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Chemistry > Chemical Properties of Direct Dental Materials W2 > Flashcards

Chemical Properties of Direct Dental Materials W2 Flashcards

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1
Q

Provide the definition for an Acid

A

H+ concentration of greater than 1X10^-7M… LOW pH
Increases the concentration of H+ in a solution
Donates H+ through dissociation (HA -> A)
LOOSES the H+

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2
Q

Provide a definition of a Base

A

H+ concentration less than 1x10^-7….High pH
Raises pH by providing OH- (accepting H+)
GAINS the H+

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3
Q

pH equation

A

-log10 [H+]

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4
Q

What is the log scale in/increase by

A

1pH unit = 10 fold change in H+

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5
Q

What constitues a strong acid how does it differ to a weak acid?

A

Strong acid = Dissociates completely in aqueous solution (100% ionised in solution)
vs
Weak acid = majority of molecules remain undissociated ie. doesnt dissociate coompletely

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6
Q

Definition of a buffer

A

Solutions that resist changes in pH when small quantities of acid or base are added

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7
Q

How does a buffer work in acidic conditions?

A

Lots of H+ = the buffer takes on H+ to help the raise the pH of the solution

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8
Q

How does a buffer work in basic conditions?

A

Little/no H+ = the buffer donates H+ to help the lower the pH of the solution

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9
Q

Define Amphoteric

A

Substance acts as either an acid or a base

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10
Q

HA (acid)
H20 (base)
What are the conjugates

A

A- = conjugate base (has donated H+)
H30+ = conjugate acid (has accepted H+)

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11
Q

What is an example of an amphoteric molecule

A

An amino acid
In the presence of a base the amino group donates a H+ (acts as a acid)

In the presence of an acid the carboxyl group takes up a H+ (acts as a base)

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12
Q

What is the term for equilibrium of charge

A

zwitterion

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13
Q

Is water amphoteric, and if so what is donated/taken up in the presence of a base vs an acid

A

Yes, as it can act as an acid or a base
In the presence of an acid, H20 acts as a base ie. takes up H+ = H30+ (conjugate acid)
In the presence of a base H20 acts as an acid ie. donates H+ = OH- (conjugate base)

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14
Q

What is H30+ (hydronium ion) often shortened to?

A

H+

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15
Q

At equilibrium (25 degrees) water has equal concentrations of…

A

H30+ (H+) and OH-

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16
Q

What is Kw

A

Equalibrium constant for water (when at equilibrium!)
(dissociation constant - percentage of dissociation)
= [H30+]x[OH-]
= 10^-14 or pKw (14)

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17
Q

How do you calculate Kw when given the pH of solution and temperature

A

Reverse log!
First find [H+]
[H+] = 10^-pH
[H+] = 10^-7
The find [OH-]
[OH-] = [H+] = 10^-7 M at 25 degrees
Therefore Kw = (10^-7) x (10^-7) = 10^-14

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18
Q

What level of H+ and OH- constitute a neutral solution, acidic solution and basic solution?

A

Neutral solution: H+ = OH-
Acidic solution: H+ > OH-
Basic solution: H+ < OH-

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19
Q

pH + pOH = ?

A

14

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20
Q

Provide the definition for a conjugate base

A

Molecule that is left behind after the acid looses the H+
ie. A- (OH-)

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21
Q

Provide the definition for a conjugate acid

A

The molecule formed after the base gains a H+
ex. H30+ (H+)

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22
Q

Compare the terms ‘strength’ and ‘concentration’

A

Strength: proportion has reacted with water to produce ions (percentage of dissociation)
Concentration: how much of acid is dissolved in solution (dissolving in water)

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23
Q

Acid dissociation constant (Ka) is…

A

Equilibirum constant for acid dissociation (quantifies strength of acid) ie. how much dissociated

Products [H+] [A-]
_______ _______
Reactants [HA]

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24
Q

What happens to pH as the concentration of the acid/and or Ka, increases

A

pH decreaes because you are getting more dissociation of the acid
high Ka = low pH

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25
Q

Ka to pKa equation…

A

pKa = -log Ka

High Ka = Low pKa
The lower the pKa the more acidic the solution

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26
Q

What does Acid etching achieve?

