Tooth decay, also known as caries or a cavity, is the most prevalent disease in the world. Tooth decay affects over 2 billion people, yet it is a preventable disease as long as you know its process and how to avoid it. Acid-producing bacteria and carbohydrates, especially sugar, are what causes cavities and tooth decay. Of course, many other factors will also contribute to or prevent the formation and advancement of tooth decay. But this article and the corresponding video explore how a bacteria called Streptococcus Mutans, acid, and sugar cause cavities.

What Is Streptococcus Mutans?

There are about 200 to 300 different species of bacteria on the surface of human teeth. Most of these bacteria species create a healthy and beneficial plaque for your teeth. However, some bacteria species within the plaque destroy your teeth and gums. Streptococcus Mutans is one of the few bacteria species that will cause and propagate tooth decay within dental plaque. It is also the main species that will cause cavities. Of particular interest, Streptococcus Mutans has also developed protection so that it can survive and thrive in acidic environments. Therefore, Streptococcus Mutans is what causes cavities.

Streptococcus Mutans cannot do enough damage to harm the teeth at low levels. However, at high levels, the bacteria will damage your oral health. The question is, “how do Streptococcus Mutans levels increase?” The answer is, "sugar."
Streptococcus Mutans under microscope
Stained Streptococcus Mutans under a microscope.

How Does Sugar Cause Cavities?

Within dental plaque, the bacteria species called Streptococcus Mutans will take carbohydrates, especially sugar, and create an acidic byproduct. The acid produced by S. Mutans has two roles in the production of cavities. First, the acid demineralizes the tooth so bacteria can invade the tooth and cause further demineralization. Once the bacterial demineralization is deep in the enamel, it becomes sticky, dark, and shows as a shadow on x-rays. Second, the acid will kill off beneficial bacteria within the plaque, making way for more Streptococcus Mutans to proliferate. This process is a vicious cycle because the more acid Streptococcus Mutans produces, the more abundant it becomes, creating more acid. Once the acid pH of plaque drops below 5.5, the tooth will start to demineralize.

It should be obvious now that sugar and Streptococcus Mutans are what cause cavities. Now that you know the process, click on this link for the best daily oral hygiene routine to prevent tooth decay.
Percentage of Streptococcus Mutans surviving acid
Survival of acid-adapted Streptococcus Mutans. Gong Y, Tian XL, Sutherland T, Sisson G, Mai J, Ling J, Li YH. Global transcriptional analysis of acid-inducible genes in Streptococcus mutans: multiple two-component systems involved in acid adaptation. Microbiology (Reading). 2009 Oct;155(Pt 10):3322-3332. doi: 10.1099/mic.0.031591-0. Epub 2009 Jul 16. PMID: 19608608.

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