Pellicle and plaque

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Pellicle and plaque
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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

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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

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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)

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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

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Composition of Plaque
Plaque
B- Bacteria
A- Matrix

• 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)

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• Water soluble fraction
• 1/3 of dry weight. Consist of
• proteins,
• peptides,
• free amino acids,
• sugars and
• polysaccharides (mainly glucose derivatives)

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• Water 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 glyco-proteins
  (total 13-17)
• 10 mineral matter mainly calcium, phosphate
  and fluoride. Differs according to position and
  type of tooth

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• - 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

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• Early plaque (specially in the gingival area)
  contains some epithelial cell which lyses and
  provide another source of protein for bacteria.

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The Composition of plaque fluid
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• Note
• Plaque fluid is supersaturated with ions.
  Certain substances in saliva (probably acidic
  proteins) inhibit precipitation

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Hypotheses on the formation of plaque matrix

• 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

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• Chemical changes in salivary proteins
• Bacterial enzymes remove sugars from
  salivary glyco protein decrease solubility
  ppt.
• Effect of calcium ions
• Increase Ca in saliva ppt of protein
  and agglutination of bacteria.

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• Possible bacterial contribution to plaque matrix
• At least part of matrix comes from bacteria
  (unproven)

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The entry of bacteria into plaque

• Factors causing clumping or agglutination of
  bacteria
• Reduction of pH to lt 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

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Summary of findings

1. A glycoprotein in saliva has agglutination
   properties readily adsorbs on to apatite.
2. This favours adhesion of bacteria to teeth
   surface
3. It acts as bridges between the organisms
4. Calcium ions enhance the effect
5. Only certain organisms react with agglutinating
   factor (depend on cell wall composition)

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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

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Bacteria of Plaque

• Mostly acid producing- some proteolytic (over
  cavities)
• Young plaque (1-2 days old)
• 70 Gram ve cocci
• 20 rods
• Old plaque after 2 days proportion of cocci
  rods decrease to 50 by day 7 the rest are
  filamentous organisms

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Poly saccharide synthesis by plaque bacteria

• Dextrans or glucans
• Bulky gelatinous mass outside bacterial
  cells formed from sucrose
• Sucrose dextran fructose
• could be 10 of dry wt of plaque,
  insoluble,
• is metabolized by enzyme in plaque
• Link is 16 13 equally
• reduce permeability of plaque

sucrase
dextran
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• Levans
• Sucrose levans glucose
• Fairly soluble.
• Linked in 26 position.
• Rapidly metabolized by plaque enzyme.
• Extra cellular

levan
sucrase
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• Intra cellular 14 glucans
• - Formed by some bacteria (filamentous)
• - Formed from a variety of sugars (e.g. glu,
  maltose sucrose)
• - Broken down between meals

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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

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Factors involved in the rise of pH

1. Outward diffusion of lactic acid produced from
   glycolysis of glucose
2. Conversion of lactic acid into less ionized
   acetic and propionic acids
3. 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. (gt.5) the effect is masked by
   increased acid production

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• Alkali production by plaque
• NH2 group of urea is used to synthesize a.a.
  which are deaminated to release NH3
• A.A amines
• CO2

decarboxylation
at pH 5 Increased buffering capacity

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Factors in plaque which influence its caries
producing power

• 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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• 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