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Dental Materials Y3 > Impression Materials for Removable Pros > Flashcards

Impression Materials for Removable Pros Flashcards

(47 cards)

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1
Q

What are the 3 main branches of impression materials

A
  • Hydrocolloids
  • Elastomers
  • Non-elastic materials
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2
Q

What types of Hydrocolloid are there

A
  • reversible (agar)

- irreversible (alginate)

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3
Q

What types of elastomer are there

A
  • Polyethers
  • Polysulphides
  • Cond. and Add. Silicones
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4
Q

What types of non elastic impression materials are there

A
  • Impression compound
  • Zinc Oxide Eugenol (ZOE)
  • Impression Plaster
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5
Q

What do mucodisplacive (muco-compressive) impression materials do

A

These are viscous and record an impression of the mucosa under load
Resulting removable prosthesis e.g. dentures, result in a distribution of load during function

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6
Q

How does taking an impression using mucodisplacive impression materials reduce fracture risk

A

The record of the mucosa under load makes a prosthesis that compensates for the differing compressibility of the denture bearing area, reducing the risk of a fracture due to flexion.

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7
Q

Why might the retention of the prosthesis made from mucodisplacive impression materials be compromised

A

As the tissues recorded in the impression will return to their original position at rest

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8
Q

Give some examples of mucodisplacive impression materials

A
  • Impression compound
  • High viscosity alginates
  • High viscosity elastomers (e.g. polyether)
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9
Q

What do mucostatic impression materials take an impression of

A

These displace the tissues less and record an impression of the un-displaced mucosa

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10
Q

What might cause instability of the denture produced from mucostatic impression materials

A

During function the tissues may distort and cause instability

NOTE: mucostatic dentures generally have better retentions than mucodisplacive as there is a closer adaptation to the mucosa at rest

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11
Q

Give some examples of mucostatic impression materials

A
  • Impression plaster
  • Zinc Oxide Eugenol (ZOE)
  • Low viscosity alginates
  • Light body addition silicone
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12
Q

Where are non-elastic impression materials used

A

Where there are no undercuts and in edentulous patients

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13
Q

AY BAWS CAN I HABE DE NOTE PLEASSE

A

Any significant deformation produces a permanent deformation

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14
Q

Describe the composition of impression plaster (mucostatic - non-elastic)

A
  • beta hemihydrate of calcium sulphate
  • potassium sulfate - anti-expansion agent
  • Borax - counteracts fast set caused by K2SO4
  • Colouring agents - contrast with model plaster
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15
Q

What happens to impression plaster (mucostatic - non-elastic) when you add water

A

the beta-hemihydrate converts to the dihydrate and there is expansion on setting (controlled by anti-expansion agent K2SO4)

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16
Q

When is the only time impression plasters are used

A

Only in edentulous cases

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17
Q

AY BAWS CAN I HABE DE NOTE PLEZ

A
  • Mucostatic non-elastic impression material so doesn’t displace soft tissue
  • Material sets hard
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18
Q

What happens if the impression plaster fractures when you try to remove it from the mouth after an impression

A

You should retrieve the pieces and glue them back before casting

NOTE: a separating medium should be used

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19
Q

Describe the composition of impression compound (mucocompressive non-elastic material)

Study These Flashcards
A
  • resins and waxes
  • talc as a filler
  • Stearic acid as a lubricant

Talc = hydrated magnesium silicate

20
Q

How do you used impression compound (mucocompressive non-elastic material) in clinics

Study These Flashcards
A
  • Thermoplastic material
  • Softened by heating the sheet in water at ~60C
  • Placed in a stock tray which is then positioned in the mouth
21
Q

Describe the thermal conductivity of impression compound

Study These Flashcards
A
  • Poor thermal conductivity/flow properties
22
Q

What won’t impression compound reproduce in the mouth

Study These Flashcards
A

Undercut areas

23
Q

What is the advantage of impression compound having a high viscosity

Study These Flashcards
A
  • If full depth of the sulcus is required to support the subsequent denture you can do it with impression compound (border moulding)
24
Q

Describe the contents of the pastes used in ZOE mucostatic non-elastic impression materials

Study These Flashcards
A

Paste 1:

  • Zinc Oxide
  • Zinc acetate

Paste 2:

  • Eugenol
  • Inert filler (e.g. talc or kaloin)

