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BDS 2 > Materials > Flashcards

Materials Flashcards

1
Q

what is MTA? What is it used for

A

MTA is biodentine and is biocompatible and has very good outcomes. This can help dentine bridge formations. This is used as a liner for pulp exposures that is then topped with a permanent restoration.

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2
Q

what should a root canal filling materials characteristics be?

A 
radiopaque 
non-toxic 
inert
biocompatible
long shelf life
easily  introduced into the canal
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3
Q

what type of materials can be used as root fillers

A

resin based
Zinc Eugenol
CaOH

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4
Q

what material do we use for inter visit medication and why

A

non-setting CaOH with barium
pH > 12 so very few bacteria can survive in this presence over 4 weeks
radio-opaque so we can see on radiograph if it is filling canal

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5
Q

how does Ca(OH)2 act against bacteria

A 
Damages bacterial cytoplasmic membranes 
Denatures proteins
Damages DNA 
Inactivates bacterial enzymes 
results in the destruction of phospholipids and the breakdown of lipopolysaccharides
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6
Q

when do we use setting and non-setting calcium hydroxide

A

setting : as a direct pulp cap

non-setting: inter visit dressing medication

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7
Q

what brand of non-setting calcium hydroxide do we use

A

hypo-cal

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8
Q

what is mixed with Calcium hydroxide to make it radio-opaque

A

barium

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9
Q

why is it important that no Hypo-cal exits the canal apex

A

causes sterile burn and will be degraded by the periodontal tissue

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10
Q

what are some components of filler material e.g. odontopaste for RCT

A

broad spectrum antibiotic to attack bacteria
anti-inflammatory to reduce inflammation and pain
calcium hydroxide

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11
Q

what are the properties of metal, glass, ceramics and polymers

A

metals are malleable, strong, shiny, conductors,
ceramics/glasses are brittle, strong, not conductors - hard manufacture
polymers are strong, flexible, heat changing, dont conduct, not birttle, easy manufacture

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12
Q

what are direct restorative materials and what are the properties of a good direct material

A 
materials that can be applied in 1 session 
command set
quick
easy
cheap
aesthetic
restore function
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13
Q

what are indirect dental materials

A

multi-step production that can be removable or non-removable

veneers, dentures, crowns, bridges

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14
Q

explain pre-market testing

A

ensuring materials fit to safety guidelines by FDA and other organisations
in-vitro to test toxicity and genoticity
in vivo to test against tissue and organs

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15
Q

who are the FDA

A

food and drug administration that test safety of materials/foods/drugs

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16
Q

what is the CE mark

A

certified to be sold and safe in the EEA European economic area
everything must have this symbol or risk of being fined and jailed

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17
Q

what are some allergenic metals

A

nickel 25%
palladium 24%
cobalt 15%

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18
Q

what is the likelihood of patient reaction to material allergen compared to reactions to cosmetics

A

dental material is less than 0.1%

cosmetics 10%

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19
Q

what material is used for primary impressions - adv/disadv

A

alginate
elastic so can come out of mouth easily
cheap
adaptable with ratio

quickly becomes unstable if not cast
allergies

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20
Q

if we use hotter water, how does this affect alginate

A

faster setting

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21
Q

how do we mix ZnOE

A

1:1 ratio of red and white paste

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22
Q

what is stress

A

the force per cross sectional area put on a material

force / m^2 = (M)Pa m^-2

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23
Q

what is strain

A

Strain is the fractional change in the dimensions caused by the force
change in length / original length

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24
Q

why is stress an important consideration in restoration

A 
stress is force per cross sectional area
if our restoration has 1 small high point
all force will be put on this small area
increasing the stress
causing fracture and causing PRF
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25
Q

what is resilience and where would it be on a stress/strain graph

A

resilience is the total energy a material can absorb before undergoing inelastic deformation
area under STRAIGHT line

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26
Q

what is toughness and where is this on a graph of strain and stress

A

amount of energy a material can absorb before fracture

area under whole graph

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27
Q

what is another name for elastic area

A

resilience

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28
Q

is ultimate tensile strenght of fracture strenght higher

A

UTS

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29
Q

what is the elastic limit

A

amount of energy a material can absorb and still go back to original state

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30
Q

how is fatigue measured (2)

A

fatigue life - number of uses until failure

fatigue fatigue limit/strength - amount of stress until failure of set number of cycles

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31
Q

what is hardness

A

ability to withstand surface indentation under compressive force

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32
Q

why must dental materials be HARD and have high fatigue

A

hardness is ability to withstand surface indentation from compressive force
indentations would reflect light and be anaesthetic
very high fatigue as they are used many times under high stress

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33
Q

what is thermal conductivity and thermal diffusivity

A

TC: rate of flow from cold to hot
TD: ratio of energy heating up material to energy passes through (to pulp = bad)

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34
Q

why do we want low thermal expansion (and what has high?) in restorations

A

when we drink hot drinks, we don’t want materials to expand as this puts stress on enamel leading to fractures
metals are bad for this

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35
Q

what are 2 important necessities of dental materials involving thermal expansion

A

low as possible

matching adjacent materials

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36
Q

are most setting/curing procedures endothermic or exothermic?

A

exothermic

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37
Q

what are some ideal properties of primary impression material

A

high dimensional stability -stay the same dimensions over time
non-toxic
no major thermal expansion
unique low viscosity to flow into sulci but also high viscosity to record details and compress

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38
Q

which of silicone, alginate, ZnOE and polyethers can be used for undercut impressions and why

A 
silicone
alginate
polyethers
NOT ZNOE 
all elastic apart from ZnOE
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39
Q

how many types of plaster are there

A

5

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40
Q

what colour/name are the different plasters and what are their uses (1-4)

A

1 + 2 = white, dental plaster for diagnostic models e.i. making secondary special tray
3 = yellow, model dental stone = opposing models during dentures
4 = die stone = very accurate and low expansion for bridges and crowns

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41
Q

as we go from plaster II to plaster III what changes

A

ratio of plaster to water
hardness increases
expansion decreases
compressive strenght increases

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42
Q

for model casting during denture making, what types of plaster of paris do we use, in what ratio and with how much water

A

II (plaster) and III (stone) in 1:1 ratio

mix this powder: water as 1:2.5

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43
Q

what metals are used in dentistry

A

gold - crowns
amalgam - restoration
stainless steel - braces
titanium - implants

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44
Q

what is a ‘transition’ of a material

A

re-organisation of the atoms

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45
Q

why are metals shiny and malleable

A

shiny because sea of delocalised electrons can absorb light, get excited and then release photons
malleable as the ions are all positives don’t repel each other so come move into one another. Ionic lattices cannot do this

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46
Q

what are ceramics

A

Inorganic, non-metallic compounds, usually crystalline in nature

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47
Q

what are ceramics

A

Inorganic, non-metallic compounds, usually crystalline in nature
brittle, hard materials with high melting points

