Transcript composition changes with age of plaque

Pellicle and
plaque
Pellicle
A layer directly on top of enamel 1-3μm
thick (could reach 10 μm), free from
bacteria, and is not removed by a tooth
brush, but can be removed by a
“prophylaxis”, or scale and polish, with
abrasive paste
Plaque
Deposit which forms on the enamel
surface if the teeth are not cleaned.
 It is removed from the smooth surface
(but not always from fissures) by tooth
brushing.
 It is composed of a matrix and
bacteria, and is the source of acids
dissolving the teeth in caries, as well as
the substances which inflame the
gingivae leading to periodontal disease

Composition of Pellicle
Protein high in glu + ala (+gly sometimes)
and low in S-containing a.a.
 Carbohydrates
 The protein resembles proteins from
submandibular saliva, precipitated by
acetic acid
 Old pellicle may contain muramic acid (a
constituent of bacterial cell wall)

Mode of formation

Selective adsorption of certain salivary
proteins by the apatite of enamel
(source not clear yet), but acidic
proteins are preferred for their ability to
bind to apatite surface
Composition of Plaque
Plaque
A- Matrix
B- Bacteria
• Composition vary from different areas
• Two fractions-Water sol. and Water
insol.
• 80-85% water (mean 82% of wet weight,
50% in cells & 32% in matrix)
 Water
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soluble fraction:
1/3 of dry weight. Consist of:
proteins,
peptides,
free amino acids,
sugars and
polysaccharides (mainly glucose
derivatives)
 Water
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insoluble fractions:
70% of dry weight consist of insoluble
matrix and most of the bacterial content
Contains:
10-14% lipids, 10% minerals
40% protein of high MW
11% carbohydrates + some in glycoproteins (total 13-17%)
10% mineral matter: mainly calcium,
phosphate and fluoride. Differs according to
position and type of tooth
- composition changes with age of
plaque:
• Decrease Ca and Pi between day 1-2,
then increase to day 4
• Concentration of carbohydrates
follows a reverse pattern
•
Early plaque (specially in the gingival
area) contains some epithelial cell
which lyses and provide another
source of protein for bacteria.
The Composition of plaque fluid
 Note:
Plaque fluid is supersaturated with
ions. Certain substances in saliva
(probably acidic proteins) inhibit
precipitation
Hypotheses on the formation of
plaque matrix
1.
2.
Iso electric precipitation of salivary
proteins:
increased pH ppt of salivary
proteins
Spontaneous precipitation:
Surface action by existing plaque
denaturation of some salivary
proteins & ppt
3.
Chemical changes in salivary
proteins:
Bacterial enzymes remove sugars
from salivary glyco protein
decrease solubility
ppt.
4.
Effect of calcium ions:
Increase Ca in saliva
ppt of protein
and agglutination of bacteria.
5.
Possible bacterial contribution to
plaque matrix:
At least part of matrix comes from
bacteria (unproven)
The entry of bacteria into plaque

Factors causing clumping or
agglutination of bacteria:
1.
Reduction of pH to < 5.5.
Divalent ions e.g. Ca2+ &Mg2+
Certain protein constituents of saliva &
plaque
All lead to reduction of negative charge
(i.e. mutual repulsion) of the bacteria
2.
3.

Summary of findings
1.
2.
3.
4.
5.
A glycoprotein in saliva has agglutination
properties & readily adsorbs on to apatite.
This favours adhesion of bacteria to teeth
surface
It acts as bridges between the organisms
Calcium ions enhance the effect
Only certain organisms react with
agglutinating factor (depend on cell wall
composition)
Summary for plaque formation
- pH
- Ca2+
- Bacterial enzyme
ppt of some salivary proteins
Plaque
Agglutinating glycoprotein adsorb onto tooth
surface and agglutinate bacteria specially in
prescnce of Ca2+
Bacteria of Plaque:
Mostly acid producing- some
proteolytic (over cavities)
 Young plaque (1-2 days old):
70% Gram +ve cocci +
20% rods
2. Old plaque: after 2 days proportion of
cocci & rods decrease to 50% by day
7 the rest are filamentous organisms
Poly saccharide synthesis by
plaque bacteria
1.
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Dextrans or glucans
Bulky gelatinous mass outside
bacterial cells formed from sucrose
dextran
Sucrose sucrase dextran + fructose
could be ≈ 10% of dry wt of plaque,
insoluble,
is metabolized by enzyme in plaque
Link is 1:6 & 1:3 equally
reduce permeability of plaque
2.
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Levans:
Sucrose
sucrase
levans + glucose
Fairly soluble.
Linked in 2:6 position.
Rapidly metabolized by plaque enzyme.
Extra cellular
3.
Intra cellular 1:4 glucans:
- Formed by some bacteria (filamentous)
- Formed from a variety of sugars (e.g. glu,
maltose & sucrose)
- Broken down between meals
Properties of plaque:
Insoluble in most reagents
 Has low permeability
 Firmly held on the tooth surface
 Shows a decrease in pH after the
ingestion of glucose i.e. acid producing

Factors involved in the rise of pH:
1.
2.
3.
Outward diffusion of lactic acid produced from
glycolysis of glucose
Conversion of lactic acid into less ionized acetic
and propionic acids
The pH rise factor in saliva (sialin) which is a
basic peptide containing Arg. It accelerate
glucose uptake by salivary organisms, increase
acid production & the formation of CO2 & base.
The effect is obvious at low sugar conc. At high
sugar conc. (>.5%) the effect is masked by
increased acid production
4.
Alkali production by plaque
A.
NH2 group of urea is used to synthesize
a.a. which are deaminated to release NH3
A.A decarboxylation
amines
at pH 5
B.
Increased buffering
capacity
+
CO2
Factors in plaque which influence its
caries producing power
1.
2.
3.
4.
The type of bacteria: Plaque from caries – free
subjects contain less lactobacillus acidophilus
and streptococcus mutans than plaque from
caries - active subjects
The fasting plaque pH is higher in caries – free
subjects
Acid production after ingesting sugar is greater
in caries - active subjects
The plaque calcium and phosphate were
inversely related to total caries experience
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1.
2.
Note:
Fasting pH is higher in caries –
resistant than in caries – prone areas
within the same mouth
The calcium and phosphate
concentrations are higher in caries –
free areas