods into acids, which then begins to dissolve the mineral structures in teeth. This attack can lead to tooth decay, also known as dental caries.

image44Tooth decay occurs in several stages, the first of which is reversible.  In the first stage, the acid begins to dissolve calcium and phosphate crystals inside a tooth. A white spot may appear on the enamel in this weakened area, and the surface will often be roughened. At this stage, the tooth can be repaired with the help of proteins and minerals (calcium, phosphate, and fluoride) in the saliva. Saliva also helps neutralize the acid levels from bacteria that attack the tooth.


If the decay is allowed to continue until it breaks through the outer enamel structure of the tooth, the damage becomes permanent. Many times patients will not be able to notice the cavity at this stage.

image46However, the decay must be cleaned out and the cavity filled. Left untreated, the decay will get worse and can eventually affect the blood and nerve supply of the tooth, potentially causing severe pain. That’s why it is important to have regular exams and treat caries at a very early stage, when the process can be reversed.

To help prevent your teeth from decaying, you can do several basic things:

Reduce the number of bacteria in your mouth by brushing, flossing, and professional cleanings

If you have dry mouth (xerostomia), you may also want to consider ways to improve salivary function, such as chewing sugarless gums, especially those with xylitol, which can help reduce bacteria levels and increase the flow of saliva.

Reduce dietary acidic attacks on your teeth.

Strengthen your teeth’s defenses with fluoride, sealants, and agents that contain calcium and phosphate ions.

For a good graphical overview of the decay process, follow the link for an excellent illustration on how a tooth decays from Aetna and Columbia University.