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48
Q

what does amorphous mean

A

atoms/crystals are not arranged in a regular way

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49
Q

what is glass

A

supercooled, non-crystalline, amorphus transparent solids

brittle

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50
Q

what are glass ceramics and why are they useful in dentistry

A

glass structures with inorganic additions that when slowly heated, form crystals
glass + opaque inorganic makes the material translucent
similar to enamel so good for composite and also reduced shatter as energy from fracture has to reflect off of crystals and loose energy

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51
Q

what is a mucostatic material

A

a material that has the viscosity to flow and not displace the soft tissues
low viscosity

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52
Q

what is a mucocompressive material

A

high viscosity - will not flow until we compress it against the tissues

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53
Q

what type of material are alginate and ZnOE

A

alginate is mucocompressive, flexible hydrocolloid

ZnOE is a mucostatic rigid material

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54
Q

what affects dimensional accuracy of impression materials

A

shrinkage and expansion of the material

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55
Q

what is rheology

A

study of the flow of materials

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56
Q

what graph shows us if something is a (non-) Newtonian material

A

shear stress against shear rate graph

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57
Q

what is a Newtonian fluid

A

a fluid that doesn’t change viscosity under shear stress

shear stress directly proportional to shear rate

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58
Q

what is a non-newtonian fluid

A

a fluid that changes viscosity under shear pressure

shear pressure is not directly proportional to shear rate

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59
Q

what two types of newtonian fluid are there

A

shear thickening - thicken under stress e.i. piutty

shear thinning - ketchup

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60
Q

what impression material is shear thinning

A

silicone impression material

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61
Q

why is wettability important for impression materials

A

means that all of the surfaces will be recorded and we will have less voids

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62
Q

what is TEC and what is a high TEC

A

thermal expansion co-efficient

high TEC means that the material expands a lot under heat

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63
Q

why is dental wax bad for impressions

A

very high TEC so would have poor dimensional accuracy

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64
Q

what are plasticisers

A

materials that we add very small amounts of that have large structural/functional affects

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65
Q

why is ZnOE good for impressions

A

good dimensional accuracy
low TEC
stable on storage
good surface accuracy

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66
Q

why may ZnOE not be good for impressions

A

it is mucostatic so cannot be used for deep undercuts

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67
Q

what is plaster of paris

A

gypsum

calcium sulphate dihydrate

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68
Q

what chemicals cals are added to plaster and why (for making of models)

A

potassium sulphate to reduce expansion but this accelerates setting time
Borax decellerates setting time to counteract potassium sulphate
added because plaster expands 0.3-0.6% which is dimensionally noticable

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69
Q

how much does plain plaster expand and how can we change this

A

0.3-0.6%

addition of potassium sulphate and borax

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70
Q

what are some rigid materials for impressions

A

ZnOE
plaster
impression compo
dental waxes

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71
Q

what is C factor

A

the stress put on adhesive surfaces from shrinkage of composite polymers
depends on how many surfaces in contact with

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72
Q

how do we reduce C factor when placing composite

A

place in small, wedged increments to reduce the number of surfaces each placement is in contact with

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73
Q

how far can light cure through composite resin

A

2 mm

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74
Q

what are the classes of C factor and their ratios

A 
Class I =  5 bonded : 1 unbonded = 5
Class II = 4 bonded : 2 unbonded = 2
Class III = 3 bonded : 3 unbonded = 1
Class IV = 2 bonded : 4 unbonded = 0.5
Class V = 1 bonded : 5 unbonded = 0.2
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75
Q

if a filling material was shear thinning, how could we make it fill voids?

A

use sonic vibrations

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76
Q

what are bulk fill composites

A

polymer resins that we can place in upto 4mm thickness wedges and still light cure effectivly
reduced polymer shrinkage

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77
Q

what are the three phases and components of composite resins

A

organic phase - resin matrix
dispersed phase - inorganic filler
interfacial phase - coupling agent

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78
Q

what is the function of the organic matrix in composites

A

forms the polymer backbone and provides tensile strength

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79
Q

what is the function of the inorganic filler material of composite resins

A

improves mechanical properties like wear and compressive strength
redcues shrinkage

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80
Q

what is the function of the coupling agent in composite resins

A

the bind the organic phase matrix tot he dispersed phase

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81
Q

what is the most common monomer used for the organic matrix of composites

A

methacrylates

big- GMA

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82
Q

why might multiple methacrylate’s be used in the organic phase of a composite

A

alter physical properties like viscosity

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83
Q

why do we not used chemical cured resin composites

A

not controlled by operator

more time pressure and leads to worsened fillings

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84
Q

how are light cure resins initiated and what is the name for this process

A

photoinitiated addition free radical polymerisation
free radical vinyl polymerisation
Camphoroquinone at 470nm wvl

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85
Q

how does free radical vinyl polymerisation work

A

470nm light forms free radicals
high energy chemical group
seek out vinyl double bond of methacrylate and break the bond
internal energy released which opens another methacrylate bond - bond together

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86
Q

how do coupling agents work

A

coat the surface of filler particles
improve adhesive surface
create stronger bonds between filler and matrix with a hydrophillic (organic) end and hydrophobic (inorganic) end

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87
Q

what are some disadvantages of using silanes for filler

A

loose potency over time
age in storage
sensative to water

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88
Q

what have we used for fillers for the past 50 years

A

silanes

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89
Q

why can we not let a composite resin get wet whilst un-cured

A

water break the silane bonds
silane is the coupling agent
breaks adhesion of matrix and filler
looses integrity

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90
Q

what do we find in the organic phase of resins

A

methacrylate monomer
initiator
inhibitor
pigments

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91
Q

why are macrofilled filler particles not good

A

large 10-50micrometer particles
scatter light –> very opaque
high wear rate
high polymerisation shrinkage

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92
Q

why is hybrid filler better than microfilled

A

allows more packing and more particles

less polymerisation shrinkage

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93
Q

why is micro filled better than hybrid filler

A

worse aesthetics

large particles reflect light and make it more opaque

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94
Q

why is it hard to disperse nanoparticles and not allow them to conglomurate?