A

Roughens tooth surface by local demineralisation of enamel and dentine = tags/pores so that resin can bond better
Usually 35% phosphoric acid for 15-30 seconds

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27
Q

Equation for percentage dissociation of a weak acid

A

% dissociation = A-
___ x 100
HA

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28
Q

What is Kb and the equation to figure it out

A

Equilibrium constant for basic dissociation reaction
- Extent of ionisation (percentage dissociation) of a weak base

= [BH+][OH-] Products
__________ ie. _______
[B] Reactants

pKb = -log Kb

Large Kb = strong base
ie. high level of dissociation = high pH (low pKb)

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29
Q

What are the symptoms of Xerostomia

A

Dry oral mucosa
Dry and fissured tongue
Bad breath
Generalised caries
Generalised plaque accumulation

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30
Q

What is Rheology

A

Study of deformation and flow of materials against variables: temp, pressure, time and applied stress

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31
Q

What is Viscosity

A

Resistance to flow or strain

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32
Q

What is setting time

A

the time taken for a material to reach its final set state

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33
Q

Increased viscosity = what type of flow?

A

High resistance to flow

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34
Q

What is wetting?

A

Wetting is used by bonding mechanisms that have adhesive properties
- Wet adherant surface ex. Tooth

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35
Q

What does the contact angle refer to?

A

The ability of a material to wet adherant surface (measure of wetting)
- Low contact angle (less than 90 degrees) corresponds= GOOD wetting ie. high wettability or hydrophilicity
- High contact angle (more than 90 degrees) = BAD wetting ie. globule/hydrophobicity

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36
Q

What surface energy is good for adhesion

A

Tooth surface needs to have a higher surface energy than the adhesive (resin)

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37
Q

Why do we etch the surface of the tooth

A

Increases the surface energy of the tooth therefore optimising the chance for chemical bonding and mechanical interlocking

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38
Q

What condition is associated with low blood pH

A

Metabolic acidosis
Symptoms: high blood pressure, kidney disease, diabetes

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39
Q

What condition is associated with high blood pH

A

Metabolic alkalosis
Associated with adrenal disease or alcohol abuse

40
Q

What is the normal pH range for Saliva

A

pH 6.2-7.6

41
Q

What effects the pH of Saliva

A

Food and Drink
Bacteria in the oral cavity
Age

42
Q

At what pH does demineralisation begin?

A

pH 5.5 = Enamel breakdown, Dentine exposure, discomfort

43
Q

What is a Buffer

A

Solutions that maintain a pH when a small amount of acid or base is added.
ie. resistant to changes in pH

44
Q

What are the the three systems that buffer saliva pH

A
  1. Carbonic acid/Bicarbonate
  2. Phosphate buffer
  3. Protein buffer
45
Q

What is the major buffering system for STIMULATED saliva

A

Bicarbonate (carbonic acid)

46
Q

How does the bicarbonate buffering system work?

A

Stimulated salvia (during meal)
= increased saliva
= increased bicarbonate concentration
bicarbonate combines with acid (H+ ions) = carbonic acid
as carbonic acid is a weak acid it dissociates into water and Co2.
All done in the presence of carbonic anhydrase VI (secreted by serous acinar cells) which releases Co2 as a gas.

47
Q

What system is refered to as ‘phase buffering’

A

bicarbonate buffering system

48
Q

What happens with the bicarbonate buffering system in basic conditions?

A

Strong base (OH-) react with the carbonic acid
= bicarbonate and H+ ions
= reducing the potential for an increase in pH

49
Q

What is the major buffering system for UNSTIMULATED saliva

A

Phosphate buffer

50
Q

Why is the phosphate buffering system limited?

