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Dental Materials Y2 > Elastomeric Impression Materials > Flashcards

Elastomeric Impression Materials Flashcards

1
Q

What are the 3 main types of materials in elastomeric impression materials

A

Polysulphides

Silicones

Polyethers

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2
Q

What is light body elastomeric material used for

A

Impression for inlays, onlays, crowns

Light body used to capture detail. Heavy body placed in tray and placed over light body to form impression, providing stability for better accuracy

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3
Q

What body of elastomeric material is used for impression for removable dentures

A

Regular body

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4
Q

What body of material is used for cleft palate patients

A

Heavy body

Does to flow as easily to prevent choking of baby

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5
Q

Do polysulphide impression materials set quickly or slowly

A

Slowly. Has the longest setting time of all impression materials

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6
Q

What is the active ingredient in polysulphide impression material

A

Polysulphide polymer

80-85%

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7
Q

What is the purpose of titanium oxide, zinc, silica, copper carbonate in polysulphide material

A

Give body so that it can be made into a paste

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8
Q

What is role of lead oxide in polysulphide impression material

A

Active ingredient in accelerator

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9
Q

Why is copper hydroxide and cumene hydroperoxide used in polysulphide impression when lead peroxide and oxides are more stable

A

Lead peroxide and lead oxide have tendency to stain clothing and are smelly

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10
Q

What properties do chain lengthening and cross linking confer to polysulphide impression material

A

Chain lengthening increase viscosity

Cross linking confer elasticity

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11
Q

What is purpose of tray adhesive for polysulphide

A

Enhance adhesion of impression material to tray

Inhibit thermal shrinkage of impression material

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12
Q

What must you do after applying tray adhesive onto tray before you take impression for polysulphide

A

Wait for 5-10 min for ketone/chlorofoam to evaporate before placing impression material

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13
Q

What is the setting time of polysulphide impression material

A

10-16min, 10min in mouth since increased temperature increases setting rate

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14
Q

What are the factors that influence setting time of polysulphide material

A

Temperature (increase temperature increase setting time)

Use of retarder like oleic acid (dilute chain, decrease setting rate)

Presence of water (accelerator, make sure teeth and tray are dry)

Base/accelerator ratio (1:1, if more base, take more time to set)

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15
Q

What is permanent deformation of polysulphide material

A

2-3%

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16
Q

What is strain in compression of polysulphide material

A

4.5-10%, quite flexible

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17
Q

Can cast be made soon after taking polysulphide impression

A

Yes, elastic recovery is fast enough

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18
Q

Is polysulphide impression dimensionally stable

A

Good only in first few hours. Dimensional change -0.2 to -0.6%

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19
Q

What causes dimensional shrinkage (lack of dimensional stability) of polysulphide

A

Rearrangement of bonds during polymerisation

Evaporation of volatile components and thermal contractions

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20
Q

Can polysulphides be silver plated

A

Yes

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21
Q

What problems of polysulphides do condensation polymerised silicones address

A

Long setting time

Stain clothing

Unpleasant odour

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22
Q

Function of placing alkyl silicate and organo-tin compounds of condensation polymerised silicone in separate bottles

A

Prolong shelf life

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23
Q

Describe the reaction to form condensation polymerised silicone

A

Cross linking between terminal groups of silicone polymers (base) and alkyl silicate in presence tin octoate (reactor)

Ethyl alcohol is by product

Exothermic reaction

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24
Q

What is the main problem with condensation polymerised silicone

A

Liberates ethyl alcohol as by product which will evaporate and cause material to shrink

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25
Q

What is the material for tray adhesive for condensation polymerised silicone

A

Poly dimethyl siloxane or reactive silicone+ethyl silicate

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26
Q

How long does condensation polymerised silicone take to set

A

6-10 mins, not sensitive to changes in temperature or humidity

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27
Q

How to control setting time of condensation polymerised silicone

A

Change base/accelerator ratio. Retarding effect more pronounced

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28
Q

What is dimensional change of condensation polymerised silicone

A

-0.6% after 24 hours due to evaporation of alcohol and polymerisation shrinkage

Cast or dies should be made within 1h after impression removed from mouth

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29
Q

Can condensation polymerised silicone be silver plated

A

Difficult

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30
Q

What is the catalyst in addition polymerised silicone

A

Chloroplatinic acid (in accelerator)

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31
Q

What is present in base paste of addition polymerised silicone

A

Silicone with terminal silane hydrogen (vs condensation where just silicone polymer) and reinforcing filler

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32
Q

What is function of palladium black in accelerator paste of addition polymerised silicone

