Understanding Oral Biofilm
Management hinges on knowing what it is and how it forms
Gregori M. Kurtzman, DDS, MAGD, DICOI
Research has dramatically changed our understanding of periodontal disease and its affects on the body. For decades the information on periodontal disease remained virtually unchanged, but in the last 10 years scientific advances connecting the mouth with systemic health show that periodontal disease is the key to a number of systemic issues, either creating them or complicating them.
Many common health issues have been connected to oral biofilm, such as cardiovascular disease (CVD),1 diabetes,2 pulmonary disease,3 chronic kidney disease,4 and osteoporosis.5 Evidence has also linked prostate disease,6 colon cancer,7 pancreatic cancer,8 and poor pregnancy outcomes (ie, preterm birth and low birth weight)9 to the oral biofilm that induces periodontal disease. But, what exactly is oral biofilm?
Oral Biofilm: What is It?
We used to call it plaque, a soft and sticky deposit containing food particles and bacteria that is continually forming on teeth and gums, but it is now understood that the deposit is more complex than previously thought. A better definition of biofilm is a specific but highly variable entity consisting of micro-organisms and their products embedded in a highly organized intercellular matrix.10 Biofilm consists of a variety of micro-organisms involved in a wide range of physical, metabolic, and molecular interactions. The cooperative nature of the microbial community within the biofilm provides advantages to the participating bacteria, from a broader habitat range enhancing growth to greater resistance to host defenses and antimicrobial agents that also enhance the microbial communities’ pathogenicity.11
Yet to understand how to manage biofilms, we need to understand what a biofilm is. Costerton first introduced the term in 1978, and it was used to emphasize that the bacteria congregated in a “living film” that interacted with the environment.12
Biofilm will form on virtually any surface that is immersed in a natural aqueous environment. A biofilm confers certain properties to the bacteria contained within that are not seen in bacteria in a planktonic state. Bacteria growing in a biofilm are physiologically distinct from planktonic cells of the same organism, which, by contrast, are single cells that are floating in a liquid medium such as saliva or blood.13 The formation of biofilm is a complex process that has several distinct phases (Figure 1). The process begins with adsorption of a sticky film onto the tooth surface derived from bacterial and host molecules. This is followed by a passive transport of bacteria that is mediated by weak long-range forces of attraction. These forces are covalent with hydrogen bonds and create strong, short-range forces that result in an irreversible attachment to the surface. These primary colonizers form a biofilm by autoaggregation between the same bacterial species and coaggregation between dissimilar species of bacteria, which results in a functional organization of the contained bacteria.14 This leads to the microenvironment changing from aerobic to a facultative anaerobic environment with the contained bacteria multiplying and secreting an extracellular matrix, resulting in a mature biofilm.
As the biofilm further matures, incorporation of new bacterial members from other sites into the biofilm leads to the formation of a complex community. Following maturation, portions of the biofilm break off and are dispersed to other sites to initiate new biofilm or exert issues systemically. Biofilm development occurs over a 2- to 3-day period, which means even with professional cleaning and homecare, biofilm reestablishes quickly. Additionally, biofilm can vary from site to site—even when the sites are adjacent to each other—demonstrating different varieties of bacteria in adjacent pockets, complicating their management (Figure 2).
The slime coating encasing the biofilm offers major protection to the bacteria contained within from host defense mechanisms and “toxic” substances such as oral antibacterials or systemic antibiotics. Quorum sensing (cell density-mediated gene expression) that is observed with biofilm-associated bacteria also increases biofilm resistance to host-mediated responses.15 Through quorum sensing, the regulation of genes for antibiotic resistance may provide protection to the bacteria of the biofilm. Additionally, bacterial communication can influence community structure by encouraging the growth of species beneficial to the biofilm and discouraging the growth of competitors.
How Can Oral Biofilm Be Managed?
Mechanical debridement of the pocket only removes 50% of the initial biofilm present.16 But, re-growth of the biofilm occurs within 3 hours, resulting in a 4-fold (400%) increase in biofilm mass.16 Because the sulcular environment is difficult for most patients to reach with brushing and flossing, homecare is compromised no matter how diligent the patient tries to be. Toothbrush bristles, unable to extend more then 3 mm into the pocket, are unable to mechanically contact biofilm located at deeper depths. A similar problem occurs with oral irrigators. Irrigation to the bottom of the pockets on all teeth is technically difficult and most patients are not diligent in daily use. Even when biofilm is removed by mechanical means, the bacteria regrow and replicate so rapidly that they are impossible to control mechanically. Post-cleaning, biofilm redevelopment is more rapid and complex, exceeding pre-cleaning levels within 2 days.17,18
We need a method that is easy for patients to use, improves patient compliance, reaches the depths of the pockets, and effectively breaks down the biofilm while preventing it from rebuilding on a daily basis. Antibiotics offer limited answers to this need. Bacteria embedded in the biofilm are up to 1,000-fold more resistant to antibiotics compared to planktonic bacteria.19 The use of antibiotics either systemically or in oral rinses and site application are unable to eliminate or manage the biofilm bacteria adequately.20,21 This has implications both with natural teeth and also periodontal issues developing around dental implants leading to peri-implantitis.21
Chlorhexidine has been reported to have an effect on young biofilm but the bacteria in mature biofilm and nutrient-limited biofilms are more resistant to its effects.22,23 Hydrogen peroxide, on the other hand, has been documented as a very effective means of not only eliminating the biofilm but also preventing its reformation without the bacterial resistance issues found with other site-specific treatment modalities. Hydrogen peroxide has been documented as being used daily up to 6 years with no adverse effects or carcinogenic activity, and it has been shown to decrease biofilm and enhance wound healing, improving gingival bleeding.24 Further, no allergic reactions have been reported and bacterial strains demonstrate no resistance.