Impresion Material Flashcards
What are the non elastic materials?
Impression wax
Impression plaster
Zn O eugenol
Impression compound
How can we classify impression material?
Elastic and non elastic
How can we classify elastic impression materials?
Elastomer
Hydro colloid
What are the hydro colloids?
Alginate
Agar
WHat are the elastomers?
Polyether
Silicone
Polysulfide
What are the silicones?
Addition and condensation
What is the purpose of an impression material?
To produce an accurate replica of the hard and soft tissues
When can you use ridgid materials?
When there are no boney undercuts so edentulous
When can you use elastic impression materials?
Can engage in undercuts
When is impression compound used?
Modify stock trays and special trays and used as a foundation for a wash impression
Wha pt type of material is impression compound?
Thermoplastic
What are the two type of impression compound?
Type 1: lower fusing impression material
Type 2: higher fusing tray material
What temp is impression compound softened at?
55-60 degrees
What is the molecular weight of alginate?
20000-200000
What is alginate based upon?
A colloidal suspension of mucopilysaccahirdes in water
Alginic acid
What states does alginate exist in in dentistry?
Gel and sol state
What is the molecular structure of alginate?
Polymer
What is the setting reaction for alginate?
Sodium alginate + calcium sulphate -> sodium sulphate + calcium alginate
Calcium forms cross linking between polymer chains to form a 3d network
What is the constituent of alginate?
Few: fillers : 52% Soldiers: sodium alginate 18% Can: calcium sulphate dihydrate: 14% Pass: potassium suplphate: 10% Simple: sodium silicofluroide: 4% science: sodium Phosohate : 2%
What is the purpose of the fillers in alginate?
Controls consistence
What is the purpose of the sodium alginate ?
Hydrogel former
What is the purpose of calcium sulphate dihydrate?
Calcium ions for x linking
What is the purpose of potassium sulphate?
Setting
What is the purpose of sodium Phosohate?
Controls working time
What is the purpose of sodium silicofluroide?
Controls pH
What are the advantages of alginate?
Detail okay for dentures
Short setting time
Cheap
What are the diasadvantes of alginate?
Not good enough for crown and bridge
User dependant mixing
Moisture contamination limited shelf life
Susceptible to syneresis AND Imbibition
Muse be kept damp and model pored quickly
Low teear strength
How thick must the layer of alginate be?
3-5mm
What are Polysulfide?
Polymer with mercaptan groups.
SH
How does Polysulfide set?
Mercaptan groups are oxidised by an accelerator and hydrogen is removed releasing water
What are the advantages and dis of Polysulfide?
Highest tear stengh
Good detsail
Bad taste and smell
What are polyethers?
Polymer with imine functional groups
CH2-N-CH2
T/F Polyether need an activator?
T
Aromatic sulfonate ester
How does polyethers set?
Cross linking between the chains
What are the ad and dis of Polyether?
AD: good detail, good dimensional stab, least hydrophobic, v low setting shrinkage
Dis: stiffest, single viscosity only, swells in moisture, difficult to disinfect
What are silicones?
Si-O backbone with alkyl groups
What are condensation cured silicones?
Polydimethyl siloxane polymer with OH terminal groups
What antivator is needed in condensation cured silicones?
Tetraethyl silicate
TES
What are addition cure silicones?
Polydemetyl siloxane polymer with vinyl terminal groups
C=CH2
What is then activator needed in additions cured silicones?
Platinum catalyst and silanol
Which materials have the greatest setting shrinkage?
They all since they are polymers
T/F setting shrinkage is bad?
Not always since gives some room for cement but you want litlle or no shrinkage
Which material contracts or expands the most?
Polyether
ACS and CCS are the same
Why do polymers shrink on setting?
Difference in temp between room and mouth
Which polymer has the best storage and long term stability?
ACS
This is how use CCS release alcohol and polysufides release water
T/F you ewnt your impression materials to be hydrophilic?
T
T/F you want impression materials to have a low tear strength?
F
Low means it tears easily ie when being pulled from undercuts
High means it doesn’t tear
You want a mod high tear strength
What are the advantages and dis of condensation cured?
Good details
Wide range of Viscosity
Small setting shrinkage
BUT hydrophobic, release alcohol song must be poured quick, TES hydrolysed in moisture, harder to mix than ACS
What are the advantages and dis of addtion cured?
Good: detail, wide range of viscosity, very good dimensional stab, v low setting shrinkage
BUt: V hydrophobic
What material do you use for primary impression of completes?
Impression compound in edentulous tray and wash impression with alginate for better detail
When impression compound at correct temperature it has shiny surface
Alginate
What materials can you use for secondary impressions?
Upper and lower arch with minimal or no undercut use a CLOSE FITTING TRAY with LIGHT BODIED SILCONE or ZINc OXIDE (NB can use medium bodied as well for lower)
Upper and lower arch with flabby ridge or marked undercut then SPACED TRSY OF 1.5mm With ALGINATE or MEDIUM BODIED SILICONE
