Plaque Formation and Retention Flashcards
How is dental plaque defined clincally?
A structured, resilientm yellow-greyish substance that adheres tenaciously to the intraoral hard surfaces, including removable and fixed restorations
What is dental biofilm?
Well-oragnised microbial community
Can be found on any solid surface exposed to bacteria containing fluid
Oragnic matrix makes up approx 30% of total plaque volume and serves as food reserve and cement by binding organisms to one another and other surfaces
What is the structure of a biofilm?
Mushroom shaped colonies, each community with its own customised living environment
Extracellular slime layer protects the bacteria/bacterial colonies from antibiotics, antimicrobials, and host response
Fluid channels extend through the slime layer to help with movement of nutrients throughout the biofilm and rid itself from waste products
What is the clinical appearance of dental biofilm
Dense, non-calcified, highly organised bacterial mass accumulated over tiem on teeth / hard materials in the mouth
It collects rapidly in inaccessible areas of the mouth (cervical region, pits, and fissures, and interproximal surfaces)
Can be seen as white to off white accumulation of variable thickness, mature plaque is yellow-grey in colour
Without disturbance, placque can form up to the height of the crown
What is the compositon of dental biofilm?
Matrix (50 - 70%) + microorganisms (50 - 30%)
Proteins derived from saliva
- Carbohydrates
- Leukocytes / ethrocytes
- Cell remnants
- Food debris
- Bacterial enzymes (collagenases, proteases)
- Endotoxins (provoke inflammation and immune response)
- Lactic acids (prodcued by bacteria as by-product of carbohydrates)
- Mineral salts (calcium, phosphorous, magnesium, sodium, and potassium)
What is phase 1 of the dental biofilm?
Film coating
- Structure less film of salivary glycoprotein that forms withing minutes of brushing on the surface of a newly cleaned tooth
- Helps heal, protect, and repair enamel surface but becomes populated by bacteria within minutes of formation
- 2 layers = thin and difficult to remove, thicker and globular and easy to detach
What is phase 2 of the dental biofilm formation?
Binding of a single organism
- Within few hours after formation of the pellicle, bacteria attach to the outer surface
- Bacteria can have extracellualr substances and fimbriae to enable them to attach to the tooth
What is phase 3 of the dental biofilm formation?
Multiplication
- Bacteria stick to the teeth and produce substances that stimulate other free-floating bacteria to join the colony
What is phase 4 of the dental biofilm formation?
Continued growth / Extracellular slime formation and microcolony formation
- Bacteria stick to teeth and extracellular slime layer is formed by slimey, glue-like excretions to help glue bacteria together
- Anchors the bacteria to tooth surface and provides protection for attached bacteria
- Population initially grows along the cervical areas of the teeth then spread out over and away from the tooth surface
What is phase 5 of the dental biofilm formation?
Mature biofilm
- Formation slows and at 24 hours necomes visible to the human eye
- Between 24 - 48 hours, the flora becomes increasingly ocmplex with an increase in anaerobic bacteria
- As plaque ages gram +ve organisms reduce and anaerobic bacteria predominate
- Number of cocci decreases while filaments and spirochetes increase
- In deep layers, bacteria is inactive / dead and the matrix is degraded
- After 2 weeks, no major changes to structure and composition of plaque
What is the importance of colonisation and organisation?
The ability to adhere and aggregate is important in the development of the bacterial biofilm
The first bacteria to colonise the tooth surface are nonpathogenic and lay the foundation for the growth of the biofilm
Periodontal pathogens are UNABLE to colonise the biofilm until the nonpathogenic species are attached
What is the sequence of the bacterial attachment zones?
Within hours, pellicle films form over the crown of the tooth adn early colonisers attach supragingivally
6 hours = surface of the tooth crown become covered
Day 7 = mature supragingival biofilm forms
3 - 12 weeks = subgingival biofilm starts to form
What is subgingival plaque biofilm?
Develops in the gingival crevice (periodontal pocket)
Supragingival plaque still present, but increase flora diversity
Almost all organisms are anaerobic bacteria, a large numebr are rods and spirochetes
What are the three zones of plaque biofilm?
- Tooth associated
- Tissue associated (epithelium)
- Unattached bacteria
Describe the bacteria attached to the tooth surface
Plaque attaches and extends from the gingival margins to the base of the junctional epithelium
Appear to have the ability to invade the dentinal tubules of the cementum
Inner layers are dominated by gram +ve bacteria, but gram -ve bacteria are also present
Describe the bacteria attached to the epithelium
Adhere to the epithelium of the pocket wall
Can invade the gingival connective tissue and can be found on the surface of the alveolar bone
Research suggests that tissue-associated plaque is the most detrimental to the periodontal tissues
What is unattached bacteria?
Bacteria contained in the periodontal pocket taht si free floating and are not part of the biofilm
What are the 3 key bacterial characteristics that increase virulence?
- Invasion (ability to penetrate the epithelial lining of pocket wall and invade the connective tissue through ulceration)
- Endotoxins
- Exotosins
What are bacterial endotoxins?
Endotoxins aka lipopolysaccharides or LPS are released when the cell walls of bacteria begin to break up
Promotes tissue destruction, bone resorption, and the breakdown of collagen fibres in gingival connective tissue through ulcerations epithelial lining
What are bacterial exotoxins?
Harmful proteins from the bacteria that act on host cells from a distance (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 fibres in ginigval connective tissue
- Promoting apical migration of junctional epithelium along root
- Causing widening of intercellular spaces
- Diminishing ability of immunoglobulins and other proteins in defending the host
What are factors contributing to the composition and formation of plaque?
- Host immune factors
- Mechanical oral hygiene practices
- Nutrients provided by host (more carbs = production of dextrans, thicker plaque)
- Saliva flow rate and components of saliva may affect attachmen and growth of bacteria
- Bacterial interactions
- pH levels
- Oxygen requirements
What is materia alba?
- Often present along with plaque, but different
- Structureless mixture of bacteria, food debris, dead epithelial cells, leukocytes, and salivary deposits
- Loose white to yellow deposit, usually in neglected mouths
- Can be removed easily and washed away with water spray
What is dental calculus?
- Adheres to teeth and other solid objects within the oral cavity
- Mineralised dental plaque (at least 3 weeks after plaque established)
- Mechanism of the initiation of plaque mineralisation is unknown
- Not common on primary dentition, but increasingly common from teen years into adulthood
- Appears in radiographs if thick enough
What is the composition of calculus?
70 - 90% inorganic materal, 30 - 10% water and organic amtrix of protein and carbohydrates
Mainly calcium phosphate
What are the characteristics of supragingival calculus?
- Hard, brittle material that is relatively easy to detach from tooth surface with 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 salivary duct orifices, lingual surfaces of mandibular incisors, buccal surafces of maxillary upper molars
What are the characteristics of subgingival calculus?
- 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
