These prokaryotes (particularly Gram-positive bacteria such as Lactobacillus spp., Streptococcus mutans, and Actinomyces spp.) exist in oral biofilms; the sticky, slimy coating in the mouth that is most noticeable before brushing away that bad morning breath.
What Is Plaque?
Dental plaque is a biofilm of material that adheres to, and can build up on, teeth; a living slime layer made of millions of bacterial cells, salivary polymers, and bacterial wastes and other extracellular products. Unchecked, this biofilm can easily reach a thickness of hundreds of cells on the surfaces of the teeth, and, over time, plaque build-up can become mineralized, eventually forming calculus (tartar).
Bacteria, Not Sugar, Causes Cavities
Especially as children, we’ve all been told that if we eat too many sweets we’ll get cavities. This leads to the misconception that the sugar is directly causing holes to develop in our teeth. This is not specifically how tooth decay develops.
Demineralization & Remineralization of Teeth
Pearly whites are made mostly of minerals, including calcium. Demineralization (the loss of minerals) and remineralization (the gain of minerals) of the teeth is constantly occurring, based on specific chemical features of the surrounding saliva, including pH (the relative acidity / alkalinity).
Sugar, Bacterial Metabolism and Acidic Waste Products
When plaque builds up, the microorganisms in the area of the biofilm nearest the tooth surface begin to metabolize their food using anaerobic respiration (metabolism without the use of oxygen). Anaerobic metabolism of sugars results in the production of very acidic bacterial waste products.
Eating lots of refined, simple sugars, also feeds oral bacteria, which eat the carbs and then produce these acidic metabolic waste products, creating a high level of acidity on the surface of tooth enamel. This acidic environment affects the mineral content of teeth.
Acidic Oral Environment and Demineralization
When the pH of the mouth drops into the acidic range (specifically below 5.5), the teeth begin to lose minerals faster than gain them. The more sugar we eat, the more we are feeding the microbes in our mouth; and the more an organism eats, the more waste it creates (be it person or pathogen). So feeding oral bacteria lots of sweets results in a more acidic environment in in that mouth and demineralization follows.
Plaque Blocks Saliva’s Protection
When there is a thick build-up of plaque on tooth enamel, the saliva that normally protects teeth is unable to penetrate the plaque and is therefore unable to neutralize the acid produced by the bacteria or remineralize the tooth surface, and tooth decay results.
Cavities and Soda Pop
Drinking sugared soda pop provides double-trouble when it comes to dental health. The refined syrupy sugars feed the bacteria and the phosphoric acid in pop (both diet and sugared), further contributes to an unhealthy acidic environment surrounding the teeth.
Preventing Tooth Decay
Failure to remove plaque through regular brushing allows these naturally occurring microorganisms to build up into the thick layer of plaque and eventually calculus. Regular brushing, flossing, reduction of sweets, and periodic dental cleanings and checkups are the best way to maintain a healthy smile. And it’s not just a dazzling smile that’s at stake.
Oral Bacteria & Disease
It is possible for oral bacteria to invade compromised tissues of the body and produce disease in other areas. Oral bacteria that move into deeper tissues can result in abscesses. Oral Streptococci traumatically introduced into tissues through wounds created during dental manipulation can potentially adhere to heart valves, initiating bacterial endocarditis, which can be fatal.
Additional Microbiology Information
For more information on bacteria and infectious disease see the SPO Virtual Microbiology Classroom, or Dr. Kenneth Todar’s online microbiology resource The Microbial World.
Sources
Bauman, R. (2005) Microbiology. Pearson Banjamin Cummings.
Park Talaro, K. (2008) Foundations in Microbiology. McGraw-Hill.
Tami Port - Tami Port is a college professor of cell and microbiology and creator of ScienceProfOnline.com, a free science education website.
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