A

pKa ranges from 6.8-7.2 (similar to the pH of the saliva)

Low phosphate avaiability/concentration in the oral cavity during eating
= effectiveness limited

At rest (not eating) concentration of phosphate is higher

51
Q

How does the phosphate buffering system work?

A

When acid is present it combines with monohydrogen phosphate (weak base) = dihydrogen phosphate (conjugate base)
If conditions become basic dihydrogen phosphate combines with OH- to form monohydrogen phosphate and water

52
Q

How does the protein buffering system work?

A

Nearly all proteins can function as buffers because they are made of amino acids (amphoteric), they can bind H+ or donate H+
Example: Salivary proteome proteins like Amylase, mucin, IgA, albumin

53
Q

At what pH does the protein buffer work?

A

buffering below pH 5

54
Q

Indications of a unblanced saliva pH

A

Bad breath, temperature sensitivity, tooth cavities

55
Q

What are dental cements used for?

A

Retention of restorations (crows ect.) or ortho bands
Pulp protection
Root canal sealers

56
Q

Describe/List the components of a Zinc Phosphate cement
Hint: 2 major components

A
  1. Powder component (base)
    ZnO
  2. Liquid component (acid)
    H3PO4
57
Q

What happens when the powder and liquid components of a Zinc Phosphate cement are mixed

A

Acid attacks and dissolves the outer layer (ZnO - base)
= release Zn2+ ions into liquid
= formation of Zn3PO4 + H2O (hydrated zinc phosphate)

58
Q

What happens to the pH of Zinc Phosphate cement

A

pH goes from 1.6 at 2 minutes
to
6-7 after 34 hours

59
Q

What is the action of local anaesthetic?

A

interupts neural conduction by blocking Na2+ gated channels ie. inhibiting influx of Na2+ = no AP

60
Q

What happens from the time a local anaesthetic is injected to its onset and how does this depend on pH

A

Local anestetic stable in solution (time of injection): quaternary, water soluble
- Cant penetrate neural membrane

When exposed to pH 7.4: tertiary, lipid soluble
- Diffuses through neural membrane = onset

61
Q

What is the pKa for local anaesthetics?

A

Ionisation constant:
Predicts the proportion of molecules that are lipid soluble vs water soluble form (50% of each form)

62
Q

Local anesthetic isnt working on a patient with an infection… why?

A

Infection = acidic environment
= favours quaternary water soluble form
= fewer molecules penetrating the nerve
= no onset

63
Q

Why are intermolecular forces critical for dental materials

A

Intermolecular forces affect flow, viscosity and surface wetting which are critical parameteres to material performance

64
Q

What does Hydrogen bonding involve?

A

Strong dipole-dipole force involving F,O,N lone pairs interacting with a H also bonded to a F,O,N.

ie. H atom bonded covalently to a F,O,N (DONOR ATOM) - makes delta positive and therefore connected to…
a F,O,N (ACCEPTOR ATOM)

65
Q

In hydrogen bonding what is the Donor atom?

A

Electron withdrawing group ex. H-F, H-O or H-N

Donor = H going away from that atom

66
Q

In hydrogen bonding what is the Acceptor atom?

A

Avaiable lone pair on the acceptor atom ex. F,O,N - interacts with the slightly positive H atom

Acceptor = lone pairs!

67
Q

Draw a Hydrogen bond example

A

H20 (acceptor) bonded to H of another H20 (donor)

68
Q

Rank the relative strengths of the intermolecular forces

A

Weakest
- London Dispersion forces
- Dipole Dipole
- Hydrogen Bonding
Strongest

69
Q

Surface energy (tension) definition

A

Energy required to overcome intermolecular forces to create a new surface in a liquid
Associated with a liquid or solid surface

  • Arises because molecules at the surface are not attracted equally in all directions to molecules around them, at the surface they are in a higher energy state (not as stable) as tthose below them
70
Q

Good Surface Wetting involves what energy states

A

Low surface energy liquid will wet a high energy surface solid
= achieves optimal bond strength

