Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Dental Material Science > Dentures: impression, base and lining materials > Flashcards

Dentures: impression, base and lining materials Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

What are the 5 chemical classes of impression materials?

A
  • Pastes e.g. Zinc Oxides
  • Gypsum e.g. impression plaster
  • Thermoplastics e.g. Compound and Wax
  • Hydrocolloids e.g. Alginate
  • Elastomers e.g. Polyether, Silicones, Polysulphides
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is meant by the rheological properties of impression materials?

A

The viscosity of the unset material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What viscosity of impression material provides higher accuracy?

A

Low viscosity e.g. light-bodied

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Define mucostatic

A

Low viscosity materials that do not displace tissue. Shows tissue at rest

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Define mucocompressive

A

Very viscous materials displaces soft tissues - not as representative as tissues at rest but shows sulcus depth and without denture may be too big

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is meant by the mechanical properties of impression materials?

A

The properties of the set material e.g. stiffness, elasticity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What properties of impression materials will mean it distorts around undercuts?

A

Plastic and viscoelastic materials

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does rigidity of an impression material mean?

A

How easy it is to deform the material - need low stiffness to get past undercuts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What impression materials are rigid and clinically can only be used in areas without undercuts?

A
  • Thermoplastics (compound and wax)
  • Gypsum (impression plaster)
  • Pastes (Zinc Oxide)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What impression materials are elastic and clinically can be used to record undercuts?

A
  • Hydrocolloids (alginate, agar)

- Elastomers (Polyether, silicones, polysulphides)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

If there is not enough space between the tray and the tissue what does this do to the viscosity of the impression material?

A

Increases viscosity as less flow possible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are stock trays made out of?

How does the material attach in the tray?

A
  • Polymers = disposable, alloys = reusable

- Perforations or tray adhesives or rim lock (lip on tray)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How can special trays be constructed?

A
  • On a model in acrylic

- Using putty/wash systems e.g. elastomers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What 6 things affect the accuracy of the impression material?

A
  • Viscosity
  • Wetting (how well the material spreads on moist tissues)
  • Setting reaction (dimensional changes)
  • Thermal contraction (from temp change in mouth)
  • Adhesive to tray
  • Undercuts
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

If an impression material is hydrophobic what does this mean clinically?

A

Water forms droplets on the surface which leads to bubbles/blows appearing on the surface - so must have a dry field

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What will occur if the impression material undergoes polymerisation shrinkage?

A

Bonded to tray so shrinks away from tooth leading to oversized die (crown too big)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What will occur if the impression material undergoes crystal growth?

A

Expansion so leads to an undersized die (crown too small)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What temperature changes can occur during setting of impression material?

A
  • Thermal contraction - higher the coefficient of thermal expansion the more contraction. Reduction in size leads to crown not fitting
  • Thermoplastic warming/cooling - compound softened at 55 degrees then put in mouth. Temp drop can cause warping and distortion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What factors affect the accuracy of the impression when undercuts are present?

A
  • Depth of undercuts (deeper = more distortion)
  • Proper setting of the material (allow to become fully elastic not viscoelastic)
  • Removal technique
  • Thickness of impression material (tearing of thin sections)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What can dimensional changes of impression materials when they are sent to the lab be down to?

A
  • Continues setting i.e. continuation of polymerisation or crystallisation
  • Loss of volatiles such as water or ethanol evaporating
  • Stress relief
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is gypsum?

A

Plaster of paris i.e. beta-calcium sulphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Why does gypsum expand?

A

Setting reaction leads to crystallisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is added to gypsum as

a) anti-expansion agent (but accelerates setting)
b) Retarder to slow setting time

A

a) K2SO4

b) Borax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How much of powder and water do you need for gypsum to be a fluid mix?

A

100g powder to 50-60ml water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Name the properties of impression plaster

A
  • Mucostatic as low viscosity
  • Very rigid and brittle when set
  • Small expansion on setting less than 0.1%
  • Dimensionally stable
  • Non-toxic
  • Compatible with model materials
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the composition of impression compound?

A
  • Thermoplastic material e.g. natural or synthetic resins and waxes
  • Filler e.g. Talc
  • Plasticiser e.g. stearic acid
  • Pigment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the role of a)filler and b)plasticiser in impression compound?

A

a) Controls viscosity, rigidity, thermal contraction

b) Improves flow of material in and around soft tissues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is Type 1 impression compound?

