Download Factors determining the incidence of caries Micro organisms: Acid

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.
2.
3.
4.
5.
6.
The enamel becomes decalcified
A small white spot appear
Discoloration becomes pronounced
The tooth surface softens and decay
penetrates through the enamel into the
dentine
Caries spreads laterally and in depth
Cavitation occurs
7.
8.
The lesion deepens, and pulp
becomes affected, first reacting to
stimuli (e.g.sweets, temp.), then
damaged and dead
Bacteria travels down the root canal,
out through the apex causing
abscesses
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Factors determining the incidence
of caries
1.
2.
a.
b.
Micro organisms: Acid producing
bacteria, especially if they produce
extracellular polysaccharides, will
increase risk
Host factors:
Decreased saliva secretion increase
incidence
Buffering power of saliva to raise pH
decrease incidence
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c.
d.
The morphology of the teeth: well
spaced teeth decrease incidence,
while fissures & pits increase it.
The composition of the teeth: certain
trace elements decrease incidence
(e.g. F, Mb and B), while others (e.g.
Cu & Mn) increase it
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3.
4.
Time: frequency of consumption of
carbohydrates, and length of time in
the mouth are related to incidence.
Good oral hygiene can counter act
this
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.
2.
3.
4.
5.
Substances that decrease solubility of
calcium phosphate
More phytate &/or calcium
Antibacterial substances
Substances that inhibit aggregation of
bacteria :- decrease plaque formation
Absence of free sugar (most
important)
Theories for the cause of caries
1.
2.
The proteolytic theory: presence of
proteolytic bacteria lead to hydrolysis
of protein (collagen) leading to
progression of caries
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.
2.
3.
4.
In thick plaque, pH below critical point
pH in carious cavities is lower
Caries intensity correlates with acid
production and count of acid producing
bacteria
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


1.
2.
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
Actinomyces viscosus
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
1.
2.
Diet has two types of effects
Dietary effects: local effects contributing
to substrates for bacterial growth & direct
interaction with teeth
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.
2.
Eskimos, whose diet was formerly
almost exclusively of fish, meat and
fat, had a low incidence of dental
caries while on their primitive diet
The prevalence of dental caries in
different countries parallels the extent
of sugar consumption in those
countries
3.
4.
In many areas of Europe where sucrose intake
was severely restricted during World War II,
caries incidence in children decreased
dramatically
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 cariesfree or else have a very low caries prevalence
5.
6.
Amongst present-day children of preschool age there is a marked
correlation between caries experience
and the extent of eating between main
meals
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.
II.
Vitamin D could lead to incidence of
caries
Some trace elements
caries &
some
it



1.
2.
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
Effect morphology of teeth (rats)
Effect crystal structure & solubility
Caries resistance
Many 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
