Plaque formation and retention

LO: Describe the structure, composition, clinical appearance and distribution of dental plaque biofilm

Structure:

- mushroom shapes colonies

- extracellular slime layer for protection

- fluid channels for passage of fluid, nutrients and waste

Clinical appearance:

- dense, non-calcified bacterial mass

- white, off white, yellow to gray

- adheres to hard surfaces and inaccessible areas of mouth, dentures, appliances, retainer

- Variable thickness

Composition:

- 15-20% bacterial cells

- rest is matrix

LO: Recall the physiological properties of dental plaque and calculus

Dental plaque is a soft, sticky biofilm of live microorganisms, proteins, and polysaccharides. Dental calculus is hardened plaque that has mineralized. While plaque can be removed at home, calculus is firmly anchored to teeth and requires professional scaling to remove

LO: Describe the 5 phases of plaque formation

1. initial attachment of microbes to pellicle (salivary glycoproteins and antibodies that protect enamel from acid attack)

2. Permanent attachment (produce substances to attract microbes)

3. Maturation phase (extracellular protective matrix formation)

4. Maturation phase 2 (Microbial blooms, gram +ve gradually reduce to anaerobic)

5. Dispersion (escape from matrix to colonise other surfaces)

LO: Recall and explain the differences amongst bacterial attachment zones

• Tooth surface - invade dentinal tubules of cementum

• Epithelial lining/Tissue associated - invade gingival CT towards alveolar bone - most damaging to tissues

• Other bacteria already attached to tooth or epithelial lining

• Free-floating in the sulcus - waiting for the right time to join biofilm

LO: Describe bacterial virulence factors

Mechanisms that enable biofilm bacteria to colonise, invade and damage tissues of the periodontium:

- Adherence and colonisation

- Invasion: ability to penetrate epithelial lining and connective tissue via ulceration

- Endotoxins: LPS, cell wall break -> release LPS -> inflammatory response -> cytokines, host destruction and resorption

- Exotoxins: harmful protein based toxins released by bacteria or harmful enzyme production

LO: Compare and contrast material alba, dental plaque and calculus

Material Alba:

- present along with plaque

- loss white to yellow deposite, easily removed with water

- Structure-less mix of bacteria, food, dead cells and saliva

Plaque:

- organised, sticky biofilm, removable at home with brushing and mechnical disruption

- water, microorganisms and organic matrix

Dental calculus:

- Biofilm that has calcified

- Hard, needs disruption with specialised instruments

- Made up of calcium phosphate and dead microorganisms

LO: discuss the control of biofilm

Is best achieved by physical disruption of plaque - brushing, flossing, and cleanings at dentists.

Biofilm bacteria is highly resistant to antibiotics and immune system due to extracellular slime layer.

LO: Compare and contrast characteristics of supra- and sub-gingival calculus

Supragingival:

hard, brittle, easy to detach

light yellow

minerals are derived from saliva

Subgingival:

yellow, dark green, brown or black

minerals derived from gingival crevicular fluid

detection during clinical exam and radiograph

harder than supragingival and more firmly adhered to the tooth surface

What is dental calculus

Biofilm that has calcified, initiation of plaque mineralisation is not known

What is dental biofilm

Well organised microbial community, found on any solid surface exposed to bacteria containing fluid, organic matrix is 30%