Oral ecology

Oral ecology refers to the organisms that live in a mouth. Bacteria in biofilm were first detected under the microscopes of Antony van Leeuwenhoek in the 17th century. Various bacteria and saliva are two of the major components in oral microbiology, having the capability to be harmful, but also performing beneficial and necessary roles in the immune system. Proper oral hygiene aims to control the harmful effects and prevent disease transmission.

Discovery and history

Bacteria were first detected under the microscopes of Antony van Leeuwenhoek in the 17th century. Leeuwenhoek, a Dutch scientist, performed many experiments testing and observing bacteria. He observed plaque on his own teeth— “a little white matter” as he called it.[1] Under microscopes he saw “that in the said matter there were many very little living animalcules, very prettily a-moving,” which was the first sighting of oral bacteria as we know it.[1] Leeuwenhoek tested the mouths of others, as well as his own. Two men that he tested had never cleaned their teeth in their lives and Leeuwenhoek found “an unbelievably great company of living animalcules…in such enormous numbers, that all the water … seemed to be alive.”[1] Thus Leeuwenhoek discovered oral bacteria or “animalcules,” the name he gave bacteria in general.[2]

Later studies have shown that he actually saw mats of bacteria, what we know today as biofilms. Biofilms are communities of bacteria, or micro-organisms, attached to surfaces in the body. Oral biofilms are more commonly referred to as plaque. Biofilms form almost everywhere bacteria are. In the mouth, they naturally form on any stationary surface, namely teeth, gums, and the tongue.[3] Leeuwenhoek made important findings of bacteria with his first observation and analysis of dental plaque, and since then much more has been discovered about the mouth and its ecology.

Ecology and types

The human mouth contains around 500 to 1,000 different types of bacteria with various functions as part of the human flora and oral microbiology. About 100 to 200 species may live in them at any given time.[4] Individuals that practice oral hygiene have 1,000 to 100,000 bacteria living on each tooth surface, while less clean mouths can have between 100 million and 1 billion bacteria on each tooth.[5] While some of the bacteria in our mouths are harmful and can cause serious illness, much of our oral bacteria are actually beneficial in preventing disease. Streptococci make up a large part of oral bacteria.[6]

There are four main species within streptococci: the mutans, salivarius, anginosus, and mitis groups. Streptococcus mutans make up a large majority of what affects our mouths[7] and create acids which may cause decay.[8] The enzymes “leach down the tooth and begin to dissolve the ligaments and bone that help to hold the teeth in your mouth.”[9] By turning simple sugars and carbohydrates into acids and enzymes that dissolve tooth enamel, this bacteria can leave a person with lasting dental problems.[10] According to Dr. Robert Gandola, a dentist, “A number of bacteria can cause decay [and many] are suspected in periodontal (gum) disease.”[11]

Oral bacteria work with our immune system to keep our bodies disease free by fighting disease-producing germs that try to come in through the mouth. For example, some of these bacteria produce organic acids that kill the organisms that cause intestinal problems.[5] Without these good bacteria, our immune systems would be constantly bombarded by airborne and saliva-transferred germs. Bacteria are also needed to control the growth of fungus. “Balance between all the different bacteria and fungus are critical” or else the “fungus overgrows and takes over.”[11] So, ironically, though bacteria have the potential to harm us, our mouth and the good bacteria in it are the body's first line of defense. These bacteria are transmitted to a human early in their childhood through their contact with their caretakers by kisses or food premastication.[12]

Bacterial growth in the mouth/teeth

Numerous kinds of bacteria grow in the mouth. “They are competing for food and places to grow” and the many hard surfaces in the mouth provide an ideal place for bacteria and biofilms to grow and reproduce.[11] Unlike most other places in or on the body, the mouth does not desquamate (shed).[13] A tooth's distinct surface and stagnant nature makes it optimal for populations and growth of micro-organisms and bacteria, resulting in dental plaque. To grow and flourish in the mouth, biofilms go through four main stages of growth.[13] First, bacteria must be deposited from saliva onto a surface where it can attach. Then the bacteria, or micro-organisms, grow and replicate. Since bacteria can grow exponentially in short periods of time, it can quickly and easily create biofilms. Third, the biofilm matures and accumulates more mass on the surface. Bacteria can continue to divide and grow by binary fission until nutrients begin to run out or their growth is inhibited.[13] When this happens there is the final stage, the dispersal or detachment, causing the death of the bacteria.[14] Some oral bacteria, Streptococcus gordonii for example, cannot last for long periods without nutrients, while other types of bacteria can survive for weeks.[14] While in their prime, biofilms can cause major damage to a person's teeth and gums. Though damaging, biofilms can be partly removed by brushing and flossing and “some of it comes off with rinsing or eating.”[11]

Saliva

Saliva keeps the ecosystem of the mouth in balance. It contains its own bacterial enzymes that are beneficial to our health. An example of these are lysozomes. These antibacterial agents in saliva kill bacteria in our mouths and protect from potentially dangerous diseases.[15] In addition, saliva contains phosphate and calcium ions that help repair microscopic chinks made in the teeth by the bacteria's acid.[5] The major organic constituents of saliva are proteins and glycoproteins.[15] Proteins in saliva float around and influence the mouth's ecosystem in multiple ways. Some of the proteins provide nutrients for bacteria, while others cause bacteria to clump together so they are unable to stick to any surface and are washed away. The main function of saliva is to flush out all of the micro-organisms that could potentially threaten our health.[16] The flow of saliva constantly bathes the mouth and detaches all micro-organisms that are not already firmly attached to a surface.[5] This makes it difficult for bacteria to adhere to surfaces to even begin to form biofilms. Many harmful micro-organisms, therefore, are unable to attach quick enough to a surface before they are caught in saliva and swallowed.[17] Although saliva does a lot to keep our bodies healthy, it cannot completely keep all bacteria from adhering to tooth, tongue or gum surfaces.

