Dental Caries

Definition

Caries is a disease resulting in the destruction of the hard structure of the teeth

Stages in the development of caries

1. The enamel becomes decalcified2. A small white spot appear3. Discoloration becomes pronounced4. The tooth surface softens and decay

penetrates through the enamel into the dentine

5. Caries spreads laterally and in depth6. Cavitation occurs

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7. The lesion deepens, and pulp becomes affected, first reacting to stimuli (e.g.sweets, temp.), then damaged and dead

8. Bacteria travels down the root canal, out through the apex causing abscesses

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Factors determining the incidence of caries

1. Micro organisms: Acid producing bacteria, especially if they produce extracellular polysaccharides, will increase risk

2. Host factors:a. Decreased saliva secretion increase

incidenceb. Buffering power of saliva to raise pH

decrease incidence

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c. The morphology of the teeth: well spaced teeth decrease incidence, while fissures & pits increase it.

d. The composition of the teeth: certain trace elements decrease incidence (e.g. F, Mb and B), while others (e.g. Cu & Mn) increase it

3. Time: frequency of consumption of carbohydrates, and length of time in the mouth are related to incidence. Good oral hygiene can counter act this

4. Substrates for acid production provided in diet

Caries as a disease of civilization

Evidence links caries to civilization This is due mainly to changes in dietary

habits, e.g. increased carbohydrates intake by Eskimos and eating refined instead of natural forms of carbohydrates by African tribes

Factors in unrefined food lead to decreased incidence of caries

1. Substances that decrease solubility of calcium phosphate

2. More phytate &/or calcium

3. Antibacterial substances

4. Substances that inhibit aggregation of bacteria :- decrease plaque formation

5. Absence of free sugar (most important)

Theories for the cause of caries

1. The proteolytic theory: presence of proteolytic bacteria lead to hydrolysis of protein (collagen) leading to progression of caries

2. The phospho protein theory: phospho protein phosphatse in plaque acts on phosphoproteins in enamel, but this is not tested in humans

3. The proteolysis-chelation theory: some products of bacterial action on enamel, dentine, saliva & food constituents form complexes with calcium from plaque causing a decrease in the concentration required to maintain saturation, and leading to more solubility

4. The acid theory of caries: Bacteria in saliva + carbohydrate (sugar) lead to acid production dissolving appetite

This the most likely theory

Evidence

1. In thick plaque, pH below critical point

2. pH in carious cavities is lower

3. Caries intensity correlates with acid production and count of acid producing bacteria

4. In germ-free rats, caries was produced by inoculation with acid producing organisms

The importance of diffusion:

Since caries is a penetrating lesion, the inward diffusion of the acid must play an important role in its development

Evidence shows that the concentration of unionized lactic acid outside the enamel is more important than low pH

Unionized acid diffuses more easily inward, becomes diluted and ionized, allowing reaction with apatite to form free calcium and phosphate

These ions diffuse outwards, and may precipitate as CaHPO4, explaining the apparently intact outer layer of enamel over the cavity

Therefore, the critical pH may not only be the level at which the environment of enamel becomes unsaturated with apatite, but it also maybe the pH at which sufficient conc. Of unionized lactic acid exists to ensure inward diffusion

The bacteria responsible for caries

Two species were isolated from carious mouths and were suggested as causal organisms:

Streptococcus mutants, and Lactobacillus acidophilus or odontolyticus Other filamentous bacteria producing lactic acid

were isolated from caries lesions of the root surfaces. These bacteria, the genus Actinomyces are of two species

1. Actinomyces viscosus2. Actinomyces naeslundi , both are found

predominantly in the gingival region and cause; inaddition; severe periodontal disease

Relationship between lactobacilli and streptococcus mutans

streptococcus mutans alone can produce caries, but the combination is more effective

streptococcus mutans stop acid production at pH 4.3, but lactobacilli continue to below pH 4

