Johnston: Impression Materials Flashcards
When referring to the balance of dimensional changes associated with impressions and casts, which has a (-) change and which has a (+) change?
Impression (-)
ex. Alginate will start to shrink over time
Cast or Die (+)
ex. Gypsum products will expand
Together: Alginate + Gypsum = ZERO (ideal)
When referring to the balance of dimensional changes associated with “investment” and “restoration” which will have a (-) change and which will have a (+) change?
Investment: + + +
Restoration - - -
Must add up to ZERO
What are the three physical classifications of impression materials?
Rigid
Plastic
(Visco)Elastic
What are two examples of rigid impression materials used in dentistry?
ZOE
Plaster
What are two examples of plastic impression materials used in dentistry?
Wax
Compound
What are the two broad categories of (visco)elastic impression materials used in dentistry?
Hydrocolloids
Synthetic Elastomers
Which type of physical-classification of impression materials is used for edentulous patients only?
Rigid or Brittle Materials
ex. Zinc Oxide & Eugenol Impression Paste
Dental Impression Plaster
What are two examples of Hydrocolloid impression materials? How do the two differ?
Hydrocolloids (type of visoelastic material)
- Reversible Hydrocolloid (Agar)
- Irreversible Hydrocolloid (Alginate)
What are synthetic elastomers?
Synthetic elastomers are a type of visoelastic impression material that are made by polymerizing oligomers into elastomers
What are the three categories of synthetic elastomers in dentistry? Is there a possible fourth category?
- Polysulfide
- Silicone
- Polyether
(4. New Product: combination of Silicone and polyether)
What are the two types of Silicone viscoelastic impression materials?
- Addition
2. Condensation
What is the difference between “light body” and “heavy body” impression materials?
Light Body is applied via syringe or wash
Heavy Body is applied via tray or putty
Light Body has low viscosity and high contraction
Heavy Body has high viscosity and low contraction
True or False: Light and Heavy body are used together with light body surrounding/capturing the area of interest.
True
Hydrocolloid impression materials are characterized by water bound within a _____ _______.
Colloid Matrix
Hydrocolloid impression materials (both reversible and irreversible) lack _____ ______ with time and require ______ pouring of casts.
Dimensional Stability
Immediate
What are the benefits to using irreversible hydrocolloid material (such as alginate)?
Convenient
Relatively inexpensive
What is the benefit and downfall associated with reversible hydrocolloid material (such as agar)?
Benefit: Good initial dimensional accuracy
Downfall: Requires special heating/cooling equipment
True or False: Reversible and Irreversible Hydrocolloid impression materials may not be used in combination.
False: they MAY be used in combination
When categorizing polymers, they can be either thermoplastic or thermoset. What is the difference?
Thermoplastic: NO CROSS-LINKING, physical state is
reversibly controlled by temperature
Thermoset: CROSS-LINKING is IRREVERSIBLE and occurs
during the transformation from monomer
to polymer
What is an example of a thermoplastic polymer? Thermoset polymer?
Thermoplastic = wax Thermoset = synthetic elastomer
What are the addition polymerization mechanisms? Give three examples. Which is used in Dentistry?
Addition polymerization is the change from monomer to polymer WITHOUT by-products.
- Free Radical Dental
- Ring opening
- Ionic
What type of polymerization reaction do polysulfide materials use?
Condensation
Polysulfide materials have ____ molecular weight oligomers containing reactive ______ groups.
Low
Mercaptan
True or False: Polysulfide impression materials conform well to a prepared tooth and result in good surface detail.
True
During the polymerization reaction of polysulfide materials, lead dioxide or copper hydroxide will oxidize and form a polysulfide _____ with a _____ condensate.
Rubber
Water
*remember: polysulfides polymerize through condensation reactions
Polysulfides and Polyethers both require _________.
Rigid Custom Trays for minimal thickness of impression material
Why do polysulfides and polyethers require custom trays?
To provide minimum thickness of impression material
What is the major flaw associated with polysulfide impression material?
They do NOT recover from permanent deformation very well (deformation is associated with removal of the material from the mouth)
True or False: When using Polysulfide material, the casts should be poured as quickly as possible.
True.