A

Absorb hydrogen formed due to impurities in the material which would make cast very porous

Not a by product of addition reaction

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33
Q

Describe reaction in addition polymerised silicone

A

Addition of silane hydrogen groups at terminal ends (base) across terminal vinyl double bonds (accelerator) via cross linking

No by product

34
Q

Why is it important for the prep to be dry for addition polymerised silicone

A

Chain itself is hydrophobic, would cause material to be unable to capture fine details

35
Q

What is the setting time in addition polymerised silicone

A

3-7 minutes

36
Q

What must you do before you pour the cast for addition polymerised silicone

A

Spray debubbleliser/surface acting agent because impression material is hydrophobic and cast would be unable to capture details

37
Q

How is the dimensional stability of addition polymerised silicone

A

Very stable. Shrinkage -0.05 to -0.06% in 24 hours

Hence able to send impression to lab

38
Q

Why must you remove excess debubblizer?

A

Excess pools of debubblizer in the impression will result in areas with changed water-powder ratio, and tooth in that area will be weaker

39
Q

Why is addition polymerised silicone more conducive for silver-plating compared to condensation polymerised silicones?

A

There is ethyl alcohol byproduct formed during condensation polymerised silicone process, so this alcohol will bubble up during silver plating process

40
Q

How do you improve adhesion of silicone to the trays?

A

Increase number and size of perforations- should be the size of those in alginate stock trays, to prevent the material from separating from the tray when removing from the mouth

41
Q

What is the main advantage/improvement of quadrafunctional hydrophilic siloxanes (QHS) (also known as aquasil) in comparison to traditional addition polymerised silicones?

A

Not as hydrophobic.

If the material is too hydrophobic, it will not adhere to wet tooth surface/ preparation surface, so surface details will not be registered accurately- mounting of cast will be inaccurate

Optimisation of flow characteristics- easy application without requiring too much pressure

42
Q

What are the 4 forms of aquasil and what are their applications?

A

Soft putty- two similar proportions of the material
Monophase- Single paste system, both syringe and tray material
Low viscosity- used with high viscosity material, syringe around the preparation
Ultra low viscosity where you have problems with good moisture control

43
Q

What is the main constituent found in aquasil that is not found in traditional addition poymerised silicones

A

QM resin- serves to help build up the body for the material

  • improves tear strength (important when material is under undercut and you need to remove from the mouth)
  • A weak tear strength would result in thin layer between soft tissue and margin of preparation tearing when removing stone cast from the impression. Second pour will be less accurate
44
Q

What are thixotropic properties?

A

The property that makes a material able to flow without dropping
- if you squeeze the material on surface of the teeth on maxilla, it will wet the teeth and stay on the surface without dripping down

Good thixotropic properties– material is has high enough viscosity

45
Q

Which benefit of polyether is achieved in aquasil

A

Good wettability, achieved by surfactant partially incorporated into the formula

46
Q

Which disadvantages of polysulphide are avoided in aquasil

A

Bad taste and odour

Poor dimensional accuracy, deformation (condensation polymerised silicones as well)

47
Q

What are the two components of Imprint 4 material?

A

Base and catalyst

48
Q

What is silica filler for in Imprint 4, and which component is it found in

A

Gives the material body, to form a paste

It is found in both the base and catalyst components of Imprint 4

49
Q

What does monofunctional UCS setting accelerator do in Imprint4?

A

Reduces setting time markedly, 2.5-3 minutes compared to 5minutes for aquasil

Difficult to do full mouth impression

50
Q

What component of Imprint 4 improves hydrophilic capabilities?

A

Siloxane terminated polyethylene glycol- allows crosslinking of the chains which improves hydrophilic capabilities

51
Q

How do new “hydrophilic” addition silicones (like aquasil and imprint 4) compare to other elastomeric impression materials in terms of hydrophilicity?

A

Not as hydrophilic as polyethers, not as hydrophobic as condensation and traditional addition silicones
- Still need to spry surface active agent

52
Q

What precaution must you take when mixing addition polymerised putty silicones?

A

Do not mix using gloved hands- do not handle retraction cords with latex gloves, as the impression may not set at the area with the retraction cords

53
Q

Which material has the shortest shelf life?

A

Condensation silicones because of their catalyst system

54
Q

Is addition or condensation polymerised silicones superior in dimensional stability?

A

Addition- no byproduct formed

55
Q

What is the strength of polyether?

A

Longterm accuracy

56
Q

What do triglycerides in polyether do?

