Caries from a histological perspective Flashcards
How does bacterial colonisation of enamel caries occur?
- On normal enamel, there is a thin coating of saliva termed as “acquired pellicle” containing glycoproteins and proteins
- Some bacteria may have surface receptors which specifically bind to the molecules on the acquired pellicle
- The bacteria will digest the glycoproteins on the acquired pellicle. If food is part of the pellicle, then bacteria will digest that, and consequently release acid.
What are the cariogenic bacteria involved in enamel caries?
- Streptococcus mutans
- Streptococcus sobrinus
- Lactobacilli
What are the substrates which make bacteria become cariogenic? (4)
- Sugar
- Sucrose, glucose and fructose
- Simple carbohydrates that are fermentable
- E.g. nursing caries; milk has sugar, sugar stays on tooth for whole night, little saliva= caries
Describe the salivary factors which are protective against caries. (7)
Saliva contains:
- Antibacterial components: IgA, IgG, IgM, C3, Lysozymes (breaks down peptidoglycan)
- Remineralising and buffering components: Calcium, Phospate, Bicarbonate (buffering)
- Flow: mechanical clearance
- Lactoferrin: Iron binding (we need iron, so do bacteria, so lectoferrin ensures we get iron instead of bacteria, so bacteria can’t metabolise very well), and direct antimicrobial
- Sialoperoxidase: Antimicrobial properties
- Definsins: drill holes in surface of bacteria
Phosphates
Proteins; made up of acidic and basic amino acids to buffer
Bacterial metabolism SIALIN which increases pH
What are extracellular polysaccharides? How do they form?
- Extracellular polysaccharides; glucans are chains of glucose molecules
- Glucans are made by bacteria that can generate chains of glucose materials using an enzyme called glucosyl transferases
Some glucosyl transferases make straight chains, some make branches. Branches are less soluble
- Bacteria makes glucans chains so that they can store it away in the extracellular environment and access it later
- This greatly increases the volume of plaque
What is the effect of Stephan’s curve on caries?
- Frequent snacking of fermentable carbohydrates throughout the day causes the pH to drop below the critical 5.5 pH where more demin happens than remin
- The more time the plaque spends below critical pH of 5.5, the more time the mouth is acidic = caries
- Limiting snacking between meals means less time is spent below critical pH
What is the pattern of xerostomia and caries?
- People with xerostomia have rampant caries; caries in 10 or more, otherwise healthy teeth, within a short amount of time
- This is because they have low saliva flow, subjecting their mouths to high acidity for prolonged periods
- Saliva has protective properties
List the overall zonal structure of caries.
Contains four zones;
- Surface zone
- Body of lesion
- Dark zone
- Translucent zone
Describe the surface zone of enamel caries.
- The surface zone is more highly mineralized with higher fluoride levels and lower magnesium levels
- The surface zone remains relatively normal because it is an area of active reprecipitation of mineral derived both from the plaque/ food/ saliva
- The surface zone gains dissolved ions from deeper areas of the lesion because the ions diffuse outwards
Describe the body of lesion in enamel caries.
- The body of the lesion may become stained by external pigments from food, tobacco, and bacteria
- The lesion is now clinically recognizable as a brown spot.
- Contains apatite crystals larger than those found in normal enamel and contains large pores
- It is suggested that these large crystals result from the reprecipitation of mineral dissolved from deeper zones
- With continuing acid attack there is further dissolution of mineral both from the external border of the apatite crystals and from their cores
- The lost mineral is replaced by unbound water
- There is increased prominence of the striae of Retzius in the body of the lesion, the explanation for which is unknown
Describe the dark zone of enamel caries.
- This zone contains small pores
Some of the pores are large, but others are smaller than those in the translucent zone, suggesting that some remineralization has occurred due to reprecipitation of mineral lost from the translucent zone - It is thought that the dark zone is narrow in rapidly advancing lesions and wider in more slowly advancing lesions when more remineralization may occur.
Describe the translucent zone of enamel caries.
- This is the first recognizable histological change at the advancing edge of the lesion
- It is more porous than normal enamel
- The translucent zone is sometimes missing, or present along only part of the lesion.
Why is dentine caries different from enamel caries?
- Dentine differs from enamel in that it is a living tissue. Thus, it can respond to caries
- Dentine is made up of collagen; a protein
- When dentine caries occurs, it undergoes proteolysis; the breakdown of proteins into polypeptides/ amino acids
What are the zones involved in dentine caries?
1: Zone of destruction
2. Zone of invasion
3. Zone of demineralisation
2. Zone of sclerosis
Describe the zone of destruction.
- When enamel has been cavitated, bacteria infect the dentine
- There may be a Zone of Destruction within the dentine, where the dentine becomes necrotic, and liquifies
- The liquified areas are called Liquefaction Foci
