W2: Impression Materials Techniques and Special Trays Flashcards
Give examples of non-elastic impression materials
ZOE (paste)
Plaster
Dental impression Compound
Which type of material is impression compound?
Impression compound is a non-elastic impresion material
Is plaster an elastic or non-elastic impression material?
Non-elastic
What are the two subdivisions of elastic impression materials?
Elastic impression materials are further subdivided into hydrocolloids and non-aqueous elastomers
Is impression compound an elastic or non-elastic impression material?
Non-elastic
Is ZOE an elastic or non-elastic impression material?
Non-elastic
Which materials are elastic hydrocolloids?
Agar Reversible and alginate irreversible
Which materials are non-aqueous elastomers?
Polysulfides, polyethers, condensation sillicone, addition sillicone
Are impression waxes elastic or non-elastic impression material?
Non-elastic
What are the general requirements for biomaterials used to make complete denutres?
- Bicompatible materials (minimal harmful affects on the oral tissues)
- Non-toxic
- Non-irritating
- Non-allergic
- Non-carcinogenic
- Chemically minimally degradable
- The material must fufill clinical objectives by possessing appropriate optimal physical properties
What are the optimal physical properties the material must posses to fufill clinical objectives?
The material should have:
* Adequate mechanical properties (e.g. hardness, elasticity, strength)
* Adequate thermal coefficeint of expansion
* Adeqaute conductivity properties
* Accetable aesthetic properties
* Easy to clean
* Ease of fabrication and manipulation (relatively easy to work with)
* Readily available
* Econmical
* Easy/inexpensive maintenance (material repairs and additions)
What are the optimal qualities for prosthdontic impression materials?
Optimal qualities are:
- low viscosity to adapt to oral tissues (but viscious enough to remain in the tray)
- Hydrophillic (adequate wettability of the oral tissues to accurately adapt and capture the oral structures)
- Pleasant odour and taste
- set into a rigid solid or rubber state in a resonable timeframe
- adequate elastic recovery with no permanent deformation upon removal from the mouth after impression taking
- adequate tear strength (avoids tears/breakage upon removal)
- remain dimensionally stable after setting and until cast pouring
- impression is able to remain dimensionally stable to be repoured from the cast
- compatibility with cast material
- bicompatible, non-toxic, absence of irritant constituents
- sufficent colour and opacity for proper impression evaluation by the clinician
- readily disinfected (without significant mechanical property loss or loss of accuracy)
- adequate shelf-life storage
- Cost-effective (this includes material processing time and equipment)
What were non-elastic impression materials initially used for?
For taking final impressions for edentulous patients
Why were non-elastic materials replaced by elastic materials?
Non-elastic impression materials were not able to be withdrawn without fracture from undercut areas in the mouth
What is a preliminary cast?
Result of primary impression
What is a final cast?
Result of secondary impression
If a material has adequate wettability of the oral tissues what does this mean?
This means that material is hydrophillic
Which impression material has a negligible setting shrinkage of less than 0.1% with no signifcant changes thereafter?
TEST
ZINC OXIDE EUGENOL (ZOE)
What does adequate elastic recovery refer to?
Adequate elastic recovery refers to the material to strech and return it its natural form (such as a rubber band) and not tear at suceptible areas (under cuts)
What is dimensional stability?
Dimensional stability refers to the impression to remain at its current state (not shrink or expand).
It is important for materials to remain dimensionally stable during transport to other laboratories/until pouring up of the impression.
What are benefits of using ZOE impression material?
Good surface detail and accuracy
ZOE is a non-elastic impression material, what can happen at the undercut area?
ZOE can fracture at the undercut areas
How does set ZOE react to plaster or stone?
Set ZOE is not compatible with plaster or stone but the impression is submerged in warm water to ease removal off of the cast model
Is ZOE impacted by the weather/surrounding environment?
Yes, water, heat, humidity increase the setting reaction of ZOE (some factors can be adjusted to increase or decrease setting time by the operator, turn on air-conditioning etc.)