Brainscape's Knowledge GenomeTM

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


See full index

BDS2; Dental materials > DML9: Elastic impression materials > Flashcards

DML9: Elastic impression materials Flashcards

1
Q

In elastomers how do the polymers react

A

The two paste-polymers cross-link via an addition or condensation reaction

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

What are the ideal properties of an impression material

A
  1. Pleasant odour, taste, colour
  2. Adequate shelf-life
  3. Non-toxic irritants
  4. Economically commensurate
  5. Easy to use
  6. Good setting requirements
  7. Readily wets oral tissues
  8. Elastic properties without permanent deformation after strain
  9. Adequate strength so it doesn’t break on removal
  10. Dimensional stability over temp and humidity ranges
  11. Compatible with cast and die materials
  12. Accurate
  13. Readily disinfects
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

When are elastomers used

A
  • To produce accurate replica of teeth and surrounding tissues
  • For construction of full/partial dentures, crowns, bridges and inlays

This is due to their strength and dimensional stability being better than alginates and agar (however, they are more expensive)

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

How are elastomers dispensed and when does the reaction begin

A

Two-paste system (the viscous pastes sets into an elastic material upon mixing) This is done via tubs of putty or tubes of the material

  • the cross-linking reaction begins as soon as the two components interact via condensation/addition reaction

One-paste system begins reacting as soon as LED light unit is directed

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

What is the purpose of double barrel cartridges and Pentamix pouches for the dispensing of elastomers

A

These avoid incomplete mixing and prevent the introduction of air bubbles into the elastomer as these will be replicated in the casts and therefore affecting the products made from casts

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

Why does a condensation reaction of elastomer affect the dimensional stability of the set material

A

Because there is elimination of a small molecule which causes the shrinking of the set material

  • Addition reaction does not result in this as there is no by-products so it is more dimensionally stable
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a cross-link

A

Covalent bond linking one polymer to another

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

Outline how different paste viscosities are matched for elastomer materials

A
  • Light-bodied wash + Putty/ High viscocity

- Heavy/medium (mono phase) + Light-bodied

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

Why is wash light-bodied

A

Because it contains the least amount of filler

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why does putty have to be hand mixed

A

Because it cannot be extruded through a nozzle as it contains the maximum amount of filler making it very viscous

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

Why can a light-bodied/wash material be used in isolation

A

Because it doesn’t have the strength and body required as it contains little filler - this means it will tear easily when removing the tray from the mouth

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

Why is a light-bodied material beneficial when using a heavy-bodied base

A

Because it records the fine details and the heavy-bodied base can act as a support to the light material which is adhered to it

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

Outline the twin mix/ one stage technique for elastomer impressions

A
  1. Syringe the wash material around the teeth
  2. Load putty into the tray and insert immediately into mouth after syringing the wash material
  3. Putty sets faster than the wash so make sure to leave some of both materials on the side to determine final set
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Outline the double impression/ two stage technique for elastomer impressions (no-spacer method)

A
  1. Use the putty to take a rough impression of the mouth

2. After preparing teeth syringe the wash material onto them and reinsert the putty impression over the wash

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Why are relief channels needed in the double impression/ two stage technique for elastomer impressions

A

So that the putty can hold the wash in palce

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

Outline the double impression/ two stage technique for elastomer impressions (spacer method)

A
  1. Place polythene sheet over teeth
  2. Use putty to take impression over the polythene sheet
  3. After set, remove the putty impression and the polythene sheet
  4. Place wash material in the space provided by the putty impression and set in mouth
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Why are relief channels not needed when the spacer method is used in the two stage/ double impression technique

A

Because the polythene sheet acts as a spacer which removes the need for relief channels

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

What is the dual viscosity technique for impression taking

A

This is where a heavy and light bodied paste is used in combination

  • heavy/medium bodied material is extruded into tray
  • light bodied material is syringed around teeth/ tray
  • tray is seated in mouth and material sets
  • light bodied material can flow into undercuts and record fine details
  • heavy bodied is more rigid so acts to support the light bodied
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the disadvantages of one and two stage techniques for elastomer impressions

A

One stage: both materials have to be mixed simultaneously and both of these are two-paste systems

Two stage: this takes more time to do

20
Q

Give an example of a condensation silicone and the nature of these materials

A

Poly(dimethyl siloxane) = PDMS

These are hydrophobic materials so the mouth must be dry when taking impressions otherwise there will be many defects

21
Q

Outline what is in both pastes in a condensation silicone

A

Poly(dimethyl siloxane)

  1. Base paste
    - silicon polymer with terminal OH
    - inert filler
  2. Catalyst paste
    - tetraethocy orthosilicate (cross-linking agent)
    - dibutyl tin dilaurate (catalyst)
    - inert filler
22
Q

What is eliminated in the setting of poly(dimethyl siloxane)

A

Ethanol

23
Q

What are the advantages of Poly(dimethyl siloxane)

A

Condensation silicon elastomer impressions are

  • stonier and have better dimensional stability
  • more elastic so recover from deformation rapidly
  • have adequate tear strength
  • have adequate elongation at break
24
Q

What are the disadvantages of Poly(dimethyl siloxane)

A

Condensation silicone elastomer impressions

  • shrink in air
  • they are hydrophobic so detergents need to be used to confer a degree of wettability
  • can expand in disinfecting solution when too much detergent is incorporated
  • mouth needs to be as dry as possible
  • erratic setting behaviour when a liquid catalyst is used
  • limited shelf-life
25
Q

