Teeth

When you haven’t brushed your teeth recently and they feel a bit fuzzy – that’s bacteria! A sticky layer of lots of different bacteria all growing together on your teeth is called ‘plaque’. Plaque is a type of biofilm. We all have lots of bacteria naturally living on our teeth and some plaque is part of a normal healthy mouth. However, if you don’t keep your teeth clean by brushing them, some types of bacteria in the plaque start to feed on sugar in your food and produce acid, which damages your teeth.

The mouth contains the most complex and accessible microbial community in the human body. It is home to an estimated 700 different types of bacteria adapted to different regions in your mouth, for example the mucosal surfaces (e.g. cheeks, tongue), the crevice between your gum and tooth, on and between your teeth (including any pits and fissures). Different bacterial species are found in each zone. This is because each zone has a particular microenvironment and bacteria vary in which environment they prefer. No two people will have exactly the same bacteria, so is a bit like your fingerprint – unique to you!

On your teeth plaque forms as a normal, healthy process. Plaque is a wonderful example of a bacterial biofilm: a multi-layered community of bacteria made up of different species, all within a protective sticky coat. However, if left unchecked as a result of poor dental hygiene, some species of bacteria start to use the sugars we eat for themselves and in the process produces acid. This acidic environment does two things: it prevents growth of other less harmful bacteria because they can’t survive in an acidic environment, and the acid attacks the enamel of the teeth.

If the enamel coating of teeth is damaged, then bacteria have access to the inner areas of the teeth and can travel all the way through the harder layers to the pulp at the centre of the teeth. This can cause abscesses and be very painful.

Bacterial biofilms on teeth (plaque) begin when bacteria adhere to the salivary pellicle of teeth, rather than the teeth themselves. The pellicle is rich in proteins and sugars, including proline-rich proteins, mucins, ⍺-amylases and statherins to which the ‘early colonisers’, the species which form the ‘base’ of the biofilm, can adhere. These early colonisers include species of oral Streptococcus, Veilonella and Actinomyces.

Other species, the ‘late colonisers’, such as species of Fusobacterium, Porphyormonas, Prevotella, Tannerella, and also spirochaetes then adhere to the early colonisers via specific molecular interactions (protein-protein or protein-carbohydrate bonds) forming a multi-layered, multi-species biofilm. Co-aggregation of different species can lead to some plaque-typical formations such as ‘corn cob’ formations, which are aggregates of Streptococcus species adhering to central more filamentous bacteria such as Fusobacterium species.

The bacteria in biofilms produce a sticky, extracellular polysaccharide matrix coat that protects them against antimicrobials and maintains the environment inside the biofilm. The environment of the plaque biofilm varies across gradients of oxygen, pH, nutrients and metabolic biproducts from the bacteria within the biofilm. Different microenvironments across these gradients support the growth of different bacterial species and species succession within the biofilm is dependent on these changing microenvironmental factors.

The buffering action of saliva as well as the use of fluoride and good dental hygiene can all help redress the balance in dental plaque.

Further reading about biofilms on teeth

Valm A. (2019) The structure of dental plaque microbial communities in the transition from health to dental caries and periodontal disease. J Mol Biol. 431: 2957–2969. DOI: 1016/j.jmb.2019.05.016.

Marsh PD, Bradshaw DJ. (1995) Dental plaque as a biofilm. J Ind Microbiol. 15:169-75. https://doi.org/10.1007/BF01569822 PMID: 8519474.

Zijnge V, van Leeuwen MBM, Degener JE, Abbas F, Thurnheer T, Gmür R, et al. (2010) Oral biofilm architecture on natural teeth. PLoS ONE 5: e9321. https://doi.org/10.1371/journal.pone.0009321.

Streptoccus mutans
There are over 700 different types of bacteria that live in your mouth – some of them are good for you but others are not. One species that can cause problems is Streptococcus mutans which grows in biofilms, all over your teeth. When it grows it produces acid that can make your teeth decay. Understanding how Streptococcus mutans forms […]