Basic Guide to Oral Health Education and Promotion. Alison Chapman
href="#ulink_88f59232-dfb5-59d6-adf7-472073261502">Figure 2.2 Mature plaque and gingivitis in a neglected mouth.
Source: Alison Chapman.
In a healthy mouth, there is a natural balance of bacteria, but when illness or antibiotics (for example) upset the balance of the mouth’s flora, or when teeth are not cleaned often and/or appropriately, plaque matures. Waste products from the bacteria, enzymes and toxins then cause an inflammatory response in the gingival tissues leading to gingivitis (Figure 2.2). Depending on an individual’s response, gingivitis can progress to periodontal disease.
Biofilms
Dental plaque is a type of biofilm, and the concept of a biofilm is of huge importance not only to dentistry, but also to the wider medical world and many sectors of industry. Since the 1990s, there has been a huge amount of research into biofilms, which reflects our growing understanding of their importance.
A biofilm, in simple terms, is a thin layer of bacteria that adheres to a surface. Over 95% of bacteria in nature exist in a biofilm state as opposed to living independently, and over 500 species of bacteria have been identified in oral plaque biofilms. Contact lenses, rocks in rivers and aspirator tubing in the dental surgery are all examples of surfaces colonised by biofilms.
Within a biofilm, bacteria are not just sitting alongside one another passively; they are communicating, interacting, and gaining benefits from one another – acting as a team. This is what makes a biofilm so virulent, resilient, and difficult to manage.
Bacteria
Bacteria is the most common microorganism found in the plaque biofilm, and can be classified as to whether they need oxygen (aerobic) or not (anaerobic) to survive.
Aerobic bacteria
The majority of bacteria in a healthy mouth come from the oxygen‐dependent (aerobic) streptococci genus, which colonise areas of the mouth where oxygen is readily available. When resistance is lowered, they can give rise to sore throats and other illnesses, but are generally less potentially harmful than their non‐oxygen‐dependent (anaerobic) relatives.
The most common species of streptococci bacteria found in the oral cavity are:
Streptococcus sanguis.
Streptococcus mutans.
Streptococcus mitis.
Streptococcus salivarius.
Aerobic bacteria feed on sucrose from the human diet and produce sticky substances that enable other more harmful organisms to attach themselves, causing plaque to become more dense and harmful to tissues.
Anaerobic bacteria
Anaerobic bacteria are a more potentially pathogenic (disease causing) bacteria, when displaced from their normal habitat. They produce enzymes and toxins and do not need oxygen to survive. They can be found in deeper layers of plaque and in areas of the mouth, such as periodontal pockets, which render them difficult to remove. Examples of anaerobic bacteria are:
Fusiforms.
Vibrios.
Spirochaetes.
Other microorganisms found in plaque
As well as bacteria, other microorganisms found in plaque, include fungi and viruses.
Fungi
Fungi, such as Candida albicans, are also commonly found in plaque. As with bacteria, these do not affect oral health unless the body’s resistance is lowered and the immune system is upset, in which case they can cause dental thrush or stomatitis (see Chapter 8).
Viruses
The most common virus in the oral cavity is herpes simplex, which gives rise to cold sores (see Chapter 8).
The matrix
In addition to providing an abundant food source for bacteria, plaque also collects other debris present in the mouth, which forms the matrix (in which the colonising bacteria feed and reproduce).
The following substances make up the matrix:
Proteins and carbohydrates (from food debris).
Dead cells (from oral tissues).
Red blood cells.
White blood cells.
Antigens (involved in the body’s immune response).
Enzymes and toxins (produced by bacteria).
Lactic acid.
Mineral salts.
Stages in plaque formation
Stage 1
Saliva plays a large part in the formation of plaque, and within a few minutes of cleaning, the tooth is covered in a sticky film made from salivary proteins, called the salivary pellicle. This provides receptors for early bacterial colonisers to attach to. Initially, these connections are weak and easily broken. These early aerobic bacteria are gram‐positive (stain violet when exposed to Gram’s stain in the laboratory), and feed on sugars from the diet.
Stage 2
Bacteria begin to produce substances that anchor them to the pellicle, thus increasing the adhesive properties of plaque. The matrix builds, with some matrix components made by bacteria themselves.
Stage 3
Bacteria begin to produce carbon dioxide and also excrete waste products. The environment becomes more attractive to gram‐negative species (which stain red when exposed to Gram’s stain). The plaque becomes thicker and denser as it matures, and contains diverse species that have a potential to cause disease. Mushroom‐shaped ‘clouds’ of matrix form with channels running between them to facilitate the movement of nutrients and waste products (Figure 2.3).
Stage 4
As the biofilm thickens, some bacteria start to die or break off to form new colonies. Bacteria within the colony reproduce to replace those that have broken away or died, and the cycle continues.
Figure 2.3 Mature plaque (scanning electron microscope).
Source: Dr Rachel Sammons. Reproduced with permission of Institute of Clinical Sciences, College of Medical & Dental Sciences, The University of Birmingham.
Local risk factors in the retention of plaque
The importance