Diseases

Diseases transmitted through saliva

Each day numerous bacteria grow in a person's mouth. Many diseases are related to oral bacteria. Proper oral care and habits often protect against and reduce the effects of some harmful bacteria.

Because of the amount of bacteria in each person's mouth, there is a transfer of bacteria through saliva when lip balm, drinks, toothbrushes, or anything else is shared. Said bacteria transfer can lead to human illnesses. Some of these diseases that result are relatively inconsequential while others could potentially have a serious impact on one's life. Some examples of the milder diseases passed through saliva include: herpes simple virus (cold sores or canker sores), flu virus, cold virus, various bacteria that cause periodontal disease (inflammation or infection of gum tissue), venereal diseases, and candida albicans (fungus).[18]

Mononucleosis (mono), known among teenagers as the “kissing disease”, is another prominent condition that can come from saliva exchange, although it is not caused by bacteria, it is a contagious viral disease in the herpes virus family. Mono can “be spread when a person coughs, sneezes, or shares objects such as drinking glass or water bottles.”[19] There are only certain stages when it is contagious, mostly during the fever stage,[19] but during those times it is transferable through saliva exchange.

Some serious and possibly life-threatening diseases have been found to be connected to oral hygiene. These diseases are not passed through saliva, but are still influenced by the mouth's ecology and bacteria. Streptococcus mutans, a common oral bacteria discussed above, is a pathogen that causes pneumonia, sinusitis, otitis media, and meningitis.[10]

Prevention

Although disease is possible through oral interactions, there are many ways to prevent or reduce the risk of infection and disease. Brushing and flossing teeth regularly are the most basic ways to reduce these risks. These two hygiene tips help to get rid of bacteria that try to stick to surfaces in the mouth to form plaque (oral biofilms).[11] Brushing and flossing the teeth disrupts biofilms and their ability to permanently damage the teeth or gums. The less one brushes their teeth, the better chance that bacteria will form plaque, which may potentially cause serious oral health issues.[20]

Diet has an influence in our oral health as well.[21] Much of the bacteria in our mouths are nourished by simple sugars and carbohydrates.[11] An excess of candy, soda, or other simple sugars is an easy way to let bacteria thrive in our mouths. Fluoride is extremely effective in protecting enamel on the teeth. “Fluoride, a chemical that appears naturally in groundwater in many areas of the world, quickly bonds with the tooth's enamel to maintain its smooth crystalline surface and deter bacteria from gaining a toehold.”[5] The Oral-B website advises people to “drink tap water when possible” because “if bottled water is your main source of drinking water, you could be missing the decay-preventative benefits of fluoride.”[22] Also, a study in the Journal of the American Dental Association states that “antiseptic mouthwashes have been associated with a 28 to 34 percent reduction in dental plaque biofilms at six month follow-ups. Chlorhexidine gluconate [mouthwash] rinses, when combined with toothbrushing, have been reported to reduce oral biofilms . . . by 50 to 55 percent.”[3] Going to a dentist can help people who have difficulty with oral hygiene learn how to begin these preventive measure, as well as determining what symptoms one's oral ecology may be causing.

Notes
  1. University of California Museum of Paleontology
  2. Slavkin, HC. "Biofilms, Microbial Ecology and Antoni Van Leeuwenhoek."
  3. Slavkin, HC. "Biofilms, Microbial Ecology and Antoni Van Leeuwenhoek."
  4. How Microbes Defend and Define Us
  5. Stevens, Jane E., and Jack Desrocher. "Oral ecology."
  6. "Streptococcus mutans." Encyclopædia Britannica.
  7. Marsh, Philip, and Michael V. Martin. Oral Microbiology. pg. 20
  8. Banas, Jeffrey A.; Drake, David R. (2018-07-31). "Are the mutans streptococci still considered relevant to understanding the microbial etiology of dental caries?". BMC Oral Health. 18 (1): 129. doi:10.1186/s12903-018-0595-2. ISSN 1472-6831. PMC 6069834. PMID 30064426.
  9. Dentist Robert Gandola, interview
  10. "Streptococcus mutans." Encyclopædia Britannica.
  11. Dentist Robert Gandola, email.
  12. Diane, Mapes (March 30, 2010), "Mom's kiss can spread cavities to baby", NBC News
  13. Kuramitsu, Howard K., and Richard P. Ellen. Oral Bacterial Ecology; the Molecular Basis.
  14. Thomas, John G. and Lindsay A. Nakaishi. “Managing the Complexity of a Dynamic Biofilm.”
  15. Kuramitsu, Howard K., and Richard P. Ellen. Oral Bacterial Ecology; the Molecular Basis
  16. Marsh, Philip, and Michael V. Martin. Oral Microbiology.
  17. DePaola, Dominick P., Frederick A. Curro, and Domenick T. Zero. "Saliva: The Precious Body Fluid."
  18. Robert Gandola, email.
  19. Dreher, Nancy. "What you need to know about mono."
  20. Favot, Christa. “What is Living in my Mouth? Biofilms, Carbohydrate, and Acid Blasts.”
  21. “Avoiding Tooth Decay.” Oral-B.
  22. “Avoiding Tooth Decay.” Oral-B.

References
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