What is dental caries ?
Dental caries is a disease that cause demineralization of dental hard tissues by acids, produced by bacteria from acting on fermentable carbohydrates.
Important Features of dental caries
- Fermentation of carbohydrate to organic acids by micro-organisms in plaque on the tooth surface.
- Rapid acid formation, which lowers the pH at the enamel surface below the level (the critical pH) at which enamel will dissolve.
- When carbohydrate is no longer available to the plaque micro-organisms, the pH within plaque will rise due to the outward diffusion of acids and their metabolism and neutralization in plaque, so that remineralization of enamel can occur.
- Dental caries progresses only when demineralization is greater than remineralization. The realization that demineralization and remineralization is an equilibrium is key to understanding the dynamics of the carious lesion and its prevention.
How Dental caries Progress?
- An early carious lesion of the enamel is subsurface; that is, most of the mineral loss occurs beneath a relatively intact enamel surface.
- This contrasts strongly with the histological appearance of enamel after a clean tooth surface has been exposed to acid, where the surface is etched and there is no subsurface lesion. This dissolution of the surface of enamel, or etching, is a feature of enamel erosion caused, among other things, by dietary acids.
- The explanation for the intact surface layer in enamel caries seems to lie in diffusion dynamics: the layer of dental plaque on the tooth surface acting as a partial barrier to diffusion. Further erosion occurs at much lower pHs than caries.
- Dental plaque forms on uncleaned tooth surfaces and is readily apparent if toothbrushing is stopped for 2-3 days. Contrary to popular opinion, plaque does not consist of food debris, but comprises 70% micro-organismsabout 100 million organisms per milligram of plaque.
- Diet influences the composition of the plaque flora considerably, with mutans streptococci much more numerous when the diet is rich in sugar and other carbohydrates, and these organisms are particularly good at metabolizing sugars to acids.
- Within 2-3 min of eating sugar or rinsing with a sugar solution, plaque pH falls from an average of about 6.8 to near pH 5, taking about 40 min to return to its original value. Below pH 5.5 demineralization of the enamel occurs, this is known as the critical pH.
- The clinical appearance of these early lesions is now well recognized. They appear as a white area that coincides with the distribution of plaque. This might be around the gingival margin, or between the teeth
- If the process of dental caries continues, support for the surface layer will become so weak that it will crumble like an eggshell, creating a cavity.
- Once a cavity is formed, the process of dental caries continues in a more sheltered environment and the protein matrix of enamel and then dentine is removed by proteolytic enzymes produced by plaque organisms.
Can Dental Caries be Healed?
- The ability of early carious lesions ('precavitation carious lesions') to remineralize is now well understood; periods of demineralization are interspersed with periods of remineralization, and the outcome health or diseaseis the result of a push in one direction or the other on this dynamic equilibrium.
- The shorter the time during which plaque-covered teeth are exposed to acid attack and the longer the time remineralization can occur, the greater is the opportunity for a carious lesion to heal.
- Satisfactory healing of the carious lesion can only occur if the surface layer is unbroken, and this is why the 'precavitation'stage in the process of dental caries is so relevant to preventive dentistry.
- Once the surface has been broken and a cavity has formed, it is usually necessary to restore the tooth surface with a filling. The carious process is driven by the plaque on the surface and therefore it is possible to arrest the caries by effective removal of plaque even after cavitation has occurred. However, the lost tissue cannot be replaced.
How Do dental caries First occur ?
- The first stage of dental caries to be visible is the 'white spot' precavitation lesion stage.
- This can occur within a few weeks if conditions are favourable to its development. In the general population, though, it commonly takes 2-4 years for caries to progress through enamel into dentine at approximal sites.
Natural Defense Against dental caries ?
- The most important of the natural defences against dental caries is saliva. If salivary flow is impaired, dental caries can progress very rapidly. Saliva has many functions.
- The presence of food in the mouth is a powerful stimulus to salivation, with strong-tasting acid foods being the best stimulants. Saliva not only physically removes dietary substrates and acids produced by plaque from the mouth,but it has a most important role in buffering the pH in saliva and within plaque.
- Fast-flowing saliva is alkaline reaching pH values of 7.5-8.0and is vitally important in raising the pH of dental plaque previously lowered by exposure to sugar and carbohydrates.
- Because teeth consist largely of calcium and phosphate, the concentration of calcium and phosphate in saliva and plaque is thought to be important in determining the progression or regression of caries.
- well known that fluoride aids the remineralization process. Although it may seem sensible to try to maximize the availability of calcium, phosphate, and fluoride in the environs of the tooth, in practice, fluoride is much the most important.
