pH, Buffers, and Role in Caries Formation (Serwer 2) Flashcards
The tooth is ___% enamel and the mineral is primarily ______, which is a __________.
- 96%
- Hydroxyapatite
- Crystalline calcium phosphate
Some bacteria produce ______ when they metabolize sugars anaerobically. The production of this substance by tooth-attached bacteria initiates most tooth decay by dissolving the mineral of enamel.
Lactic acid
Bonsted-Lowry Acid
A substance that donates a hydrogen ion to another substance. Stomach contents are known to be “acid.”
Bonsted-Lowry Base
A substance that accepts a hydrogen ion from another substance.
Calcium phosphate is more soluble when the concentration of H+ _____.
Rises
Bacteria coat surface of teeth and secrete polymers to form a film called a _____. The oral cavity has 200-300 species of bacteria.
Biofilm
The bacterium that starts a “tooth decay” biofilm can be _________, which produces lactic acid from glucose after splitting sucrose with invertase.
Streptococcus mutans
S. mutans lives in an acidic environment better than most other oral bacteria, so it is known as _______.
Acidoduric
One key polymer secreted is _____.
Dextran
Dextran formation
n sucrose → (glucose)n + n fructose (enzyme = dextransucrase, works only on sucrose).
Micrometer
10-4 cm: about 2.0x the width of a typical bacterial cell like E. coli.
Nanometer
10-7 cm: 0.1 - 0.5x the radius of most proteins.
Angstrom
10-8 cm: About the radius of a hydrogen atom.
Lactic acid is produced by _______. The biofilm sequesters acid and keeps it next to the tooth enamel.
Anaerobic metabolism
Chemically, we describe a compound as being a strong or weak acid, based on the extent to which the acid proceeds to release a _______.
Hydrogen ion
pH represents the hydrogen ion (H3O+ or H+) concentration
on a logarithmic scale as…
pH = -log([H3O+])
Keq equation
[Products]/[Reactants]
For HCl + H2O –> H3O+ + Cl-
Keq = [H3O+][Cl-]/[HCl][H2O]
For weak acid, use the Hendersen-Hasselbach Equation, which is…
pH = pKa + log([A-]/[HA])
pH = pKa when _______.
A weak acid is 50 % disassociated
The titration curves of all monoprotic, weak acids have the ______. The midpoint is at a pH value equal to the ______.
- Same shape
- pKa value
____ and ____ are the major buffers in saliva.
Phosphate (pKa2=7.2) and Bicarbonate (pKa1=6.1)
In amino acids ____ groups are protonated at low pH and ____ group protonated at high pH. The Zwitterionic from has ______ charge.
- Both
- Neither
- Neutral
_______ is buffer-derived resistance to change in pH caused by the addition of acid or base.
Buffering Capacity
Buffering Capacity is determined by….
- the _______ of pH from the pKa of the buffering species: The closer the pH is to the pKa, the higher the buffering capacity is (based on the HH equation).
- the of the buffering species: The higher the concentration of the buffering species is, the higher the buffering capacity is.
- Distance
- Concentration
pH under dental plaque when carious lesions start
5.0 - 5.2
pH is important in dentistry for the control of ________.
Local anaesthetics
Hydroxyapatite in…
- Enamel ____ %
- Dentin ____ %
- Bone ____ &
- 95%
- 70%
- 65%
As % F increases, teeth become _____ caries prone; as % CO3 increases, teeth become _____ caries prone.
- Less
- More
Variability includes lattice dimensions, average crystal size, % mineral, and crystallinity index or splitting function (SF ____ as crystallinity rises).
Rises
Tricalcium phosphate, Ca3(PO4)2 or ______, has ___ crystalline forms (B is one of them).
- Whitlockite
- Three
Tricalcium phosphate can be made by heating hydroxyapatite in the absence of ______ and is found in rocks and bone and used in bone grafts, toothpaste, and baby powder.
Oxygen
The OH- group of Hydroxyapatite is replaceable by ____________. PO4-3 is sometimes replaced by ______. Silicate (SiO3-2) can be made to partially substitute for ________.
- F-1, Cl-1, CO3-2
- HPO4-2
- Both PO4-3 and OH-1
Hydroxyapatite
Ca10(PO4)6(OH)2
β-TCP (whitlockite)
Ca3(PO4)2 (Used in toothpaste)
Dicalcium phosphate dihydrate (brushite)
CaHPO4·2H20 (initiator of kidney stones), monetite when anhydrous
Octacalcium phosphate (OCP)
Ca8H2(PO4)6·5H2O
Fluorapatite (FA)
Ca5(PO4)3F+ (most common form of natural mineral phosphate)
Since HPO42− is more soluble than the (PO4)3- that is present in Ca10(PO4)6(OH)2, the equilibrium is shifted towards ________.
