inorganic components of saliva Flashcards
why is H+ the most important constituent of saliva (despite not being a true inorganic component)
its concentration determines pH of oral environment
typical salivary pH in adults
6 - 7.4 but varies according to salivary flow
babies = more alkaline
why is pH important
- salivary enzymes only operate in a restricted pH range = optimal pH
- for determining solubility behaviour of other salivary proteins which precipitate onto tooth surface when pH is equal to their isoelectric point at which they have no net charge
- maintaining ionic product for HAp
what dental disease are protons key to
CARIES
they drive HAP dissolution
what does pH fall to following carbohydrate intake and why
as low as 4.5
- fermentation of carbohydrates by plaque microorganisms generating organic acids
why is pH important for HAP (mineral component of teeth)
- HAP is an inorganic calcium phosphate salt
- it dissolves below critical pH of 5.5
- so some dissolution of mineral occurs each time we ingest sugary food (demin)
how is the plaque pH restored to neutrality following sugar intake
salivary buffering (takes around 20-40 minutes for pH to be restored to value above critical pH) salivary components play key role in this gradual restoration to neutrality
what happens when salivary buffering takes place
1) demin reversed
2) new mineral precipitated
3) so teeth can repair themselves if conditions are favourable
4) THIS IS REMIN
what data is crucial to understanding the caries process
stephan curves / response
what happened when - imfeldt coworkers (1977)
1) chewed wax for 3 minutes then rinsed mouth with a 0.025% sucrose solution
neutral pH initially
plaque falls to 5.5 pH after sucrose
salivary buffering means plaque pH rises
pH rise accelerated when chew wax again
what happened when - imfeldt coworkers (1977)
2) then chewed wax for 3 minutes then rinsed mouth with a 1.25% sucrose solution
sugar rinse more concentrated
plaque falls to even lower pH of 4.5
again restored almost to neutrality by chewing wax
what happened when - imfeldt coworkers (1977)
3) then chewed wax for 3 minutes then rinsed mouth with a 2.5% sucrose solution
3rd sucrose rinse
plaque pH falls dramatically
even after chewing wax pH only rises to 6.5
what happened when - imfeldt coworkers (1977)
4) chewed wax for 3 minutes then rinsed mouth with a 5% sucrose solution
BUT then given 3% urea sample
predictable pH fall to almost pH 4
urea increases pH by conversion to ammonia
plaque pH restored to neutrality
what happened when - imfeldt coworkers (1977)
5) chewed wax for 3 minutes then rinsed mouth with a 10% sucrose solution
BUT then given 3% urea sample
pH falls to below 4 and remained low
rapidly reversed by urea solution
pH restored to neutrality
what does data from the imfeldt coworkers (1977) experiment illustrate
1) effect of giving microorganisms access to fermentable carohydrates
2) consequences - pH dec
3) HAP mineral dissolves below pH 5.5, longer it remains below = more tooth mineral lost
4) higher conc of sucrose = lower resulting plaque pH
5) stimulation of saliva incs its buffering capacity
6) telomeric measurement = an important research tool when determining cariogenic potential of food
as salivary flow rate increases…
salivary buffering also increases
what is the general rule of saliva pH
increase flow rate = increase pH
- pH of saliva varies with flow rate
- higher flow rates increase salivary buffering
what happens when saliva is stimulated
- the higher the flow rate the higher the resulting pH
- higher flow rate neutralises acidic pH more quickly
what ions are the most important buffer in saliva
BICARBONATE (HCO3^-)
important buffer at HIGH flow rates
where are bicarbonate ions produced
striated epithelium of the secretory ducts and parotid gland
SO their concentration in saliva = reflection of metabolic activity of salivary glands
what is the range of bicarbonate ions
a) unstimulated
b) typical concentration
b) highest flow rates
a) <1mM
b) 15mM in mechanically stimulated saliva (ie when chewing)
c) 60mM
what happens to bicarbonate conc when stimulation begins
- highest salivary flow results in highest increase in bicarb conc
why is bicarbonate a good buffer for protons
pKa value of 6.1 so equal concentrations of carbonic acid and bicarbonate ions at pH 6.1
what is the reversible reaction for carbonic acid
h+ + HCO3^- -> H2CO3 -> (carbonic anhydrase) H2O + CO2
what enzyme catalyses the conversion of H2O + CO2 into carbononic acid H2CO3
CARBONIC ANHYDRASE (present in salivary glands AND saliva)
