1. Pellicle and plaque

3. 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

4. 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

5. 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)

6. 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

8. 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)

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

10. 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

12. - 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

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

14. The Composition of plaque fluid

15. Note:
Plaque fluid is supersaturated with ions. Certain substances in saliva (probably acidic proteins) inhibit precipitation

16. 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

17. 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.

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

19. The entry of bacteria into plaque
Factors causing clumping or agglutination of bacteria:
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

20. Summary of findings
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)

21. Summary for plaque formation
- pH Ca Bacterial enzyme
ppt of some salivary proteins
Plaque
Agglutinating glycoprotein adsorb onto tooth surface and agglutinate bacteria specially in prescnce of Ca2+

23. 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

24. 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 1:6 & 1:3 equally
reduce permeability of plaque
sucrase
dextran

25. Levans: Sucrose levans + glucose Fairly soluble.
Linked in 2:6 position.
Rapidly metabolized by plaque enzyme.
Extra cellular
levan
sucrase

26. 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

27. 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

30. Factors involved in the rise of pH:
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

31. 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 +

32. 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

33. 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