Elastic Impression Flashcards
non aquas Elastomeric
Groub of synthtic polymer that atr vhemicaliy cross linked and can be streched and returns to its original shape
Non-aqueous Hydrocolloids
Dif in the setting meachnism and physical and chemical properties
Base paste + base catalist = either by product or not
Polysulfides
Has a base filler and
Catalist or reacter filler - lead dioxide - gives strenght and brown stain
Polysulfides raction
It has a water by product
Lossing of the material can affect the dimintional stability of the impression
Polysulfides
Proprties
Working time/ 5-7 which is the longest amoung the elastomers
Setting time /8-12 long
High tear strenth and elastic proprties
Why the Polysulfides not liked by the paitents
Odor taste
Long setting time
Premanent stain on the clothes -Lead peroxides-
Polysulfides
Clinical Tips During Manipulation
Humdifiy and tm decrease the working time
Hydrophobic - nomouiseter during preparation
Slight contraction during polymrizition - costum impression tray-
Polysuflied For maximum accuracy,
Pouring the cast: impression must be poured within 30 min. to 1 hr.
Condensation Silicone material
2 paste system
2 putty system
Two putty system
Putty used as a tray in conjction with the lo viscosty silicon
Putty wash technique
Condensation Silicone by product
Eythel-alchol and wen its evaporate it will cause contraction of the impression
Condensation Silicone
Properties:
• OVERCOME some of polysulfide’s disadvantages
Odorless and pigmented
Less setting time / 6-8 min
Less afected by the heat and tm / humidity
Who’s more stable
The polysufied more stable than the condensition silicon but the silicon moe stable than the reversible hydrocolloid
Condensation Silicone
Clinical Tips During Manipulation
Its hydrophobic in nature during the pouring its harder to avoid air bubbles in con silicon than any other elastomric material
Addition Silicone
Polyvinyl Siloxane (PVS)——-Vinyl Polysiloxane (VPS)
§ The base paste contains:
- Polymethylhydrosiloxane
- Divinylpolysiloxane.
§ The catalyst (or accelerator) paste contains:
- Divinylpolysiloxane
- Platinum salt.
Addition silicon by product
It has no byproduct so its dimintionally stable
But if there is any reminings from the polyether then a 2nd reaction will happen which will produce hydrogen gas and still wont affect the stability
Addition Silicone
Properties:
Similar to condensation silicone in may aspects, EXCEPT
Affected by the tm
More dimintionly stable
Addition Silicone
Properties: abt the hydrophobic
Some formulition has a hydrophilic proprties Surfactant/ Surfactant migrates toward the surface of the impression material and makes the surface more wettable by water.
Addition Silicone
Clinical Tips During Manipulation
- Delayed Pouring (Earlier product)
Hydrogen gas evolved result in > pinpoint voids in the gypsum casts poured soon after removal of the impression from the mouth.
-Immediate Pouring (Newer product)
Manufacturers may add a noble metal, such as palladium, as a scavenger for the released hydrogen gas
-No latex gloves during mixing
§ Setting inhibition caused by some brands of latex gloves
Polyether
§ The material is supplied as two pastes
The base paste contains:
- the polyether polymer,
- Filler: colloidal silica
- Plasticizer : glycol ether or phthalate.
The accelerator paste contains: - an alkyl-aromatic sulfonate
- in addition to Filler &Plasticizer
Polyether byproducts
None
Polyethyer Properties:
Short working time / decreased the number of teeth that will be captured during one impr
Short setting time
Stefness of the matirial
Alrergic reaction
Properties of the polyether
Hydrophilic in natrure
Stable only if stored dry
VPES
New impresion
Polyeteh+vps
Excelent flow
High tear strenght
Hydrophilicty
Elastisty
Making impressions with elastomeric materials
Fabrication of gypsum models ,casts and dies involves 6 major steps:
1- prepare the try
2-prepare the tissue
3-prepare the matirial
4-taking the impression
5-remove the impression
6-prepare the stone cast
Prepare the tray
To use less impression matirial as possible
Equal distribution of the impresion between the object and the tray -Especially for polysulfide impression material-
In case of severe undercuts the tray is avoided
Adhesive application
Prior to impression making, uniform thickness of adhesive should be applied to the tray
Prepare the tissue
Gingival retraction cord to displace
the gingival tissue laterally
away from the margin of the preparation.
Manipulation Of Impression
Materials
§ Hand mixing
§ Static mixing
§ Dynamic mechanical mixing
This technique transforms two fluid (or paste-like) materials into a homogeneous
mixture without mechanical mixing
Static mixing
Device uses motor to drive parallel plungers, forcing the materials
into a mixing tip and out into an impression tray or syringe.
Dynamic mechanical mixing
Making the Impression - multible mix techniqe
Light body - syrenige
Heavy body- tray
Multiple-mix technique
One step> light paste on the prepared tooth and over the tray which has the heavy body then take the impreasion by one step
2 steps > adhisve on the tray heavy body on the tray and take the ipressionn then place the light material on the prepared tooth then over the tray and take the impression again
Monophase technique
Meduim body
Polyether and addition silicon
Monophase mixing
Only one mixture is made and a part of the material is placed in
the tray and another portion in syringe for injection in the prepared tissues.—-> which will makes its viscisty to reduse and it will easliy flow over the teeth and tray
Putty-wash technique
Condensation silicone
- To minimize the effect of associated dimensional changes .
Removal of the impression
Remove after completly cured
Impression should be ready for removal within at least 10 min from time of mixing, allowing 6-8 min for impression to remain in mouth.
Remove the impression
The first step: is to break the addhision between the impression and tray
Second step: stretch the impression to drive at the height of contour
has the lowest viscosity and ranks as one of the least stiff of the elastomeric impression materials of a similar consistency.
Polysulfide
All elastomeric impression materials are viscoelastic, and it is necessary to use a quick snap to minimize plastic deformation of the impression during the final step of the removal
Impo
