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  1. Dr Ahmed Hassan Dental plaque
  2. Dental Plaque  Dental plaque (also called as microbial plaque, dental plaque biofilm) is a dense, nonmineralized, highly organized complex mass of bacterial colonies in a gel-like intermicrobial matrix.  The matrix protects the bacteria from the defensive cells of the body (neutrophils, macrophages, and lymphocytes).  It adheres firmly to the acquired pellicle and also to the teeth, calculus, and restorations.
  3.  Acquired pellicle is an amorphous layer that forms over exposed tooth surfaces, as well as over restorations and dental calculus.  It begins to form within minutes after all external material has been removed from the tooth surfaces with an abrasive.  Although, pellicle performs a protective function, acting as a barrier to the acids, it also serves the initial site of attachment to the bacteria and begins the first stage of biofilm development.
  4.  A biofilm community comprises a. bacterial microcolonies, b. an extracellular slime layer, c. fluid channels, and d. a primitive communication system.  As the bacteria attach to a surface and to each other, they cluster together to form sessile, mushroom-shaped microcolonies that are attached to the surface at a narrow base
  5. Biofilm (under Electron Microscope)
  6.  Each microcolony is a tiny, independent community containing thousands of compatible bacteria.  Different microcolonies may contain different combinations of bacterial species. a. Bacteria in the center of a microcolony may live in a strict anaerobic environment, b. while other bacteria at the edges of the fluid channels may live in an aerobic environment.  Thus, the biofilm structure provides a range of customized living environments (with differing pHs, nutrient availability, and oxygen concentrations) within which bacteria with different physiological needs can survive.
  7. The extracellular slime layer is a protective barrier that surrounds the mushroom shaped bacterial microcolonies (Fig. 25.2).
  8.  The slime layer protects the bacterial microcolonies from a. antibiotics, b. antimicrobials, and c. host defense mechanisms.  A series of fluid channels penetrates the extracellular slime layer.  These fluid channels a. provide nutrients and oxygen for the bacterial microcolonies and b. facilitate movement of bacterial metabolites, waste products, and enzymes within the biofilm structure.  Each bacterial microcolony uses chemical signals to create a primitive communication system used to communicate with other bacterial microcolonies.
  9.  Clinically, plaque presents as a transparent film and therefore, difficult to visualize.  It can be detected with an explorer by passing the explorer over the tooth surface near the gingival margin to collect plaque, which makes it easier to see.  Plaque disclosing solutions that stains the invisible plaque is used for easy detection of plaque.  It stains the plaque and makes it visible to the eyes. These solutions disclose the extent and
  10. FORMATION OF DENTAL PLAQUE BIOFILMS  Dental bacterial plaque is a biofilm that adheres tenaciously to tooth surfaces, restorations, and prosthetic appliances.  The pattern of plaque biofilm development can be divided into three phases [Figs 25.3A to C]: 1. Attachment of bacteria to a solid surface; (pellicle formation) 2. Formation of microcolonies on the surface; (initial colonization) 3. Formation of the mature, subgingival plaque biofilm.
  11. Stages of biofilm Stage A Stage B1 (A) Attachment (B) Colonization
  12. Stages of biofilm Stage B2 Stage C (B) Colonization (C) Mature biofilm
  13. Pellicle Formation  The initial attachment of bacteria begins with pellicle formation.  The pellicle is a thin coating of salivary proteins that attaches to the tooth surface within minutes after cleaning.  This layer is thin, smooth colorless and translucent and is called as acquired salivary pellicle. Initially pellicle is bacteria free.  The function of salivary pellicle is mainly protective.
  14.  The pellicle acts like double sided adhesive tape, a. adhering to the tooth surface on one side and b. on the other side, providing a sticky surface facilitating bacterial attachment to the tooth surface.  Following pellicle formation, bacteria begin to attach to the outer surface of the pellicle.  Accumulation is greatest in sites which are protected from functional friction and tongue movement.
  15.  Bacteria connect to the pellicle and each other with hundreds of hair-like structures called fimbriae.  Once they stick, the bacteria begin producing substances that stimulate other free floating bacteria to join the community.  Within the first two days in which no further cleaning is undertaken, the tooth’s surface is colonized predominantly by gram-positive facultative cocci, which are primarily streptococci species.  It appears that the act of attaching to a solid surface stimulates the bacteria to excrete an extracellular slime layer that helps to anchor them to the surface and provides protection for the attached bacteria.  Within first few hours species of Streptococcus and a little later Actinomyces attach to the pellicle and
  16. Formation of Microcolonies  Microcolony formation begins once the surface of the tooth has been covered with attached bacteria.  The biofilm grows primarily through cell division of the adherent bacteria, rather than through the attachment of new bacteria.  Next, the proliferating bacteria begin to grow away from the tooth.  Plaque doubling times are rapid in early development and slower in more mature biofilms.  Bacterial blooms are periods when specific species or groups of species grow at rapidly accelerated rates.