Therefore, the joint effect is more intense Lactobacilli seems to be involved in the

initial attack, and is found at tha front of the lesion

Local effects in caries Caries is localized, indicating the role of

local conditions This might be partly due to differences in

composition of plaque (bacterial and matrix)

Evidence also suggests that different types of bacteria cause caries at different sites (e.g. tetracycline reduces smooth surface caries, to a greater extent than pit and fissure caries

The role of diet in caries

Diet has two types of effects

1. Dietary effects: local effects contributing to substrates for bacterial growth & direct interaction with teeth

2. Nutritional effects: effects of assimilated food stuff

1.Dietary effects

There is evidence relating consumption of carbohydrates (particularly sucrose) to caries

A- Indirect Evidence for importance of dietary carbohydrates in caries

1. Eskimos, whose diet was formerly almost exclusively of fish, meat and fat, had a low incidence of dental caries while on their primitive diet

2. The prevalence of dental caries in different countries parallels the extent of sugar consumption in those countries

3. In many areas of Europe where sucrose intake was severely restricted during World War II, caries incidence in children decreased dramatically

4. The study of human biochemical genetics has also provided evidence that sucrose plays a special role in caries. A rare enzyme deficiency involving a lack of fructose-I-phosphate aldolase results in hereditary fructose intolerance. Foods containing fructose cause nausea, vomiting, tremors, and convulsions in affected individuals. As sucrose is a glucose-fructose disaccharide, it also produces these effects, and is avoided by such pateints, who are often found to be caries-free or else have a very low caries prevalence

5. Amongst present-day children of pre-school age there is a marked correlation between caries experience and the extent of eating between main meals

6. Rampant caries, in which the anterior teeth may be almost completely dissolved away, is found in babies who are given comforters filled with syrup or honey to suck for prolonged periods of time

B- Populations on controlled diets

a) The caries score (decayed, missing and filled teeth, DMFT) was followed over years for different groups given carbohydrates sources of increasing degree of stickiness compared to a control group given a diet low in carbohydrates, with the calories supplied by sugar normally , replaced by margarine

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b) A study conducted at an orphanage, indicated that refined carbohydrates increase the caries score. While resident, the children were given a diet that excluded refined carbohydrates , and had low caries score (DMFT), but this increased dramatically after they left and changed their diet to include sugar and refined carbohydrates

Interaction between carbohydrates & dental plaque

Epidemiological evidence & experimental studies indicated the following:

1. Carbohydrate free diet thin plaque

2. Presence of sucrose more plaque (gelatinous)

3. Sucrose is more cariogenic than glucose or fructose with respect to smooth surfaces

4. Extra cellular polysaccharides are produced by bacteria from sucrose this help in:

a) Adherence to smooth surface

b) Retain acid in close proximity to tooth surface

c) Shield against buffering by saliva

The above are less important in fissures

Other dietary effects Addition of Calcium sucrose phosphate

(CaSP) caries Acidic drink could dissolve enamel

caries incidence Fibrous food reduce plaque formation ,

therfore, caries Foods that saliva flow caries e.g.

salty foods Foods that pH & increase Ca content

caries e.g. cheese

2 -Nutritional effects

I. Vitamin D could lead to incidence of caries

II. Some trace elements caries & some it

Minerals associated with increased caries include: Copper, magnesium, Se, zinc, vanadium & lead

Minerals associated with decreased caries include :

F, Sr, B, K, nickel, Mo, Li Mechanism: suggestion

1. Effect morphology of teeth (rats)

2. Effect crystal structure & solubility

Caries resistanceMany factors not strong by themselves

combine to caries e.g. Highly buffered saliva with high flow rate Ca, P, HCO3 in saliva High F/CO3 of enamel The most important factor is the type of

bacteria presence of antibodies to cariogenic

bacteria might help to caries also

Finally the morphology of teeth plays a role

Note:

Cause of caries differs from person to another

Remineralization

Carious lesions up to white spot stage can cease to develop and might disappear

Caries progresses by alternate demineralization, when pH falls, and partial remineralization when the pH rises

Saliva could remineralization, but F speeds process