Impression Materials Flashcards
Describe 6 general ideal properties of impression materials
- Non-toxic
- Non-irritant
- Clean to use
- Acceptable taste and odour
- Long shelf life
- Able to sterilise
Describe 4 ideal properties for impression materials with regards to the clinician using it
- Easy manipulation
- Adequate mixing time
- Adequate working time
- Adequate setting time
Name 6 ideal properties of impression materials with regards to its usability
- Ability to record fine detail
- No dimensional or thermal change
- Bonds to tray
- Elastic
- Tear resistance
- Hydrophilic
Describe the most common classification of impression materials
- Elastic materials
2. Non-elastic materials
Name 2 divisions of elastic materials with their subdivisions
- Synthetic elastomers
- Polysilicones
- Polysulphides
- Polyethers
- Hydrocolloids
- Reversible (agar)
- Irreversible (alginate)
Describe 4 divisions of non-elastic materials
- Impression plaster
- Impression compound
- Zinc oxide / eugenol paste
- Impression waxes
Describe adhesive used for impression materials
- Always required except zinc oxide / eugenol
- Retains material against tray
- Prevent distortion and encourage setting change to be towards tray
What is the definition of a solution?
A homogenous consisting of a single phase e.g salt and water
What is the definition of a suspension?
A mixture of two distinct phases e.g water and rice
What is the definition of a colloid?
A heterogenous mixture of two phases where they are no easily differentiated e.g droplets of oil in water
What is the definition of a hydrocolloid?
Particles suspended in water and can exist as a liquid (sol) or as a solid (gel)
Describe the use of aqueous hydrocolloids in terms of sols and gels while taking impressions
- Placed intra orally as sol and converted to gel in setting process
- Agar is a heat setting process
- Alginate is chemical setting process
Describe the dimensional stability of hydrocolloids
- Lose water easily by evaporation and syneresis and also easily absorb water by imbibition
- Poor dimensional stability and accuracy
Describe the properties of agar
- 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
Name 5 components of agar
- Agar
- Borax
- Potassium sulphate
- Alkyl benzoate
- Water
Describe the reason for inclusion of borax, potassium sulphate and alkyl benzoate in agar
Borax - Strengthens gel but retards set of dental stone
Potassium sulphate - Prevents the retard in set of dental stone
Benzoate - Preservative
Name 3 indications for use of alginate
- Study models
- Production of custom trays
- Appliance production
Name 6 components of alginate and their functions
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
Describe the setting reaction of alginate
- 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
Name 5 advantages of alginate
- Cheap and easy to use
- Biocompatible
- Hydrophilic
- Can be used in stock trays
- Good working time
Name 5 disadvantages of alginate
- Tears easily
- Dimensionally unstable
- Detail reproduction can be insufficient for crown and bridgework
- High permanent deformation
- Does not bond to tray
Name 2 alginate products
- Kromopan 100
2. Hydrogum 5
Name 2 indications for impression compound
- Preliminary impressions for edentulous patients
2. Extension modification of trays for any impression
Name 3 components of impression compound
- Thermoplastic material (waxes and resins)
- Plasticisers (stearic acid)
- Fillers (CaCo₃)
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)
Describe what is contained in the reactor paste of zinc oxide / eugenol paste
Eugenol
Zinc acetate (accelerator)
Kaolin, talc (filler)
Describe 5 properties of zinc oxide / eugenol paste
- Non toxic
- Mucostatic
- Good surface detail in thin surface
- Good dimensional stability on setting and storage
- Can irritate the patient
Name 4 uses of zinc oxide / eugenol in dentistry not related to prosthodontics
- Cements
- Temporary fillings
- RCT
- Surgical dressings
Name 2 types of polysilicones
- Addition
2. Condensation
What is the most commonly used synthetic elastomer?
Addition polysilicones
Name 3 indications of condensation silicones
- Mostly laboratory based
- Duplication of models
- Duplication of complete denture technique
Describe the composition of condensation silicones
Base - polymethylsiloxane, tetraethylorthosilicate and filler
Catalyst - Metal organic ester
By-product - Ethyl alcohol
Describe the manipulation of condensation silicones
- Mix thoroughly
- Putty wash technique reduces effect of polymerisation shrinkage
- Stock tray used
Name 4 advantages of condensation silicones
- Better elastic properties
- Clean and pleasant
- Stock tray
- Good working and setting time
Name 3 disadvantages of condensation silicones
- Poor dimensional stability
- Hydrophobic
- High shrinkage
Name 3 indications of addition silicones
- Crowns and bridges
- Dentures
- Bite registration
Describe composition of addition silicones
First paste - Vinyl poly(dimethylsiloxane) and pre-polymer
Second paste - Siloxane pre-polymer
Catalyst - Chloroplatinic acid
Name 2 techniques for manipulation of addition silicones
- Single phase technique
2. Putty wash technique
Name 5 advantages of addition silicones
- Highly accurate
- Good dimensional stability
- Multiple casts
- Easy to mix
- Good tear resistance
Name 4 disadvantages of addition silicones
- Expensive
- Sulphur inhibits set
- Short working time
- Possible hydrogen gas release (palladium added to negate this)
Name 2 indications for polyethers
- Crown and bridgework
2. Bite registration
Describe the composition of polyethers
Base - Difunctional epimine-terminated pre polymer, fillers, plasticisers
Catalyst - Aromatic sulphonic acid ester, fillers
Describe the type of polymerisation of polyethers
Cationic polymerisation
Name 5 advantages of polyethers
- Highly accurate
- Good dimensional stability
- Good surface detail
- Pour within one week
- Good wettability
Name 5 disadvantages of polyethers
- Expensive
- Short working time
- Rigid - Difficult to remove
- Low tear strength
- Absorbs water - Changes dimension
Name 3 components of decontamination
- Cleaning
- Disinfection
- Sterilisation
What is disinfection?
Process aims to kill all potentially pathogenic organisms or render them inert to reduce risk of transmission of infection
What is sterilisation?
Process aims to destroy all forms of microbial life including spores
Describe 3 steps of decontamination of an impression
- Wash under clean running water until visibly clean
- Disinfect (Perform-ID - Impressions can only be surface sterilised due to deformation)
- Wash thoroughly again
