acidogenic bacteria – Bacteria that have the capability of producing acids through their metabolic pathways. In reference to dental caries, the main acidogenic or acid-producing species of bacteria is Streptococcus mutans. Through the process of glycolysis, acidogenic bacteria break down mono- and disaccharides into lactic acid. Lactic acid diffuses through the plaque biofilm to reach the enamel surface, where it may cause demineralisation, depending upon other factors such as availability of buffering agents and the saturation with calcium.
buffering capacity – Saliva and the fluid in dental plaque possess the ability to buffer. Buffering adjusts the pH of any solution such as saliva or plaque fluid, and can resist changes in pH. Buffering capacity is the degree of buffering that can be brought about.
cariogenic – The ability to cause dental caries. A cariogenic diet contains sugars. Some bacteria in dental plaque (S. mutans) are cariogenic. The mere presence of cariogenic sugars or cariogenic bacteria is not enough to cause the initiation of the caries process. Many other factors play a role, and taken together they may or may not contribute to the process that leads to dental caries.
clearance time – The interval of time necessary for any substance to be cleared from the mouth by the process of salivary secretion and saliva flow. Factors that affect clearance time, other than saliva flow rate, include the form and ‘stickiness’ of the item to be cleared and the saliva-stimulating potential of the item. A glucose solution will be cleared much faster than sticky caramel.
critical pH – The pH at and below which demineralisation of enamel occurs. The research of Stephan and Miller originally demonstrated this critical pH to be approximately 5.5 (see Stephan’s curve). Due to other chemical factors, especially the saturation of the immediate environment of the enamel surface with respect to calcium and phosphate, the presence of buffering agents, and the fluoride availability, the critical pH may vary and is considered to be between 4.5 and 5.5.
demineralisation – The chemical process by which minerals (mainly calcium) are removed from the dental hard tissues – enamel, dentine, and cementum. The chemical process occurs through dissolution by acids or by chelation, and the rate of demineralisation will vary due to the degree of supersaturation of the immediate environment of the tooth and the presence of fluoride. In optimal circumstances, the minerals may be replaced through the process of remineralisation.
dental plaque – An organised community of many different microorganisms that forms itself into a biofilm and is found on the surface of the tongue and all hard surfaces in the oral cavity. Dental plaque is present in all people and can vary from being comprised of totally healthy microorganisms (commensals) to being very harmful (pathogenic), predisposing the patient to dental caries or periodontal diseases. Note: Dental plaque is not food debris, nor does it contain food debris. Dental plaque can only be completely removed by mechanical means such as toothbrushing or prophylaxis. Food debris can be removed by rinsing.
fermentable carbohydrates – Nearly all carbohydrates in the diet are can be broken down and metabolised by microorganisms. Mono- and disaccharides (sugars such as glucose and sucrose) are most readily metabolised and are therefore the most cariogenic, as they are metabolised to produce lactic acid.
remineralisation – The chemical process by which minerals (mainly calcium) are replaced into the substance of the dental hard tissues - enamel, dentine and cementum. The process requires an ideal environment that includes supersaturation with calcium and phosphate ions, and adequate buffering. In the presence of fluoride, remineralisation is enhanced.
‘Stephan Curve’ – The term refers to a graph published by Stephan and Miller in the 1940s. The graph reflected Stephan and Miller’s research demonstrating the fall in pH in the mouth following a glucose rinse. They demonstrated that a pH of 5.5 or less may result in demineralisation, and that the pH level may remain below this ‘critical level’ for approximately 20 minutes; with pH returning to normal or resting levels in about 30 to 60 minutes.