Solubilization
Dissolution is increased with substitutions of…
- Carbonate CO3–
- Strontium Sr++
- Magnesium Mg++
Dissolution is decreased with substitutions of…
-Fluoride F-
Solubility _____ as crystallinity increases.
Decreases
In general, the dissociation of salt (all calcium phosphates are salts) is described by _______.
AaBb –> aA+ + bB-
The equilibrium constant, (called K) is described by _________.
K = [A]a[B]b/[AaBb]
The solubility product constant (Ksp) is described by ___________.
Ksp = [A]a[B]b
Net ____ from calcium phosphates occurs when Ksp > [A]a[B]b.
Net ______ occurs when Ksp < [A]a[B]b.
As Ksp decreases, the solubility ______ and the stability of the solid ______.
- Loss
- Deposition
- Decreases
- Increases
For calcium phosphates, Ksp is ___ dependent because the phosphate becomes protonated as pH is lowered.
The Ksp is _____ as pH is lowered because phosphate protonation lowers solubility.
In other words, solubility ______ in acid.
- pH
- Raised
- Increases
Ksp of HA
3.37 x 10^-58
Ksp of Fluorapatite
2.5 x 10^-60
Ksp of Human enamel
7.2 x 10^-53 to 6.4 x 10^-58
Net mineral ______ occurs above/right of a curve; net _____ below. As pH decreases, total [Ca2+] concentration for deposition increases.
- Deposition
- Dissolution
Caries progression is relatively slow in ______ because of remineralization.
More rapid in _____ because of increased sequestering of H+ and denaturation of collagen, the protein scaffold for dentin mineral.
“Piling on” of other aciduric bacteria, including various _______.
- Enamel
- Dentin
- Lactobacilli
Fluoride in the water supply (~10 ppm) reduces caries incidence by ______.
The mechanism is replacement of OH- by F- in the hydroxyapatite of enamel (fluorapatite). Although, at high levels Fl- is a metabolic poison, it is not concentrated enough for long enough to block the propagation of bacteria when derived from water fluoridation.
30-50%
The effects on caries occur because fluorapatite is (1) less ______ than hydroxyapatite and (2) less ______.
Topical fluoride treatment (1% or 10,000 ppm) is effective.
- Acid-soluble
- Bacteria-adherent
Minimize ingestion of ______ between meals. During meals, the additional saliva reduces the effect on pH.
Use sucrose substitutes: ______, for example, found in many fruits and vegetables, which is xylose (5 carbon aldose) with the aldehyde group converted to OH.
- Sucrose
- Xylitol
Natural Control of Caries:
- _______ of salivary bicarbonate and phosphate
- ______ and neutralization of acid by tooth mineral
- Lowering of _____ intake
- Continuous flow of _____, which dilutes and clears both H+ and sugars.
- Buffering
- Adsorption
- Sugar
- Saliva
________ = chlorinated analogue of sucrose
Splenda (sucralose)
_______ = glucose with the aldehyde group replaced with an OH. Sorbitol is called a polyol or sugar alcohol. It also interferes with bacterial adherence to teeth.
Sorbitol
As the pH decreases, the concentrations of the more charged forms of phosphate ______ and, thus, the mineral component of teeth dissolves more rapidly. Bacteria lower pH when growing on teeth in a _____.
- Decrease
- Biofilm
Based on pKa, the permeation of lignocaine (pKa = 7.9) is expected to be ____ the permeation of procaine (pKa = 9.0) at pH 7.2.
- less than
- greater than
- the same as
- Indeterminate
-Greater than
Based on its charge, fluoride is expected to substitute for ____ in hydroxyapatite.
- phosphate
- sodium
- calcium
- hydroxyl groups
-hydroxyl groups
If the pH is 4.5 and [A-]/[HA] is 10, what is the pKa?
- 2.5
- 3.5
- 4.5
- 5.5
- 14.5
-3.5
Dextran differs from amylopectin in ______.
- being branched
- being a non-glucose polymer
- being used for dental impressions
- having β-1,6 linked linear chains
- having α-1,6 linked linear chains
-having α-1,6 linked linear chains
In calcium phosphate, as pH decreases, Ksp ____ and solubility ____.
[A] decreases, increases [B] increases, increases [C] decreases, decreases [D] increases, decreases [E] increases, remains the same
[B] increases, increases
____is used in toothpaste.
[A] Hydroxyapatite [B] Fluorapatite [C] Brushite [D] Whitlockite [E] Octacalcium phosphate
[D] Whitlockite
