IMPRESSION MATERIALS Flashcards
Negative reproduction
Impression
Positive reproduction
Model or cast
Compression of tissues during impression to stimulate amount of pressure during function
Pressure (functional)
Oversize tray,no border molding,Zoe impression paste
Non selective (mucostatic)
Uses custom trays,best suited for withstanding forces of mastication
Selective
Most common,used to any patient
Perforated stock trays
Any individual jaw
Advantage: stability,lack of displacement
Custom trays
Most important factor in takin accurate impression
Size of impression tray
Hydrocolloid
Alginate
Agar hyrdrocolloid
Elastomeric
Addition silicones
Polyether
Condensation silicone
Polysulfide
Bite registration
Addition silicones
Polyether
Rigid
Impression compond
Zinc oxide eugenol
Types of impression materials in dentistry
Hydrocolloid
Elastomeric
Bite registration
Digital
Rigid
-Flexible cross linked polymers when set
-dominate the market mainly as a result of their greater accuracy, dimensional stability with time, and
ability to record detail as compared with the hydrocolloid materials.
-The first elastomeric impression mate
Elastomeric impression Materials
-AKA: polysiloxanes (VPS)
-Two paste or a two putty system
-no volatile by-product (such as water or ethanol) is formed in this reaction, minimal dimensional change occurs during polymerization.
Addition silicone
It is poorly wetted by water with a contact angle of 90°
hydrophobic surface
is readily wetted by water with a low contact angle.
hydrophilic surface
-have properties similar to the addition silicones.
-is hydrophilic and exhibits good wetting properties, even in a moist field.
-have the disadvantage of limited dimensional stability over time and older materials had poor taste.
-supplied as a base and catalyst system.
Polyether
Notes as short working times 1.5 to 3 minutes
Addition silicones
- This impression material is supplied as a base and an accelerator
-The multifunctional ethyl silicate produces a network or cross-linked structure that partly accounts for the low values of permanent deformation and flow
-are not used commonly in the dental office but rather are used as an accurate duplicating material in the dental laboratory.
-The setting reaction is sensitive to moisture and heat, with increases in either resulting in shorter setting and
working times
Condensation silicone
-Also called rubber base or mercaptan
-supplies as two paste
-The permanent deformation values of 2% to 3% (elastic recovery of 97% to 98%)
-shrink 0.3% to 0.4% dur- ing the first 24 hours
Polysulfide
Impression compound
ZOE
Rigid impression material
Impression compound is composed of?
-resins
-waxes
-organic acids
-fillers
-coloring agents
-sticks or cones
Low fusing material 45c
Type 1
High fusing material 70c
Type 2
High fusing material 70c
Type 2
Hard set of ZOE?
TYPE 1 OR 2?
TYPE 1
Soft set of ZOE?
Type 1or 2?
Type 2
-material consists of a matrix of amorphous zinc eugenolate that holds the unreacted zinc oxide particles together.
-Elastomeric impression materials almost have eliminated the use of zinc oxide–eugenol impression pastes for
edentulous impressions.
Zinc oxide eugenol
Tube 1 base?
Zink oxyde 87%
Tube 2 reactor?
Eugenol 12-15%
1st impression material, least dimentionally stable
Hydrocolloid
Process of absorbing water
Imbibition
Process of releasing water= shrinkage
Syneresis
Mixture of 2 phases
Colloid
Colloid that contains water
Hydrocolloid
-First successful flexible aqueous impression material use in dentistry
-longest shelf life
Agar “irreversible hydrocolloid”
The agar gel is converted to a sol by heating in water, usually boiling, 100° C, and becomes a gel again by cooling to 43.3° C
Hysterisis
Agar hydrocolloid impression material is called a
reversible hydrocolloid
Agar Component:
Main component
Agar
Agar Component:
Strengthen the gel
Borax
Agar Component:
Plaster hardner
Sulfates
Agar Component:
Most abundant
Water
Components:
Fillers
Wax
Agar Component:
Plasticizer
Glycerine
Agar Component:
Bactericidal
Thymol
-is one of the most widely used aqueous dental impression materials
-used extensively to prepare study models of either the entire dental arch or a segment of it.
-They also are used to prepare gypsum models for the preparation of athletic mouth protectors.
Alginate
Function:
To dissolve in water
Sodium or potassium alginate salt
Function:
to react with dissolve alginate to form insoluble calcium alginate
Calcium sulfate
