Oral Microbial Colonization and Dental Caries Notes

Oral Microbial Colonization

Acquired Pellicle

  • Thin, tenacious film composed of proteins, carbohydrates, and lipids.
  • Forms over exposed tooth surfaces and restorations.
  • Thickest near the gingival margin and undisturbed areas.
  • Forms within minutes after eruption or removal of dental deposits.
  • Fully formed within 30-90 minutes.
  • Microorganisms adhere to the pellicle.
  • Becomes an insoluble coating over teeth, calculus, restorations, and dentures.
  • Types:
    • Supragingival: Clear, translucent; requires a disclosing agent to be visible.
    • Subgingival: Continuous with supragingival pellicle; can embed in tooth structure.
  • Importance:
    • Protection: Barrier against acids, reduces demineralization
    • Lubrication: Keeps the surface moist and prevents drying.
    • Attachment: Aids in the adherence of microorganisms.
    • Calculus Attachment: Calculus can attach to the pellicle.
  • Removal: disrupted by mechanical oral hygiene procedures, such as brushing and scaling.

Biofilm

  • 3-D structured community of microorganisms.
  • Encapsulated in an extracellular matrix (polysaccharides, proteins, and other compounds).
  • Microcolonies are separated by open water channels for nutrient supply.
  • Attaches to pellicle, calculus, appliances, etc.
  • Contains over 700 species in the oral cavity.

Dental Biofilm Formation Stages

  1. Formation of Pellicle: Initial attachment site
  2. Multiplication and Colonization: Bacteria adhere and multiply.
  3. Matrix Formation: Microcolonies produce extracellular substances for firm attachment.
  4. Biofilm Growth: Further development and cell-to-cell communication.
  5. Maturation: Colonies mature and release cells to colonize other areas

Stages Explained

  • Stage 1 - Formation: Bacterial cells attach to the pellicle.
  • Stage 2 - Multiplication and Colonization: Micro-colonies multiply in layers, growing up and out.
  • Stage 3 - Matrix Formation
    • Continued secretion of substances with multiplication of bacteria forms matrix.
    • Adhesion and stickiness protect the community, making it difficult to remove with brushing.
    • Structure enhances the ability to survive and adapt to environments.
    • Antibiotics are less effective due to the protective matrix.
  • Stage 4 - Biofilm Growth
    • Further development of biofilm with cell-to-cell communication.
    • Increase in size as colonies mature and release cells to spread and colonize other areas.
    • Gingivitis develops in 10-21 days when biofilm is left undisturbed.
  • Stage 5 - Maturation

Complex Structure of Mature Dental Plaque

  • Bacteria in a biofilm are not evenly distributed.
  • Each microcolony is a tiny independent community containing thousands of compatible bacteria.
  • Each sulcus can have different combinations of bacteria, pH levels, temperature, and oxygen requirements.
  • This diversity helps ensure biofilm survival; uniformity would make eradication easier.

Supragingival and Subgingival Biofilm

  • Supragingival biofilm organizes before subgingival biofilm.
  • Supragingival Biofilm
    • Consists of gram-positive, aerobic bacteria (requires oxygen).
  • Subgingival Biofilm
    • Includes gram-negative, anaerobic bacteria (does not require oxygen).
    • Examples: Actinomyces, T. forsythia, F. nucleatum.

Composition of Biofilm

  • Inorganic Components
    • Calcium, Phosphorus, Magnesium
    • Fluoride
  • Organic Components
    • Carbohydrates
    • Proteins

Clinical Considerations

  • Biofilm is found in multiple areas.
  • Supragingival formation begins at the gingival margin and spreads coronally.
  • Heaviest on proximal surfaces, least on palatal surfaces.
  • Influenced by crowding, rough surfaces, and occlusion.
  • Disruption of biofilm is achieved with mechanical methods.

Detection of Biofilm

  • Direct vision: Thin biofilm is not visible; stained or thick biofilm may be.
  • Explorer/Probe: Tactile detection (rough or slippery); removal.
  • Disclosing agent: Stains biofilm for visualization.
  • Clinical record: Track location and thickness over time.

Role of Biofilm in Disease

  • Biofilm plays a role in the initiation and progression of caries and periodontal infections.
  • Pathogenic microorganisms are found in oral biofilms.
  • Aids in the formation of calculus.
  • Optimal oral hygiene depends on daily biofilm disruption.

Dental Caries

Definition

  • Dental caries is an infectious, transmissible disease of dental structures.
  • Characterized by demineralization of mineral components.

Our Role

  • Detect the disease in early stages.
  • Prevent further infection.
  • Educate the patient.

Microorganisms Involved

  • Mutans Streptococci
    • Acid-forming bacteria.
    • Involved with the initiation of the caries process.
    • Help form biofilm by creating a sticky environment.
  • Lactobacilli
    • Acid-forming bacteria.
    • Contribute to the progression of a carious lesion.
  • Xerostomia and frequent fermentable carbohydrates promote the growth of these microorganisms.

pH of Biofilm

  • Biofilm helps maintain a caries-causing acidic environment.
  • Acid formation begins immediately after eating.
  • The pH of biofilm is lowered when eating; before eating, pH is 6.2-7.0.
  • Enamel demineralization occurs at pH 4.5-5.5.
  • Root surface demineralization occurs at pH 6.0-6.7.
  • The frequency of acid exposure is more damaging than the quantity.

Variables in Disease Process

  • Bacteria
  • Fermentable carbohydrates
  • Tooth structure
  • Saliva

Acid Production

  • Acidogenic bacteria in biofilm metabolize acid from fermentable carbohydrates.
  • Fermentable Carbohydrates
    • Sucrose, glucose, fructose, cooked starch
    • Frequent ingestion influences the amount of acid produced.
  • Acid formed passes between enamel rods or onto root surfaces.
  • Dissolves enamel crystals, creating the initial carious lesion, known as the "White Spot" lesion.

Demineralization and Remineralization

  • Demineralization
    • Natural process where minerals of tooth structure are dissolved into solution.
    • With repeated exposure to acids, demineralization can outpace remineralization.
  • Remineralization
    • Process of moving minerals back into the subsurface of enamel.
    • Saliva:
      • Buffers acid.
      • Supplies minerals.
    • Fluoride:
      • Inhibits demineralization.
      • Enhances remineralization.
      • Inhibits bacterial growth.
    • Fluorapatite Crystal Formation - the hydroxyl ion is completely replaced by the fluoride ion
      • Crystal is more perfect and less soluble.
      • Very resistant to dissolution by acid.

Components of Remineralization

  • Neutralization of acid.
  • Concentration of calcium and phosphate higher outside the tooth than inside.
  • Calcium and phosphate diffuse back into the tooth via concentration gradient and regrow a new crystal surface.

Positive Role of Saliva

  • Neutralizes acid by its buffering components (bicarbonate, phosphate, and peptides).
  • Increases pH toward neutral.
  • Buffering halts subsurface dissolution of mineral.
  • Provides minerals (calcium/phosphate) to replace those dissolved.
  • Saliva is supersaturated with calcium and phosphate.

Stages of Carious Lesions

  • Initial Infection: Invisible Lesion
    • Acidogenic bacteria cling to tooth.
    • Create biofilm.
    • Produce acid that dissolves tooth minerals.
  • White Area Lesion: Early Stage
    • Appears dull and smooth.
    • Careful when exploring surface to not break, inhibits remineralization process.
    • Can re-mineralize with saliva (calcium, phosphate, fluoride).
  • White Area: Later Stage
    • Also known as White Spot Lesion.
    • Appears dull, slightly rough.
    • Remineralization can still occur.
    • Don’t break through the surface with an explorer.
  • Cavitated Lesion
    • Visual exam: Directly seen.
    • Instrument exam: Bacteria can spread to other surfaces.
    • Radiographic exam: Bitewing radiographs with open contacts.
    • Early caries do not extend into dentin.
    • Large lesions need to be examined for pulpal involvement.

Subsurface Lesions

  • Occlusal Caries

Caries Balance

  • Balance between caries progression and reversal.
  • Balance between pathological and protective factors.
  • Pathologic Factors
    • Cariogenic bacteria (S. mutans, Lactobacillus).
    • Frequency of ingestions of fermentable carbohydrates.
    • Reduced salivary function (radiation, medications, disease, genetic).
  • Protective Factors
    • Calcium and phosphate from saliva.
    • Fluoride exposure.
    • Salivary flow.
    • Nonfermentable carbohydrates in diet.
    • Antibacterial benefits from extrinsic sources (e.g., Chlorhexidine).