plaque pH and salivary flow Flashcards
The type of bacteria which predominates in dental plaque depends on :
- Substrate supply
- Dietary and endogenous substrates
- Oxygen content
- Aerobic vs anaerobic bacteria?
- pH of plaque fluids and saliva
- Ionic strength
- Toxin content
how are different substrates converted into glucose
what is the product of glycolysis
Sucrose split into glucose
Starch digested into glucose
Glucose to pyruvate
how does pyruvate generate organic fatty acids?
- Lactic acid
- Remove one proton
- Carbonyl group changed to hydroxyl group
- Acetic acid
- Remove CO2
- Carbonyl group removed
- Acids are produced
- Carboxyl groups COOH make them acidic
during the early biofilm, how does the pH change?
open plaque architecture
- aftering cleaning and brushing teeth
- bacteria colonise surface of enamel
- forms a loose biofilm
- mainly urea converted into H2CO3 and ammonia
- raises the biofilm
how does pH change in the mature biofilm?
closed plaque architecture
- dense biofilm
- Forms in the presence of bacteria which utilise carbohydrates to produce acid products
- decrease in pH
what is stephan’s curve? draw
what does it show?
the change in dental plaque pH in response to the consumption of a beverage or food
- pH returns to normal after time
- Initial decrease takes time
- bacteria take some time to digest glucose to pyruvate
- After it has all be digested
- Saliva flow responsible for recovery of pH to normal
- 30-50 minutes usually
- Saliva flow responsible for recovery of pH to normal
- Critical pH - below
- Enamel demineralisation
what is the effect of chewing on plaque pH and stephan’s curve
Chewing increases saliva flow
- More rapid pH equilibration
cheese - neutralisation of pH
advantages of artificial sugars
- Body does not digest these artificial sugars to energy
- pHs do not reduce so much compared to sucrose
disadvantages of artificial sugars
- Can result in them remaining undigested in the gut
- Gut tries to dilute their concentration
- Takes up water from outside
examples of artificial sugars
lycasin: mixture of dextrins
xylitol and sorbitol: sugar alcohols
sorbose: a ketose
how does the carbonate/bicrabonate salivary buffering system work?
- Carbonic Anhydrase VI (CA VI) is secreted by serous acinar cells of the parotid and submandibular glands.
- CA VI assists rapid inter-conversion of carbon dioxide and water into carbonic acid, protons and bicarbonate ions.
- Chewing and spicy food stimulates salivary flow.
- Increase function of carbonic anhydrase
- Chewing and spicy food stimulates salivary flow.
- Increase in flow rate increases the bicarbonate concentration.
- pH rises above the pKa of bicarbonate.
what is xerostomia usually caused by?
age
medication
what buffering systems exist within plaque fluids?
- bicarbonate / carbonate
- inorganic phosphates
- amino acids
what factors influence acid production in dental plaque?
- Open or closed plaque architecture
- Enamel structure / gingival recession
- Oral hygiene regime and time of day
- (circadian rhythms, saliva flow, …)
- Diet
in what ways does diet influence acid production in dental plaque?
- Liquid foodstuff provides a more soluble supply of nutrients to bacteria but are rapidly removed by swallowing.
- Fibrous foods require chewing and increase salivary flow.
- Acidic and spicy foods stimulate salivary flow.
- Sticky foods adhere to surfaces.
- Dry gritty foods impact in fissures on the enamel surface.
- Frequent eating increases cariogenicity.
