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Rubber cup polishing has been an effective method for completing prophylaxis and controlling biofilm growth, and on-going research has expanded dentistry’s knowledge regarding the formation, growth, development, behavior and effects of biofilm.
Biofilm, especially dental plaque biofilm, can greatly affect the health of its host and lead to the development of many diseases. Understanding biofilm characteristics and its communities, and ensuring proper control, enables disease prevention. In particular, rubber cup polishing with disposable prophy angles can provide an effective method for controlling biofilm growth and preventing oral and systemic disease progression.
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Introduction to biofilm
The colonization of bacteria within the oral cavity begins at birth and constantly changes with age.1 Initially, single planktonic cells develop throughout the oral cavity, creating ecosystems in which bacteria, principally Streptococci, reside on tooth surfaces to form the first stages of biofilm.2
Biofilm describes the generic community of colonized cells on a surface. Dental plaque biofilm includes all of the characteristics of biofilm architecture and microbial community interaction, but, more specifically, it develops in the oral cavity, consists of more than 700 contributing oral microbial species and demonstrates a distinct method of conditioning the tooth surface.3-6 Research has determined that dental plaque biofilm consists of highly specialized, coordinated, multi-species forms of microorganism life located permanently on the tooth surface in a matrix, surrounded by a layer of extracellular polysaccharides that ensure the microorganisms are more resistant to immunological defense systems and less susceptible to antimicrobials.4-6
Biofilm formation occurs when proteins from the saliva are absorbed onto the enamel surface, after which the acquired pellicle then quickly forms. The pellicle alters the enamel surface, making it more inviting for bacterial colonization.7 Within minutes, early colonizers appear and arrange themselves in clusters, permanently adhering to the pellicle.7 As the collected cells begin to divide, they produce a sticky extracellular matrix that combines with the cells’ microstructures to provide cohesion of the colonies and adhesion to the enamel.7 These connected cells then create the communities known as biofilm or microbiomes. The cells in the microbiomes produce chemicals that communicate within the biofilm to direct its growth in order to create fluid channels between the cells to deliver nutrients, remove waste products and transfer chemical signals.7
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Scientists first identified bacteria on tooth surfaces through a microscope lens, but it wasn’t until the introduction of scanning electron microscopy that key developments in understanding biofilm occurred.8 When Jones et al.9 utilized scanning and transmission electron microscopy to examine biofilms, they determined that the biofilms in a wastewater treatment plant were composed of a variety of organisms, and that the matrix material surrounding the enclosing cells was a polysaccharide.9 Continued biofilm research has relied on scanning electron microscopy, as well as such advanced tools as confocal laser scanning microscopy to characterize biofilm ultrastructure and explore genes involved in cell adhesion and biofilm formation.8
Researchers initially utilized free-floating or planktonic bacteria to study biofilm development, because planktonic form demonstrates ease-of-use while handling.10 However, laboratory research involving planktonic bacteria did not translate into similar results when applied in vivo or in vitro to biofilms.11 In addition to representing a variety of bacteria, dental biofilm is also a dynamic and constantly changing metabolic structure, making it challenging to replicate.1 Therefore, actual oral environments are necessary as scientific models when studying biofilm behavior.12 This requires utilizing rapid video-over 400 frames per second-to note the changes in biofilm behavior.
Continue to page two to learn about biofilm growth and development...
Biofilm growth and development
Both beneficial and pathogenic bacteria coexist throughout the human body, and the key for maintaining health in all systems is to establish balance. This balance, known as microbial homeostasis, brings stability to the environment through a dynamic balance of both synergistic and antagonistic microbial interactions.13 Breakdown of homeostasis in the oral microbiome can lead to changes in the microflora balance, potentially predisposing sites to disease due to the microbiological imbalance within the biofilm.13-16 Processes of decreasing and increasing biofilm pH occur prior to the respective practices of tooth surface de- and re-mineralization.1 In healthy conditions, these processes occur without causing permanent tooth enamel surface damage, and with the balance of the system remaining in place.1 Therefore, oral health maintenance occurs when biofilms are regularly disrupted.
