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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
Describe what is contained in the base paste of zinc oxide / eugenol paste
- Zinc oxide - Oil (create paste) - Hydrogenated resins (increases setting time and cohesion) - Water (accelerator)
26
Describe what is contained in the reactor paste of zinc oxide / eugenol paste
Eugenol Zinc acetate (accelerator) Kaolin, talc (filler)
27
Describe 5 properties of zinc oxide / eugenol paste
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
Name 4 uses of zinc oxide / eugenol in dentistry not related to prosthodontics
1. Cements 2. Temporary fillings 3. RCT 4. Surgical dressings
29
Name 2 types of polysilicones
1. Addition | 2. Condensation
30
What is the most commonly used synthetic elastomer?
Addition polysilicones
31
Name 3 indications of condensation silicones
1. Mostly laboratory based 2. Duplication of models 3. Duplication of complete denture technique
32
Describe the composition of condensation silicones
Base - polymethylsiloxane, tetraethylorthosilicate and filler Catalyst - Metal organic ester By-product - Ethyl alcohol
33
Describe the manipulation of condensation silicones
- Mix thoroughly - Putty wash technique reduces effect of polymerisation shrinkage - Stock tray used
34
Name 4 advantages of condensation silicones
1. Better elastic properties 2. Clean and pleasant 3. Stock tray 4. Good working and setting time
35
Name 3 disadvantages of condensation silicones
1. Poor dimensional stability 2. Hydrophobic 3. High shrinkage
36
Name 3 indications of addition silicones
1. Crowns and bridges 2. Dentures 3. Bite registration
37
Describe composition of addition silicones
First paste - Vinyl poly(dimethylsiloxane) and pre-polymer Second paste - Siloxane pre-polymer Catalyst - Chloroplatinic acid
38
Name 2 techniques for manipulation of addition silicones
1. Single phase technique | 2. Putty wash technique
39
Name 5 advantages of addition silicones
1. Highly accurate 2. Good dimensional stability 3. Multiple casts 4. Easy to mix 5. Good tear resistance
40
Name 4 disadvantages of addition silicones
1. Expensive 2. Sulphur inhibits set 3. Short working time 4. Possible hydrogen gas release (palladium added to negate this)
41
Name 2 indications for polyethers
1. Crown and bridgework | 2. Bite registration
42
Describe the composition of polyethers
Base - Difunctional epimine-terminated pre polymer, fillers, plasticisers Catalyst - Aromatic sulphonic acid ester, fillers
43
Describe the type of polymerisation of polyethers
Cationic polymerisation
44
Name 5 advantages of polyethers
1. Highly accurate 2. Good dimensional stability 3. Good surface detail 4. Pour within one week 5. Good wettability
45
Name 5 disadvantages of polyethers
1. Expensive 2. Short working time 3. Rigid - Difficult to remove 4. Low tear strength 5. Absorbs water - Changes dimension
46
Name 3 components of decontamination
1. Cleaning 2. Disinfection 3. Sterilisation
47
What is disinfection?
Process aims to kill all potentially pathogenic organisms or render them inert to reduce risk of transmission of infection
48
What is sterilisation?
Process aims to destroy all forms of microbial life including spores
49
Describe 3 steps of decontamination of an impression
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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