Dental Biofilm (Plaque) Essentials

Definition

  • Dental plaque = biofilm: soft, non-mineralised microbial deposit on teeth & prostheses.
  • Biofilm: matrix-enclosed, surface-adherent community of microorganisms co-operating for mutual survival.

Biofilm Components

  • \approx80\% water; dry weight \approx70\text{--}80\% bacteria.
  • Two phases: microorganisms + extracellular matrix.
  • Heterogenous, with micro-niches differing in \text{pH} and \text{O}_2 levels.

Extracellular Polysaccharides (EPS)

  • Produced by resident bacteria; major bulk of matrix.
  • Functions:
    • Adhesion & aggregation support.
    • Reserve carbohydrate source.
    • Increases thickness, stickiness ⇒ harder to remove.
    • Imparts white, gelatinous appearance.

Formation Stages

  • Stage 1 – Initial colonisation (minutes–hrs)
    • Random contact → selective binding.
    • Early colonisers: aerobic, Gram-positive cocci & short rods.
    • Isolated micro-colonies on surface irregularities.

  • Stage 2 – Early growth (8\text{--}48 h)
    • Rapid cell division; plaque mass doubles in \approx48 h.
    • Cocci + emerging filamentous forms.
    • EPS production ↑ → insoluble, thicker matrix.

  • Stage 3 – Maturation (\ge48 h)
    • Complex community: rods, fusobacteria, spirochetes.
    • Classic “corn-cob” architecture: streptococci on filamentous core within EPS web.
    • Environmental shifts (lower \text{pH}, reduced \text{O}_2) select species.
    • Host inflammatory response begins.

Mature Biofilm Characteristics

  • Overlaid by saliva; may trap food debris & epithelial cells → materia alba (water-removable).
  • Can be stained by tea, drugs, chromogenic bacteria.
  • Not removed by rinsing; increasing resistance to tooth-brushing as it matures.

Clinical Significance

  • Gingivitis: anaerobic bacterial by-products trigger gingival inflammation; species profile more critical than quantity.
  • Dental caries: cariogenic bacteria (e.g. S.\,mutans, lactobacilli) ferment carbs → organic acids (lactic) → demineralise \text{hydroxyapatite}.

Key Takeaways

  • Biofilm is an organised, resilient microbial community distinct from loose deposits.
  • EPS is central to biofilm adhesion, structure, and resistance.
  • Plaque mass and composition change rapidly within first 48 h; effective oral hygiene must disrupt early.
  • Mature biofilm underlies both caries and periodontal pathologies; management targets mechanical disruption + species control.