3rd Yr- CSB- Extra-coronal restorations > Elastomeric Impression Materials > Flashcards

Elastomeric Impression Materials Flashcards

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1
Q

Why do we take an impression and pour a gypsum model

A
  1. To study the case
  2. To diagnose the case
  3. To plan the line of treatment
  4. To educate the patient about their dental needs
  5. To construct indirect restorations
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2
Q

What are we looking for from an impression material?

A
  1. Consistency
  2. Flow properties
  3. Optimum setting time
  4. Dimensional stabiliy
  5. Ease of handling
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3
Q

What is an elastomeric impression material?

A

A material that is used when an extremest accurate impression is essential

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4
Q

What is an elastomer?

A

It is a natural or synthetic rubber which has the silty to undergo deformation under the influence of a force and regain its original shape once the force has been removed

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5
Q

What are elastomers made up of

A

Large molecules or polymers that link together when mixed into a 3D network
When stretched the network uncoils and snaps back to original shape when the force is removed

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6
Q

List the ideal properties of setting material

A
  1. Non-toxic and non irritant
  2. acceptable to the patient (in terms of setting time, taste and consistency)
  3. Surface reproducibility
  4. Dimensional stability
  5. Ease of mixing
  6. Compatible with model materials
  7. Cheap and long shelf life
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7
Q

Name the 2 categories elastic impression materials fall under

A
  1. Aqueous hydrocolloids

2. Non aqueous elastomers

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8
Q

Give examples of aqueous hydrocolloids

A

Agar

Alginate

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9
Q

Give examples of non aqueous elastomers

A

Silicone Condensation

Silicone Addition

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10
Q

Name the 3 materials that non aqueous elastomers can be made of?

A
  1. Polysulfide
  2. Silicones
  3. Polyester
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11
Q

Why can we not use alginate as a an Elastomeric Impression Materials

A
  1. Tears easily
  2. Dimensionally unstable and is single cast only
  3. Lower detail reproduction
  4. High permanent deformation
  5. Difficult to disinfect
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12
Q

Name the 2 parts elastomers impression materials usually come in

A
  1. Base

2. Catalyst

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13
Q

How is the base packaged in elastomeric impression materials

A

Packaged as a paste in tube, as a cartridge or as a putty in a jar

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14
Q

What is the catalyst part of elastomeric impression materials sometimes called?

A

The accelerator

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15
Q

How is the catalyst packaged in elastomeric impression materials

A

As a paste in a separate tube, as a cartridge or as a liquid in a bottle with a dropper top

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16
Q

Name the different forms elastomeric materials can come in

A
  1. Light bodied
  2. Regular/ medium bodied
  3. Putty
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17
Q

What is the viscosity of elastomeric materials governed by?

A

Their filler content

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18
Q

What is light bodied elastomeric material sometimes referred to as?

A

Syringe or wash type

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19
Q

What are the benefits of light bodied elastomeric materials

A

They flow in and about the details of prepared teeth

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20
Q

What are regular/ medium bodied elastomeric materials sometimes called?

A

Tray type materials

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21
Q

What are the benefits of tray type materials

A

They are thickener and their stiffness helps to force the light bodied material into close contact with the prepared teeth
This ensures a more accurate impression of the details is prepared

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22
Q

What is the main difference between the different forms fo elastomeric materials?

A

Their viscosity (determined by their filler content)

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23
Q

Name the three stages of curing elastomeric materials

A
  1. Initial set
  2. Final set
  3. Final cure
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24
Q

What does the initial set stage of curing elastomeric materials result in?

A

Results in the stiffening of the paste without the appearance of elastic properties