Kaolin = aluminium silicate

25
When are ZOE mucostatic non-elastic impression materials used
- Edentulous cases | - Often when relining a denture
26
Describe some of the properties of ZOE mucostatic non-elastic impression materials
- Brittle material when set - bits can fracture off - Accurate in thin section - Initial low viscosity and pseudo plasticity
27
Describe the uses of hydrocolloid elastic impression materials
- Complete/partial dentures - Orthodontics - base plate - Study models and working casts - Duplicating models
28
Is a high viscosity alginate (hydrocolloid) mucocompressive or mucostatic
Mucocompressive NOTE: Low viscosity alginate = mucostatic
29
What are the advantages of using alginates (hydrocolloids)
- Material is cheap and reliable Setting behaviour is v good: - Na3PO4 suppresses setting so material is a viscous paste while impression tray is seated in the mouth - When setting reaction begins its quick af so impression taking time is short
30
What are the disadvantages of using alginates
Water loss: - Shrinkage after setting so poor dimensional stability - Impression covered with damp napkin/sealed inelastic bag Alginate immersed in disinfecting solution: - swells - then shrinks - prolonged immersion in disinfecting solution impractical Poor Tear strength - large undercuts can't be reporduced Highly viscoelastic material: - snap removal technique needs to be employed - permanent deformation up to 1.5%
31
What are the advantages of using agar (hydrocolloid)
- Once equipment is set up its easy to use - Material is cheap Impressions have good surface detail: - fine detail recorded due to setting behaviour
32
What are the disadvantages of using agar (hydrocolloid)
- Impressions must be cast up immediately due to water loss - Also absorbs water - Compatibility with model materials - Agar has a poor tear strength (but better than alginates) - Highly viscoelastic material: snap-removal technique needed, permanent deformation up to 1%
33
Are high viscosity elastomer mucocompressive or mucostatic
Mucocompressive NOTE: Low viscosity elastomers = mucostatic
34
What are elastomers used for and why
Due to their strength and dimensional stability they're used to: - Produce accurate replicas of teeth and tissues to make full and partial dentures, crowns, bridges and inlays - Border moulding of special trays, duplicating materials for refractory casts, bite registration
35
What is a disadvantage of elastomers
- Costs more than alginates/agar
36
What are the advantages of condensation silicones (Poly-dimethyl siloxanes = elastomer?)
- More elastic than polysulfides and polyethers | - Tear strength and elongation at break are adequate - undercuts can be reproduced
37
What are the disadvantages of condensation silicones (Poly-dimethyl siloxanes = elastomer?)
- Shrinks in air (affects dimensional stability) | - Hydrophobic material (contain some detergent for wettability)
38
What are the advantages of using addition silicones (poly-vinyl dimethyl siloxanes = elastomers?)
- Best dimensional stability compared to all other impression materials (v little shrinkage) - Elastic recovery is v good
39
What are the disadvantages of using addition silicones (poly-vinyl dimethyl siloxanes = elastomers?)
- Free water in plaster reacts with unreacted Si-H groups and releases hydrogen, resulting in a porous model - wait at least 20-30mins before casting - %elongation and tear strength are generally less than that of Condensation silicones - Hydrophobic material (detergents added for wettability) - Don't use natural rubber gloves - setting can be v impaired (S poisons Pt catalyst)
40
What are the advantages of polyether (impregum) mucodisplacive (due to their stiffness)
- Good dimensional stability in AIR | - Quick setting compared to polysulfide and reliable
41
What are the disadvantages of polyether (impregum) mucodisplacive (due to their stiffness)
- Original impregum = very stiff material - Original impregum = 50% elongation + high stiffness = tearing on withdrawal - Permanent deformation - Dimensional stability on prolonged contact with water or water vapour (don't wrap in damp napkin) - disinfection is a problem
42
What are the advantages of using polysulfide elastomer impression materials
- Its the strongest of all impression rubbers (elongation at break ~500%)
43
What are the disadvantages of using polysulfide elastomer impression materials
- Dimensional stability (shrinks by 0.1-0.2%) - slow setting - Dirty to handle and has an unpleasant smell - plastic recovery is not as good as the silicone and polyether materials
44
Are elastomers or hydrocolloids preferred for producing duplicating materials
- Elastomers are recommended as duplicating materials for fixed restorations - Agar and alginates can be readily used in the preparation of partial dentures
45
What materials are most commonly used for dentate patients
- Alginate - Agar - Non-aqueous elastomers
46
What materials are most commonly used for edentulous patients
- Impression compound - Impression plaster - ZOE - Alginates - Non-aqueous elastomers
47
List as many desirable qualities of an ideal impression material as possible
- Pleasant odour, taste and aesthetic colour - Adequate shelf life for requirements of storage and dsitribution - Free from toxic irritant constituents - Economically commensurate with the results obtained - Easy to use - Setting characteristics that meet clinical requirements - readily wets oral tissues - Elastic properties free from permanent deformation after strain - Adequate strength to not tear upon removal from mouth - Dimensional stability over temp and humidity ranges - readily disinfects without loss of accuracy

Dental Materials Y3 (9 decks)

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