3. Impression Materials Flashcards
What is an Impression?
! A 3d ____ imprint/image of oral tissues used for making a ____ cast
negative
positive
Properties of an ideal impression material
Accuracy
! Reproduction of ____
! ____ stability
! ____
! Adherence to ____ tray
! Compatibility with ____ materials
1: Reaction continues and shrinks over time (poor dimensional stability); elasticity - must be elastic in order to recover from any ____ experienced upon removal
detail
dimensional
elasticity
impression
die
deformations
Accuracy of Impression Materials
2: standardization of materials - ways to measure accuracy according to ____ standards
left: metal mold, measure dimensions across ____ and ____, and then impression of standard die and make a cast, and measure them and compare to the standard; right: ADA requires for an accurate impression, the impression material should be able to record a line that is ____um thick; the 3 pictures show diff materials and how well they record the lines; most detailed is the ____ picture
ADA
arch
tooth heights
bottom
Elastic Recovery of Hydrocolloid Impressions
3: cross-section of impression surround a tooth; once set, remove and it becomes deformed (____ once removed); then, it is the finished materials, aglinate and agar > more perm deformation for ____ than ____
10%
alginate
agar
Application of Tray Adhesive
! Use right adhesive for impression material
! Inadequate adhesion= ____ and ____
4: within a ____ solvent, impression sticks to the adhesive and doesn’t come undone from the tray; diff classes of impression materials have diff ____ - they are ____
dislodgment distortion volatile adhesives matching
Adhesives in Impression Tray
! Adhesives improve ____ of impressions
1: rim-lock on stock tray, can take impression w/o adhesive and it won’t come out, however, once it sets it shrinks ____ the tooth; with an adhesive, it shrinks ____ from the tooth, you get a slightly larger space resulting in a slightly ____ die (this is preferable! You don’t want shrinkage towards the tooth, the indirect restorations will fit better)
accuracy
toward
away
larger
Ideal Properties
Handling Characteristics
- ____ time
- ____ time
- ____ life
- The 2 materials put together and you start ____ (working time begins). Once you finish the viscosity ____ and eventually is too ____ for you to record any impression (working time ends). We want a working time that is reasonable, not too long. Usually 2-3 min is good enough
- “Beginning of mix until the material is ____.” This is anywhere from 5-8 min sometimes 9 min. Don’t want this to be too long bc it can be uncomfortable for the pt with that thing sitting in their mouth
- Refers to how long you can keep the material before using it. Whereas ____ refers to the stability after you have taken the impression and storing it.
We can also have mixing time: from the beginning of ____ until ____. Typically 1 min
working
setting
shelf
mixing
increases
viscous
set
dimensional stability
mixing
complete
Ideal Properties
Biologic Properties
! ____ and discomfort
! Disinfection
– 1% ____
– 2% Glutaraldehyde
– ____
____ Considerations
! Initial cost of equipment
! Cost of materials
toxicity
sodium hypochlorite
iodophors
economic
Classification of impression material
1. Based on the ____ state of the ____ material
! ____
! Non- ____ or rigid
physical
set
elastic
elastic
Elastic /Non-Elastic Materials
Elastic
Elastomers
- ____
- non-____
Non-elastic \_\_\_\_ plaster Impression compound \_\_\_\_ Impression waxes
aqueous
aqueous
impression
zinc oxide-eugenol
Elastic Impression Materials
! ____ Elastomers
! Hydrocolloids
– ____
– ____
! Non Aqueous Elastomers – Addition ____
– Condensation ____
– ____
– ____
aqueous alginates agar-agar silicones silicones polyethers polysulfides
- Mechanism of setting
! Reversible physical change
! Irreversible chemical reaction
! Reversible
– ____, Wax, ____
! Irreversible – Alginate \_\_\_\_ – Elastomers- \_\_\_\_, Silicones, \_\_\_\_ – Impression \_\_\_\_ – Zinc Oxide-Eugenol
3: impression compound is a ____-based material
compound
agar hydrocolloid
hydocolloid polysulfide polyether plaster wax
- According to their use in dentistry
! Impression materials for edentulous patients
– All ____
! Materials for dentate patients
– ____ materials
Technically there are no ____ for edentulous pt and all impression materials can be used for them. You cant always assume though that you can use a ____ impression material for them
materials
elastic
undercuts
Agar-Agar Reversible Hydrocolloid
! Organic ____ colloid from ____
hydrophilic
sea weed
Agar-agar
Reversible hydrocolloid
Components Agar: \_\_\_\_, \_\_\_\_ Borax: \_\_\_\_, \_\_\_\_ K2SO4: \_\_\_\_, \_\_\_\_ Alkyl Benzoate: \_\_\_\_, \_\_\_\_ Dyes and Flavor: \_\_\_\_, \_\_\_\_ Water: \_\_\_\_, \_\_\_\_
The picture shows that its gel-like when its set so its rather fragile and needs the ____ for strength
Potassium sulfate - manufacturers put it in and allows it to ____ well
____ is the majority of the material (85%) dont get caught up with the agar its still much more water
12.5 dispersed phase 0.2 strength 1.7 accelerator (die) 0.1 inhibits mould trace appearance and taste 85.5 continuous phase
borax
set
water