They do not recover well from permanent deformation
Water condensate produced during reaction = evaporation = shrinkage
Silicone empression materials (polysiloxanes) are inherently __1__ but addition type can be made more __2__.
- Hydrophobic
2. Hydrophilic
Which type of silicone was first introduced?
Condensation type (hydrophobic)
How can silicone impression materials be made more hydrophilic?
(Original Condensation type are hydrophobic.)
Addition type is made hydrophilic via:
1. Addition of surfactant
2. Chemical incorporation of hydrophilic moieties into
the silicone backbone
Which impression material is classified as: a low molecular weight oligomer containing terminal hydroxyl groups that will eventually form a rubber and release ethyl alcohol?
Condensation Silicone
True or False: When using condensation silicone impression material, the casts should be poured as quickly as possible.
True
Which type of impression material will release alcohol as a result of the polymerization reaction?
Silicone
Addition silicone materials are low molecular weight polymers with terminal silane and vinyl groups that are now supplied with a _______ to make the material more hydrophilic.
Surfactant
Addition silicone materials go through _____polymerization in the presence of chloroplatinic acid (platinum) in order to cross-link/chain-lengthen.
Ionic
typically we talk about free-radical polymerization
High contact angles are associated with ________ materials and incorporation of _______.
Hydrophobic
Air bubbles
Do condensation or addition silicone materials have a higher likelihood for bubbles due to high contact angles?
Condensation - Hydrophobic- high CA - bubbles
Platinum or Palladium is used in association with Addition silicone materials in order to absorb some of the _______ produced through a secondary reaction of -OH groups.
Hydrogen Gas
True or False: When using addition silicone impression material, the casts should be poured as quickly as possible.
FALSE!
Addition silicones will liberate Hydrogen gas…
pouring should be delayed long enough to liberate it
(THINK: addition silicones: you should wait an ADDITIONal minute)
True or False: For extensive impressions, working time of addition silicones may be lengthened but it may adversely affect other properties.
False: the retarder may be added, yes! but, it will NOT adversely affect other properties
Contamination of addition silicone impression material with sulfur or dithiocarbamate (rubber gloves) before setting will either _____ or ______.
Lengthen the set time
Cause the material to not set at all
What is a common contaminate of addition silicone that is prevalent in dental offices or labs?
Dithiocarbamate contamination from latex rubber gloves
What type of polymerization reaction is associated with polyether impression materials?
Ring opening
Addition silicone materials go through _____ polymerization, whereas polyethers go through _____polymerization.
Ionic
Ring opening
Which viscoelastic impression material is associated with possible contact dermatitis?
Polyether
-contact with unmixed ester
When using polyether impression materials, a thinner diluent may be available to adjust and control _____.
Viscosity
The requirements for ideal impression materials are:
- Low _____
- Long _______
- Bio_________
- ________ to patient
- Cost
- Shelf-life
- compatability
- Pleasant
Before setting, ideal impression materials should have 1. ______ of manipulation, 2. Control over ____ _____, and 3. ____ ____ on moist oral structures.
- ease
- setting time
- Good wetting (low contact angle)
During setting, what are two requirements for ideal impression materials?
- No dimensional change
2. Short setting time
After setting, ideal impression materials should have:
- _____ flexibility
- ______ tear strength (rate of strain)
- ______ elastic recovery
- _____ dimensional change from applied stress
- High
- High
- High
- No
High tear strength is a function of _____ of strain.
Rate
After setting, ideal impression material should have no dimensional change from ______ _____ or _____ _____.
Applied stress
Upon Standing
Ideal impression materials should be compatible with ____ and with ____ materials.
disinfectants
cast or die materials
Why is it important for impression materials to be compatible with die or cast materials?
- In order to reproduce fine details
- To limit the contact angle
- To limit chemical retardation of the cast
When looking at a graph that compares impression materials to “reproduction limit,” how does Alginate compare to other materials?
Alginate has a HIGH reproduction limit…meaning it does not capture fine details as well as the other materials
When considering dimensional accuracy of impression materials, in which direction does shrinkage typically occur?
Shrinkage occurs TOWARD the tray from above the plane (HEIGHT)
Which impression material has the highest dimensional change upon standing and lowest elastic recovery?
Polysulfide