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Biofilms consist of a microbially derived sessile community composed of cells irreversibly attached to a substratum, interface, or to each other, and which are part of an extracellular polymeric matrix substance that the cells have produced.8 The sessile growth pattern brings a variety of microbes together to form a microbiome of the biofilm community. Biofilms contain a variety of species termed microbial communities that require a cooperative communal nature, but provide advantages to the participating microorganisms.17 Microbial communities provide an enhanced resistance to antimicrobial agents and host defense, a broader habitat range for growth, and an increased ability to cause disease.18
Biofilms use glucan polymers synthesized by several isoforms of the glucosyltransferase enzyme that is present in certain species of oral bacteria to provide structural and binding materials.2,19 By promoting adhesion and accumulation of cariogenic Streptococci on the tooth surface, glucans enhance the pathogenic potential of dental biofilm plaque and contribute to the bulk and structural integrity of the plaque.20 The combination of acidogenic and aciduric Streptococci mutans and their ability to synthesize extracellular glucans increases the potential for the development and establishment of cariogenic biofilms.13,21 In moist and nutrient-rich conditions, biofilm growth is frequently enveloped with copious exopolmeric capsules that form its sticky protective layer.22
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With its intricate structure and adhesive nature, biofilm proves difficult to remove from tooth surfaces. Its tooth surface adhesion requires more than 30 to 40 seconds of disruption to prevent disease, and even then the microorganisms can be hard to eradicate. During the 182nd meeting of the National Advisory Dental and Craniofacial Research Council in 2006 at the National Institutes of Health, Dr. Sangeeta Bhargava, Program Director of the Immunology and Immunotherapy Program at the Center for Integrative Biology and Infectious Diseases, estimated that over 80% of human bacterial infections could be related to biofilm.23 Research has linked biofilms as a factor for the development and continuation of disease. Since biofilm can provide a safe harbor to pathogenic bacteria and microorganisms, it increases their ability to proliferate and decreases the affects of antibiotic or antimicrobial interventions.
Continue to page three to learn about biofilm behavior...
Undisturbed biofilm creates a self-sufficient microbiome with a complex structure. The composition of the extracellular matrix provides a complex barrier to prevent disruption within the community. Additionally, the oxygen gradients within the microbiome provide a suitable environment for all types of microorganisms, with anaerobic and more pathogenic bacteria living interiorly, and aerobic bacteria living more exteriorly. The complex structure of the biofilm community includes channels to bring in nutrients, remove waste, and enable biofilms to grow and develop.
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In addition to using channels for transporting nutrients and waste, members of biofilms communicate through quorum sensing. This defining characteristic of microbial biofilm, including multi-species dental plaque biofilm, involves communication either from cell to cell or from microcommunity to macrocommunity.17 Quorum sensing provides a mechanism for bacteria to not only communicate, but also to monitor each other’s presence and modulate gene expression in response to changes in population density.39
Biofilm communities maintain their stability by utilizing saliva as a delivery system and major source of nutrients for microorganisms.40 Additionally, when biofilm cells are metabolically inactive, growth and development of persister cells occurs.41 These cells have been identified as those tolerant to antibiotics, and they continue to multiply while antibiotics destroy other microorganisms in the biofilm.42,43
However, saliva also contains the proline-rich glycoproteins that facilitate attachment of bacteria to the pellicle covering tooth surfaces.18 Although necessary for microbiome survival, saliva does provide antibacterial, antiviral, and antifungal properties. It includes lysozymes that cause bacteriolysis, lactoferrin that inhibits bacterial growth, lactoperoxidase that blocks glucose metabolism, and other protein components.44,45
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Various gradients within the biofilm either contribute to or inhibit growth. Differences in pH can alter the biofilm significantly, creating a hospitable or pathogenic environment for specific microorganisms. Additionally, the oxygen gradient provides an environment for a variety of species, and fluctuation in oxygen levels simply causes the microorganisms to adapt and change. With so much flexibility, dental biofilms prove very difficult to control.
Continue to page four to learn about the article references and related publications...
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