Dental Plaque I&II Flashcards
What is the oral flora at birth?
Newborns cavity is sterile
Transient flora from birth canal might be acquired but no oral microbiome
What happens to the oral cavity after birth?
Mouth rapidly acquired organisms from mother and environment.
What does the initial flora consist of?
Streptococcal and staphylococcal species with lactobacilli, neisseria and yeasts
Streptococcus salivarius is the most common and forms pioneer community
What is the oral flora like during infancy and early childhood?
Ever increasing range of microorganisms, some become established as part of commensal flora
Eruption of teeth provides new attachment surfaces
Anaerobes in few numbers due to absence of deep gingival crevice
Actinomyces and lactobacilli are found regularly
What is the oral flora like in adolescence?
Greatest number of organisms occur in mouth when permanent teeth erupt
Teeth have deep fissures, larger interproximal spaces and deeper gingival crevices allowing a great increase in anaerobes
What happens in the oral flora in the move from childhood to adulthood?
Increase of bacteroides and spirochetes with maturity of dental plaque
What happens to the oral flora of edentulous patients?
Disappearance of S mutan, S anguis, spirochaetes and many anaerobes due to loss of available sites for colonisation
What are the factors affecting growth of microorganisms in the oral cavity?
Temperature, anaerobiosis, pH, nutrients, host factors, Antimicrobial agents and inhibitors
Describe temperature as a factor affecting growth of microorganisms in the oral cavity
Great temperature variation (hot/cold food)
Microbes have to be very adaptable
What is the influence of temperature on bacteria?
Heat shock proteins
Virulence - periodontal pockets with active disease have a higher temp
How does anaerobiosis/redox potential affect bacteria?
Different oxygen concentration at different locations in the oral cavity
What varies pH conditions in the mouth?
Exogenous materials entering the mouth (acidity of foods)
Bacteria in dental plaque producing acids
Damage to enamel (due to acids)
What is pH of caries free subjects?
7.2
What maintains pH in the mouth?
Saliva
What is pH in severe caries patients?
5.5
Where can bacteria get nutrients from in our mouths?
Diet
Saliva
GCF - very rich source bacteria
Microbial products
Host products
What host factors combat the bacteria?
Saliva - fluid flow washing bacteria away and enzymes in it enhancing or inhibiting
Crevicular fluid - contains antibodies and complement proteins
Lysosomes - degrade bacterial peptidoglycan
Lactoferrin - binds to iron limiting bacteria growth that need iron
Impact of Antimicrobial agents and inhibitors on bacteria in the oral environment
Defensins and histatins are Antimicrobial and help to keep the microbial population in check
Desquamation - when cells are shedded from the mucosa or gums, that will also get rid of an excess of bacteria
What is a biofilm?
A community of bacteria within a polymeric matrix produced by the microorganisms themselves
What is the slime of a biofilm?
Polysaccharides, DNA, proteins
Formation of biofilm
Attachment
Cell-cell adhesion - start to clump and make a matrix
Proliferation - bacteria start to grow and multiply
Maturation
Dispersion - some bacteria are expelled from the biofilm
Planktonic bacteria - dispersed bacteria might go off and form a new biofilm
What are the features of the bacteria in the outermost layer of the biofilm?
Actively growing and have all the nutrients and oxygen
Slough off and initiate biofilm formation downstream
What are the features of the bacteria in the second layer of the biofilm?
Downregulated metabolic activity
Can still utilise the nutrients, exchange genes and have potential for multiple drug resistance
What are the features of the bacteria in the innermost layer of the biofilm?
Attached to substratum
Earliest part of biofilm
Downregulate and are least metabolically active, lacking nutrients and oxygen
What is EPS?
Extracellular polymeric substance = slime
How do biofilms increase antibiotic resistance?
Since bacteria are not all killed by antibiotics in a biofilm:
- could pass on antibiotic resistant genes
- antibiotic might not be able to penetrate the biofilm
- antibiotic might get degraded by something in the matrix
Why are biofilms important clinically?
Difficult to treat them
Great threat to dental implants, prosthetic devices etc
Can form on teeth
What is quorum sensing?
Type of decision making process used by a decentralised group to coordinate behaviour
How do bacteria use quorum sensing?
Serves as a communication network. Biofilm bacteria will release communication systems to change their behaviour so they can optimally work to overcome the host immune system.
What does plaque comprise of?
Living, dead and dying bacteria and their products. And host compounds mainly derived from saliva.
What is the dental cuticle?
Covers newly erupted teeth. Consist of 2 layers - inner amorphous layer and outer cellular layer (enamel organ)
Abrasion from mastication ensures it is soon lost
What is the acquired pellicle?
Layer that forms even after brushing, immediately again due to saliva. An amorphous organic film composed of glycoproteins from saliva and GCF.
What is the function of the acquired pellicle?
Lubrication of tooth surface
Semi permeable barrier
Protective properties
Mineral homeostasis at the enamel saliva interface
Modulation of bacterial adherence
How does the acquired pellicle form?
Positive calcium ions of the enamel surface tend to dissolve in saliva with negatively charged salivary proteins
A thin layer of glycoproteins is deposited on the tooth surface within minutes of exposure to oral environment
Then protein interaction with the protein coated sirface
What is the composition of the acquired pellicle?
