1. Dental plaque (bacteria biofilm)
Dr.hussein al dabbagh

2. The dental professional comes into contact with two of the most widespread of all human diseases - dental caries and periodontal diseases

3. Dental plaque is defined clinically as a structured resilient yellow-grayish substance that adheres tenaciously to the intraoral hard surface, including removable and fixed restorations. The tough extracellular matrix makes it impossible to remove plaque by rinsing or the use of sprays. .

4. Materia alba refers to soft accumulations of bacteria, food matter, and tissue cells that lack the organized structure of dental plaque and are easily displaced with a water spray.

5. Dental plaque Dental plaque is a multi-species biofilm,
Some bacterial species may be of greater relevance in the development of caries and periodontal diseases.

6. To understand the role of dental plaque in caries
must first know how dental plaque forms ?
how changes in the proportions of different plaque bacteria
can contribute to the development of this oral disease?

7. Using highly sensitive molecular techniques microbial identification, it has been estimated that more than 500 distinct microbial phenotypes can be present as natural inhabitants of dental plaque. In fact, this number may be much greater

8. Supragingival plaque: is found at or above the latter; when in direct contact with the gingival margin it is referred to as marginal plaque.
Subgingival plaque : is found below the gingival margin between the tooth and the gingival pocket epithelium

9. Dental Plaque: A Microbial Biofilm

10. Between sub gingival plaque and the tooth there is an electron dense organic material called Cuticle which may contain remnant of epithelial attachment lamina which connect the junctional epithelial to the tooth.

11. Accumulation of a Dental Plaque Biofilm:
The process of the plaque formation can be divided in to several phases
The formation of the pellicle on the tooth surface.
Initial adhesion/attachment of bacteria.
Colonization/plaque maturation.

12. Formation of the Pellicle
All surfaces in the oral cavity including hard and soft tissues are coated with a layer of organic material known as the acquired pellicle. The pellicle on tooth surface consists of more than 180 peptides, proteins, glycoprotein including keratins, mucins, histidine-rich, and proline-rich proteins, phospho-proteins.

13. The Acquired Pellicle
The coating of salivary origin that forms on exposed tooth surfaces is called the acquired pellicle.
It is acellular and consists primarily of glycoproteins derived from saliva B АР ЕS

14. Initial adhesion/attachment of bacteria:
Tooth brushing removes most but not all bacteria from exposed surface of teeth. However, re-colonization begins immediately, and bacteria can be detected within 3 minutes of introducing sterile enamel into the mouth.

15. It is the specific interactions between microbial cell surface "adhesion" molecules and receptors in the salivary pellicle that determine whether a bacterial cell will remain associated with the surface.

16. Colonization/plaque maturation:
The primary colonizing bacteria adhered to the tooth surface provide new receptors for attachment by other bacteria, in a process known as "coadhesion".

17. The transition from early supgingival dental plaque to mature plaque growing below the gingival margin involves a shift in the microbial population from primary gram-positive organisms to high numbers of gram-negative bacteria.

18. Microbiologic specificity of periodontal diseases:

19. The nonspecific plaque hypothesis maintains that periodontal disease result from the "elaboration" of noxious products by the entire plaque flora. According to this thinking, when only small amounts of plaque are present, the noxious products are neutralized by the host. Similarly, large amounts of plaque would produce large amounts of noxious products, which would essentially overwhelm the host's defenses.

20. Several observations contradicted these conclusions
Several observations contradicted these conclusions. First, some individuals with considerable amounts of plaque and calculus, as well as gingivitis, never developed destructive periodontitis. Furthermore, individuals who did present with periodontitis demonstrated considerable site specificity in the pattern of disease.

21. Specific plaque hypothesis:
The specific plaque hypothesis states that only certain plaque is pathogenic, and its pathogenicity depends on the presence of or increase in specific bacterial pathogens results in periodontal disease because these organisms produce substances that mediate the destruction of host tissues.