A

Lower temperature fusing

  • High flow value just above mouth temperature
  • Sheet form used for preliminary imps for edentulous pts
  • Stick form used for marginal additions to stock trays
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is Type 2 impression compound?

A

High temperature fusing

  • Low flow value at or just above mouth temp
  • Rigid at mouth temp so used as tray model
  • Rarely used
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is the softening temperature of impression compound?

A

55-60 degrees

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What are the properties of compound?

A
  • Mucocompressive (material has high viscosity) so poor detail reproduction
  • No setting reaction so final material is rigid and non-elastic
  • Thermal contraction - after removal stress relief can occur
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What will happen to impression compound if:

a) Water is too cool
b) Water is too hot
c) Softening time too short
d) Softening time too long

A

a) Compound wont flow sufficiently
b) Compound will be sticky and painful for the patient
c) Wont flow
d) Leaching of plasticiser so won’t flow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Impression paste is typically supplied as two pastes. What is in these pastes?

A

1) ZnO, Zn-actetate, Oils

2) Eugenol, filler (e.g. kaolin)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is the setting reaction of ZnO and eugenol in impression paste?

A

Acid base reaction

  • Chelation reaction
  • Ionic reaction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What accelerates the setting reaction of ZnO and eugenol in impression paste?

A

Water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What are the properties of impression pastes?

A
  • Low viscosity (can only be used in thin sections)
  • Mucostatic
  • Pseudoplastic i.e. viscosity reduces under stress
  • Good accuracy and dimensional stability
  • Eugenol can be irritant
  • Rigid and non-elastic so can’t record undercuts
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What is the definition of a colloid material?

A

Somewhere in between a suspension and a solution. Particles are dispersed in another material (continuous phase) but form a homogenous solution and don’t settle out

38
Q

In terms of colloid solution types, what are
a) Sols
b) Gels
In impression taking what is the transition?

A

a) Solid dispersed in liquid, behave like liquids e.g. paint
b) Liquid dispersed in solid, behave like solids

Sol to gel

39
Q

What is the definition of

a) Solution
b) Suspension
c) Composite

A

a) Liquid of homogenous mixture of solute and solvent - one phase
b) Liquid continuous phase with solid discrete phase - 2 phases
c) At least 2 phases that can be individually recognised

40
Q

What are dental hydrocolloids based on?

A

Polysaccharides

41
Q

What is the arrangement of the polysaccharides in hydrocolloids when they are in

a) Sol form
b) Gel form

A

a) Random arrangement of fibrils, material fluid
b) Cross links form between fibrils, hydrogen bonding (weak) - reversible or covalent/ionic bonding (strong)- irreversible

42
Q

For the hydrocolloid agar

a) Is it reversible or irreversible
b) What material is added to strengthen the gel
c) What material is added to compensate this
d) Why is it heated to 100 degrees, then 65 degrees then 45 degrees

A

a) Reversible - but not reusable as contamination
b) Borax
c) K2SO4
d) 100= converts to sol
65= maintain as sol
45 = convert to gel and lowers temp before entering mouth

43
Q

What are the properties of agar?

A
  • Hydrophilic
  • Gel form is cross-linked polymer (flexible to move past undercuts)
  • Viscoelastic
  • Low tear resistance
  • Poor dimensional stability
44
Q

In gel form agar is viscoelastic, so what does distortion depend on?

A
  • Depth of undercut
  • Thickness of material - greater impression bulk means more elastic behaviour
  • Time under stress - quick snap release means more elastic behaviour ie. rapid removal
45
Q

Why does agar have a poor dimensional stability?

A

Initially has a high water content so loses water over time:

  • Syneresis = polymer chains collapse in towards each other
  • Imbibition = gains water
  • Evaporation of water on surface
46
Q

What does alginate powder contain?

A
  • Sodium or Potassium salt of alginic acid (12%)
  • Calcium sulphate/ gypsum (12%)
  • Sodium phosphate (2%)
  • Filler e.g. diatomaceous earth
  • Flavours, dyes, indicators
47
Q

What is the setting reaction of alginate?

A
  • Water and powder mixed to form sol

- Ca2+ replaces Na+ ions so crosslinking with ionic bonding possible forming a gel

48
Q

What is the working time and setting time controlled by?

A
  • Sodium phosphate and calcium sulphate
  • Sodium phosphate added as a retarder to delay the reaction
  • Temperature of water added (hot water=faster setting)
49
Q

What are the properties of alginate?