Why is it important that too much detergent isn’t used along with condensation silicones

A

Because the detergent is hydrophilic so if there is too much used, the material will expand in the disinfecting solution

26
Q

Give an example of an addition silicone and describe its nature

A

Polyvinyldimethylsiloxane = PVDMS

This is a hydrophobic material

27
Q

Outline what is in both pastes of an addition silicone

A

Polyvinyldimethylsiloxane

  1. Base paste
    - silicone polymer with terminal vinyl groups
    - inert filler
  2. Catalyst paste
    - silicone oligomer with Si-H groups (cross-linking agent)
    - platinum salt catalyst (required for set)
    - inert filler
28
Q

What is an oligomer

A

Low molecular weight polymer

29
Q

What are the advantages of addition silicone materials for impressions

A

Polyvinyldimethylsiloxane

  1. Best dimensional stability
  2. No by-products as set by addition cross-linking
  3. Good elastic recovery from deformation
30
Q

What are the disadvantages of addition silicone materials for impressions

A

Polyvinyldimethylsiloxane

  1. When pouting, water in paster/stone reacts with unreacted Si-H groups to release hydrogen, giving a porous model (to avoid this, pour impression after 30 mins)
  2. % Elongation and tear strength is less than that of condensation silicones but still adequate
  3. Setting can be impaired by rubber gloves (S poisons Pt catalysts)
  4. Hydrophobic material so detergents are needed for wettability
31
Q

Give an example of a polyether and describe its nature

A

Impregum

Hydrophilic material meaning a dry mouth isn’t needed

32
Q

What can cause hypersensitivity in polyether impression materials

A

Alkyl benzene sulphonate catalyst in impregum can cause tissue hypersensitivity

33
Q

Outline what is in both pastes of polyether impression materials

A
  1. Base paste
    - polyether polymer (terminal ethylene-imine groups)
    - fillers
    - plasticisers (to reduce viscosity)
    - pigments, flavourings, triglycerides
  2. Catalyst paste
    - initiator (cationic starter = sulphonium tetra borate salt)
    - fillers
    - plasticisers
    - pigments
34
Q

What is the purpose of inorganic fillers in polyethers

A

These cause the impression to have high rigidity and maintains its dimensional stability which is compromised as the material is hydrophilic

35
Q

What is the purpose of plasticisers in polyethers

A

To modify viscosity of the paste

36
Q

What is the purpose of triglycerides in polyethers

A

To increase intrinsic viscosity (decreases when outside force of shearing speed is increased) - this provides resilience with flowability under pressure

37
Q

How are polyethers such as impregum set

A

By cationic addition reactions via ring opening of the ethylene-imine group

38
Q

What are the advantages of polyethers

A
  1. Good dimensional stability in air (cannot be stored in humid environment)
  2. Quick + reliable setting compared to polysulphide
  3. Clean to handle and odour less
39
Q

How has impregum polyether been modified to give the improved impregum pentagon soft impression material

A
  • has easier removal
  • improved taste
  • optimal convenience and handling

This has been done by reducing proportion of filler which decreases the final hardness and modifying the proportion of high and low viscosity plasticisers

40
Q

What are the disadvantages of polyethers

A
  1. Stiff material
  2. High stiffness means there is tearing on withdrawal
  3. Permanent deformation as the material isn’t elastic
  4. Dimensional stability is poor on prolonged contact with water as the material will swell (issue for disinfection and cannot be wrapped in damp napkin)
41
Q

Outline the composition of both pastes in a polysulphide rubber

A
  1. Base paste
    - polysulphide polymer containing S-S links
    - filler (ZnS/TiO2)
    - plasticiser (phthalate ester)
  2. Catalyst paste
    - lead dioxide (PbO2) = cross linking agent
    - filler (same as base)
    - plasticiser (same as base)
    - sulphur
    - stearic/oleic acid
42
Q

How do polysulphide impression materials react

A

The base paste reacts with PbO2 in catalyst paste via a condensation polymerisation reaction (thiokol reaction)

43
Q

What are the advantages of polysulphide impression materials

A

Strongest of all impression rubbers

44
Q

What are the disadvantages of polysulphide impression materials

A
  1. Shrinkage on setting due to condensation reaction
  2. Slow setting
  3. Dirty to handle and unpleasant smell
  4. Elastic recover isn’t good
45
Q

Give examples of non-elastic impression materials and when they are used

A
  1. Impression plaster
  2. Impression compund
  3. ZOE

These are used in edentulous cases as it sets as a hard material which would pull out the patients teeth

46
Q

What are the properties of non-elastic impression materials

A
  • Mucostatic impression materials so don’t displace soft tissue so no trays are needed
  • Material sets hard, only used in edentulous cases
  • Poor thermal conductivity/flow properties so doesn’t reproduce undercut areas
  • It has high viscosity so if the full depth of sulcus is required to support subsequent denture this can be achieved with non-elastic impression materials
47
Q

Outline the properties of ZOE impression pastes

A
  1. Brittle when set so can fracture off
  2. Accurate in thin sections
  3. Initial low viscosity and pseudoplastcity
  4. Mucostatic impression material

BDS2; Dental materials (11 decks)

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