A

vander waals forces are very important at nanoscale

they come together and form globules of nano-particles

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95
Q

why is it not very important that nanoparticles increase wear of composite fillers

A

hybrid composites dont fail because of wear

no need to improve it

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96
Q

how does oxygen affect placement of composites and how do we counteract this

A

oxygen inhibits polymerisation
top layer is partially polymerised and weak - opaque
use finishing burrs to remove top oxidised layer

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97
Q

where are polymers used and which polymers

A

methacrylate polymers used for composites
poly methyl methacrylate acrylic used in denture
rubber dam
mixing bowls
protective eyewear
PPE

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98
Q

what are some advantages of PMMA

A 
relatively cheap
easy to mix
translucent and aesthetic
good strength
good rigidity
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99
Q

what are the 3 classes of polymer with their subclasses

A

structural:

  • linerar
  • cyclic
  • brnahced
  • cross branched

molecular:

  • thermosetting
  • thermoplastic
  • elastomers

source:

  • natural
  • synthetic
    • addition
    • condensation
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100
Q

what bonds are formed between monomers of polymers

A

very strong intramolecular covalent bonds

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101
Q

how does chain length affect strength of polymer

A

increased length = increased strength

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102
Q

how do side groups affect polymer strength

A

allow for intermolecular forces e.g. hydrogen bonding

increases strength

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103
Q

are branched or unbranched polymers more strong

A

unbranched straight polymer chains
pack together better increasing density and more crystalline
stronger

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104
Q

compare the structure of amorphous and crystalline polymers

A

amorphous have random structure

crystalline polymers have small domains of structured crystalline ordering with aligned chains of polymer

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105
Q

what are thermoplastics and relate to structure

A

type of polymer
become flowable and shape able when heated and set on cooling
due to straight, unbranched chains with minimal cross linkage

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106
Q

what are thermosetting polymers and relate to structure

A

polymers that when heated, set and form strong irreversible covalent cross links
become hard and non-malleable

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107
Q

what are elastomers

A

stretchy polymers that can be stretched and return to original shape

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108
Q

what is Tg, explain and what does this depend on

A

glass transition temperature
temperature below the boiling point where polymer becomes more flowable
lower Tg comes with weaker/lack of secondayr bonds/cross links

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109
Q

what are the 4 steps of polymerisation

A

activation
initiation
propagation
termination

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110
Q

what three methods of polymerisation activation re there

A

heat
chemical (amides)
or light

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111
Q

what is a free radical

A

atom with unpaired electron, very reactive

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112
Q

what is initiation of polymerisation

A

where the free radical is formed

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113
Q

what is propagation of polymerisation

A

free radical attacks double (vinyl) bond
of monomer
forms a new larger radical (monomer) that attacks and bonds to another monomer

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114
Q

what si the common initiator for heat and chemical cure polymers

A

Benzoyl Peroxide

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115
Q

what is the initiator for light cured resins

A

Camphoroquinone

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116
Q

what is condensation polymerisation

A

reaction of two monomers makes a larger molecule and release a small molecule e.g. water

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117
Q

what small molecule is released in silicone condensation polymerisation

A

methanol

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118
Q

what are miscible liquids

A

mix well

form a homogeneous mixture when mixed

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119
Q

what is a homogeneous liquid

A

all molecules in uniform structure

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120
Q

what are co-polymers

A

polymers with more than 1 monomer to enhance porperties

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121
Q

what is a blend

A

where monomers are mixed prior to setting/moudling

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122
Q

what is youngs modulus

A

elastic modulus

gradient of stress/strain graph

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123
Q

what is a composite

A

combination of materials in which the products’ properties are superior to both individual properties

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124
Q

what is a resin composite

A

highly crosslinked resin polymer
reinforced by dispersion of silica/filler
bound together by the coupling agent

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125
Q

what does the addition of a plasticizer to a polymer do? two affects on properties

A

reduces bonding between chains
reduces Tg - glass transition temp
reduces elastic modulus - steepness of stress/strain curve

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126
Q

What are some advantages and disadvantages of MTA

A

Non toxic
Non resorbable
Biocompatible
Minimal marginal leakage

Long setting time

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127
Q

what is adhesion

A

forces that bind two dissimilar materials together

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128
Q

what are some unwanted clinical adhesions

A

adhesion of bacteria to pellicle

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129
Q

what distance between objects must there be to be classed as ‘adhesion’

A

less than 0.0007 micrometers

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130
Q

explain the difference between solid/solid and solid/liquid contact

A

solid liquid contact is intimate as liquid can flow to 0.0007micrometers close
solid solid contact is not intimate because at microscopic level, there is roughness and lack of contact

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131
Q

what mechanical property alters an adhesives ability to cover a substrate

A

wettability

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132
Q

what is required for good wettability

A

imbalance between surface energy of solid (greater than)

and surface tension of liquid

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133
Q

what is surface energy of a solid

A

imbalance of energy of the surface level of atoms of a solid

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134
Q

if the surface energy of a solid is lower than the surface tension of a liqud, how does this affect wettability

A

poor wettability

good wettability = surface energy > surface tension

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135
Q

if a liquid is poured on a solid and it forms little watter droplets, what is causing this

A

poor wettability

surface tension of liquid > surface energy of solid

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136
Q

how do we measure wettability

A

measure the angle the water droplet forms with the surface
if lower angle, more wettability
if larger angle, more hydrophobic

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137
Q

what types of physical bonding can we have in adhesion and why is it important

A

weak reversible bonds
weak Vander Waals forces
non-permanent dipole dipole interactions
hydrogen bonding
not good for adhesion of materials but can be a precursor for chemical bonding

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138
Q

what are the three main types of adhesion important for dental materials

A

chemical bonding - ionic/covalent/metallic
micromechanical interlocking
entanglement

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139
Q

what is micromechanical interlocking

A

where the surface has microscopic undercuts

adhesive flows into these undercuts and then sets becoming harder, locking into undercuts

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140
Q

what is molecular entanglement

A

material with a highly porous surface and add a monomer that is absorbed into the porosities and then when cured, crosslinks form and embed the two materials together forming a hybrid layer.

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141
Q

what is the conditioner of dentine bonding

A

phosphoric acid etch 35%

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142
Q

what is a ‘conditioner’ for adhesion

A

a chemical that alters surface of a material making it more susceptible for adhesion

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143
Q

is methacrylate or acrylate more reactive? why?

A

methacrylate less reactive

extra methyl group makes the reactive atoms less available

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144
Q

what is a ‘sealer’ in adhesives

A

component that flow into porosities and sets forming a seal with the base material through molecular entanglement and micromechanical interlocking

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145
Q

how does acid etch work

A

removes smear layer
demineralizes the surface layer of dentine/enamel exposing collagen for molecular entanglement
(if in dentine) opens up dentinal tubules, mechanical interlocking
4 micrometre demineralized layer

146
Q

what is a primer/coupling agent in an adhesive

A

a molecule in the adhesive that links the (hydrophilic) surface to the (hydrophobic) filling material e.i. composite

147
Q

what is HO - CH3 - CH3 - Methacrylate

A

hydroxyl ethyl methacrylate

HEMA

148
Q

why are spacers important in composite resins

A

avoid repulsion of hydrophobic and hydrophilic ends

149
Q

is dentine hydrophilic or hydrophobic and why

A

hydrophilic - mainly composed of organic material

150
Q

is enamel hydrophilic or hydrophobic

A

hydrophobic

mainly composed of in-organic material

151
Q

how might a hydroxy group be advantageous in a resin for dentine bonding

A

dentine contains collagen and hydroxyapatite
hydroxy group can form chemical bonds with amino acids in collagen
can also form bonds with hydroxy groups of hydroxyapatite

152
Q

what methacrylate resin contains a hydroxy group

A

HEMA - hydroxy ethyl methacrylate

153
Q

which part of a resin adhesive binds to the composite

A

methacrylate group - hydrophobic

154
Q

which part of a resin adhesive binds to dentine

A

hydroxy/reactive/hydrophilic end (not the methacrylate side)

155
Q

what is the structure of a primer/coupling agent within resin adhesives

A

bifunctional monomer containing a hydrophilic and hydrophobic head

156
Q

what are two characteristics of a resin sealant

A

contains methacrylate groups

light curable

157
Q

why is dentine less reliable for adhesion than enamel

A

more dynamic
more organic and hydrophilic
smear layer
problems with shrinkage and wettability due to wet surface

158
Q

how much do polymer composites shrink by

A

2-3%

159
Q

what causes polymerisation shrinkage

A

as monomer forms chemical bonds
wander vaals spaces become bonds
molecules become more compact taking up less space and contract

160
Q

why is polymerisation shrinkage bad for composite restorations

A

puts contractional stress on cavity walls

may separate from cavity walls allowing microleakage and secondary caries

161
Q

why do we dry a composite bond (2)

A

evaporate solvent

disperse evenly over surface

162
Q

what happens if we dry dentine too much (2)

A

collagen forms a thick dense layer that the primer cannot penetrate
fibrils and dentinal tubules collapse preventing entrance of adhesive agent
may pull odontoblasts up dentinal tubules, killing the odontoblasts and causing sclerosis

163
Q

what 3 stages to composite adhesion are there

A

etch
prime
seal

164
Q

what does ‘moh’s scale determine

A

hardness

165
Q

describe the inorganic structure of enamel

A

hexagonal hydroxyapatite crystals rods 6 micrometres in diameter
perpendicular to tooth surface

166
Q

why must an area being restored by composite resin be kept relatively dry

A

resin is very hydrophobic
saliva/wet is very hydrophilic
repel each other and not allow good adhesion and wettability
Microleakage

167
Q

what percentage phosphoric acid do we use in acid etch

A

35%

168
Q

when restoring enamel with composite, what 3 things do we do before bonding

A

patient selection - decide if surfaces can be kept dry or not and decide weather to use resin or GIC
enamel prophylaxis - cleaning pellicle and bacteria/salivary proteins that would reduce the bonding strength
acid etch

169
Q

what are ideal properties of composite resins

A

aesthetic - translucent, colour adaptable
non-toxic
stable in state and colour
form a good seal and transition with tooth structure
dont reuqire lots of cavity prep like amalgam

170
Q

why is composite better than amalgam

A

doesn’t contain mercury - better for pt and environment
adhesive to tooth structure, less microleakage
tooth coloured and aesthetic
less mechanical pre - no need to remove sound tooth for undercut

171
Q

how long do composites roughly last

A

~10 years

172
Q

how much is 1 capsule of composite resin

A

£2

173
Q

what are some disadvantages of composite resins

A

polymer shrinkage leads to contractive stress and microleakage
not bind directly to surface, need bond, technique sensitive

174
Q

what are inhibitors important for in composite resins

A

prevent curing of polymer to improve shelf life

175
Q

why is amalgam better than composite and when do we use it

A

more wear strength to resist tooth grinding
less shrinkage
less dependant on dry surfaces
more useful for posterior restorations and cusp replacements

176
Q

why might we not be able to control moisture for a restoration

A

age
cavity very close to gingival margin
unable to place rubber dam or isolation

177
Q

what is the minimum thickness of amalgam, what happens if we go thinner

A

1.5-2mm

very brittle in thin sections

178
Q

is composite or amalgam cheaper

A

amalgam

179
Q

when should we colour match composite to teeth and why

A

before any procedure
dehydration may alter shade
blue rubber dam may reflect on shade

180
Q

what are resin tags

A

resin filled tubules

181
Q

what

A
182
Q

what is a solution

A

homogeneous mixture consisting of a single phase

particles smaller than 10^-7cm

183
Q

what is colloid

A

colloid is a heterogeneous mixture of two phases, where the two phases are not readily differentiated.
particle size between 10^-7cm and 10^-5cm

184
Q

what is a suspension

A

mixture of 2 phases

particle sizes of more than 10^-5cm

185
Q

what are hydrocolloids

A

heterogenous group of long chain polymers

form viscous dispersion or gel when mixed with water

186
Q

what is a sol

A

hydrocolloid in its viscous form

187
Q

what is a ‘gel’

A

hydrocholloid in its jelly like state

188
Q

what is the transition name from sol to gel

A

gelation

189
Q

what is the difference between agar and alginate

A

agar is a reversible hydrocolloid - gelates due to temperature change
alginate is a irreversible hydrocolloid - gelates due to chemical reaction

190
Q

what types of gelation are there

A

irrerversible - chemical

reversible - temperature

191
Q

are hydrocolloids inserting in their sol or gel phase

A

sol

192
Q

what else is found with agar impression material

A

potassium sulphate and borax to prevent expansion and reduce setting time

193
Q

when is agar impression material used

A

replicating dentures

194
Q

how do we get from alginic acid to set alginate (2)

A

alginic acid + sodium ions –> sodium alginate

sodium alginate + calcium ions –> crosslinks, gel state

195
Q

what two ions are necessary and why for alginate production

A

alginic acid + Na+ = sodium alginate
sodium alginate + Ca2+ = cross links between COO groups
gel state achieved

196
Q

what derived alginate

A

alginic acid

197
Q

what chemical reaction occurs for irreversible setting of alginate

A

Calcium allows cross linkages between alginate polymer chains via COO groups

198
Q

what is Syneresis and where is this relevent in dentistry

A

oozing of liquid out of gels

water oozes out of alginate impressions causing shrinkage

199
Q

what is imbition and what is its relevance in dentistry

A

swelling of gels by the uptake of water
alginate impressions swell through sorption of water
affects shape and accuracy o alginate impressions

200
Q

why does alginate have poor shelf life and dimensional stability

A

alginate is a hydrocolloid gel
can shrink due to syneresis - loss of water over time
can expand due to imbition - sorption of water
expansion/shrinkage depends on thickness and so different thicknesses expand/shrink at different rates

201
Q

when are polysulphides used and why

A

for bridge and crown work impressions

very high accuracy and high dimensional stability

202
Q

what 3 types of elastomer are there

A

polysulphides
polyethene
silicones

203
Q

what catalyst is required for polymerisation of condensation silicone impression material and what is released

A

tin Sn catalyst

3 molecules of ethanol

204
Q

what catalyst is reuqired for addition silicone impression material polymerisation