A
  • Hydrophilic
  • Poor dimensional stability, evaportation of water, syneresis, imbibition
  • Flexible (good for undercuts)
  • Elastic/viscoelastic
  • Low strength - easy to tear and needs 3-5mm of material between tray and tissue
50
Q

What is alginate not used for?

A

Where great accuracy and dimensional stability is needed e.g. crown and bridge work

51
Q

What is an elastomer?

What do the elastomeric impression materials usually come as?

A

A polymer with rubber like properties

Liquid polymers - ‘pre-polymers’ that are not terminated so can still polymerise

52
Q

What are the flexible repeating units of

a) Silicones
b) Ethers

A

a) Si-O-Si-O

b) C-O-C-O

53
Q

For the elastomeric material Silicones, what is the reaction for the condensation type?

A

Silicone pre-polymer and silica added to make paste
Catalysed by tin
Crosslinking and alcohol formed as by-product

54
Q

What is the dimensional stability like for the elastomeric condensation type silicones?

A
  • Better than hydrocolloids and polysulphides

- Ethanol evaporates so significant dimensional change over time

55
Q

What are addition type silicones known as?

A

Polyvinylsiloxanes

56
Q

For the elastomeric impression material addition type silicones (Polyvinylsiloxanes), what is in

a) Paste 1
b) Paste 2

A

a) Liquid silicone polymer with Si-H groups. Filler.

b) Liquid silicone polymer with Si-CH=H2 groups. Filler. Catalyst - chloroplatinic acid

57
Q

Why should you wait before pouring the model if you are using the addition silicone polyvinylsiloxane?

A

Hydrogen released from catalyst so will make pits in the model

58
Q

Why do the light bodied silicones shrink most during polymerisation?

A

They have less filler

More filler = higher viscosity = lower shrinkage

59
Q

What are the properties of Polyvinylsiloxane?

A
  • Good dimensional stability
  • Elastic when set
  • Good tear resistance
  • Good accuracy and fine detail
  • Hydrophobic - can lead to impression faults so needs a dry field
60
Q

What is the composition of elastomeric Polyethers?

a) Paste 1
b) Paste 2

A

a) Imine (triangular group) terminated polyether. Plasticiser. Filler
b) Aromatic sulphonate. Plasticiser. Filler

61
Q

What is the elastomeric Polyethers setting reaction?

A

Ring opening cationic polymerisation - addition polymerisation
No by product just chain extension

62
Q

What are the properties of polyethers?

A
  • Short setting time
  • Dimensionally stable but can absorb water and swell
  • Elastic when set
  • Before setting are hydrophilic and fluid for good detail reproduction
  • Very rigid when set and can remove mobile standing teeth
63
Q

What are the problems with the catalyst in Polyvinylsiloxane?

A

Latex gloves and freshly placed methacrylate’s pollute catalyst and prevent polymerisation

64
Q

Why should denture bases be

a) Strong
b) Tough
c) Stiff
d) Elastic deformation
e) Hard

A

a) Prevents dentrue fracturing
b) Withstand energy transfer from being dropped
c) Shouldn’t deform during everyday activities
d) Maintain shape in function
e) Weakened by surface scratches. Must withstand abrasive cleaners

65
Q

Why is heat transfer a problem with denture bases?

A

PMMA is an insulator but need to maintain health of underlying soft tissue so warn of potential scalds

66
Q

What molecule are acrylic denture bases based on?

What is the difference between the 2 types of acrylic base materials?

A

Monomer methyl methacrylate (MMA)

Method of polymerisation i.e. heat curing or self curing

67
Q

What is the composition of the acrylic denture base?

a) In the powder
b) In the liquid

A

a) Beads of PMMA, peroxide, pigment

b) Methylmethacrylate monomer, dimethacrylate (crosslinker), Hydroquinone (stabiliser), amine compound (activator)

68
Q

Acrylic denture bases set by free radical addition polymerisation. What are the stages of this setting reaction?

A

1) Activation
2) Initiation
3) Propagation
4) Termination

Exothermic reaction

69
Q

When manufacturing acrylic bases what are the distinct physical properties of the dough moulding process?

A

1) Slurry/ creamy when powder and liquid mix
2) Sandy (monomer soaking into PMMA and beads swell)
3) Stringy (swollen beads join together but are not polymer chains)
4) Doughy (but polymerisation hasn’t occurred)

70
Q

What occurs during dough moulded denture production?

