Prevention of Caries By Saliva

• What is meant by the static & dynamic effects of saliva?


  Static - Saliva is just present and not moving around

  
  

  Dynamic - Saliva is moving over tooth surfaces
• What are the static effects of saliva?

  Antibacterial

  
  

  Supersaturated Ca/P

  
  

  Pellicle formation (acquired enamel pellicle- layer of protective proteins which sit on the tooth's surface)

  
  

  Plaque substrates e.g Urea

  
• What are the dynamic effects of saliva ?

  Buffering (bicarbonate increases with flow)

  
  

  Clearance of sugars and acids

  
  

  Supersaturation (increases with flow)

  
• How effects do plaque substrates have?

  Urea can be converted by Urease into ammonia.

  
  

  Ammonia helps to maintain High pH

  
  

  High pH is useful when buffering acids
• What is specific to each gland?

  Salivary protein profile

  
• What percentage does each salivary gland contribute to whole mouth saliva?

  At rest, the submandibular/sublingual gland contributes the most.

  
  

  When stimulated, the parotid gland contributes the most

  
• How is saliva made?

  By an osmotic driven process

  
  

  -Salivary glands secrete lots of sodium & chloride into the ducts that lead into the mouth & this helps to draw water by an osmotic process
• What are the 2 main types of cells and what do they do?

  Acinus : make the saliva

  
  

  Striated Duct : modify it

  
• How do the ion concentrations in parotid saliva change?

  When going from a resting to stimulated state,

  
  

  Na+, Cl- and HCO3- concentration increases

  
  

  Phosphate and Ca2+ stays relatively the same

  
• How does saliva have a bacteriostatic effect?

  Saliva has many PRPs, SIgA & mucins which bind bacteria through glycosylation, then aggregate and it's removed by swallowing (maintains bacterial levels = Bacteriostatic)

  
  

  On the other hand, lactoferrin, cystatins, histatins & lysozyme actively kill bacteria
• What does it mean to say saliva is supersaturated compared to enamel?

  If teeth were left in water, they'd dissolve

  
  

  -Whereas saliva has high levels of Ca2+ & phosphate to prevent this,

  
  

  -BUT saliva requires chelators to prevent high levels of CaP precipitating- statherin & acidic PRPs
• Which proteins are important in forming a stable pellicle of proteins on the surface of teeth?

  Hydroxyapatite binding proteins e.g. statherin, acidic PRPs & histatin 1 (all contain phosphate groups)
• How is saliva able to form a thin film over all of our teeth (this is a dynamic effect)?

  It has quite a low surface tension & can spread easily over the mucosa & also the teeth

  
  

  It's also constantly moving, with the film velocity being fastest next to ductal openings
• What happens at the location where the film is the fastest?

  -That's where there is the greatest buffering due to urea causing rise in pH

  
  

  -But one of the side effects is that's where you find the greatest accumulations of calculus
• What is the reason for finding the most calculus where the film moves the fastest?

  In those areas, the pH always stays very high so that it never gets dissolved away
• What is Stephan's curve?

  He added sucrose to plaque and found that the pH decreased.

  
  

  He found that the recovery of pH was due to buffering in the saliva

  
  

  Critical pH of enamel (5.5) = when enamel starts to dissolve

  
• Show the effect of saliva on Stephan's curve.

  
• What is the main buffering mechanism within saliva?

  HCO3- + H+ --> H2CO3--> CO2 + H2O

  Carbonic anhydrase VI is what converts carbonic acid to CO2 + H2O

  
• What is the effect of increasing salivary flow rate?

  Increased clearance of sugars & acids

  Increased buffering by bicarbonate

  Increased bicarbonate, increases pH

  Increased pH makes saliva more saturated with calcium (leads to calculus)

  More anti-bacterial proteins
• What will increase caries susceptibility?

  Low salivary flow rate

  Foods with high levels of sugar/ fermentable carbohydrate/ liquid/ acidic

  Regular snacking

  Low salivary bicarbonate/ urea/ CaP levels

  Poor oral hygiene (snacking during night)