71
Q

Rheology definition

A

Study of the deformation and flow characteristics of matter against variables (temperature, pressure time and applied stresses)

72
Q

Viscosity definiton

A

Measure of the fluids resistance to flow
ie. Internal friction of molecules (how easy molecules move past each other)

73
Q

What effects Viscosity

A
  • molecule size
  • predominent intermolecular forces
74
Q

Will a large hydrocarbon have a greater or lower viscosity and surface area

A
  • high viscosity/surface energy (bigger the molecule the harder to slip over eachother and greater dispersion forces)
    ie. Increase size, increasing dispersion forces = increased viscosity AND surface energy
75
Q

Why does falling water take the form of a droplet

A

liquids (such as water) can change their shape to minimise their surface energy

76
Q

What effects surface energy?

A
  • Intermolecular forces
  • Functional groups
  • Crystal planes presenting at the surface
77
Q

What does cleaning a surface do in relation to surface energy?

A

cleaning the contaminated surface raises surface energy of the surface (you want as high of a surface energy as possible)

78
Q

Does metallic bonding, H bonding dipole or dispersion forces have the highest surface energy

A

Metallic = highest
H-Bonding
Dipole
Dispersion = lowest

79
Q

How does viscosity and surface energy relate

A

As surface energy increases, so does viscosity (usually)

80
Q

What effects Wetting?

A
  • surface energy of the solid and liquid
  • rheology (flow) of the liquid/suspension
81
Q

What contact angle is relevant for ‘perfect wetting’

A

0 degrees = perfect wetting

82
Q

What does contamination do to a surface

A

lowers solid surface energy (decreasing wettabillitty)

83
Q

How can you raise surface energy

A

cleaning the biofilm/pellicle off enamel raises surface energy and therefore wettability

84
Q

How can you lower surface energy

A

By using surfactants in liquids (surface active agents) = lower surface energy by disturbing the molecules at the surface

Hydrophobic tails congregate and align at the surface of the liquid and heads buried in the water = lowering surface energy with increasing concentration

85
Q

What is an example of a surfactant

A

Sodium lauryl sulphate (SLS)

86
Q

What happens at very high concentrations of surfactants in liquids

A

FA’s self assemble into micelles

87
Q

What is capillary action?

A

The spontaneous rising of a liquid in a narrow tube as a result of high cohesive (intermolecular - H BONDING) and high adhesive (liquid/wall - Surface energy) forces

88
Q

How is capillary action relevant to dentistry

A

Capillary action of saliva occurs in crevices around/between teeth
Denture retention is assisted by adhesvie action and capillary action

89
Q

How is spectroscopy used in the dental context

A

1) Digital shade guide (spectrophotometer)
2) Vein visualisation (aka Vein mapping)
3) Intra Oral Scanners

90
Q

What is the most common technique of shade matching

A

Visual shade matching

91
Q

What are the disadvantages of Visual shade matching

A
  • Conditions of light, experience, age, eye fatigue, colour blindness effects the shade choice
92
Q

How do you determine how acidic or basic a molecule is

A

1) electronegativity
2) size of atom
3) resonance

93
Q

How does electronegativity effect acidity

A

The more electronegative a element is the more it creates a dipole (ie. a more positive H) = more acidic

94
Q

How does atom size effect acidity

A

The larger the atom the more the electrons move around and there is greater distance between ion and H+ ie. long bond length = H+ more likely to dissociate = more acidic

smaller molecules its harder to pull off atoms

95
Q

How does resonance effect acidity

A

Resoance: different bond orientations/confirmations
= stabilises conjugate base
Stronger acids have stable conjugate bases!

96
Q

How does the trend of acidity move when you go towards the right of the periodic table (across periods) and down groups

A

Stronger acid going to right across period (relating to electronegativity)
Stronger acid going down a group (relating to size of atom)

97
Q

How many steps are involved in salvia testing

A

5 steps
First 3 on unstimulated saliva
Last 2 on stimulated saliva

Chemistry (7 decks)

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