A

platinum Pt

205
Q

what do surfactants do to the physical properties of fluids

A

increase wettability

206
Q

when are elastomers used and why

A

bridge, crown, implant, overdenture work

very high surface accuracy

207
Q

which is the best elastomer for impressions and why

A

polyethene’s

most hydrophilic so cover wet surfaces best

208
Q

what is the structure of metals

A

crystalline structure of regular arranged cations with a sea of electrons

209
Q

how many crystalline structures for metals are there and which are most relevant to dentistry

A

7
Face centred cubic
body centred cubic

210
Q

if FCC or BCC more dense and why

A

FCC as this gets 4 ions per square unit whereas BCC gets 2 ions per square unit

211
Q

metals are polycrystalline. What does this menas

A

made up of many small crystals

when freezing they expand to meet each other and form a grade boundary

212
Q

how are grain boundaries form in solid metals

A

metals are polycrystalline
when liquid there are many small crystals
when solidifying, crystals grow
when they meet other crystals, grain boundaries are formed

213
Q

what is the implication of grain boundaries

A

grain boundaries are very high energy

when etching metals, the high energy grains will etch more

214
Q

is a stronger metal one with small or large grains and why

A

small

fractures are reflected at each grain

215
Q

what is an alloy

A

mixture of metal and another type of atom - usually metal

216
Q

what type of mixed structures can we get from alloys

A

interstitial solid solution
substitutional solid solution
intermetallic compound

217
Q

explain interstitial solid solution

A

solute atom < solvent atom
solute added and fit into spaces between ions
disrupting regular lattice making less malleable as layers cannot freely slide over each other
solid solution means will fully dissolve in each other and fully mix together

218
Q

explain a substitutional solid solution

A

metal ions swapped for other metallic ions of similar diameter (within 15%), valency and same crystalline structure
Cold and copper are an example

219
Q

what is a solid solution

A

mixture of metals that fully dissolve in one another and mix completely

220
Q

describe an intermetallic compound

A

combination of 2 or more metals that form a regular structure with a discrete composition or stoichiometric ratio

221
Q

what type of alloy is amalgam

A

intermetallic compound

222
Q

what are the 3 criteria of a substitutional solid solution

A

similar atomic diameter within 15% difference
same valency
same crystalline structure

223
Q

what is a phase

A

homogeneous physically distinct part of a system that is separated from other parts by a definite physical boundary

224
Q

what does a phase diagram show

A

gradual crystallisation of alloys

shows break points of where crystallisation starts and ends, depending on composition of metals in alloy

225
Q

where do we find the solidus and liquidus line and what do they show

A

on phase diagram
liquidous line shows break point of crystallisation initiation from liquid to solid/liquid
solidus lie shows break point for completed crystallisation from solid/liquid to solid

226
Q

when is a eutectic phase diagram used

A

metals are partially soluble in each other

227
Q

what is the eutectic point of an alloy

A

point of composition at which on decrease in temperature there would be an immediate change from liquid to solid at a lower melting point than both constituents
forming a homogeneous laminar structure of the two metals

228
Q

what metals are in amalgam in descendnig order of %

A 
silver
tin 
copper
zinc
mercury
229
Q

what two types of amalgam can we get

A

conventional amalgam

High copper amalgam

230
Q

what rough percent’s of metals are in conventional amalgam

A 
silver ~65-75%
tin ~25%
copper ~6%
zinc ~2%
mercury ~ remainder
231
Q

in low copper amalgam, what percent is mercury

A

~50%

232
Q

how do we find the gamma phase on an amalgam phase diagram

A

3rd pure phase along

233
Q

what is the gamma phase made up of and what type of alloy is this

A

silver and tin - Ag3Sn

similar size but different valency and structure so intermetallic compound

234
Q

what is the formula for gamma phase

A

Ag3Sn

silver 3 tin

235
Q

what types of particle can be in amalgam and what implications of this

A

lathe cut - fine lathe cut set faster with higher surface area
spherical cut - easier to work with and shape
mixture - alters setting time for learners

236
Q

what is the gamma equations for conventional amalgam with state symbols

A

gamma (s) + Hg (l) –> gamma (s) + gamma 1 (s) + gamma 2(s)

237
Q

what is the word equation of gamma gamma 1 and gamma 2

A

gamma = silver tin alloy
gamma I = silver mercury
gamma II = tin mercury

238
Q

how much more silver/tin is there than tin/silver and why

A

3 times more silver than tin

gamma phase is Ag3Sn

239
Q

out of gamma, gamma 1 and gamma II which will be least prevelent and why

A

gamma II tin mercury
limiting factor is tin
Gamma is Ag3Sn
3 times less tin than silver

240
Q

how many phases does amalgam contain

A

3
gamma - Ag3Sn
gamma I - Ag2Hg3
gamma II - Sn7-8Hg

241
Q

what is gamma I phase

A

Ag2Hg3

242
Q

what is gamma II phase

A

Sn7-8Hg

243
Q

why might we get a tooth fracture after amalgam restoration

A

residual caries
unsupported enamel or thin enamel
weak enamel tissue e.g. hypophosphotasia

244
Q

which part of amalgams is most likely to fracture

A

isthmus

transition between occlusal and proximal surface

245
Q

what is the leading cause of restoration failure

A

secondary caries

246
Q

what will the prognosis of an amalgam restoration be if the amalgam is not mixed well and why

A

poor due to secondary caries

poor condensation and excess mercury formation leading to microleakage

247
Q

why might we get gross amalgam fractures

A

placing amalgam too thinly

if there is not sufficient undercut/retention, restoration will fall out

248
Q

why do we avoid sharp internal angles

A

these create high stress areas, should be rounded

249
Q

what amalgam specific characteristics of cavity prep and placement are there

A

grooves and undercut for retention
90 degree Cavo surface angles so no thin placement
minimum depth of 2mm
good mixing to provide good condensation and no excess mercury

250
Q

what is marginal breakdown and why does it occur

A

breakdown of tissue/restoration at margin between tooth and restoration
occurs if there is a poor Cavo-surface angle

251
Q

what are some causes of marginal breakdown (4)

A

poor Cavo surface angle (not 90 degrees)
underfilling/overfilling leading to pressure points
creep/corrosion
Marginal expansion

252
Q

what is marginal expansion amalgam and what does it lead to

A

when in close contact to moisture
Zn from amalgam reacts forming ZnO and hydrogen forming gas bubbles
expanding amalgam putting pressure on dentine and pulp
causes voids and leads to weakness and fracture

253
Q

what is creep and how does it affect dentistry

A

the slow movement or deformation of metal when under constant mechanical stress
creep on amalgam fillings causes marginal breakdown

254
Q

what is corrosion

A

electrochemical degradation of metals over time caused by a difference in electrochemical charge

