CAP 4 + 5- Plaque pH studies Flashcards
what is the product of bacteria breaking down glucose to release energy?
lactic acid
what is the value of the critical pH of plaque?
5.5
what happens below the critical pH of 5.5?
hydroxyapatite dissolves
Name 4 plaque pH studies.
- Metal probes e.g. antimony, irridium
- Glass pH electrodes
- Radio telemetry
- Removal of plaque samples
List the stages of R M Stephan 1944 experiment.
- Plaque on anterior tooth
- Antimony electrode within plaque
- Recorded pH
- 2 minute rinse: 25ml of 10% glucose
- Recorded pH every 10 mins
What are the Stephan curve characteristics?
- Rapid pH drop
- slow pH rise
- Variable time course :15-50 minutes
Describe the rapid drop in pH.
> speed microbes metabolise CHO:
- glucose + sucrose -rapid
- large carbohydrates e.g. starch - slow
Name substrates that cause rapid diffusion and lots of acid (lactic) to cause a low pH.
Glucose or sucrose
Name substrates that cause less acid (mixed) to cause a not so low pH.
starch which salivary amylase breaks into glucose and maltose
what effects the lowest pH of the Stephan curve?
- Microbial composition of plaque
- Nature of CHO source
- Rate of diffusion in and out of plaque
what causes the rise in pH?
- acid diffusing out
- salivary bufferin (bicarbonate in salvia neutralises acid)
where does most of the buffering occur?
striated ducts
Describe Stephan curve of caries-free subjects.
– started higher + finished higher
– stayed above the critical pH
Describe Stephan curve of caries-active subjects.
– started lower + finished lower
– remained below the critical pH for long periods
what food produce a Stephan-like response?
carbohydrates (CHO foods)
What is the acidogenic potential of food?
the ability of food to produce acid
what does the acidogenic potential of food depend on?
- nature of food
- properties of the host
- bacteria in dental plaque
What can be used as alternative sweeteners?
Nutritive sweeteners :
- sugar alcohols
- bulk sweeteners
Name 3 nutritive sweeteners.
- Sorbitol
- Mannitol
- Xylitol
What is the result of using alternative sweeteners?
- slowly fermented by bacteria
- only slight pH drop
What are alternative sweeteners used in?
– chewing gum (mannitol)
– confectionary and toothpastes (xylitol)
what is a problem with alternative sweeteners?
potential laxative effects
what is used to bring pH back up after testing different sweeteners?
Urea
what are the other alternative sweeteners used that are non-nutritive?
Intense sweeteners
what quantities are intense sweeteners used?
small quantities
Name and describe 3 intense sweeteners.
> Saccharin: – ~300x sweeter than sucrose – Bitter aftertaste > Aspartame: – Candarel and NutraSweet > Acesulfame-K – 300 X sucrose – Soft drinks and sugar free chewing gum
What are the conditions to term a food “tooth friendly”?
If plaque pH does not fall below pH 5.7 within 30 mins of ingestion
Describe the variables in the nature of food.
- Amount and type of fermentable CHO in food
- Physical form ( sticky and retained vs liquid and swallowed)
- Buffering capacity of food
- Sialogues (saliva-flow promoters) in food
- Sequence of foods in a meal
Describe the host factors.
- Food eating habits (sequence)
- frequency of food intake
- buffering capacity of saliva
- calcium and phosphate concentrations in saliva
- fluoride content of enamel
What is the differences between snacking diet and have 3 main meals.
In the snacking diet the pH drops below critical pH more often than the 3 times its drops at meal times
what is the best way to end a meal?
end a meal with a non-acidogenic food e.g. cheese
what are the disadvantages of frequent snacking?
– More low pH episodes
– Less time for pH to recover
what does salvia contain?
– HCO3- (buffer )
– Ca2+ and PO43-
when does salivary flow increase?
– Masticatory-salivary reflexes
– Gustatory stimulants
When does salivary flow decrease?
– At night
– Xerostomia - Gland damage (e.g. Radiotherapy)
Where is there more salvia between the mandible and the maxilla?
more salvia at floor if mouth
when is the less buffering capacity?
less saliva
Describe the salvia flow and plaque pH when eating a sweet.
– increased saliva flow
– plaque pH may rise, before dropping
Describe the salvia flow and plaque pH when eating a non-fermentable substance.
– increased saliva flow
– pH increase to resting (neutral pH) levels
what is important in salvia flow and plaque pH?
Sequence of food consumption
what should not be last in a meal?
sugar-containing foods
what is good for dental health?
sugar-free chewing gum
what are the factors affecting acid production with bacteria in plaque?
- numbers of acidogenic bacteria
- types of acid produced
- numbers of acid-consuming bacteria
- numbers of base-producing bacteria
- metabolic state of bacteria when food is ingested
what acid sources cause acid erosion on the palatal surface?
- dietary acid
- gastric acid
what happens when plaque builds over enamel?
enamel carie lesion forms
What happen when lactic acid touches enamel?
erosion of the outer surface of enamel
Describe Silverstone’s artificial caries experiment.
> Teeth exposed to acid lose enamel mineral > Clinically: erosion > Histologically: – Generalised loss of enamel – No zone structure – No surface layer > Silverstone (1968): – Teeth were placed in lactic acid containing diffusion- limiting gels – Enamel caries-like lesions
what forms when lactic acid is added to enamel when there is an diffusion limiting gel is in place?
lesion identical to an enamel caries lesion
what is the summary of Silverstone’s artificial caries experiment?
- Polysaccharides and other gel-like components of dental plaque reduce diffusion of dissolved enamel mineral away from the tooth surface
- This results in the characteristic zoning of the enamel lesion