22. Acceptance of the specific plaque hypothesis was spurred by the recognition of A. actinomycetemcomitans as a pathogen in localized aggressive periodontitis. The association of Socranksy's "red complex" bacteria which are p. gingivalis, T. forsythia , and T. denticola with periodontal disease was based on the analysis of 40 different bacteria in >13000 plaque samples.

23. these studies have shown that periodontal disease can occur even in the absence of defined "pathogens" such as red complex bacteria, and conversely that "pathogens" may be present in the absence of disease.

24. Ecologic plaque hypothesis:
According to the ecologic plaque hypothesis, both the total amount of the dental plaque and the specific microbial composition of plaque may contribute to the transition from health to disease.

25. Bacterial adherence :
Most bacteria in nature are surrounded by highly hydrated matrices called " glycocalyces"; these are often made up of "heterolpolysaccharides", which bacteria can produce from any carbohydrate source, many bacteria bear long appendage at their surface which may extend beyond the surface of the glycocalyx, these appendages are called pilli or fimbriae.

26. An important characteristic of the living cells is that they carry negative electric change and thus tend to repel each other electrostatically, the tooth surface is also negatively change and repels the cells, the cells are also influenced by electrodynamic forces (Van Der Waal's force) which are attractive and repulsive forces will create a gap between the bacteria and the forces tooth surface, this gap is influenced by the presence of ions, hydrogen ions and cations (+ve) change will narrow the gap, the importance of the glycocalyx has extension beyond the highly changed surface of the bacterial cell and can bridge the gap between bacteria and the tooth surface.

27. the adhesion of bacteria to the tooth surface is highly specific mechanism, there are molecules called "adhesins" on the bacteria recognize specific receptor molecules on the tooth surface, these adhesins located on the pili.

28. The binding sites on the pellicle, are also host proteins, including:
immunoglobulins (i.e., antibodies),
the enzyme lysozyme, and
proteins of the complement system.
These host proteins originate from saliva and gingival sulcus fluid.

29. On the other hand some of the salivary mucins (agglutinins and secretory immunoglobulin A) may react with bacterial surface structure and block adhesins so in that way it will prevent the bacteria from adhering to the oral surface

30. Molecular Mechanisms of Bacterial Adhesion

31. . The negatively charged carboxyl group of a bacterial protein is attracted to a positively charged calcium ion (i.e., electrostatic attraction), which in turn is attracted to a negatively charged phosphate group of a salivary phosphoprotein in the acquired pellicle.

32. Bacteria also have external cell-surface proteins termed adhesins, which have lectin-like activity, because they can bind to carbohydrate components of glycoproteins.
Тhe adhesins may be located on bacterial surface appendages, such as fimbriae ().
Fimbria-associated adhesins probably mediate bacterial adhesion via ionic or hydrogen-bonding interactions.

33. . The fimbrial surface appendage extends from the bacterial cell to permit the terminal adhesin portion to bind to a sugar component of a salivary glycoprotein

34. Another molecular mechanism of bacterial adhesion is calcium bridging.
In this process positively charged,
divalent calcium ions in the saliva help to link the negatively charged cell surfaces of bacteria to the negatively charged acquired pellicle

35. With dietary sugars entering the plaque, anaerobic glycolysis results in acidogenesis (acid production) and accumulation of acid in the plaque.
If no acid-consuming organisms (e.g., Veillonella) are available to use the acids, the plaque pH drops rapidly from 7.0 to below 4.5.
This drop is important because enamel begins to demineralize between pH 5.0 and 5.5.

36. One possible outcome of the drop in pH may be the dissolution of the mineralized tooth surface adjacent to the plaque, resulting in carious cavitation of the tooth.
This process provides the bacteria access to the inorganic elements (e.g., calcium and phosphate) needed for their nutritional requirements.

37. *The nutrients of sub-gingival bacteria are provide by the following:
Gingival exudates or fluid which contains proteins, carbohydrates, minerals and vitamins and they form a good nourishment to the bacteria.
Dead cells of the periodontal tissue when periodontal lesions are initiated.
The metabolic products produced by one group of bacteria may serve as energy source for other bacteria.

38. END