In the oral cavity, bacteria are found in suspension in saliva or forming a gel-like film known as oral biofilm, or more commonly as bacterial plaque. 

Oral biofilm (bacterial plaque) is a structure that is comprised of 80-85% extracellular matrix containing a mixture of proteins, mineral salts, polysaccharides from food intake, bacteria, saliva and whose remaining 15-20% is made up of colonising bacteria. Its formation in the oral cavity is continuous and it adheres to soft and hard oral surfaces (teeth, tongue and mucosa). It is the main aetiological agent in the development of caries and gum diseases, as well as of other oral conditions including bad breath. 

Dental Caries 

The World Health Organization considers dental caries to be "the world's third epidemic" after cardiovascular disease and cancer, because of its extension and frequency. It is the most common oral disease in human beings and the leading cause of destruction and/or loss of teeth. 

It is a multifactorial infectious disease that is characterised by the destruction of hard tissues of the teeth caused by acids produced by oral biofilm (bacterial plaque). Caries is often described as bacterial-induced enamel erosion. Sugary foods that remain in the mouth are metabolised by bacteria residing in oral biofilm. 

These bacteria feed on the sugar and produce acids that cause the pH in the oral cavity to drop, and that attack the mineral structure of the enamel. This acid attack is initially neutralised by the remineralising and buffering effects of saliva, but if this attack is repeated, saliva cannot reverse the imbalance and dental tissues therefore become demineralised. 

This destruction affects the enamel first and then the innermost parts of the tooth including the dentin, reaching the dental pulp if it progresses. 

Caries risk factors 

Four determining factors participate in caries development: 

• Host: Host predisposition due to hereditary, age-related and endocrine factors, tooth structure abnormalities (tooth morphology, texture, composition), pits and fissures on the tooth surface, saliva (quantity and quality), etc. 

• Specific microbiota: The oral cavity holds both protective and pathogenic bacteria. Caries develops in areas of the enamel surface where microbiota finds the right environment for their proliferation. The bacteria that are mainly responsible for this process are Streptococcus mutans, generally associated with initial caries development, and Lactobacillus acidofilus, responsible for metabolising sugars and producing acids that cause demineralisation. • Diet: Diets high in sugar accelerate bacterial activity. 

• Time: The longer the tooth exposure to acids caused by bacteria, the greater the risk is for caries. Having a history of tooth decay is highly associated with an increased caries occurrence. 

Treatments 

Caries must be treated for it to be stopped, but proper treatment will depend on the time in which it is detected. 

The first sign of caries is a white spot on enamel. In this first stage, the initial caries lesion can be detained if it is treated with fluoride compounds, as fluoride inhibits demineralisation and has a remineralising effect on tooth enamel, thereby strengthening teeth and making them less soluble in acids. 

If caries is not treated and continues to progress, it can end up making perforations in teeth, through which bacteria penetrate and continue to destroy the remaining, innermost dental structures. If it affects the dentin (the innermost layer that lies under the enamel) and without affecting the pulp, treatment will consist of removing diseased tissue and sealing (placing a filling). If the decay runs deeper, affecting the pulp, a root canal procedure will be performed, in which the tooth is devitalised to remove the pulp (nerve), affected tissue is cleaned, and then the tooth is reconstructed. In the most severe cases, if the infection not only affects the tooth but also the bone that supports the tooth, it is likely the tooth will be lost. 

Prevention 

Prevention of this disease is done by maintaining proper oral hygiene habits. The main method for removing oral biofilm is toothbrushing. Therefore, it is important to brush teeth after every meal using a correct brushing technique together with oral hygiene tools (toothbrush, interproximal brushes, dental floss and tape, etc.) adapted to the needs of each individual and whose design allows for maximum oral biofilm removal. Specific toothpastes and alcohol-free mouthrinses should also be used to achieve complete oral hygiene. And we must not forget that a balanced diet, without continuous intake of high sugar foods and drinks, is also important. 

It is equally important to visit the dentist on a regular basis, at least once a year, for a professional oral cleaning and check-up to detect any possible caries development. 

Therefore, it is very important that all oral healthcare professionals help to promote good oral health to prevent both dental caries and other oral diseases.