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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
Ka to pKa equation...
pKa = -log Ka High Ka = Low pKa The lower the pKa the more acidic the solution
26
What does Acid etching achieve?
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
27
Equation for percentage dissociation of a weak acid
% dissociation = A- ___ x 100 HA
28
What is Kb and the equation to figure it out
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)
29
What are the symptoms of Xerostomia
Dry oral mucosa Dry and fissured tongue Bad breath Generalised caries Generalised plaque accumulation
30
What is Rheology
Study of deformation and flow of materials against variables: temp, pressure, time and applied stress
31
What is Viscosity
Resistance to flow or strain
32
What is setting time
the time taken for a material to reach its final set state
33
Increased viscosity = what type of flow?
High resistance to flow
34
What is wetting?
Wetting is used by bonding mechanisms that have adhesive properties - Wet adherant surface ex. Tooth
35
What does the contact angle refer to?
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
36
What surface energy is good for adhesion
Tooth surface needs to have a higher surface energy than the adhesive (resin)
37
Why do we etch the surface of the tooth
Increases the surface energy of the tooth therefore optimising the chance for chemical bonding and mechanical interlocking
38
What condition is associated with low blood pH
Metabolic acidosis Symptoms: high blood pressure, kidney disease, diabetes
39
What condition is associated with high blood pH
Metabolic alkalosis Associated with adrenal disease or alcohol abuse
40
What is the normal pH range for Saliva
pH 6.2-7.6
41
What effects the pH of Saliva
Food and Drink Bacteria in the oral cavity Age
42
At what pH does demineralisation begin?
pH 5.5 = Enamel breakdown, Dentine exposure, discomfort
43
What is a Buffer
Solutions that maintain a pH when a small amount of acid or base is added. ie. resistant to changes in pH
44
What are the the three systems that buffer saliva pH
1. Carbonic acid/Bicarbonate 2. Phosphate buffer 3. Protein buffer
45
What is the major buffering system for STIMULATED saliva
Bicarbonate (carbonic acid)
46
How does the bicarbonate buffering system work?
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
What system is refered to as 'phase buffering'
bicarbonate buffering system
48
What happens with the bicarbonate buffering system in basic conditions?
Strong base (OH-) react with the carbonic acid = bicarbonate and H+ ions = reducing the potential for an increase in pH
49
What is the major buffering system for UNSTIMULATED saliva
Phosphate buffer
50
Why is the phosphate buffering system limited?
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
How does the phosphate buffering system work?
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
How does the protein buffering system work?
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
At what pH does the protein buffer work?
buffering below pH 5
54
Indications of a unblanced saliva pH
Bad breath, temperature sensitivity, tooth cavities
55
What are dental cements used for?
Retention of restorations (crows ect.) or ortho bands Pulp protection Root canal sealers
56
Describe/List the components of a Zinc Phosphate cement Hint: 2 major components
1. Powder component (base) ZnO 2. Liquid component (acid) H3PO4
57
What happens when the powder and liquid components of a Zinc Phosphate cement are mixed
Acid attacks and dissolves the outer layer (ZnO - base) = release Zn2+ ions into liquid = formation of Zn3PO4 + H2O (hydrated zinc phosphate)
58
What happens to the pH of Zinc Phosphate cement
pH goes from 1.6 at 2 minutes to 6-7 after 34 hours
59
What is the action of local anaesthetic?
interupts neural conduction by blocking Na2+ gated channels ie. inhibiting influx of Na2+ = no AP
60
What happens from the time a local anaesthetic is injected to its onset and how does this depend on pH
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
What is the pKa for local anaesthetics?
Ionisation constant: Predicts the proportion of molecules that are lipid soluble vs water soluble form (50% of each form)
62
Local anesthetic isnt working on a patient with an infection... why?
Infection = acidic environment = favours quaternary water soluble form = fewer molecules penetrating the nerve = no onset
63
Why are intermolecular forces critical for dental materials
Intermolecular forces affect flow, viscosity and surface wetting which are critical parameteres to material performance
64
What does Hydrogen bonding involve?
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
In hydrogen bonding what is the Donor atom?
Electron withdrawing group ex. H-F, H-O or H-N Donor = H going away from that atom
66
In hydrogen bonding what is the Acceptor atom?
Avaiable lone pair on the acceptor atom ex. F,O,N - interacts with the slightly positive H atom Acceptor = lone pairs!
67
Draw a Hydrogen bond example
H20 (acceptor) bonded to H of another H20 (donor)
68
Rank the relative strengths of the intermolecular forces
Weakest - London Dispersion forces - Dipole Dipole - Hydrogen Bonding Strongest
69
Surface energy (tension) definition
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
Good Surface Wetting involves what energy states
Low surface energy liquid will wet a high energy surface solid = achieves optimal bond strength
71
Rheology definition
Study of the deformation and flow characteristics of matter against variables (temperature, pressure time and applied stresses)
72
Viscosity definiton
Measure of the fluids resistance to flow ie. Internal friction of molecules (how easy molecules move past each other)
73
What effects Viscosity
- molecule size - predominent intermolecular forces
74
Will a large hydrocarbon have a greater or lower viscosity and surface area
- 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
Why does falling water take the form of a droplet
liquids (such as water) can change their shape to minimise their surface energy
76
What effects surface energy?
- Intermolecular forces - Functional groups - Crystal planes presenting at the surface
77
What does cleaning a surface do in relation to surface energy?
cleaning the contaminated surface raises surface energy of the surface (you want as high of a surface energy as possible)
78
Does metallic bonding, H bonding dipole or dispersion forces have the highest surface energy
Metallic = highest H-Bonding Dipole Dispersion = lowest
79
How does viscosity and surface energy relate
As surface energy increases, so does viscosity (usually)
80
What effects Wetting?
- surface energy of the solid and liquid - rheology (flow) of the liquid/suspension
81
What contact angle is relevant for 'perfect wetting'
0 degrees = perfect wetting
82
What does contamination do to a surface
lowers solid surface energy (decreasing wettabillitty)
83
How can you raise surface energy
cleaning the biofilm/pellicle off enamel raises surface energy and therefore wettability
84
How can you lower surface energy
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
What is an example of a surfactant
Sodium lauryl sulphate (SLS)
86
What happens at very high concentrations of surfactants in liquids
FA's self assemble into micelles
87
What is capillary action?
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
How is capillary action relevant to dentistry
Capillary action of saliva occurs in crevices around/between teeth Denture retention is assisted by adhesvie action and capillary action
89
How is spectroscopy used in the dental context
1) Digital shade guide (spectrophotometer) 2) Vein visualisation (aka Vein mapping) 3) Intra Oral Scanners
90
What is the most common technique of shade matching
Visual shade matching
91
What are the disadvantages of Visual shade matching
- Conditions of light, experience, age, eye fatigue, colour blindness effects the shade choice
92
How do you determine how acidic or basic a molecule is
1) electronegativity 2) size of atom 3) resonance
93
How does electronegativity effect acidity
The more electronegative a element is the more it creates a dipole (ie. a more positive H) = more acidic
94
How does atom size effect acidity
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
How does resonance effect acidity
Resoance: different bond orientations/confirmations = stabilises conjugate base Stronger acids have stable conjugate bases!
96
How does the trend of acidity move when you go towards the right of the periodic table (across periods) and down groups
Stronger acid going to right across period (relating to electronegativity) Stronger acid going down a group (relating to size of atom)
97
How many steps are involved in salvia testing
5 steps First 3 on unstimulated saliva Last 2 on stimulated saliva

Chemistry (7 decks)

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