255
Q

why is high copper amalgam used

A

reduces unfavourable gamma 2 phase - Sn7-8Hg

gamma 2 phase responsible for creep and corrosion

256
Q

which treaty does mercury containing amalgam concern

A

minimata

257
Q

who cannot have amalgam fillings

A

children under 15

breastfeeding or pregnant women

258
Q

what are advantages of amalgam

A

Relatively cheap (but increasing)
Relatively non-technique sensitive
Can work in moist conditions however still better in dry conditions
Strong
Durable
Long shelf life
No need for adhesive, no biocompatibility problems

259
Q

what are disadvantages of amalgam

A

Not environmentally friendly with the minamata treaty
Toxic mercury inside, even though safe when set, is still a concern. The most significant mercury release is upon placement and removal of amalgam.
Unaesthetic and may feel wrong
Media reports of unsafety
Limited to posterior
Non adhesive so we have to prepare more cavity and therefor lose more tooth
Minimum thickness of 2mm

260
Q

why is a 90 degree cavosurface angle important in amalgam restorations

A

prevents fracture of thin amalgam and protects enamel prisms

261
Q

which part of the body does mercury affect

A

acts as a neurotoxin, cumulative affect

hard to remove from body

262
Q

why is amalgam bad for the environment

A

small amounts released as waste
works its way up the food chain to large fish e.g. tuna
ingested and cumulative affect on e.g. pregnant women

263
Q

when is amalgam hopefully going to be phased out and what treaty lead to this

A

2030

Minamata treaty

264
Q

other than mercury, what other aspects of amalgam are hazardous to the body

A

silver
tin
zinc

265
Q

what are the relative tensile strengths of gamma, gamma I and gamma II

A

Gamma strongest
Gamma I next strongest
Gamma II weakest

266
Q

what is an admix alloy

A

mixture of lathe cut and spherical particles

267
Q

how do we get an admix alloy in amalgam

A 
admix = spherical and lathe cut
silver tin (gamma) is cut from an ingot = lathe cut
silver copper (in Cu rich amalgam) is spherical
mixture of this with Hg leads to an admix
268
Q

what is the copper rich amalgam reaction

A

gamma + AgCu + Hg –> gamma + gamma I + Cu6Sn5

Ag3Sn + AgCu + Hg –> Ag3Sn + Ag2Hg3 + Cu6Sn5

269
Q

what copper tin compounds cna be formed depending on starting AgCu somposition

A

Cu6Sn5 or Cu3Sn

270
Q

how much copper is in copper rich amalgam

A

> 12%

271
Q

are gamma, gamma I and gamma II cathodic or anodic

A

gamma and gamma I are cathodic

gamma II is anodic

272
Q

why does gamma II make conventional amalgam more corrosive and susceptible to creep and how do we solve this

A

is is very anodic (compared to cathodic gamma and gamma I)
large difference in electrocurrent = susceptible to corrosion
use high copper amalgam to remove gamma II phase = less corrosive

273
Q

what are some advantages of high copper amalgam over conventional - explain each

A

more resistant to corrosion = Cu6Sn5 less anodic than gamma II
higher tensile strength = Cu6Sn5 stronger than Gamma II
easier to finish and compact = Cu6Sn5 is spherical making it easier to finish
lower mercury content = less mercury components, less risk

274
Q

compare lathe cut and spherical particles

A

lathe cut are made from cutting an ingot of alloy
spherical are made by atomisation of molten alloy
lathe cut require more mercury
lathe cut are harder to condense and require a broader condensation point
spherical have a smoother, better finish after burnishing
lathe cut have less undercut and stronger contact points

275
Q

what is one advantage of lathe cut and 1 advantage of spherical particles

A

lathe cut - stronger proximal contacts

spherical - less mercury, smoother finish, easier to compress, mslaler compresive point

276
Q

give some side affects of mercury poisoning

A

respiratory failure
memory loss
hypertension

277
Q

give 4 examples of when mercury is released in dentistry

A

leaky amalgam capsule
spillage when mixing
when finishing dental amalgam restorations
when removing dental amalgam restorations

278
Q

what is a liner material, where are they placed

A

applied in a thin layer, usually less than 0.5 mm thick, to seal the dentine.
They are placed in the deepest aspect of the cavity, close to the pulp.
They are usually calcium hydroxide but can also be calcium silicate cements (MTA and Biodentine) which are biocompatible and promote remineralization.

279
Q

compare MTA to calcium hydroxide for a liner

A

MTA is biocompatible and is stronger so allows thicker layers

280
Q

what functions do CaOH have as a liner

A

very high alkaline pH 11 - stimulates pulp to lay down dentine to separate pulp from restoration
stimulates remineralisation as it contains calcium
antimicrobial to prevent reinfection

281
Q

what are disadvntages of CaOH as a liner

A

soluble

mechanically weak

282
Q

compare liners and bases

A

liners placed in thinner sections closer to pulp - simulate tertiary dentine
bases placed in thicker sections above liners to replace dentine
liners are biocompatible (calcium), bases are not (polymer e.g. GIC)
liners are weaker, bases are stronger

283
Q

how does GIC set

A

acid base reaction between 2 phases mixed in an amalgamator

284
Q

Give some advantages and disadvantages of GIC

A

contains calcium, fluoride and phosphate –> remineralisation
non-toxic
non-biocompatible
low solubility so can be used in high salivary situations
strong good for bases
Bulk fill
No polymerisation shrinkage

Not as hard as composite
Not as aesthetic as composite

285
Q

compare Fuji 9 and Fuji 2 GIC

A

Fuji 9 is self setting by acid base reaction, 6 minutes, time pressure
Fuji 2 is RM-GIC so dual setting - contains camphorquinone for light set

286
Q

when is ZnOE used as a base and why is it usually avoided

A

only for temporary base quick and cheap
soluble and weak
risk of pulpal necrosis
inhibition of composite resin polymerisation

287
Q

when would we apply a liner

A

with a very small pinpoint pulp exposure
rarely for carious exposure as presence of bacteria = RCT
mechanical exposure
after 2 days of expsoure = very poor prognosis
could use liner as a IPC to stimulate tertiary dentine

288
Q

what are some ideal base material properties

A

safe, nontoxic and biocompatible
provide thermal insulation
provide good seal with tooth and definitive restoration material
tooth coloured so no staining or shadowing

289
Q

what are benefits of having a base rather than just a definitive restoration

A

seal dentine = reduced microleakage = less postoperative sensitivity with reduced risk of pulpal inflammation.
Thermal insulation = less sensitivity to hot or cold.
Mechanical protection = resistance to packing or elimination of undercuts = better supported restoration and further pulpal protection.
Stimulation of new tertiary dentine to further protect the pulp due to calcium and phosphate

