Elastomeric Impression Materials Flashcards
Why do we take an impression and pour a gypsum model
- To study the case
- To diagnose the case
- To plan the line of treatment
- To educate the patient about their dental needs
- To construct indirect restorations
What are we looking for from an impression material?
- Consistency
- Flow properties
- Optimum setting time
- Dimensional stabiliy
- Ease of handling
What is an elastomeric impression material?
A material that is used when an extremest accurate impression is essential
What is an elastomer?
It is a natural or synthetic rubber which has the silty to undergo deformation under the influence of a force and regain its original shape once the force has been removed
What are elastomers made up of
Large molecules or polymers that link together when mixed into a 3D network
When stretched the network uncoils and snaps back to original shape when the force is removed
List the ideal properties of setting material
- Non-toxic and non irritant
- acceptable to the patient (in terms of setting time, taste and consistency)
- Surface reproducibility
- Dimensional stability
- Ease of mixing
- Compatible with model materials
- Cheap and long shelf life
Name the 2 categories elastic impression materials fall under
- Aqueous hydrocolloids
2. Non aqueous elastomers
Give examples of aqueous hydrocolloids
Agar
Alginate
Give examples of non aqueous elastomers
Silicone Condensation
Silicone Addition
Name the 3 materials that non aqueous elastomers can be made of?
- Polysulfide
- Silicones
- Polyester
Why can we not use alginate as a an Elastomeric Impression Materials
- Tears easily
- Dimensionally unstable and is single cast only
- Lower detail reproduction
- High permanent deformation
- Difficult to disinfect
Name the 2 parts elastomers impression materials usually come in
- Base
2. Catalyst
How is the base packaged in elastomeric impression materials
Packaged as a paste in tube, as a cartridge or as a putty in a jar
What is the catalyst part of elastomeric impression materials sometimes called?
The accelerator
How is the catalyst packaged in elastomeric impression materials
As a paste in a separate tube, as a cartridge or as a liquid in a bottle with a dropper top
Name the different forms elastomeric materials can come in
- Light bodied
- Regular/ medium bodied
- Putty
What is the viscosity of elastomeric materials governed by?
Their filler content
What is light bodied elastomeric material sometimes referred to as?
Syringe or wash type
What are the benefits of light bodied elastomeric materials
They flow in and about the details of prepared teeth
What are regular/ medium bodied elastomeric materials sometimes called?
Tray type materials
What are the benefits of tray type materials
They are thickener and their stiffness helps to force the light bodied material into close contact with the prepared teeth
This ensures a more accurate impression of the details is prepared
What is the main difference between the different forms fo elastomeric materials?
Their viscosity (determined by their filler content)
Name the three stages of curing elastomeric materials
- Initial set
- Final set
- Final cure
What does the initial set stage of curing elastomeric materials result in?
Results in the stiffening of the paste without the appearance of elastic properties
What is special about the initial set stage of curing elastomeric materials?
The material can only be manipulated in this first stage
What does the final setting stage of elastomeric material begin with?
Begins with the appearance of elasticity
What does the final setting stage of elastomeric material result in?
A gradual change to a solid rubber like mass
Before the elastic properties of the final begins to develop where must the material be?
Must be placed in the mouth
How long does the final cure last?
1-24 hours
Name the different types of elastomeric materials
- Polysulfide
- Polyether
- C silicone
- A silicone or polyvinyl siloxane
Name the main types of elastomeric materials you’ll find in practice
- Polyether
2. A silicone
What is the problem with polysulfide and c silicone?
They both require condensation reactions which results in a byproduct
What is the base of Polysulfide Impression Material made up of
Mercaptan polysulfide
What is the cross linking agenda of Polysulfide Impression Material
Sulfue and or lead dioxide
What catalyst is found in Polysulfide Impression Material
Copper hydroxides
Zinc peroxide
Organic hydro peroxide
Name the fillers found in polysulfide Impression Material
Zinc sulfate
Lithopone
Calcium sulfate dehydrate
Name the first dental elastomers
Polysulfide
Give some of the indications for polysulfide
- Complete dentures
- Remove-able fixed parietal dentures
- Crown and bridges
Name the common polysulfides used in clinics
- Permlastic (Kerr)
2. Omni-Flex
State the Polysulfide Reaction
mercaptan + lead dioxide -> polysulfide rubber + lead oxide + water
How is the polysulfide Impression Material used?
- Adhesive placed onto tray in a uniform layer
- Equal lengths of paste used
- Mix paste throughly for a minute
- Let the material set for 8-12 mins
- Pour within the hour
What are the advantages of polysulfide Impression Material
- Lower cost compared to silicones and polyethers
- Long working time
- High tear strength
- High flexibility
- Good detail reproduction
What are the disadvantages of polysulfide Impression Material
- Poor dimensions stability
- Gives a water by product
- Single pour and you need to put within the hour
- Need custom trays
- Messy as it is a paste- paste mix
- Bad odour and may stain clothing
- Long setting time
Name the base that makes up the polyether impression material
Polyether
Name the cross linking agent that makes up the poly ether impression materials
Sulfates
Name the catalyst found in poly ether impression materials
Glycol based plasticisers
Name the filler found in polyether impression materials
Silica
Give some of the advantages of of polyether impression materials
- Highly accurate
- Good dimensional stability
- Stock or dual arch trays
- Good surface detail
- Pour within one week
- Can make multiple casts
- Good gettability as it’s hydrophilic
What are some of the disadvantages of polyether impression materials
- Expensive
- Short working time
- Rigid and stiff
- Bitter taste
- Low tear strength
- Absorbs water which can change the dimensions
The fact that polyether impression materials are stiff makes what difficult?
Makes it difficult to remove the impression without rocking
How can we overcome the problem of removing polyether materials from there cast?
Break the seal and rock slightly to prevent tearing
What happens if polyether mixes with moisture?
Added moisture will increase the impressions marginal discrepancy
Name the base that makes up c silicone impression materials
Poly dimethyl siloxane
Name the cross linking agent found in c silicone impression materials
Alkyl orthodontics silicate
OR
Organo hydrogen siloxane
Name the catalyst found in c silicone impression material
Organo tin compound
Name the filler found in c silicone impression materials
Silica
What is a problem associated with c silicone impression materials (in terms of their activation reaction )
They undergo condensation which results in a by product that we do not want
Name the by product of c silicone impression
Ethyl alcohol
What are the advantages of c silicone impression materials
- Better elastic properties
- Clean and pleasant
- Stock tray used
- Good working and setting time
What are the disadvantages of c silicone impression materials
- Poor dimensional stability
- High shrinkage due to polymerisation reaction
- Need to pour almost immediately (within 30 mins)
- Hydrophobic so poor wettabilty
- Limited shelf life
What is another name for a silicones
polyvinlysiloxanes
How are the polyvinlysiloxanes (A silicones) supplied?
Supplied as a paste/paste in an auto mixing gun
OR
As a putty
Describe the 2 pastes that make up polyvinlysiloxanes (A silicones)
One paste has silicone with thermal vinyl groups (C=C) and chlorplantinic acid catalyst
The other has silicone with hydrogen groups and silica filler
Does the activation reaction of polyvinlysiloxanes (A silicones) have a by product?
NO as it is an addition reaction
What can happen if the 2 pastes that form polyvinlysiloxanes (A silicones) arent mixed properly
Hydrogen gas is given off in the set impression
This can cause air bubbles in the model if it is poured immediately
Name the 2 pastes that make up polyvinlysiloxanes (A silicones)
- Vinyl poly(dimethylsiloxane) prepolymer
2. Siloxane prepolymer
Name the catalyst found in polyvinlysiloxanes (A silicones)
Chloroplatinic acid
What are the advantages of polyvinlysiloxanes (A silicones)?
- Highly accurate
- High dimensional stability so can be poured up to one week
- Stock or custom trays
- Multiple casts can be made
- Easy to mix
- Pleasant odour
What are some of the disadvantages of polyvinlysiloxanes (A silicones)?
- Expensive (due to platinum catalyst)
- Sulphur inhibits setting so don’t use latex gloves
- Short working time
- Low tear strength
- Possible hydrogen release so bubbles can ruin impression
What is the working and setting time of polyvinlysiloxanes (A silicones) affected type?
Ambient temperature and moisture
What can be added to polyvinlysiloxanes (A silicones) to make them more hydrophilic?
Topical surfactants
How to surfactants increase the wet ability of polyvinlysiloxanes (A silicones)
They reduce the contact angle
Out of all the impression materials which is the best one in terms of dimensional stability?
polyvinlysiloxanes (A silicones)
Out of the 4 materials has the best elastic recovery and which has the worst
Best: A silicone (99-99.9%)
Worst: Polysulfide (94.5-96.9%)
Out of the 4 materials which is the most flexible and which is the least?
Most: Polysulfide (8.5-20%)
Least: Polyether and A silicones
Out of the 4 materials which is the most flowable and which is the least?
Most: Polysulfide
Least: Polyether and A silicones
Out of the 4 materials which shrinks the most and which shrinks the least?
Most shrinkage: Polysulfide
Least shrinkage A silicone
What does the A in A silicone stand for
Addition