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25
What is special about the initial set stage of curing elastomeric materials?
The material can only be manipulated in this first stage
26
What does the final setting stage of elastomeric material begin with?
Begins with the appearance of elasticity
27
What does the final setting stage of elastomeric material result in?
A gradual change to a solid rubber like mass
28
Before the elastic properties of the final begins to develop where must the material be?
Must be placed in the mouth
29
How long does the final cure last?
1-24 hours
30
Name the different types of elastomeric materials
1. Polysulfide 2. Polyether 3. C silicone 4. A silicone or polyvinyl siloxane
31
Name the main types of elastomeric materials you'll find in practice
1. Polyether | 2. A silicone
32
What is the problem with polysulfide and c silicone?
They both require condensation reactions which results in a byproduct
33
What is the base of Polysulfide Impression Material made up of
Mercaptan polysulfide
34
What is the cross linking agenda of Polysulfide Impression Material
Sulfue and or lead dioxide
35
What catalyst is found in Polysulfide Impression Material
Copper hydroxides Zinc peroxide Organic hydro peroxide
36
Name the fillers found in polysulfide Impression Material
Zinc sulfate Lithopone Calcium sulfate dehydrate
37
Name the first dental elastomers
Polysulfide
38
Give some of the indications for polysulfide
1. Complete dentures 2. Remove-able fixed parietal dentures 3. Crown and bridges
39
Name the common polysulfides used in clinics
1. Permlastic (Kerr) | 2. Omni-Flex
40
State the Polysulfide Reaction
mercaptan + lead dioxide -> polysulfide rubber + lead oxide + water
41
How is the polysulfide Impression Material used?
1. Adhesive placed onto tray in a uniform layer 2. Equal lengths of paste used 3. Mix paste throughly for a minute 4. Let the material set for 8-12 mins 5. Pour within the hour
42
What are the advantages of polysulfide Impression Material
1. Lower cost compared to silicones and polyethers 2. Long working time 3. High tear strength 4. High flexibility 5. Good detail reproduction
43
What are the disadvantages of polysulfide Impression Material
1. Poor dimensions stability 2. Gives a water by product 3. Single pour and you need to put within the hour 4. Need custom trays 5. Messy as it is a paste- paste mix 6. Bad odour and may stain clothing 7. Long setting time
44
Name the base that makes up the polyether impression material
Polyether
45
Name the cross linking agent that makes up the poly ether impression materials
Sulfates
46
Name the catalyst found in poly ether impression materials
Glycol based plasticisers
47
Name the filler found in polyether impression materials
Silica
48
Give some of the advantages of of polyether impression materials
1. Highly accurate 2. Good dimensional stability 3. Stock or dual arch trays 4. Good surface detail 5. Pour within one week 6. Can make multiple casts 7. Good gettability as it's hydrophilic
49
What are some of the disadvantages of polyether impression materials
1. Expensive 2. Short working time 3. Rigid and stiff 4. Bitter taste 5. Low tear strength 6. Absorbs water which can change the dimensions
50
The fact that polyether impression materials are stiff makes what difficult?
Makes it difficult to remove the impression without rocking
51
How can we overcome the problem of removing polyether materials from there cast?
Break the seal and rock slightly to prevent tearing
52
What happens if polyether mixes with moisture?
Added moisture will increase the impressions marginal discrepancy
53
Name the base that makes up c silicone impression materials
Poly dimethyl siloxane
54
Name the cross linking agent found in c silicone impression materials
Alkyl orthodontics silicate OR Organo hydrogen siloxane
55
Name the catalyst found in c silicone impression material
Organo tin compound
56
Name the filler found in c silicone impression materials
Silica
57
What is a problem associated with c silicone impression materials (in terms of their activation reaction )
They undergo condensation which results in a by product that we do not want
58
Name the by product of c silicone impression
Ethyl alcohol
59
What are the advantages of c silicone impression materials
1. Better elastic properties 2. Clean and pleasant 3. Stock tray used 4. Good working and setting time
60
What are the disadvantages of c silicone impression materials
1. Poor dimensional stability 2. High shrinkage due to polymerisation reaction 3. Need to pour almost immediately (within 30 mins) 4. Hydrophobic so poor wettabilty 5. Limited shelf life
61
What is another name for a silicones
polyvinlysiloxanes
62
How are the polyvinlysiloxanes (A silicones) supplied?
Supplied as a paste/paste in an auto mixing gun OR As a putty
63
Describe the 2 pastes that make up polyvinlysiloxanes (A silicones)
One paste has silicone with thermal vinyl groups (C=C) and chlorplantinic acid catalyst The other has silicone with hydrogen groups and silica filler
64
Does the activation reaction of polyvinlysiloxanes (A silicones) have a by product?
NO as it is an addition reaction
65
What can happen if the 2 pastes that form polyvinlysiloxanes (A silicones) arent mixed properly
Hydrogen gas is given off in the set impression | This can cause air bubbles in the model if it is poured immediately
66
Name the 2 pastes that make up polyvinlysiloxanes (A silicones)
1. Vinyl poly(dimethylsiloxane) prepolymer | 2. Siloxane prepolymer
67
Name the catalyst found in polyvinlysiloxanes (A silicones)
Chloroplatinic acid
68
What are the advantages of polyvinlysiloxanes (A silicones)?
1. Highly accurate 2. High dimensional stability so can be poured up to one week 3. Stock or custom trays 4. Multiple casts can be made 5. Easy to mix 6. Pleasant odour
69
What are some of the disadvantages of polyvinlysiloxanes (A silicones)?
1. Expensive (due to platinum catalyst) 2. Sulphur inhibits setting so don't use latex gloves 3. Short working time 4. Low tear strength 5. Possible hydrogen release so bubbles can ruin impression
70
What is the working and setting time of polyvinlysiloxanes (A silicones) affected type?
Ambient temperature and moisture
71
What can be added to polyvinlysiloxanes (A silicones) to make them more hydrophilic?
Topical surfactants
72
How to surfactants increase the wet ability of polyvinlysiloxanes (A silicones)
They reduce the contact angle
73
Out of all the impression materials which is the best one in terms of dimensional stability?
polyvinlysiloxanes (A silicones)
74
Out of the 4 materials has the best elastic recovery and which has the worst
Best: A silicone (99-99.9%) Worst: Polysulfide (94.5-96.9%)
75
Out of the 4 materials which is the most flexible and which is the least?
Most: Polysulfide (8.5-20%) Least: Polyether and A silicones
76
Out of the 4 materials which is the most flowable and which is the least?
Most: Polysulfide Least: Polyether and A silicones
77
Out of the 4 materials which shrinks the most and which shrinks the least?
Most shrinkage: Polysulfide | Least shrinkage A silicone
78
What does the A in A silicone stand for
Addition
3rd Yr- CSB- Extra-coronal restorations
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