Most abundant are acidic and neutral amino acids
Traces of sulfur
Sugars and lipids
How does the structure of the acquire pellicle change with time?
1 min pellicle - fine granular electron dense
2 hour pellicle - buccal surface has a thin electron dense layer and outer loosely arranged layer with granular and globular compartments; palatial surface has thinner granular layer
24 hr pellicle - electron dense layer on enamel surface and a dense homogenous granular structured layer above it
What is the acquired pellicle composed of?
Tightly absorbed electron dense basal layer and a loosely arranged outer layer.
Thickest pellicle on lower posterior lingual surfaces
Thinnest on upper anterior palatal surfaces
What is the sub-surface cuticle?
When the acquired pellicle penetrates a small distance into the enamel surface
How is dental plaque formed?
Oral bacteria initially attach to acquired pellicle
Long range interactions - van der Waals forces and electrostatic repulsion (reversible)
Short range interactions - chemical interactions between receptors on the acquired pellicle and adhesions on microbial surface. Irreversible stage.
What are the pioneer group of bacteria for dental plaque?
Gram positive cocci and short rods
Predominantly streptococci, eg. S oralis S sanguinis S mitis
Where does bacterial colonisation for dental plaque start?
Near the gingival margin
Describe the rest of the bacterial colonisation of plaque?
Increased biofilm thickness leads to pioneer colonisers replaced by filamentous bacteria creating a favourable environment for gram negative anaerobic microbiota.
Biofilm formation. Final stage of colonisation by filaments, Fusobacteria and spirochetes
What is the climax community?
Increase in microbial complexity, biomass and thickness
How can waste products of bacterial metabolism impact dental plaque?
Waste products can be a nutrient intake for bacteria
Waste products can inhibit bacteria, while the dead bacteria provide a food source for other bacteria
What are the locations of supragingival plaque?
Fissure plaque, approximal plaque, smooth surface plaque gingival crevice plaque
What is calculus?
Calcified dental plaque
Where can calculus occur?
Supra-gingivally and sub-gingivally
How does calculus form?
As plaque matures its Ca and P concentration rises
Degenerating bacteria, glycoproteins and lipids act as seeding agents for mineralisation
Formation of calcium phosphate crystals which grow and coalesce to form the calcium mass
Where is calcium build up more prominent and faster?
Near the ducts of the salivary glands
As fluid from these contains a lot of bicarbonate, phosphate, ions etc
How do bacteria accelerate plaque mineralisation?
They remove natural calcification inhibitors
Raise local pH
Increase local ion concentrations
Split calcium binding proteins
What is the structure of calculus (bacteria wise)?
Outer layer - cocci, bacilli, filaments
Near enamel surface - bacteria with a reduce cytoplasm to cell wall ratio (more inactive)
Compare the microorganisms found in supra and sub gingival calculus?
Supra gingival calculus has more gram positive
Sub gingival has more gram negative
Compare the clinical appearance found in supra and sub gingival calculus?
Supra gingival calculus is white or yellow and more aerated
Sub gingival calculus is dark brown or greenish and much more firmly adherent to the tooth structure and more anaerobic
Chemical composition of calculus
Mineral content is lower in subgingival and it has more organic component
What is the plaque matrix made of?
Proteins, carbohydrates and water
How do bacteria form polysaccharides in plaque?
Bacteria can synthesis extracellular polymers from simple sugars
Plaque bacteria have glucosyl transferases (GTF) which breaks down sucrose into fructose and glucose and used the energy released to form a glucose and fructose polymer
What do plaque bacteria store glucose as?
Glycogen
What are the 3 dietary monosaccharides?
Glucose, fructose, galactos
How does bacteria ability to make polysaccharides link to plaque formation?
Bacteria deposit glucans (glucose polymer) and fructans (fructose polymer) extracellularly providing a voluminous sticky environment for the plaque organisms.
How does diet affect the acquired pellicle?
Affects adsorption of salivary components on the enamel
What dietary factor mostly affects plaque composition?
Mutans streptococci are much more numerous in plaque with sucrose rich diets
What is sucrose?
Disaccharide of fructose and glucose
What is resting plaque pH?
6.5-7
What does the Stephan’s curve show?
Plaque falls to around 5 within 2-3 minutes of rinsing mouth with a sugar solution. It then takes at least 20 mins for the pH to go back to normal through the action of saliva and it’s buffering capacity and washing away debris.
Why does pH drop so rapidly in the Stephan’s curve?
Due to the rate of sugar metabolism in the plaque
What is the horizontal red line on the Stephan’s curve?
Critical pH - there is enamel dissolution (at pH 5.7)
Hydroxyapatite is demineralised and crystals are lost
What is the majority of acid produced in the mouth?
Lactic acod
How does sugarless chewing gum prevent caries?
Stimulates salivary flow
What is the effect of xylitol?
Can induce remineralised of enamel. It is a sugar alcohol used as a sweetener.
How does plaque metabolism reduce pH?
Plaque bacteria can produce acid from host carb intake
Anaerobic metabolism produces lactic acid
Sugar consumption
How does saliva increase pH?
Acts as a buffer to acids, by containing bicarbonate ions
How can plaque metabolism raise pH?
Plaque metabolises urea to produce ammonia and raise pH.
Alkali production takes place in carbohydrate starvation periods (overnight)
When is pH highest for most people?
Before breakfast since alkali production takes place overnight
