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The Slime on Your Smile:
Biofilm Formation on the Surfaces of Teeth
Rachael Galli
May 17, 2011

Abstract
Biofilms are present all throughout the body. One place in particular is within the mouth, and even more specifically on teeth. Teeth provide perfect conditions for biofilms to form, and also help increase their resistance against forces trying to eliminate them. It is important to study these biofilms and how they work, in order to find a way to prevent them. The accumulation of these biofilms may lead to many dental diseases that are hazardous to the health and wellbeing of the host.

Introduction
Throughout the semester, biofilms have been of particular interest to me. I hope to one day be a dental hygienist, and biofilms are a very present force within the human mouth. Thus far in my academic career I have yet to sink my teeth into the very core of dental hygiene, and by completing this project it has only confirmed in me that this what I want to spend the rest of my occupational life working on. On teeth, biofilms are known as dental plaque, and is what people everywhere attempt to prevent through brushing their teeth and flossing. These biofilms have the potential to be harmful to the health of the host. There are many ways that they can become problematic, some are natural processes while others can be affected by daily life. There are also ways in which the growth of dental plaque can be inhibited, that the host can perform on their own.

Discussion
WHAT IS DENTAL PLAQUE?
Dental Plaque is the biofilms found on the surfaces of teeth. In one article they are identified as, “diverse community of micro-organisms found on the tooth surface as a biofilm, embedded in an extracellular matrix of polymers of host and microbial origin” (Marsh, 2004). This is the slime that builds up under liquid conditions, similar to what appears on rocks in a riverbed. Through a microscope, the uneven distribution of bacteria is noticeable along with, “the fluid channels that conduct the flow of nutrients, waste products, enzymes, metabolites, and oxygen” (Overman, 2006). Biofilms use what is called quorum sensing when colonizing an area, in this particular case on the teeth. They send out chemical signals in order to communicate. This makes them more complex than meets the eye, and “are not just bacterial slime layers but biological systems; the bacteria are organized into a coordinated, functional community” (Tortora, Funke, & Case, 2010)
These biofilms also display, “an open, fragmented architecture with a high surface-area: volume ratio in the outermost layers” (Filoche, Wong, & Sissons, 2010). There is what is considered a void-and-channel system that could allow for antimicrobial compounds to be transferred through; however, these channels are constantly changing due to, “biofilm age, thickness, nutrient status, and external conditions” (Filoche, Wong, & Sissons, 2010). Because the routes are always changing, the antimicrobial agent is limited in where it can go. Therefore, there are places where bacteria are heavily protected in the biofilm compared to other areas (Filoche, Wong, & Sissons, 2010).
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EFFECTS CAUSED BY DENTAL PLAQUE:
The health of the host is extremely important when it comes to the formation of dental diseases. There are two types of diseases, dental caries and periodontal disease. Dental caries are present above the gum line of the teeth, whereas periodontal disease is what takes place subgingivally or below the gum line (Filoche, Wong, & Sissons, 2010). In the case of dental caries, microbial species such as S. mutans, Streptococcus Oralis, Streptococcus mitis, and Streptococcus anginosus lead to the accumulation of cariogenic plaque, which due to its high acidity causes the demineralization of enamel and dentin. The unfortunate overall result is a cavity (Filoche, Wong, Sissons, 2010). Periodontal disease is associated with, “a cellular inflammatory response of the gingiva and surrounding connective tissue to the bacterial accumulations on teeth” (Filoche, Wong, Sissons, 2010). These responses are broken up into two subcategories, gingivitis and periodontitis. Gingivitis can lead to the development of periodontitis, in which the tooth and the bone are no longer attached by collagen fibers and can result in bone loss. Gingivitis is simply an inflamed gingiva, also know as the gums (Filoche, Wong, Sissons, 2010). Some researchers, such as microbiologist Richard Lamont of the University of Washington School of Dentistry in Seattle, are looking into the chemical signals as the culprit of certain dental plaque diseases. They have learned that Porphyromonas gingivalis is a key component in dental plaque formation, and have also found that Fusobacterium nucleatum, “provides the anaerobic conditions needed for P. gingivalis to wreak its destruction” (Potera, 1999). His research now is turned towards finding compounds that can inhibit the growth of these bacteria, and create an environment that is unreceptive to them. Also because biofilms do not need to divide, and they use signals to call for an increased number of microorganisms, they are unsusceptible to antibiotics targeted to kill only cells that divide.

