Dental Caries Etiology

• Cariology is a discipline that deals with the complex interplay between oral fluids and microbial deposits relative to changes in hard tooth tissues.
• Dental caries is a multi-factorial, transmissible, infectious oral disease.
• The disease is caused primarily by the complex interaction of cariogenic oral flora (biofilm) with fermentable dietary carbohydrates on the tooth surface over time.

Dental Caries Etiology

• Ecology is the science that studies the interaction between organisms and their environment.
• Ecosystem is a circumscribed area occupied by a biological community.
• The oral cavity has recognizable geographic limits and several habitats (pits & fissures, dorsum of tongue, mucosa, gingival sulcus...) that can harbor different microorganisms, providing them with food and shelter, thus making it a well-defined ecosystem.
• Ecological niche is the combination of food and shelter.
• The presence and absence of ecological niches within the oral cavity can account for the presence or absence of dental caries.

Contributing Factors

• Dental plaque, carbohydrates, host and time are contributing factors to dental caries.

Dental Plaque

• Dental plaque is an adherent deposit of bacteria and their products on tooth surfaces.
• The Mutans streptococci and lactobacilli are cariogenic for the following reasons:
  • They are able to produce acids rapidly from fermentable carbohydrates.
  • They live under acidic conditions.
  • They can adhere to the tooth surface because of their ability to synthesize sticky extracellular polysaccharides from dietary sugars.
  • These polysaccharides cause thickening of plaque, preventing saliva from neutralizing plaque acid.
• A clean enamel surface exposed to the oral environment, is covered with an organic film called the "pellicle" consisting of glycoprotein precipitated from saliva.
• The pellicle can attract specific types of bacteria to the tooth surface, namely streptococci due to its tenacious nature.
• Dental biofilm is a microbiological community in which bacteria adhere to the tooth surface and each other.
• The bacteria are embedded in a matrix of extracellular polysaccharides.

Dietary Carbohydrates

• Not all carbohydrates are equally cariogenic.
• Monosaccharides (glucose, fructose) are found in fruit and vegetables.
• Disaccharides (sucrose)are found in sugar cane and sugar beets and are the most cariogenic sugars.
• They have a low molecular weight (simple CAH)
• They are the most commonly used.
  • Synthesis of extracellular polysaccharide is more rapid from glucose, fructose, and lactose.
• Polysaccharides (starch) found in potatoes and rice are relatively harmless, because they are not completely digested in the mouth.

Oral Carbohydrate Clearance

• Carbohydrates concentration and the length of time they remain in the mouth during and after eating, are essential factors
• Foods are eliminated during and after mastication by the rinsing effect of saliva and the activities of the masticatory muscles, tongue and lips.
• Clearance time may be prolonged by retentive factors in the dentition (cavities, poor fillings, bridges and partial dentures) and/or by low salivary flow or viscous saliva.

Host Factors that affect Caries

• Surfaces of teeth that highly retain plaque are prone to decay (enamel pits and fissures), (smooth surface cervical to the contact area) , (the cervical margin of the tooth just coronal to the gingival margin), (exposed root surface due to gingival recession), (deficient or overhanging margins of restorations) and (tooth surfaces adjacent to dentures and bridges).
• Saliva and fluoride are factors of the tooth environment that can influence caries.
  • As saliva maintains the normal oral flora, it can contribute to protection through the following mechanisms:
    • Bacterial clearance: Salivary flow removes microorganisms that are not adherent to the oral surfaces.
    • Direct anti-bacterial activity: Salivary glands produce antimicrobial proteins that have a broad spectrum activity on microorganisms.
    • Buffering activity: Saliva has buffering capacity through its bicarbonate ion content, which reduces the potential for acid formation.
    • Remineralization capacity: Saliva is supersaturated with calcium and phosphate ions which provide for remineralization of enamel.
    • When salivary flow decreased, the food retention increases and the buffering action of saliva decreases.

Fluoride

• The remineralization capacity of saliva is enhanced in the presence of fluoride ions.
  • Enhance the precipitation of fluoroapatite from Ca and Phosphate ions in saliva.
  • Inhibits Glucosyltransferase Enzyme that can decrease bacterial adhesion (essential for glycolysis and formation of Extracellular polysaccharides)
  • F ions are directly toxic to Strept.Mutans.
  • F ions decrease the transportation of sucrose to bacterial cell.

Time

• The carious process consists of alternating periods of destruction and repair.
• Lesion arrest is the result of mechanical removal of plaque exposing the tooth to saliva for remineralization.
• Enamel, dentin and cementum are exposed to a constant supply of ions of both external (oral) or internal (pulp) origin leading to remineralization.