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
Agar-agar
Agar sol»_space;» Agar Gel (____oC)
Agar gel»_space;»> Agar sol (____oC)
Gelation temperature
Hysteresis: The difference of temperature between ____ and ____
43
100
liquefaction
gelation
Presentation and Manipulation
Heating - ____oC
Storage - ____oC (after ____)
Tempering - ____oC (when ____ arrives)
100 65 liquified 46 patient
Armamentarium for Agar Impression
! Water- cooled trays ____oC
! Snap removal
Water chennales that run around tray, once loaded, turn on water and you can cool it
snap removal - all impression materials are ____ > if you put a force on it > it recovers better than if you do it ____, if you’re removing an impression it’s better to remove with a ____ > recovers quickly/sharply/better than if you do it slowly
13 viscoelastic force slowly snap
Handling for Agar
! Working time ____ min ! Setting time ____min(variable)
- This working time doesnt correspond to what we talked about bc you’re just squeezing the liquified tube into the tray and that its well covered
- Depends on how well your ____ channels are connected to the tray for it to set properly
7-15
5
water
Biological Properties
Agar-Agar
! non ____
! non ____
! ____ shock
! ____
toxic
irritant
thermal
disinfection
Storage of Impressions
____ Rel. humidity by wrapping in moist ____
No more than ____ mins
100%
paper towels
30
Economic Considerations
Agar-Agar
Need for ____ equipment -High ____ investment
special
intitial
Alginate Composition
Source: ____ from Seaweed
____ Acid
Sodium, potassium & Ammonium salts are soluble in ____
Weve all taken alginate impressions. Its also obtained from seaweed, but has a different ____ formula
“Most of them are either ____ or ____
alginic acid
anhydro-B-mannuronic
water
chemical
sodium
potassium
mannuroate
Alginate Composition
Componnent: K Alginate: \_\_\_\_, \_\_\_\_ Ca Sulfate: \_\_\_\_, \_\_\_\_ ZnO: \_\_\_\_, \_\_\_\_ K-Ti-Fluoride: \_\_\_\_, \_\_\_\_ Diatomaceous earth: \_\_\_\_, \_\_\_\_ Sodium phosphate: \_\_\_\_, \_\_\_\_
K-Ti-Fluoride is imilar to ____ of the agar-agar as a stone hardener
ZnO/K-Ti-Fluoride: filler particles that ____ material
K Alginate/Ca Sulfate: when you add water these two react to form ____ (fast)
Sodium Phosphate: this 1st reacts with ____ until the NaP is all gone then the Ca sulfate and K alginate rxn begins
15 soluble alginate 16 reactor 4 filler 3 stone hardener 60 filler particle 2 retarder
K2SO4
strengthen
Ca sulfate
ALGINATE
Setting Reactions:
2Na3PO4 + 3CaSO4 —> Ca3(PO4)2 + 3Na2SO4
Na.nAlg + n/2CaSO4 —> n/2Na2SO4 + Ca.n/2Alg sol
This first rxn takes place until all ____ is consumed then the 2nd rxn begins to make the ____. An IMPORTANT rxn to remember
Sodium or potassium or ammonium alginate reacts with CaSO4 to make the CaAlg gel that’s the set material. When you mix water first you have a ____
Na3PO4
gel
sol
Alginates- Presentation
! Bulk - in ____ container
! ____ pouches
! Regular and Fast set
– obtained by adjusting concentration of ____
! Hard set vrs soft set
• Concentration of ____ - ____ forms available
metal predispensed sodium phosphate filler injection
Alginates- Presentation
! Bulk - in ____ container
! ____ pouches
! Regular and Fast set
– obtained by adjusting concentration of ____
! Hard set vrs soft set
• Concentration of ____ - ____ forms available
metal predispensed sodium phosphate filler injection
Alginates-Properties
Accuracy
! Detail reproduction - \_\_\_\_ um ! Elastic recovery - \_\_\_\_% ! Dimensional stability - \_\_\_\_ - imbibition ! Compressive /tear strength – \_\_\_\_ ratio – Rate of \_\_\_\_ ! Permanent deformation - \_\_\_\_
Alginate is not as accurate as agar bc it cant do ____ microns. Elastic recovery is also lower, and it has the same problems with dimensional stability if stored in a dry or moist environment
IMPORTANT point about these aqueous elastomers that has very low strength, the strength that is appropriate here is ____ strength. If there are deep undercuts and it has low strength it will tear and leave remnants of the material in the pt sulcus.
Why do we still use alginate so much then? It is ____ and we only use it for ____ impressions to make study casts
75 97.3 syneresis W/P deformation high
25
tear
cheap/convenient
preliminary
PROPERTIES
Handling
! Powder Dust/Segregation ! Proportioning (W/P ratio) ! Mixing time (\_\_\_\_ min) ! Working time \_\_\_\_ min ! Setting time \_\_\_\_ min ! Effect of temperature (\_\_\_\_oC)
If the powder is ruffled and you continue to inhale this dust you can get fibrogenesis of the lungs. You want to use a certain ____ material. The different particles can also segregate after settling for a long time so you have to stir it.
IMPORTANT point: as the room or water temp is INCREASED the reaction is ____ aka you setting time and working time is ____
1
2.5
3.5
18-24
dustless
accelerated
decreased
Alginates - Properties
Handling
! Effect of ____ ratio
! Effect of water ____
! Environmental temp
! Retardation of die stone
Too much ____ is weak impression material. Use the right measuring cylinder for the right properties.
____ is a colloid material and will affect the setting of the gypsum
water/powder
temperature
water
alginate
Biological Properties
! Dust from alginate
– ____ and carcinogenesis
– Use dustless alginate coated with ____
– Disinfection (same as ____)
fibrogenesis
glycol
agar-agar
Properties of Hydrocolloids
These tear strength values are very ____ compared to other impression materials
Reproduction limit
Agar: ____
Algin: ____
low
25
75
Storage of Impressions
____% Rel. humidity No more than ____ mins
Same as ____
100
30
agar-agar