RESEARCH STUDIES:
One particular way in which research was conducted was through the checkerboard technique. This was developed in 1994, and allowed scientists to manage large numbers of plaque samples at a time. They could also identify a panel of about forty bacterial species at one time. With this technique researchers were able to concentrate on the associations between the groups rather than solely focusing on one species. The use of this technique allowed Olsen et al. to analyze the different bacteria that make up subgingival plaque. They used 2522 clones from both healthy and non-healthy subjects; the non healthy consisted of people with refractory periodontitis, adult periodontitis, HIV periodontitis, and acute necrotizing ulcerative gingivitis. Close to sixty percent of the examined bacteria were identified within one hundred and thirty two known species ( Olsen et al., 2009). Their research concluded, “Many species or phylotypes were detected only in subjects with disease, and few were found exclusively in healthy subjects. The predominant subgingival microbial community comprised 347 species of phylotypes that fell into 9 bacterial phyla. It was estimated that there was 68 additional unseen species, thus producing a total of 415 species in subgingival plaque” (Olsen et al., 2009).
There has also been research done on the effectiveness of products such as mouthwash, and the findings were far less positive as one would hope. Dental plaque is known to have a high resistance to antimicrobial agents, and this study proved just how high that resistance was. In the case of chlorohexidine and amine fluoride, “ the biofilm inhibitory concentration… was 300 and 75 times greater, respectively, when S. sobrinus was grown as a biofilm compared with the minimum bactericidal concentration of planktonic cells” (Marsh, 2004). In order to eliminate S. sanguinis they needed to use 1050 times the minimum concentration used in order to prevent biofilm formation through chlorohexidine over a period of twenty-four hours (Marsh, 2004). This goes to show how hard it is to eliminate the biofilms present in dental plaque on the teeth.

PREVENTION OF DENTAL PLAQUE:
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Besides the usual defense of brushing and flossing, there are a dew dietary factors that can help combat the development of dental plaque. For one, cheese has been linked to a decrease in the accumulation of the biofilm. Normally there is a fall in pH that takes place why sugar is ingested. However, this drop was not seen when a piece of cheese followed the sugar (Moynihan & Petersen, 2004). It was found that, “The calcium concentration of dental plaque strongly influences the balance between de- and remineralization of enamel” (Moynihan & Petersen, 2004). They also conducted a study that found over a two year period, children who had eaten more cheese had less dental caries than children who had eaten less cheese (Moynihan & Petersen, 2004).
Another great source of calcium is cows’ milk. This also contains lactose, phosphorus, and casein that prevent the formation of dental plaque that leads to caries. There have been studies done that have provided evidence that by adding cows’ milk to a “cariogenic diet” resulted in a lowed rate of caries prevalence. It is also beneficial if there is a low salivary flow within the mouth. Moynihan and Petersen found that, “desalivated rats (i.e. caries prone) remained more or less caries-free when fed cows’ milk compared to those fed sucrose or lactose in water, and concluded that cows’ milk can be used safely by patients with low salivary flow as a saliva substitute” (Moynihan & Petersen, 2004).
Breastfeeding is also linked with the prevention of dental caries. This is true for a few reasons. First of all, there is no need for a bottle, which has been found can lead to the accumulation of biofilms and result in caries. There is also a “controlled composition” of the milk that the baby would receive (Moynihan & Petersen, 2004). That being said, there is no unnecessary addition of sugar to the milk either.
Additional foods that are beneficial in preventing dental plaque are fibrous foods. These help by, “mechanically stimulating salivary flow” (Moynihan & Petersen, 2004). Peanuts, hard cheese, and chewing gum are also useful in the same way. Fluoride, polyphenols, and flavanoids are all present in black tea that, “reduces the cariogenicity of a sugars-rich diet” (Moynihan & Petersen, 2004).

Literature Cited

1. Filoche, S., Wong, L., & Sissons, C. H. Oral Biofilms: Emerging Concepts in

Microbial Ecology. Published online in Journal of Dental Research 89, 8-18 (2010).

2. Marsh, P.D. Dental Plaque as a Microbial Biofilm. Cares Research 38, 204-211

(2004).

3. Moynihan, Paula & Petersen, Poul Erik. Diet, Nutrition, and the Prevention of Dental

Disease. Public Health Nutrition 7, 201-226 (2004).

4. Olsen, I., Preza, D., Aas, J., & Paster, B. Cultivated and Not-Yet- Cultivated

Bacteria in Oral Biofilms. Microbial Ecology in Health and Disease 21, 65-71

(2009)

5. Overman, Pamela. Biofilm: A New View of Plaque. Crest® Oral-B at dentalcare.com

Continuing Education Course, 1-7 (2006).

6. Potera, Carol. Forging a Link Between Biofilms and Disease. Published online

in Science 283, 1837-1839 (1999).

7. Tortora, Funke, & Case. Microbes and Human Disease. Microbiology, An

Introduction 10 (2010).

Images:

1. http://betohappy.blogspot.com/

2. http://sodahead.com

3. http://www.summitdentalcenter.com/blog/page/9/

4. http://bacteriality.com/2008/05/26/biofilm/

5. http://www.harbourlandingdental.com/Dental-Implants/Restoring-Functionality/Default.aspx

6. http://blogs.kansas.com/gov/2010/08/13/kansas-needs-a-cheese-plant-senator-says/

7. http://www.faqs.org/photo-dict/phrase/348/cow.html