A

1) Dough placed into gypsum moulth
2) mould sealed and pressurised - trial closure with heat cured
3) Heat cure (flask into oven), Cold cure (Pressue pot)
4) Remove after ST then grind and polish

71
Q

What are the other approaches to manufacturing acrylic denture bases?

A
  • Injectable materials
  • Pourable materials (poured when sandy, time saving but mechanical properties poor)
  • Light cured
72
Q

What is the structure of set acrylic?

A

Composite structure: continuous phase = fresh resin, discrete phase = original resin beads

73
Q

At what temperature in heat cured acrylic is

a) Peroxide activated?
b) Monomer boils and causes gaseous porosities

A

a) 65-70 degrees

b) 100.3 degrees

74
Q

Why is a heating cycle of slow rise to 70 degrees and final phase to 100 degrees used?

A
  • Reduces residual monomer
  • Maximises polymerisation
  • Reduces gaseous porosity
75
Q

Why does heat curing produce a higher degree of polymerisation?

A

PMMA glass transition temp (Tg) around 100 degrees, so monomer finds it easier to flow in polymer to active chains
Be aware that Tg is close to monomer vaporisation temperature

76
Q

What is the glass transition temperature of acrylics controlled by?
So what does high temp cure produce and low temp cure produce?

A

Molecular weight
Residual monomer

High temp = high Tg - high Mwt and low residual monomer
Low temp = low Tg - low Mwt and high residual monomer

77
Q

Why does powder have to be added to methyl methacrylate?

A

Methyl methacrylate has low Mwt so shrinks when converted to polymer. Powder reduces shrinkage.

78
Q

What is the cold cure process for setting of acrylic?

A

Activation just by mixing powder and liquid - shorter WT, no gaseous porosity

79
Q

What are the properties of PMMA?

A
  • Weak and flexible material
  • Low toughness (shatters when dropped and notch sensitive)
  • Soft material (scratches easily)
  • Low fatigue strength (Deformation midline)
80
Q

Why must care be taken when brushing denture?

A
  • PMMA soft so scratching possible

- Surface made rough - abrasive to soft tissues and site for microbial colonisation

81
Q

Why must care be taken when soaking dentures?

A 
If low Tg denture may change dimensions in hot water 
Denture bleaching (change in pigmentation) from too hot water and poor curing
82
Q

What can cause issues with biocompatibility of PMMA denture base?

A

Residual monomer irritant and cytotoxic

83
Q

What material is being used more recently for denture bases?

A

PUDMA - nylon and light cured acrylics

84
Q

For porcelain teeth

a) What are they made of
b) How are they bonded to the denture
c) What are its properties

A

a) Ceramic
b) Mechanical by pins and holes
c) Hard rigid brittle, abrasion resitant but abrasive to natural teeth, natural appearance, unnatural sound, difficult to adjust

85
Q

For acrylic teeth

a) How are they bonded
b) How are they made
c) What are they poor at resisting

A

a) Like to like bonding (denture base acrylic)
b) Polymerised using heat and pressure
c) Abrasion

86
Q

What are the indications for tissue conditioners and temp soft liners?

A
  • Temporary support to aid traumatised tissues, wound healing
  • Improve fit of ill fitting denture
  • Diagnostic aid / functional impression
87
Q

What is the composition of tissue conditioners / temporary liners

a) Liquid
b) Powder

A

a) Plasticiser = benzoate ester, solvent = ethanol

b) Higher methyl methacrylate polymer

88
Q

Why is the set material soft for a tissue conditioner and temp soft liner?

A

Plasticiser solvent and low Tg polymer as large pendent groups

89
Q

What are the properties of temporary soft liners?

A
  • Initially very soft
  • Viscoelastic so flows under load making a functional impression
  • Oxygenating cleaners cause pitting on surface
  • Harden after a few days/weeks as plasticiser leached out
90
Q

What are the indications for permanent soft liners?

A
  • Pain during mastication
  • Aid to retention (engage hard tissue undercuts)
  • Obturators - when hard or soft tissues removed to fill space
91
Q

What are the two types of permanent soft liners?

A

Acrylic based

Silicone based

92
Q

For permanent soft liners made of heat curing acrylic

a) What is in the powder
b) What is in the liquid
c) What is the setting reaction

A

a) Methacrylate polymer, peroxide, pigment
b) Monomer (methacrylate), plasticiser (lower Tg), NO ALCOHOL
c) Polymerisation - dough moulding technique and heat cure

Dental Material Science (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions