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Prosthetics > Impression Materials > Flashcards

Impression Materials Flashcards

1
Q

Describe 6 general ideal properties of impression materials

A
  1. Non-toxic
  2. Non-irritant
  3. Clean to use
  4. Acceptable taste and odour
  5. Long shelf life
  6. Able to sterilise
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2
Q

Describe 4 ideal properties for impression materials with regards to the clinician using it

A
  1. Easy manipulation
  2. Adequate mixing time
  3. Adequate working time
  4. Adequate setting time
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3
Q

Name 6 ideal properties of impression materials with regards to its usability

A
  1. Ability to record fine detail
  2. No dimensional or thermal change
  3. Bonds to tray
  4. Elastic
  5. Tear resistance
  6. Hydrophilic
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4
Q

Describe the most common classification of impression materials

A
  1. Elastic materials

2. Non-elastic materials

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5
Q

Name 2 divisions of elastic materials with their subdivisions

A
  1. Synthetic elastomers
    • Polysilicones
    • Polysulphides
    • Polyethers
  2. Hydrocolloids
    • Reversible (agar)
    • Irreversible (alginate)
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6
Q

Describe 4 divisions of non-elastic materials

A
  1. Impression plaster
  2. Impression compound
  3. Zinc oxide / eugenol paste
  4. Impression waxes
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7
Q

Describe adhesive used for impression materials

A
  • Always required except zinc oxide / eugenol
  • Retains material against tray
  • Prevent distortion and encourage setting change to be towards tray
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8
Q

What is the definition of a solution?

A

A homogenous consisting of a single phase e.g salt and water

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9
Q

What is the definition of a suspension?

A

A mixture of two distinct phases e.g water and rice

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10
Q

What is the definition of a colloid?

A

A heterogenous mixture of two phases where they are no easily differentiated e.g droplets of oil in water

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11
Q

What is the definition of a hydrocolloid?

A

Particles suspended in water and can exist as a liquid (sol) or as a solid (gel)

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12
Q

Describe the use of aqueous hydrocolloids in terms of sols and gels while taking impressions

A
  • Placed intra orally as sol and converted to gel in setting process
  • Agar is a heat setting process
  • Alginate is chemical setting process
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13
Q

Describe the dimensional stability of hydrocolloids

A
  • Lose water easily by evaporation and syneresis and also easily absorb water by imbibition
  • Poor dimensional stability and accuracy
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14
Q

Describe the properties of agar

A
  • Biocompatible
  • Can be used for highly accurate crown and bridge impressions
  • Required special equipment - Not stable on storage
  • Difficult to disinfect
  • Easily torn or distorted
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15
Q

Name 5 components of agar

A
  1. Agar
  2. Borax
  3. Potassium sulphate
  4. Alkyl benzoate
  5. Water
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16
Q

Describe the reason for inclusion of borax, potassium sulphate and alkyl benzoate in agar

A

Borax - Strengthens gel but retards set of dental stone
Potassium sulphate - Prevents the retard in set of dental stone
Benzoate - Preservative

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17
Q

Name 3 indications for use of alginate

A
  1. Study models
  2. Production of custom trays
  3. Appliance production
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18
Q

Name 6 components of alginate and their functions

A

Sodium alginate - Forms gel
Calcium sulphate - Provides calcium ions for setting reaction
Tri-sodium phosphate - Controls working time (retarder)
Potassium sulphate - Improves set of model
Fillers - Controls viscosity
Sodium silico-fluoride - Controls pH

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19
Q

Describe the setting reaction of alginate

A
  • Sodium alginate (sol) and calcium sulphate produces sodium sulphate and calcium alginate (gel)
  • Tri-sodium phosphate reacts with calcium ions so slows down the reaction producing the gel
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20
Q

Name 5 advantages of alginate

A
  1. Cheap and easy to use
  2. Biocompatible
  3. Hydrophilic
  4. Can be used in stock trays
  5. Good working time
21
Q

Name 5 disadvantages of alginate

A
  1. Tears easily
  2. Dimensionally unstable
  3. Detail reproduction can be insufficient for crown and bridgework
  4. High permanent deformation
  5. Does not bond to tray
22
Q

Name 2 alginate products

A
  1. Kromopan 100

2. Hydrogum 5

23
Q

Name 2 indications for impression compound

A
  1. Preliminary impressions for edentulous patients

2. Extension modification of trays for any impression

24
Q

Name 3 components of impression compound

A
  1. Thermoplastic material (waxes and resins)
  2. Plasticisers (stearic acid)
  3. Fillers (CaCo₃)
25
Q

Describe what is contained in the base paste of zinc oxide / eugenol paste

A
  • Zinc oxide
  • Oil (create paste)
  • Hydrogenated resins (increases setting time and cohesion)
  • Water (accelerator)
26
Q

Describe what is contained in the reactor paste of zinc oxide / eugenol paste

A

Eugenol
Zinc acetate (accelerator)
Kaolin, talc (filler)

27
Q

Describe 5 properties of zinc oxide / eugenol paste

A
  1. Non toxic
  2. Mucostatic
  3. Good surface detail in thin surface
  4. Good dimensional stability on setting and storage
  5. Can irritate the patient
28
Q

Name 4 uses of zinc oxide / eugenol in dentistry not related to prosthodontics

A
  1. Cements
  2. Temporary fillings
  3. RCT
  4. Surgical dressings
29
Q

Name 2 types of polysilicones

A
  1. Addition

2. Condensation

30
Q

What is the most commonly used synthetic elastomer?

A

Addition polysilicones

31
Q

Name 3 indications of condensation silicones

A
  1. Mostly laboratory based
  2. Duplication of models
  3. Duplication of complete denture technique
32
Q

Describe the composition of condensation silicones

A

Base - polymethylsiloxane, tetraethylorthosilicate and filler
Catalyst - Metal organic ester
By-product - Ethyl alcohol

33
Q

Describe the manipulation of condensation silicones

A
  • Mix thoroughly
  • Putty wash technique reduces effect of polymerisation shrinkage
  • Stock tray used
34
Q

Name 4 advantages of condensation silicones

A
  1. Better elastic properties
  2. Clean and pleasant
  3. Stock tray
  4. Good working and setting time
35
Q

Name 3 disadvantages of condensation silicones

A
  1. Poor dimensional stability
  2. Hydrophobic
  3. High shrinkage
36
Q

Name 3 indications of addition silicones

A
  1. Crowns and bridges
  2. Dentures
  3. Bite registration
37
Q

Describe composition of addition silicones

A

First paste - Vinyl poly(dimethylsiloxane) and pre-polymer
Second paste - Siloxane pre-polymer
Catalyst - Chloroplatinic acid

38
Q

Name 2 techniques for manipulation of addition silicones

A
  1. Single phase technique

2. Putty wash technique

39
Q

Name 5 advantages of addition silicones

A
  1. Highly accurate
  2. Good dimensional stability
  3. Multiple casts
  4. Easy to mix
  5. Good tear resistance
40
Q

Name 4 disadvantages of addition silicones

A
  1. Expensive
  2. Sulphur inhibits set
  3. Short working time
  4. Possible hydrogen gas release (palladium added to negate this)
41
Q

Name 2 indications for polyethers

A
  1. Crown and bridgework

2. Bite registration

42
Q

Describe the composition of polyethers

A

Base - Difunctional epimine-terminated pre polymer, fillers, plasticisers
Catalyst - Aromatic sulphonic acid ester, fillers

43
Q

Describe the type of polymerisation of polyethers

A

Cationic polymerisation

44
Q

Name 5 advantages of polyethers

A
  1. Highly accurate
  2. Good dimensional stability
  3. Good surface detail
  4. Pour within one week
  5. Good wettability
45
Q

Name 5 disadvantages of polyethers

A
  1. Expensive
  2. Short working time
  3. Rigid - Difficult to remove
  4. Low tear strength
  5. Absorbs water - Changes dimension
46
Q

Name 3 components of decontamination

A
  1. Cleaning
  2. Disinfection
  3. Sterilisation
47
Q

What is disinfection?

A

Process aims to kill all potentially pathogenic organisms or render them inert to reduce risk of transmission of infection

48
Q

What is sterilisation?

A

Process aims to destroy all forms of microbial life including spores

49
Q

Describe 3 steps of decontamination of an impression

A
  1. Wash under clean running water until visibly clean
  2. Disinfect (Perform-ID - Impressions can only be surface sterilised due to deformation)
  3. Wash thoroughly again

Prosthetics (16 decks)

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