what happens in the carbonic acid reaction as salivary pH falls
- forward reaction favoured
- so bicarbonate ions pick up protons
- the protons can be eliminated entirely as H2O
what does the action of carbonic anhydrase generate
carbonic acids and therefore bicarbonate ions (carbonic acid dissociates to these)
what is bicarbonate derived from
plasma
partly from metabolic activity of salivary glands themselves
what is carbonic acid conc in saliva
stable at 1.3mM
in eqbm with alveolar CO2 conc in the lungs
DOESNT ALTER with changing salivary flow rate
BUT contribution from the gland itself increases with increased flow due to increased metabolic activity
explain each part of the bicarbonate reaction
IN SALIVARY GLAND
1) catabolism in gland produces H2O + CO2
2) theyre converted to H2CO3 by carbonic anhydrase
3) H2CO3 deprotonated into HCO3^- + H+
4) excess HCO3^- is in saliva
IN PLASMA
4) the rest of HCO3^- reforms carbonic acid (protonation / addition of H+)
5) carbonic acid converted back to H2O + CO2 which goes to the lungs
which inorganic ions are present
K+ and Na+
what is the role of K+ and Na+
counter ions to preserve electrical neutrality
what are
a) K+
b) Na+
the counter ions for
a) phosphate
b) bicarbonate
what is the conc range of
a) K+
b) Na+
a) 14 - 32 mM
b) 6 - 26mM
explain the production and presence of Na+
1) actively pumped out of primary salivary fluid as passes along intercalated duct of salivary gland via NaK pumps (extent of this depends on amnt of time fluid remains in the duct)
2) SO low flow = low Na concs in saliva
3) higher flow = Na concs rise
what else may lead to a rise in Na+ concentration in saliva
damage to ductal cells (ie may be seen following radiotherapy) as will reabsorb less Na+
explain the production and presence of K+
1) added to ductal fluid throughout its passage through the duct
2) so K+ conc in saliva remains relatively constant
as flow rate increases what happens to
a) Na+
b) K+
a) increased
b) stays the same / constant
which ion is present in saliva but have unclear origin
Mg2+
what is the range of concs of Mg2+ in
a) saliva
b) primary ductile fluid
a) 0.5mM in unstimulated
0. 2mM in stimulated
b) <1mM
where do we expect Mg2+ contribution to come from
1) cellular degradation in oral environment (of host + microbial cells as contain high Mg levels)
2) early carious attack (Mg2+ rich mineral is 1st to be removed during acid attack)
as salivary flow rate increase, Mg2+ conc…
decreases
what is the origin of Ca2+
actively secreted by major salivary glands
it forms complexes with calcium binding salivary proteins (protein binding makes behaviour w flow rate variable)
what is Ca2+ important in
1) maintenance of ionic product for HAP
2) protective functions of saliva = remin of tooth mineral to prevent mineral dissolution
SO repair + maintenance of tooth mineral
what is the range of concs of Ca2+ in saliva
1 - 2 mM
usually around 1.5
= represents conc of IONIC Ca only (same amount again is in complex with other ions and salivary proteins)
as salivary flow rate increase, Ca2+ conc…
stays the same
why is it difficult to describe changes in total salivary Ca2+ conc with flow rate
contribution to whole saliva from different glands varies with flow rate
different gland secretions have different Ca concs
what can we see with Ca2+ concentration
1) parotid gland secretion = only 1/2 the Ca content compared with submandibular saliva
2) protein content changes w salivary flow rate and different proteins bind Ca to different extents
what can we see with Mg2+ concentration in saliva
dec w flow rate (simple dilution effect)
low at 0.4mM/litre in unstimulated saliva dec’ing to 0.2mM/litre in stimulated where salivary flow rate was inc’d to >1mm/min
explain the effect of flow rate on concentration of protein in saliva
- increase as flow rate incs
- at lower flow rate = more variable response
- some proteins bind Ca = complicating the predicted behaviour of Ca with changes to salivary flow rate
how are phosphate ions important in salivas role in maintaining oral health
1) act as buffer (buffer in physiological pH range so unstimulated saliva)
2) buffers in plaque
3) PRIMARY ROLE = work with Ca2+ to inhibit dissolution, remineralise teeth (maintenance of ionic product for HAP)
what is the conc of phosphate ions in saliva
2 - 13 mM
as flow rate increases, inorganic phosphate (H2PO4^- / HPO4^2-) conc…
decreases
why might phosphate decrease as flow increases
its actively added to secretion as it passes through the ducts
