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The Clinical Application of Biofilm Science

April 1, 2006
As a practicing dental hygienist and professional educator for Philips Oral Healthcare, I have the privilege of speaking to dental professionals and dental hygiene students across the country.
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As a practicing dental hygienist and professional educator for Philips Oral Healthcare, I have the privilege of speaking to dental professionals and dental hygiene students across the country. I was recently invited by the faculty of a dental hygiene program to speak to students about “Enhancing Patient Compliance Through Technology.” This is a fun, interactive course that covers motivating patients and increasing patient compliance via power toothbrush technology. I was discussing the impact of disclosing solution on patient motivation and home-care compliance when a student raised his hand, pointed to the slide showing a bright pink mouth fully disclosed, and asked, “I know the faculty makes us disclose our patients, but you don’t actually do this in the real world, do you?”

Students often wonder if the practice of disclosing patients is some evil conspiracy that dental hygiene educators invented solely to deduct clinic points! I explained that I regularly disclose my patients in the real world, and that this 30-second procedure has been used for decades by dental hygienists to help patients visualize specific areas that need home-care improvement. I said, “Conventional disclosing products are excellent educational tools for patients; however, there are significant limitations. The results are either yes or no. Is plaque present or not? It does nothing to assess plaque thickness, volume, activity, or relative pathogenicity. This is especially important considering what we now know about biofilms.”

The student replied, “Bio-what?” I proceeded to explain how our view of dental plaque changed dramatically with the advent of confocal scanning laser microscopy (CSLM). This new technology allows dental professionals to observe the three-dimensional, irregular shape of dental plaque biofilm. CSLM is able to demonstrate, for the first time, the extremely sophisticated activity occurring within the microcosm of the biofilm. Through CSLM, researchers are able to sample and view hydrated, living biofilm colonies. This is a breakthrough. Previously, if researchers were interested in studying a dental plaque specimen, they swabbed a site in the oral cavity, diluted the specimen in a nutrient broth, carefully spread the inoculated broth on a glass slide, flamed the slide to fix the specimen, then gram-stained to view dried-out, dead microbes under a microscope. This technique yielded a nonliving, nonhydrated, one-dimensional view of plaque.

Due in part to CSLM, dental hygiene continues to evolve; it has even impacted how dental hygienists view the pink stain remaining on teeth after applying disclosing solution. On a larger scale, dental hygiene has witnessed an evolution in the perceptions of plaque, calculus, and the factors involved in the progression from healthy periodontium to diseased state. In the text, “Foundations of Periodontics for the Dental Hygienist,” Nield-Gehrig and Willman outline this evolution as follows:1

Prior to 1960, dental hygienists held the belief that calculus was the sole cause of periodontal disease. Calculus was perceived as a mechanical irritant to soft tissues, and the six-month scaling interval was established. Due to limitations of technology, dental hygienists had no idea the etiologic agent wasn’t the calculus per se; it was the pathogenic bacterial biofilms contained within it. In addition to removing calculus through scaling, patients were encouraged to brush vigorously at least three times a day.

Later, in the 1960s and early ‘70s, researchers coined the phrase “nonspecific plaque theory” to describe the initiation of periodontal disease. This is the period of time when flossing became the mainstay in all oral hygiene recommendations. Plaque was thought to be the sole cause of both gingivitis and periodontitis. Dental professionals had no knowledge that some bacteria within the plaque were more pathogenic than others, therefore plaque was collectively considered “bad.” So it was thought that if patients diligently brushed and flossed, they could eliminate plaque and therefore potentially prevent disease.

By 1975, dentistry had moved into the era of the “specific plaque theory.” Through research, scientists were actually able to differentiate the hundreds of bacterial species living within the microcosm of plaque. For the first time dental professionals were told that some bacteria living within the plaque mass were relatively benign, while others were deemed extremely virulent and destructive. Researchers concluded it wasn’t so much the quantity of plaque that impacted periodontal health; rather it was the composition of the plaque that predicated disease. From a treatment standpoint clinicians still focused most of their energy on calculus and plaque removal, and educated patients that a combination of mechanical chairside therapy and home care were the only keys to successfully eradicating disease.

Today, the accepted model is the “host-bacterial interaction theory.” Dental professionals now understand, through research, that it is the combination of the invading pathogenic bacterial biofilms and the response of the host (patient) that determines disease sequence.

