Cavities and Tooth Decay: Bacterial Causes of Common Dental Issues

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  • 0:06 End of Tooth Decay?
  • 1:16 Oral Bacteria
  • 2:39 Streptococcus and…
  • 4:36 Dental Caries
  • 6:05 Prevention of Dental Caries
  • 8:06 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

Did you know that getting cavities in your teeth is an infectious disease? Cavities are a result of bacteria in the genus Streptococcus. In this lesson, we will examine how bacteria contribute to tooth decay.

The End of Tooth Decay

Consider this hypothetical scenario. If you could give your child a vaccine before they started sprouting teeth that would render them impervious to tooth decay and cavities for life, would you do it? Would you submit your baby to one more injection to eliminate a lifetime of potential dental problems? I know I would. Tooth decay affects more children in the U.S. than any other chronic infectious disease. For the child, it results in pain and stress. For the parent, it results in huge medical costs. I know I would avoid all that for myself and my child if I could.

In reality, there is no magic vaccine that can protect you from cavities. Not yet anyway. But many scientists throughout the world are currently working on developing one. I'm sure some of the critical thinkers in the group are saying, 'Wait a second, vaccines protect against catching infectious diseases. You can't catch cavities.' Actually, you can. In this lesson, I will attempt to explain just what causes tooth decay and how these exciting new vaccines might someday eliminate it.

Oral Bacteria

Your mouth is a thriving ecosystem full of bacteria. You have an estimated 50-100 billion bacterial cells in your mouth at any given time. These bacteria make up your normal oral micro flora. This population of organisms is generally harmless to you and can even serve a beneficial purpose. Having a healthy and diverse population of bacteria in your mouth can prevent pathogenic organisms like the parasitic fungus Candida from overgrowing and causing the disease thrush.

Your mouth is a perfect microbe habitat. The constant warm temperature, high moisture content, plentiful food particles, and sloughed off mouth cells provide a protective environment and plenty of nutrients. For most of human history, these bacteria floated freely in the saliva or attached to the soft tissues without causing any damage. The smooth, hard enamel on your teeth was too tough and slippery for bacteria to attach and colonize effectively.

This protected ancient man's teeth from cavities. But, after the Industrial Revolution, contemporary man developed a sweet tooth, and with it came the widespread consumption of the sugar sucrose. But, sucrose didn't come alone. It brought with it some members of the bacterial genus Streptococcus.

Streptococcus and Tooth Colonization

Fructose is the dominant sugar in most fruits and natural products and was the only source of sugar for many humans throughout history. The white table sugar so common in foods today is sucrose and comes from the sugarcane plant. Bacteria in the genus Streptococcus are very good at fermenting sucrose but not fructose. As we have begun to eat more sucrose, the Streptococcus populations in the mouth have begun to increase.

This is significant for two major reasons. First, Streptococcus sobrinus and mutans bind to proteins in saliva, and second, Streptococcus are lactic acid bacteria. Let's examine how these two factors lead to increased tooth decay. Streptococcus sobrinus and mutans are able to bind to the proteins naturally found in our saliva. These salivary proteins naturally adhere to our tooth surfaces. S. sobrinus and mutans binding to these proteins means that the bacteria are able to colonize the enamel surfaces previously free of attached bacteria.

It only takes one Streptococcus cell to stick to the enamel surface and start a chain reaction. Single cells divide, forming colonies of many cells. At first, only the Streptococcus bacteria can adhere, but soon, other species of bacteria begin attaching to the Streptococcus. This forms a continually thickening layer of bacterial cells.

Eventually a biofilm forms. An oral biofilm is a deposit of dense, gelatinous material composed of salivary proteins, trapped food debris, and enormous numbers of bacterial cells. You might know this biofilm by another name: plaque. The thick, mature plaque that you can feel by rubbing your teeth with your tongue was started by just one species of bacteria, but can now contain up to 300 different species.

Dental Caries

Why is it so bad for Streptococcus to form these oral biofilms on your teeth? Well, Streptococcus are lactic acid bacteria. This means that Streptococcus is able to ferment sucrose and produce lactic acid as a byproduct. Consuming more sucrose leads to larger populations of Streptococcus, which in turn produces larger amounts of acid.

This acid is responsible for tooth decay. Dental caries, more commonly known as cavities, are areas of tooth decay caused by the acidic byproducts of microbial metabolism. The acid removes the minerals from the tooth surface. This eventually causes holes in the enamel. The acids can continue to break down the tooth material, called dentin, that lies under the enamel. Once through the dentin, the nerves and blood supply of the tooth pulp are invaded.

Interestingly, there are still isolated populations of humans that don't have a source of sucrose in their diets. These groups have very few to no Streptococcus bacteria in their mouths. They also are generally completely cavity-free.

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