M13- plaque Flashcards
what is plaque?
the general term for the microbial community found on the tooth surface
Describe plaque.
– Associated with hard & soft-tissue surfaces
– Contains living & dead bacteria
– Includes extra-cellular bacterial products
– Involves host compounds
what is plaque essentially?
biofilm
what is a biofilm?
Name given to microbial communities attached to a surface “complex aggregation of bacteria”
what are the properties of a typical biofilm?
– spatially organized in a 3 dimensional structure
– bacterial cells enclosed in extra-cellular matrix
– increases habitat range of individual bacteria
How much bacteria exists as biofilms?
65% of human infections
what is the organic matrix of dental plaque?
glycocalyx or extracellular polymeric substances
How much space does the extracellular polymeric substance take up of dental plaque volume?
30%
what is the acquired pellicle?
the layer of material acquired by a cleaned tooth
what are the features of the acquired pellicle?
– < 1μms thick
– Mucins, salivary glycoproteins, minerals & immunoglobins
– Occurs in seconds (90-120 minutes for maximum thickness)
– Reaches a peak after which composition & form can still change
– Different Pellicles form on different oral surfaces
• (Enamel, Cementum, Oral Mucosa)
– Can be removed by vigorous brushing with an abrasive dentifrice
what does bacteria attach to?
Bacteria do not attach/adhere directly to the enamel they attach to the pellicle.
what type of reaction is the initial attachment?
reversible and non-specific interaction
Describe long range and short range bonding after contact.
- Long range (weak) - 100nm /Van Der Waal’s forces / electrostatic forces
- short range (strong) - <2nm /hydrogen bonding
what charge do most salivary glycoproteins have and what is the reason for this?
- negative charged
- sialic acid groups present
what forms between enamel and bacterial cell wall?
calcium bridge ( acquired pellicle )
how does the calicium bridge form?
- enamel -weak negative charge so positive calico ions stick to the pockets of weak negative charge
- calcium supersaturated
Describe the cell wall component of lipoteichoic acid and what it binds to.
– Gram +ve Cell wall
– amphipathic molecules
– one end lipid & hydrophobic (in membrane)
– one end glycerol phosphate & hydrophilic (-ve charge)
– bind blood group substances found in the pellicle
what effects adhesion of bacteria to pellicle?
• Ordered accumulation
– (Pioneer to Climax community)
• Frequency & relative affinity of each bacterium for the pellicle
• Attachment/adhesion, growth, and removal
• Changing environment
– aerobic-anaerobic
– pH, nutrients, ions, metabolic products
– New attachment sites, co-aggregation
what type of reaction is bacterial adhesion?
specific receptor-mediated interactions
what is considered the hallmark of transition to biofilm from pellicle?
bacterial extracellular polymeric substances - production normally associated with irreversible attachment
what helps attachment?
- adhesins
- fimbriae
what type of response is polysaccharide production?
adaptive response
what supports polysaccharide synthesis?
sucrose
what enzyme breaks down glucose and produces longer chains of glucose?
glucosyltransferase
what can be a major component of extracellular polymeric substances?
extracellular DNA
what does DNAse do?
releases bacteria and inhibits biofilm formation
what are adhesions?
– specific molecules on
bacterial surface
– recognize specific ligands or receptors on the tooth surface
– Often associated with fimbriae
what is lectin?
– Sugar binding proteins
– Recognize carbohydrate groups & bind them
– Often associated with fimbriae
What is fimbriae?
– “Hair-like” proteinacous appendages
– adhesion to enamel/pellicle
– adhesion to other bacteria
(which may contain adhesions)
Give features of streptococcus crista.
- Fibrils tend to thinner & more flexible than fimbriae
- Characteristic tuft arrangement of fibrils
- Allow coadhesion
Give overview of plaque development.
• Gram +ve & Gram -ve cocci within 2 hours
– Gram +ve : Oralis gp (mitis, oralis, sanguinis)
– Gram -ve : Neisseria, Haemophilus
• microcolonies form & spread across the tooth surface
– confluent biofilm develops
• 24 hours Streptococci predominate (95%)
– S. sanguinis most common
what are the 3 stages of succession?
Stage 1;
Streptococcus spp. (32-82%) attach to acquired pellicle
Stage 2;
Streps joined/replaced e.g. Actinomyces spp.
Stage 3;
Gram -ve species e.g. Fusobacterium
what changes are seen during the first week?
• Increased diversity of Gram +ve bacteria
– Actinomyces naeslundii
– Actinomyces israelii
• Pioneer species reduce Eh (anaerobic)
– anaerobe species survive & multiply
• Actinomyces & anaerobes increase
– Streptococci decrease (as a proportion!)
what are the two types of adhesion seen in dental plaque?
homotypic - cell to cell adhesion ( within same cell species )
heterotypic - cell to cell adhesion (different cells)
what are the two structures in heterotypic cell-to-cell adhesion?
- corn cob complexes (strep sanguines on corynebacterium)
- test tube brush complexes (gram -ve bacilli on filamentous bacterium)
Describe sub gingival plaque.
• Plaque formation – (supra/border)
• Inflammatory response
• Tissue swelling
• Deeper sulcus
– (more anaerobic)
• Inflammatory exudate – (rich in nutrients)
• More loosely structured microbiota develops