290
Q

what types of base are there

A 
base varnish
GIC
RM-GIC
ZnOE
CaOH cement
291
Q

explain the use and function of cavity varnish

A

very thin layer of ‘base’ material to underlie a definitive restoration
Natural or synthetic polymer resins dissolved in a solvent and applied to the cavity floor with brush or cotton.
The solvent evaporates to leave a thin layer of resin. Process may be repeated.
Acts as a barrier against chemical penetration of tooth tissue and may protect against microleakage and secondary caries
Being so thin, they provide little thermal insulation

292
Q

explain function and properties of CaOH base material

A

rigid self setting base material
high alkalinity = >11pH = antimicrobial and stimulates pulp to lay down tertiary dentine
low compressive strength but enough to withstand compression of amalgam
slowly soluble in water so can lead to microleakage

293
Q

what are some good properties of GIC for base material

A

Relatively robust (compressive strength >50 MPa)
adhesive
insoluble
insulating
fluoride releasing
aesthetic (also a direct restorative material).
Provides a strong marginal seal

294
Q

how does a GIC set

A

acid base reaction

295
Q

compare RM-GIC and GIC

A

GIC sets with acid base reaction, RM-GIC sets with acid base and photopolymerization
RM-GIC has addition of water miscible monomer (HEMA)
RM-GIC sets by light cure but less useful in wet locations

296
Q

why is composite better than amalgam

A 
tooth coloured
bond directly to tooth tissue
can add small bits to existing restoration
can place in increments less than 2mm
no mercury
297
Q

where might we use composite material

A

restoring carious lesion
increase OVD from tooth wear
mask discolouration
fractured anterior tooth

298
Q

what is the most common denture base material and what type of material is it

A

PMMA poly methyl methacrylate

thermoplastic polymer

299
Q

what is the initiator for PMMA and how does it work

A

Benzoyl Peroxide
readily splits in 2 forming 2 sections both with an unpaired electron (free radical)
these molecules attack the double vinyl bond on the methacrylate group causing it to open and bond with another monomer
this now becomes the free radical and repeats until termination

300
Q

what is the point of a cross linking agent for PMMA

A

creates cross links between PMMA strands
increases tensile strength
increases compressible strength

301
Q

compare hot and cold set PMMA

A

cold set:

  • more porous
  • used chairside
  • weaker
  • more prone to discolouration
  • less dense
  • used for repairs
302
Q

what properties of an ideal denture material does PMMA not have (4)

A

strength
toughness
antimicrobial (candida albicans)
low thermal conductivity

303
Q

when would we use flexible denture material

A

in places of high undercut or abnormal growths e.g. Tori

304
Q

compare the two soft liner materials

A

Silicone:

  • elastic and retain elasticity
  • weak bond to PMMA
  • poor tear strength
  • not resistant to candida albicans
  • poor wettability = poor retention

PMMA:

  • elastic but goes hard
  • good bond to PMMA
  • acceptable tear strength
  • not resistant to candida albicans but resistant to bacteria
  • good wettability
305
Q

what are some ideal properties of soft liners for dentures

A 
good bond with denture base
elastic and remain elastic 
resistant to bacteria and candida albicans
high tear strength
good wettability
dimensionally stable
306
Q

what are the 4 components of GIC

A

fluoroaluminosilicate glass
polymeric acid (multiple carboxyl groups)
water
tartaric acid.

307
Q

how does GIC set (3)

A

acid base
Dissolution
Gelation
Hadrening

308
Q

compare composite to GIC

A

composite is more durable, less brittle, more aesthetic, more soluble, worse in wet conditions, light cured, less susceptible to wear due to smaller filler particles, polymerisation shrinkage, require bond, hydrophobic

GIC is less durable, more brittle, less aesthetic (but still acceptable), insoluble so work well in wet environments, chemical cured acid base, more susceptible to wear due to larger filler particles, no shrinkage or exotherm, no bond required, hydrophilic

309
Q

what is in the liquid and powder phase of GIC Fuji 9 before mixing in an amalgamator

A

powder: Flouro-aluminosilicate glass, freeze dried polymeric acid and pigments
liquid: distilled water, tartartic acid

310
Q

what are the 3 stages in GIC chemical curing

A

Dissolution
Gelation
Hardening

311
Q

explain the first step of GIC formation

A

Dissolution:
-acidic attack of glass surface
-Water is added and this ionises the carboxylic acids to release their protons which then
react with the basic glass.
-Acidic attack of the glass surface liberates some of the glass cations including calcium,
aluminium and trivalent cations.
-The silica is then retained on the surface forming a gel on the glass surface.

312
Q

explain the second stage of GIC setting

A

Gelation:

  • early cross-linking by Ca++
  • The cations released from the glass form salt bridges with the Coo- group
  • Adjacent carboxylic acid residues become stabilized.
  • Aluminium stabilises more than calcium (so higher aluminium = stronger?)
313
Q

explain the final stage of setting GIC

A

Hardening:

  • (substitution of Ca++ by Al+++)
  • Acid degraded glass sets in a crosslinked hydrogel matrix.
  • released calcium for remineralization
314
Q

how do GIC adhere to tooth surface

A

Gelation stage

calcium ions form bridges between carboxyl groups, other carboxyl groups and calcium in calcium hydroxyapatite of enamel

315
Q

how does GIC aid remineralization

A

releases flouride
bonds to H+ causing FH formation which can interfere with bacterial metabolism
F- released to form flourapatite to remineralize tooth structure

316
Q

why is GIc better than composite

A 
Used in wet areas
Bulk fill
No polymerisation shrinkage
No adhesive needed
Biocompatible
Releases flouride for reminerlaisation
317
Q

why is GIC better than composite

A

no shrinkage or exotherm = less microleakage
no bond required - biocompatible with tooth surface
insoluble so can be used in wet areas

318
Q

when do we use GIC over composite

A 
deciduous teeth
wet environment e.g. near gingival margin Class V
Fissure sealants for remineralisation
temporary restorations 
Cavity bases
319
Q

what are the ideal properties of a filling material

A 
aesthetics (composite)
hard and tough (composite)
no shrinkage (GIC)
used in wet environments (GIC)
adhesive to tooth surface (GIC) 
safe and non-irritant
320
Q

why are resin composites and GIC hard to mix

A

composite are hydrophobic

GIC are hydrophilic

321
Q

what is a RM GIC

A

resin modified glass ionomer cement
GIC mixed with a water miscible monomer (mixed with water but not hydrophilic) -HEMA
photoinitiator

322
Q

why is HEMA a better wetting agent than PMMA

A

hydroxyethyl methacrylate and polymethylmethacrylate

hydroxyl group on HEMA makes more hydrophilic allowing more contact with wet surface

323
Q

why is HEMA used rather than PMMA in RM-GIC

A

HEMa has higher wettability due to OH group making RM-GIC far less hydrophobic than resin composites