fast transmission = reduced phosphate conc of resulting saliva as not as much time for duct to add phosphate
what is the effect of increased bicarbonate due to increased flow rate on ionic phosphate species
- pH more alkaline
- amount of H2PO4- decs
- HPO4^2- and PO4^3- inc, imp as these less protonated phosphate ions (imp to the solubility of tooth mineral)
what is the formula of hydroxyapatite (HAP, HA, OHA, apatite)
Ca10(PO4)6(OH)2
what is the ionic product for HAP
Pi = [Ca]10 x [PO4]6 x [OH]2
what is hydroxyapatite (aka apatite)
- calcium phosphate salt (most stable of all calcium phosphate salts)
- principle mineral component of all teeth and bones (mineral component of enamel and dentine)
- impure (contains carbonate, Mg, F ions etc)
other than HAP what else is found in skeletal tissue
number of diff calcium phosphate salts
depends on local conditions - pH, other ions present
how does HAP behave in solution (hint: most stable of all calcium phosphate salts)
1) spontaneously precipitate out of solution when solubility product is exceeded (governed by conc of its constituent ions in solution (Ca, phosphate + hydroxyl)
why do the properties of HAP mean it is essential saliva contains sufficient Ca + phosphate ions to maintain the solubility product for HAP
when their concs fall below the solubility product the tooth mineral will spontaneously dissolve (even @ neutral pH)
so increasing their concentration encourages spontaneous repricipitation of mineral
BUT what is the effect of Ca + phosphate ion concentrations being too high
leads to mineral precipitation at other ectopic sites in the mouth
can cause calculus, tartar, salivary gland stones
what term is given when a supernatant solution contains sufficient ions of a given salt to produce spontaneous precipitation of that salt
solution is saturated with respect to the salt
what term is given when a supernatant solution contains more than sufficient ions of a given salt to produce spontaneous precipitation of that salt
solution is SUPER saturated with respect to the salt
what is the saturation status of HAP in saliva
SUPER saturated
at neutral pH
(more supersaturated at high flow rates, favouring repair)
how is HAP different to common salts (ie NaCl)
pH has profound effect on solubility product due to phosphate ion
what is PO4^3-
ORTHOPHOSPHATE ION
- can pick up 3 H+ (ease of protonation dictated by pKa value of the different phosphate species = protonation of phosphate group is pH dependent)
what is the reversible equation for the sequential protonation of H3PO4
PO4^3- -> HPO4^2- -> H2PO4^- -> H3PO4
how does the deprotonation of H3PO4 occur at pH 2.12
1) [H3PO4] (undissociated phosphoric acid in solution) = deprotonated to [H2PO4-] (dihydrogen phosphate)
2) pH incs further (less H+)
3) phosphate ions become increasingly less protonated
4) pH 7.2 = half HPO42- (monohydrogen phosphate) and half H2PO4-
5) continued pH inc = inc PO4^3- formed
6) at pH 12.7 = half PO4^3- + half HPO42-
what does the protonation of phosphoric acid mean
when pH of oral environment changes, mineral component of tooth enamel and exposed dentine is also chemically changed
phosphoric acid in
a) acidic
b) increasingly alkaline
conditions
a) phosphate groups become increasingly protonated (more H+) resulting in formation of salts of greater solubility
b) number of protonated phosphate groups reduces
resulting in formation of salts of lower solubility
when does caries result
when dissolution is greater than repair (or repair impaired / prevented)
what salts of greater solubility are produced when protonation of phosphate groups increased
1) monocalcium phosphate (MCP, Ca(H2PO4)2)
2) brushite / dicalcium phosphate (DCPD, CaHPO4 / CaHPO4.2H2O)
3) octacalcium phosphate (OCP, Ca8(PO4)4(HPO4)2.5H2O)
4) tricalcium phosphate (TCP, Ca3(PO4)2)
5) HAP
which patients cannot repair tooth mineral when it is lost and why
XEROSTOMIA
lose ability to buffer acids
what other ions reprecipitate tooth mineral and where does it accumulate
F-
in porous enamel and dentine (inc caries lesions)
what is the conc of F- in saliva
0.001 - 0.005 mM
small conc, varies little with flow rate
incd in plaque fluid
why does F- effect solubility behaviour of HAP
- replaces OH- in HAP crystal lattice structure
- forms a more stable, less soluble in acid mineral (inhibits acid dissolution)
so how does F- promote remin (repair of tooth mineral)
facilitates HAP reprecipitation
what is the difference in salivary F- of pts living in fluoridated areas compared to non-fluoridated
2x
small absolute difference
BUT significant benefits in caries reduction
