plaque formation and retention semester 1

Question 1

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

Answer 1

Structure of a Biofilm
– Mushroom shaped colonies
– Each community has its own customized living environment
– Extracellular slime layer protects the bacteria
– Fluid channels extend through the slime layer to help with movement of nutrients throughout the biofilm and rid itself from waste products
composition:
– Organic matrix- Proteins, Food Debris, Dietary carbohydrates, Mineral salts, Bacterial enzymes, Lactic Acids etc
– Living, dead and dying bacteria and their extracellular products
– Usually made up of more than one bacterial species
– Varies between and within individuals
clinical appearance:
- Dense, non-calcified, highly organised bacterial mass
– It accumulates over time on teeth / hard materials in the mouth
– Can be seen as white to off white accumulation of variable thickness
– Mature plaque is yellow to grey in colour
– Without disturbance, the plaque can form up to the height of the crown

Question 2

Describe the 5 phases of plaque formation

Answer 2

Film Coating (Phase1)
– Structure less film of salivary glycoprotein that forms on the surface of a newly cleaned tooth
– Forms within minutes of brushing and requires friction to remove it
– Becomes populated with bacteria within minutes of formation
Binding of Single Organisms (Phase 2)
– Within a few hours after the
formation of the pellicle, bacteria
attach to the outer surface
– Bacteria can have extracellular
substances and fimbriae to enable
them to attach to the tooth
Multiplication (Phase 3)
– Bacteria stick to the teeth
– Bacteria produce substances
that stimulate other free-
floating bacteria to join the
colony
Continued Growth (Phase 4)
– Bacteria stick to the teeth
– Extracellular slimy layer is formed to help glue
the bacteria together
– Bacteria are stimulated to excrete slimy,
gluelike substance
– Bacterial population initially grows along the
cervical areas of the teeth then spread out
over and away from the tooth surface
Mature Biofilm (Phase 5)
– Biofilm formation is rapid then slows down in more mature plaque
– At 24 hours, biofilm becomes visible to the human eye
– Between 24-48 hours, the flora becomes increasingly complex with
an increase in anaerobic bacteria
– In deeper layers of mature plaque- dead, inactive bacteria and degraded matrix present
– After 2 weeks, no major changes to structure and composition of
plaque

Question 3

Recall and explain the differences amongst the 3 zones of subgingival plaque

Answer 3

Tooth Associated
– Plaque attaches and extends
from the gingival margins to
the base of the junctional
epithelium
– invade the dentinal tubules of
the cementum
– Inner layers are dominated by
gram positive bacteria
– Gram negative bacteria are also
present
Tissue associated
–Adhere to the epithelium of the
pocket wall
–Are distinctly different from the
tooth-associated bacteria
–Can invade the gingival
connective tissue and be found on
the surface of the alveolar bone
Unattached bacteria
– In addition to the attached bacteria, the periodontal pocket contains
free-floating bacteria that are not part of the biofilm.

Question 4

Define bacterial virulence factors

Answer 4

1. Mechanisms that enable biofilm bacteria to colonize, invade, and
   damage tissues of the periodontium
2. May be structural characteristics of the individual bacterium
3. May be substances produced and released by bacteria

Question 5

Describe how endotoxins and exotoxins invade and damage periodontal tissues

Answer 5

–Endotoxins (aka Lipopolysaccharides or LPS)
–Released when the cell walls of bacteria begin to break up
–Cell death stimulates biologic activities
–Promote tissue destruction
–Promote bone resorption
–Breakdown of collagen fibers in gingival connnective tissue through
ulcerations of epithelial lining
exotoxins:
– Harmful proteins released from the bacteria that act on host cells from a distance
– Eg. Aggregatiabacter actinomycetemcomitans formerly known as (Actinobacillus
actinomycetemcomitans) produces leukotoxins that destroy leukocytes in periodontal pocket or sulcus
– Bacterial enzyme production
– Enzymes are agents that are harmful or destructive to host cells by:
– Increasing permeability of epithelial lining of sulcus
– Contributing to breakdown of collagen fibers in gingival connective tissue
– Promoting apical migration of junctional epithelium along root
– Causing widening of intercellular spaces
– Diminishing ability of immunoglobins and other proteins in defending the host

Question 6

Compare and contrast material alba, dental plaque and calculus

Answer 6

material alba:
– Often present along with plaque
– Different to plaque
– Structure-less mixture of bacteria,
food debris, dead epithelial cells,
leukocytes and salivary deposits
– Loose white to yellow deposit
– Usually present in neglected
mouths
– It can be removed easily and
washed away with water spray

dental plaque:
dense, non-calcified, highly organised bacterial mass. It accumulates over time on teeth
/ hard materials in the mouth and collects rapidly in inaccessible areas of the mouth eg cervical region,
pits and fissures and interproximal surfaces. Can be seen as white to off white accumulation of variable
thickness, with mature plaque yellow to grey in colour. Without disturbance, the plaque can form up to
the height of the crown. 50-70% inorganic material.

calculus:
– Adheres to teeth and other solid objects
within the oral cavity
– Mineralised dental plaque (may require
only 3 weeks after plaque is established)
– Mechanism of the initiation of plaque
mineralisation is unknown
– Not common on primary dentition –
increasingly common from teen years
into adulthood
– Appears on radiographs if thick enough

Question 7

Discuss the control of biofilm

Answer 7

Current research shows that the body’s immune response to the plaque biofilm is
the primary cause of the destruction seen in periodontitis.
–Biofilm bacteria are EXTREMELY resistant to antibiotics, antimicrobial agents, and the body’s
immune system.
–Control of bacteria in dental plaque biofilms is best achieved by the physical disruption
of the plaque biofilm (such as brushing, flossing, and periodontal instrumentation).

Question 8

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

Answer 8

Supragingival Calculus (coronal to gingiva Margin)
– Hard, brittle material that is relatively easy to detach for the tooth
surface with a suitable instrument
– Light yellow in colour
– Occasionally stained
– Minerals are derived from saliva
– Could be deposited anywhere on teeth but most common sites:
– adjacent to the salivary duct orifices
– lingual surfaces of mandibular incisors
– buccal surfaces of maxillary upper molars

sub gingival calculus (attcached to the root surface)
– Yellow, dark green, brown or black in colour
– Minerals are derived from the gingival crevicular fluid
– Detection during clinical examination and radiographs
– Often generalised
– Location is related to the presence of gingival inflammation and
pocketing
– Harder than supragingival calculus and more firmly adherent to
the tooth surface

Question 9

how to detect sub gingival calculus

Answer 9

– Roughness revealed through tactile sensitivity
– Radiographs
– Darkening of the overlying gingiva
– Directly detaching the gingiva with a gentle air blast to
visualise the deposit
– Direct and indirect transillumination
– Flossing

Question 10

what is biofilm?

Answer 10

The plaque that forms on your teeth and causes tooth decay is also a type of bacterial biofilm. Well-organized microbial community
Can be found on any solid surface exposed to
bacteria containing fluid