324
Q

what should be some similar and dissimilar properties between ideal definitive and temporary restoration

A

similar:

  • good marginal seal
  • strong and compressible
  • fluoride releasing
  • resistant to cold/hot

dissimilar:

  • not same colour as teeth, easy to see
  • easy to remove
  • not too adhesive as this makes hard to remove
325
Q

give advantages and disadvantages of ZnOE as a temporary restoration

A 
\+white so easy to find and distinguish
\+adhesion low so easy to remove
\+antimicrobial so further defence
\+cheap and easy
\+pain relieving
  • no adhesion
  • low surface hardness
  • poor compressible strength
  • variable marginal leakage
  • poor aesthetics
  • inhibit composite polymerisation
326
Q

what affect does eugenol have on composite and what implications of this are there

A

prevents polymerisation
can’t use ZnOE as a base if composite is going directly above
use something else

327
Q

give advantages and disadvantages of Zn Oxide/Zinc/Calcium Sulphates as a temporary restoraiton

A

+absence of eugenol means set on saliva and dont inhibit polymerisation of composite
+cheap
+easy to use
+different colour to tooth

  • no adhesion and variable marginal seal
  • poor compressible strength
  • possible expansion on setting
  • poor aesthetics
  • no command set
  • no antimicrobial factors
  • no pain relieving factors
328
Q

what is the best polymer wetting agent and why

A

HEMA

hydroxyl group makes less hydrophobic and more polar

329
Q

compare ZnOE and ZnO as a temporary restoration

A

ZnO has
-no pain relieving factors
-no antimicrobial factors
+no eugenol so doesn’t inhibit polymerisation of composites

ZnOE
+pain releiving
+antimicrobrial
-eugenol inhibits polymerisation of composites

330
Q

give advantages and disadvantages of (RM)GIC good for temporary restorations

A

+adhesive to tooth structure
+good aesthetics but still distinguishable
+release fluoride
+biocompatible

  • initial weakness, gets stronger through time via hardening
  • more expensive than other options
  • harder to remove than other options
331
Q

compare ZnOE and RM-GIC as a temporary material

A 
RMGIC:
\+command set
\+release flouride
-more expensive
-harder to remove
\+better aesthetics
-not pain releiving
\+biocompatible and adhesive
332
Q

when should different temporary filling materials be used

A

composite is the ideal restorative material
small fractures on incisor: composite
grossly infected carious lesions: GIC (no retention factors)
class V near gingiva: GIC
retention e.g. occlusal: ZnOE

333
Q

what are some properties of dental modelling materials

A 
cheap
heat resistant up to 100 degrees 
hard and robust
don't react with impression materials, wax, PMMA
resistant to wear
334
Q

what 2 characteristics of an ‘ideal’ model material does plaster of Paris not fit

A

resistance to wear

non-reactive : sodium alginate reactions with calcium sulphate in gypsum

335
Q

what is the main component of gypsum/plaster of paris

A

calcium sulphate beta-hemihydrate

336
Q

what are the three types of gypsum used in the dental school, there similarities and differences

A

plaster (beta gypsum) - weaker, large porous particles, calcium sulphate beta-hemihydrate, 110-120 degrees
stone (alpha gypsum)- denser, smaller less porous particles, calcium sulphate beta-hemi-hydrate 125 degrees
improved stone - very small dense particles, calcium sulphate beta-hemi-hydrate, added MgCl

337
Q

when do we use plaster over stone and why

A

denture models as it breaks off easily and has very minimal epxansion 0.2-0.3%

338
Q

what type of gyspum do we use for bridge work (dies)

A

improved plaster stone

much stronger and more rigid

339
Q

what type of material is plaster of paris

A

non-newtonian, more viscous on vibrating
calcium sulphate beta hemi-hydrate
mined from gypsum sedimentary rock

340
Q

why do we heat mined gypsum and what is the reaciton

A

mined gypsum = clacum sulphate dihydrate
heated = calcium sulphate beta-hemihydrate
= strong rigid

341
Q

what is the process of forming plaster from pure gypsum and why do we get expansion

A

mined gypsum - calcium sulphate dihydrate
dissolved in water and supersaturated
super heated at different temperatures and pressures
Crystals grow and interlock to form a hard rigid stone substance = calcium sulphate beta-hemihydrate
The friction of the crystals meshing together causes the exotherm and due to slight TEC, expansion

342
Q

why do we get expansion on setting gypsum and how can we reduce this

A

very slight TEC
when crystals set, friction causes exotherm
causes expansion 0.3-0.6%
reduce by adding retarders to slow setting time and reduce expansion

343
Q

what can we place in-between plaster to stop sticking together

A

sodium alginate

vasaline

344
Q

what acts as a gypsum accelerator rand retarder

A

accelerator: potassium sulphate (reduced expansion)
retarder: borax

345
Q

what can affect the setting time of gypsum

A

water to powder ratio
temperature and pressure
accelerators/retarders

346
Q

what powder: water ratios do we use for plaster and stone

A

plaster: 50ml water to 100g gypsum
stone: 20-25ml water to 100g gypsum

347
Q

what causes small pink spots in plaster and why is this added

A

small amounts of sodium chloride act as a accelerator

348
Q

what affects do sodium chloride have on setting plaster

A

in large amounts: retardant

in small amounts: accelerator and cause small pink spots

349
Q

what type of material is Dycal and when is it used

A

Calcium hydroxide

pulp liner

350
Q

what type of material is IRM, MTA, Kalzinol

A

Zinc Oxide Eugenol
liner under amalgam fillings
rot filler for intervisit medication

351
Q

how does setting CaOH act as a liner

A

causes necrosis of pulp which calcifies and causes a protective layer
antibacterial
stimulates dentine formation
can cause further inflammation and pain

352
Q

compare Calcium Hydroxide, GIC and ZnOE as liners

A

all antibacterial
CaOH causes tertiary dentine and pulp necrosis and comes in 2 pastes
GIC is adhesive, plugs dentinal tubules, releases fluoride
ZnOE used under amalgam restorations

353
Q

list 5 ceramic/glasses used in dentistry

A 
GIC
Gypsum
hydroxyapatite
Porcelain
Silane fillers in composite filling
354
Q

what are PMC made out of

A

stainless steel

355
Q

how long does fuji-9 take to set

A

2-3 mins by acid base

356
Q

What type of impression material is impression compound

A

Not elastic
Rigid
For edentolous patients

357
Q

What does tin do in amalgam

A

Gamma and gamma 2 phase

Slows down setting time

358
Q

What does zinc do in amalgam

A

Increase wettability

359
Q

what is the most dimensionally stable elastomer impression material

A

addition cured silicones

360
Q

what 3 factors alter the spacing needed in secondary impression trays (3)

A

elastic limit of material
tear strength of material
presence of undercut/extent

BDS 2 (13 decks)

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