  17.  A second wave of bacterial colonizers adheres to bacteria that are already attached to the pellicle.  Coaggregation is the ability of new bacterial colonizers to adhere to the previously attached cells.  The bacteria cluster together to form sessile, mushroom-shaped microcolonies that are attached to the tooth surface at a narrow base.  The result of coaggregation is the formation of a complex array of different bacteria linked to one another.
  18.  Supragingival plaque formation is also pioneered by bacteria with an ability to form extracellular polysaccharides which allow them to adhere to the tooth and each other and these include a. Streptococcus mitior, b. S. sanguis, c. Actinomyces viscosus and d. A. naeslundii Plaque grows by both internal multiplication and surface deposition.  Internal multiplication slows considerably as the plaque matures.
  19. Maturation  Following a few days of undisturbed plaque formation, the gingival margin becomes inflamed and swollen.  These inflammatory changes result in the creation of a deepened gingival sulcus.  The biofilm extends into this subgingival region and flourishes in this protected environment, resulting in the formation of a mature subgingival plaque biofilm.  Gingival inflammation does not appear until the biofilm changes from one composed largely of gram-positive bacteria to one containing gram- negative anaerobes.
  20.  A subgingival bacterial microcolony, predominantly composed of gram-negative anaerobic bacteria, becomes established in the gingival sulcus between 3 and 12 weeks after the beginning of supragingival plaque formation.  Most bacterial species currently suspected of being periodontal pathogens are anaerobic, gram-negative bacteria.
  21. Structure and Composition  Dental plaque can be broadly classified as supragingival or subgingival.  Supragingival plaque is found at or above the gingival margin and may be in direct contact with the gingival margin.  Subgingival plaque is found below the gingival margins, between the tooth and the gingival sulcular tissue.
  22.  Approximately 70 to 80 percent of plaque is microbial and the rest represents extracellular matrix. The intracellular matrix which accounts for about 20 percent of plaque mass consists of organic and inorganic materials derived from saliva, gingival crevicular fluid and bacterial products.  Organic constituents of the matrix include polysaccharides, proteins, glycoproteins, and lipids.
  23.  The most common carbohydrate produced by bacteria is dextran.  The principal inorganic components are calcium, phosphorus, sodium, potassium, fluoride and some traces of magnesium.  Calcium ions may aid adhesion between bacteria and between bacteria and the pellicle.  The source of both the organic and inorganic components is primarily saliva and as the mineral content increases, the plaque may be calcified to form calculus.
  24. SUPRA AND SUBGINGIVAL PLAQUE Supragingival Plaque  It can be defined as the community of microorganisms that develops on the tooth surface coronal to the gingival margin (at or above the gingival margin).  When it is in direct contact with the gingival margin it is termed as the marginal plaque.
  25. Subgingival Plaque  It can be defined as the community of microorganisms that develops on tooth surfaces apical to the gingival margin (found below the gingival margin, between the tooth and the gingival pocket epithelium).  Generally, the subgingival microbiota differs in composition from supragingival plaque mainly because of the local availability of blood products and low oxygen potential which characterizes the anaerobic environment.
  26. Plaque Retention Factors  These are conditions that favor plaque accumulation and hinder plaque removal by the patient and the dental professional.  Examples of these are: • Orthodontic appliances • Partial dentures • Malocclusions • Faulty restorations • Calculus • Deep pockets • Mouth breathing • Tobacco use • Certain medications
  27. Plaque encourages caries formation by: 1. Enabling bacteria to stick to the teeth. 2. Allowing acids to accumulate around the teeth. 3. Preventing the saliva from reaching the teeth surface, so stopping it from washing them and neutralizing the acid. 4. Providing the cariogenic bacteria with a reserve energy supply, i.e.
  28. SIGNIFICANCE OF DENTAL PLAQUE  The role of dental plaque in the initiation of dental caries and periodontal infections is now well documented.  Dental caries and periodontal disease result from the bacterial products of the plaque flora.
  29. Calculus and its Relationship with Plaque  • Calculus is formed by the deposition of calcium and phosphate salts in bacterial plaque. These salts are present in salivary and crevicular fluids.  • Plaque mineralization begins within 24 to 72 hours and takes an average of 12 days to mature.  • Calculus contributes to the disease by providing for plaque accumulation. It is not the causative or etiologic factor, plaque is.  • Calculus is porous and can act as a reservoir or nidus of bacteria and endotoxin related to the disease process.