This is a localized loss of dental hard tissue that may be so small as pits or fissures in the enamel layer or may be large enough to form a cavity that reach the dentine layer or even the dental pulp .Dental caries occur in some individuals more than in others .
This due to 4 factors :
1- Tooth structure and general constitution :
Good tooth structure having good content of calcium and also good general nutrition with enough calcium causing high concentration of calcium in saliva . All these factors maintain good calcified hard tooth .
3- Diet : Cariogenic diet is the diet that enhance production of dental caries . Example are diet containing high concentration of fermentable sugars especially sucrose .Oral bacteria especially Strept.mutans ferment these sugars with production of a large amount of acid that may start demineralization of tooth enamel .
4- Cariogenic Bacteria : Strept.mutans is the most important by their action on sucrose to produce acids and the sticky gelatinous substance Dextran . Other viridan Strept. as Sangius , Salivarius , Mitior ,& Milleri . Actinomyces viscosus causes caries in the deep parts of tooth surface . Lactobacilli , e.g , L.acidophilus . These are anaerobic and microaerophilic organisms . They are acidogenic producing large amount of lactic acid from sugar fermentation . They are also aciduric organism that live and grow in low pH . Lactobacilli have no direct role in dental caries , although if present in large number indicate ability to have dental caries .
There are three theories explaining how dental caries start :
1- Acidogenic theory :
Fermentation of sugars by some oral bacteria especially Strept.mutans results in production of lactic acid and other organic acid e.g , acetic acid . These organisms are called acidogenic bacteria . These acids cause lowering the oral pH to below 5.6 and result in decalcification or removal of calcium from tooth enamel then dissolution of the organic matrix of the tooth (Hydroxyapatite) with production of a cavity which is at first very small pits or fissure then enlarge in size .This process is morde evident when the organism lies near the tooth as in tooth plaque .
The proteolytic enzymes of bacteria in oral cavity and in dental plaque attack the organic matter of the dental enamel ( hydroxyappatite ) so the tooth becomes more brittle and then crumbles down .
3- Proteolytic Chelating theory :
This theory suggest that caries start by proteolytic activity of the organisms acting on the organic matrix of the enamel liberating chelating agents that facilitate removal of calcium .
