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tis, the initial stage of periodontitis—from the gingiva and the periodontium. Left alone, the bacteria can eventually initiate alveolar bone loss, soft-tissue destruction, implant failure, and other potential systemic issues. Since dental plaque biofilm’s antagonistic behaviour takes place in an environment with an incredibly diverse microbiota, and because its cariogenic traits are not emblematic of a particular species, its bacterial compo- sition is somewhat unclear at this point. Despite this, our understanding of other elements of dental plaque biofilm continues to improve—indeed, its recognition as a biofilm only occurred in the twenty-first century. Removing dental plaque biofilm is still not that sim- ple, however. For example, the fact that its cells have the ability to express multiple types of adhesin (surface structures that facilitate attachment) means that several avenues of attachment might still be available to it, even if a main method of adhesion were to be blocked. Microbiomes A microbiome is simply the community of microorgan- isms existing in a specific environment, particularly in the human body. The oral microbiome The oral microbiome is, along with the gut microbiome, one of the two most diverse microbiotas in the human body. The Human Oral Microbiome Database states that there are approximately 700 prokaryotic taxa that have been identified as existing in the oral cavity. The oral cavity is different to other human microbial environments, as it contains several types of surfaces for microbial colonisation, such as the teeth, mucosa, tongue, attached gingiva and implants in cases of tooth loss. In addition, teeth are the only non-shedding natural surface in the human body. This allows for biofilm to accu- mulate on them relatively easily, a feature that is shared by dental restorations, implants and other oral prostheses. “There is a natural symbiotic relationship between the host and the oral microbiome,” says Dr Phil Marsh, Pro- fessor of Oral Microbiology at the University of Leeds in the UK. “The host provides a warm and favourable en- vironment for microbial growth, and the oral microbiome acts as a barrier to colonisation by exogenous microbes, modulates the host’s immune response to prevent un- wanted inflammation, and contributes to the regulation of the cardiovascular system and other physiological activities.” In a 2017 study published in the Journal of Clinical Periodontology, Marsh and Zaura sought to describe the range of microbial interactions that take place in biofilms Dr Thuy Do, a lecturer in microbiology at the University of Leeds. in the oral microbiome. They found that these biofilms display “emergent properties”, meaning that their char- acteristics cannot be understood by simply studying in- dividual organisms. Instead, analysing how they function and interact with one another proves to be more fruitful. Maintaining a healthy, balanced oral microbiome in- volves processes that are, admittedly, still not entirely un- derstood. However, there are certain factors that clearly benefit oral health. Saliva, for example, is well known for its rinsing function in the oral cavity and for its role in initiating the digestive process by enabling chewing and swallowing of food. So what exactly causes dysbiosis— a microbial imbalance between harmful and protective bacteria—to occur? Dysbiosis and its causes “There are various factors that can disturb the symbi- otic relationship between the host and oral microbiota, leading to dysbiosis and disease,” says Dr Thuy Do, a lec- turer in microbiology at the University of Leeds. “Changes in the conditions at oral sites, such as the accumulation of dental biofilms from a lack of oral hygiene, may lead to an inflammatory response from the host immune cells.” biofi lm | m o c . k c o t s r e t t u h S / b m a B © l prevention 1 2018 33