A

Better flow properties

57
Q

What does colloidal silica in polyether do?

A

Allows it to form into a paste

58
Q

What does glycolether phthalate do in a polyether?

A

crosslinking agent

59
Q

What are the main drawback of polyether?

A

Disinfection is a problem due to high hydrophilicity causing material to be imbibe water, leading to swelling

Irritation of tissue by strong acids

Bad taste and odour

Very hard, difficult to remove from mouth

60
Q

How is the dimensional accuracy and stability of polyethers?

A

Good (-0.07 to -0.10% in 24 hours), slightly inferior to addition polymerised silicones

POOR if stored in wet environment as it imbibes water

61
Q

What is rough/uneven surface on impression caused by

A

Incomplete polymerisation

  • Premature removal from mouth
  • Improper ratio or mixing of accelerator and base
  • oil or organic material on teeth

Too rapid polymerisation from high humidity or temp

62
Q

What are bubbles caused by

A

Too rapid polymerisation, preventing flow

Air incorporated during mixing

63
Q

What are irregularly shaped voids in the impression caused by

A

Moisture/debris on surface of teeth

64
Q

What is a rough/chalky stone cast caused by

A

Inadequate cleaning of impression
Excess water on surface of impression
Premature removal of cast
Improper manipulation of stone

65
Q

What causes faulty electroplating?

A
  1. Silicone- should not be plated
  2. Polysulfide polymer: Dirty surface, uneven application of silver powder, inadequate current, removal from plating too soon, reversed cathode and anode
66
Q

What causes distortion?

A 
Lack of adhesion to tray
Nonrigid tray
Impression not poured immediately
Movement of tray during polymerisation
Premature/improper removal from mouth
Too much bulk of material
67
Q

What does permanent deformation mean as a property?

A

How much recovery the impression can undergo after removing from undercut

68
Q

How do the elastomeric materials rank in permanent deformation?

A 
Least deformation
Addition polymerised silicones
Condensation 
Polyethers
Polysulphides
69
Q

How do the elastomeric materials rank in strain in compression

A 
Least stiff
Polysulphides
Condensation polymerised
Addition polymerised
Polyethers
70
Q

How do the elastomeric materials rank in working and setting time

A 
Longest time
polysulphides
Condensation polymerised
Addition polymerised
Polyethers
71
Q

How do the elastomeric materials rank in dimensional stability and accuracy

A

All are good in the first few hours

Most stable
Additionpolymerised (0.05% shrinkage, 99.7% elastic recovery)
Polyethers (WATER SENSITIVE) (0.30% shrinkage, 98.9% elastic recovery)
polysulphides (0.25% shrinkage, 97.9% elastic recovery)
Condensation polymerised silicones (because of alcohol)(0.60% shrinkage, 99.5% elastic recovery)
Least stable

72
Q

How do the elastomeric materials rank in flow?

A 
Lowest flow value
Polyether
Addition polymerised
Condensation polymerised
Polysulphides
73
Q

How do the elastomeric materials rank in hardness?

A 
Least hard
Polysulphides
Condensation polymerised
Addition polymerised
Polyethers
74
Q

How do the elastomeric materials rank in tear strength

A

Highest resistance to tearing
Polysulphides
Silicones
Polyethers

75
Q

Why do you not electroplate polyether impressions

A

Soaking the electroplating solution will cause polyether to imbibe water and change dimension

76
Q

Why can you electroplate addition polymerised silicones and not condensation polymerised silicones?

A

Byproduct release of ethyl alcohol in condensation polymerised silicones

77
Q

Which material has the poorest shelf life?

A

Condensation polymerised silicones

78
Q

How many materials are used in a single mix technique?

A

1.

Medium viscosity material used in both the syringe and tray, thus it is called single mix technique

79
Q

What is the difference between the reline technique and the laminated single impression technique?

A

In reline technique, impression is made with putty material with plastic film spacer (cellophane) between the putty and teeth OR putty cut away after impression is made. Low viscosity material is placed over the putty and wash impression is made, low viscosity material is injected over the preparation

In laminated single impression technique, the tray is filled with putty material, and it is laminated with low viscosity material before a SINGLE IMPRESSION is made

80
Q

What is a good indication for the use of single mix technique?

A

It is more possible to be used for supra-gingival preparations

81
Q

What is an advantage of multiple mix technique?

A

Accurate impression, reducing chances of bubble formation

82
Q

How many materials are used in the multiple mix technique

A
  1. Light body material for syringe, injected around preparation
    Regular/heavy body material placed on tray

Dental Materials Y2 (11 decks)

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