In microbiology and pharmacology, if researchers want to kill bacteria with antibiotics, they commonly use planktonic bacteria. These single-celled bacteria are allowed to grow on a medium, then antibiotics and/or antimicrobials are added. Researchers then see if the bacteria growing on the medium flourish or are killed. This is appropriate protocol when dealing with planktonic bacteria in a solution. However, through CSLM, dental professionals now know that this is not how bacteria exist in the oral cavity. Bacteria in the oral cavity are encapsulated within a biofilm mass. Bacteria in biofilms differ significantly from planktonic bacteria in their metabolism, gene expression, and proteins they produce.

Almost immediately after a tooth surface is cleaned, the acquired pellicle layer begins to form. Soon, single planktonic bacterial cells drift toward the surface and attach via specific bacterial adherence properties. Some bacteria have extremely strong adherence properties, while others do not. The bacteria that are successful in their quest to adhere to the surface are vulnerable due to their lack of protection from environmental exposures such as the host response or antibiotic agents. For protection, the bacterial cells sitting on a surface near one another secrete extracellular matrix. Extracellular matrix, in basic terms, is a slime-like substance that holds the bacterial cells together for a “strength in numbers” type of scheme.

Extracellular matrix also has two other purposes. First, it shields the bacteria from antimicrobial agents. This is why treating biofilms with antibiotics is difficult and in many cases ineffective. Researchers estimate that bacteria within a biofilm mass are up to 1,500 times more resistant to antibiotic regimens.2 Secondly, the gooey biofilm mass functions well in absorbing environmental nutrients vital for the bacteria’s growth, and also flushes out toxic cellular waste byproducts.

Researchers have learned that bacteria are able to talk to one another through a phenomenon called quorum sensing. Simply explained, quorum sensing is a form of chemical signaling bacteria use to communicate with one another. These signals tell the bacteria to secrete slime, stick together, and protect themselves by adhering to a surface. Their sole agenda is to discuss strategies to recruit additional benign and pathogenic bacteria in hopes of surviving a counterattack via a local or systemic antibiotic or the host’s immune system.

The biofilm is a microcosm of various microorganisms. Gram-negative as well as gram-positive bacteria reside within the bacterial plaque biofilm. Gram-negative bacteria, however, can produce toxic byproducts commonly called endotoxins (also known as lipopolysaccharides). These same bacteria also produce the sulfur byproducts responsible for oral malodor commonly associated with poor oral hygiene. If left within the biofilm, these byproducts can potentially destroy the entire biofilm structure, so an elaborate waste removal system known as water channels is used. Water channels have two primary functions: remove toxic byproducts and bring in fresh nutrients to feed the biofilm. Once released via the water channels, the toxins pose serious threats to host tissues. Endotoxins are responsible for initiating inflammation, causing soft-tissue destruction, and stimulating bone resorption (i.e., breakdown of the alveolar bone - bone loss).

As I finished explaining biofilms to this student, I said, “The technology of a power toothbrush such as the Sonicare can safely disrupt bacterial plaque biofilms mechanically and disrupt biofilms via fluid dynamic action. The Sonicare has been demonstrated in in vitro models to reduce bacterial biofilm by 32 percent, even up to 2 to 3 mm away from the reach of the bristles.”3

The student thought for a moment and said, “Listening to what you said about biofilms really changes my perspective on disclosing solution and the importance of patient education. There is so much more to a plaque score than just A or B, pink or not pink. Unless we have a CSLM chairside, we don’t know what the pathogenic potential of that biofilm really is, do we?”

He was right. Dental professionals cannot assess pathogenicity of the plaque biofilm structure chairside, and this is a limitation. However, the benefit of showing patients their own clinical evidence still makes disclosing solution one of the most powerful patient education tools available today. In 30 seconds, patients can clearly see their level of compliance. It is as clear as pink or white!

For more information on biofilms, visit Montana State University’s Center for Biofilm Engineering Web site at


1 Nield-Gehrig JS. Foundations of periodontics for the dental hygienist. Lippincott Williams & Wilkins 2003; Philadelphia: p. 56, table 4-5.

2 Costerton J, Stewart P, Greenberg E. Bacterial biofilms: a common cause of persistent infections. Science 1999; 284:1318-1322.

3 Hope C, Wilson M. Comparison of the interproximal plaque removal efficacy of two powered toothbrushes using in vitro oral biofilms. Am J Dent 2002; 15:7B-11B.