CURRENT CONCEPTS OF CARIES ETIOLGY--its causes
Dental caries is a multi factorial disease in which there is an interplay of three primary factors
1. Host - (tooth)
2. Agent - (Micro organisms)
3. Substrate (-Carbohydrates in diet)
• In addition a fourth factor time must be considered in the etiology of dental caries. When these three essential factors for dental caries exist in an individual for a considerable time, then dental caries may develop.
• The tooth is the target tissue that is destroyed in the dental caries process.
• The microorganisms are the agent that produces and secretes the chemical substances (organic substances, chelating agent and proteolytic enzymes) that cause the destruction of the inorganic components and the subsequent breakdown of the organic content of enamel and dentin.
• The local substrate provides nutritional and energy requirement for the oral microflora, there by permitting them to colonize, grow and metabolize on selective surfaces of the teeth.
I HOST
In discussing the caries tetrad, the host is an essential element.
Host factors include
a) tooth
b) salivary factors
c) habits
d) group susceptibility
e) age
f) muscular activity
g) Environment.
a) Tooth --- tooth itself is the primary host factor, but its composition morphologic characteristics and locations influence caries process.
1) Composition
• The structure and composition of teeth influence the initiation and rate of a progression of carious lesion which determines its caries susceptibility or caries immunity.
• Caries susceptibility of a tooth is inversely proportional to its fluorine, calcium and tin contents. Surface enamel is more highly mineralized and tends to accumulate greater quantities of fluoride, zinc, lead and iron than the underlying enamel. This explains why surface enamel is more resistant to caries than subsurface.
2)Morphologic Charecteristics :
The only morphologic feature which might predispose to the development of caries is the presence of deep, narrow occlusal fissures or buccal or lingual pits. Such fissures tend to trap food, bacteria and debris and since defects are especially common in the base of fissures, caries may develop rapidly in these area.
• The most susceptible permanent teeth are the mandibular first molars, closely followed by the maxillary first molars & mandibular & maxillary 2nd molar.
3) Position:
• Teeth which are malaligned, out of position, rotated or otherwise not normally situated may be difficult to clean and tend to favour accumulation of food and debris.
b) Saliva factor
pH :
Higher alkaline saliva predisposes to less decay activity The pH at which any particular saliva ceases to be saturated with Ca & PO4 is referred to as critical pH (5.5). Below this value, the inorganic material of the tooth may dissolve. With increasing concentration of H2 ions in the plaque, more phosphate ions will leave the solid apatite phase.
Quantity of and Composition of Saliva
• Caries susceptibility is usually inversely proportional to the salivary phosphate content. At neutral pH saliva is super saturated with Ca++ & PO4++ ions with respect to enamel apatite which not only prevents enamel from dissolving, but even tend to precipitate apatite in the surface enamel of carious lesions. The PO4 ions provides a significant buffering capacity at resting pH and early stages of acidic change.
• Also the higher organic content in the saliva generally indicates more stable plaque formation.
Quantity of saliva :
• The quantity of saliva secreted in a given period of time may influence caries incidence. This is especially evident in case of salivary gland aplasia and xerostomia in which salivary flow may be entirely lacking, resulting in rampant dental caries.
• Mild increase or decrease in flow may be of little significance; total or near – total reduction in salivary flow adversely affect dental caries in an obvious manner.
• A restriction in salivary flow leads to exacerbation of dental caries, as the removal of bacteria and food debris from the mouth are two important functions of saliva with respect to caries.
Viscocity :
• Serous saliva (low viscosity ) predisposes to more self cleansability than mucous (high viscosity) saliva. Higher quantities of saliva flowing into oral cavity predisposes to less decay activity.
Antibacterial & elements (Lyzozyme, salivary peroxidase)
Although these are usually found in saliva, their anticariogenicity depends on their nature, concentration and amounts.
c. Habits
Certain host habits will enhance caries activity.
e.g. poor eating habits such as desserts and snacks
bruxism
Other habits such as disciplined oral hygiene and proper dietary habits
ie. no snack between meals discourages caries activity.
d) Group susceptibility
Females are more susceptible to decay than males because teeth erupt earlier in females.
e) Age :
Age of the host is significant in caries process as decay activity is highest between ages of 14 and 20 years.
A decline in the decay rate after age 20 may be due to an enhanced consciousness about proper diet and oral hygiene.
f) Muscular activity
Host musculature ie. activities of the tongue, cheeks, lips and muscles of the face will create and guide the self cleansing activities with in the oral cavity.
g) Host’s environment :
Host environment is the final influencing factor. The phosphate content of the food and the fluoride content of water, will definitely diminish the caries activity.
II MICRO ORGANISMS :
• The second part of caries tetrad consists of the microorganisms which are brought into contact with the tooth surface via a bacterial plaque. Plaque is formed primarily of micro organisms.
• Bacteriologic studies in recent years have helped to clarify the role of various organisms in the etiology of dental caries. Specific micro organisms as well as combination of organisms including streptococcus mutants, lactobacillus, actinomyces species & others have been involved in the caries process.
The localization of micro organisms related to caries :
Type of caries Micro organisms
a. Pit & fissure S.mutans
Lactobacillus species
Actinomyces species
b. Smooth surface S. mutans
S.salivaris
c.Root surface A.viscosus
A.naeslundi
S.mutans
S.Sanguis
d. Deep dentinal caries Lactobacilli species
Actinomyces species
The plaque adheres to the tooth structure with a sticky polysaccharide carbohydrate called dextran. Streptococcus mutans is thought to play a major role in the adhesion (production of dextran) and the production of certain chemicals necessary for tooth cavitation.
III SUBSTRATE - (Carbohydrates in the diet)
The cariogenicity of a dietary carbohydrate varies with the
a) frequency of ingestion
b) physical form
c) chemical composition
d) route of administration
e) presence of other food constituents.
a). Frequency of ingestion :
• The most significant factor leading to an increased risk of caries is the frequency of consumption of fermentable carbohydrate.It is the frequency of eating fermentable carbohydrate which cause caries rather than the total quantity of fermentable carbohydrate consumed.
b) Physical form :
• Sticky carbohydrates are more caries producing than those consumed as liquids. Carbohydrates which are rapidly cleared from the oral cavity by saliva and swallowing are less prone to caries than those which are slowly cleared.
• Harden and more fibrous food material requires increased masticatory activity and consequently greater ability for cleaning the teeth surfaces of any stagnating debris.
c).Chemical composition
The carbohydrate content of the diet is one of the most important factors in the dental caries process. Sucrose is the most detrimental, followed by fructose, lactose, galactose & glucose.
• Increasing the fluoride content of a diet will decrease caries activity by decreasing the solubility of tooth structure, decreasing the surface energy of tooth surface, thereby decreasing the plaque adhesion and by interfering in the metabolism of carbohydrates by the microorganisms.
• Increasing the phosphate content in the diet will decrease the solubility product of the tooth substance in the surrounding electrolyte, there by discouraging inorganic tooth substance solubility.
d). Route of administration :
Glucose or sucrose fed entirely by stomach tube or intravenously, does not contribute to decay as they are unavailable for microbial break down.
e).Presence of other food constituents
Meals high in fat protein or salt reduce the oral retentiveness of carbohydrates. Refined, pure carbohydrates are more caries producing than crude carbohydrates complexed with other food elements capable of reducing enamel solubility or possessing antimicrobial properties.
Thus the etiology of dental caries involves an interplay between oral bacteria , local carbohydrates and the tooth surface which produces organic acids leading to demineralization of the tooth surface resulting in caries.
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