FIXED PROS - Elastomeric Impression Materials Flashcards
why are impressions taken?
- study the case
- diagnose the case
- help plan treatment
- educational tool for the patient
- construct indirect restorations
what is considered when choosing the impression material? CDFES
- consistency
- dimension stability - does it keep accurate shape
- ease of handling
- flowability
- setting time
what is an elastomer?
natural or synthetic rubber which can undergo deformation under force and regain its original shape when force is removed
e.g. rubber band
when is a elastomeric material used?
when a accurate impression is essential
what are 11 ideal properties of a impression to be used in a patient?
- cheap
- good shelf life
- non-toxic and non-irritant
- good taste
- good mixing
- easy handling
- good setting time
- compatible with other material
- good consistency
- accurate surface reproducibility
- accurate dimension stability
what are the 2 types of elastic materials? give examples of them.
Aqueous Hydrocolloids
- Agar - reversible
- Alginate - irreversible
Non-aqueous Hydrocolloids
- Polysulfide
- Silicones - Condensation and Addition (A silicones and C silicones)
- Polyether
why is alginate not used? its irreversible?
- tears easy
- dimensionally unstable - immediate pour and single caste
- low detail reproduction
- difficult to disinfect
2 components used in making the impression material.
using a base and catalyst
what is another name for the catalyst?
accelerator
what are the different types of flowability/viscocity you can have for the impression material?
light bodied
regular/medium bodied
putty
what determines the viscosity?
how much filler there is
what is a light bodied impression material known as? why is it used?
syring type
wash type
- flowable
- good details
what are medium/regular bodied impression materials also known as? why would it be used?
tray type
- so stiff
- helps to force light-bodied in close contact with prepared tooth and surrounding tissue
= more accurate impression
how is a putty made?
must be manually kneaded
what are the 3 steps of curing?
initial set
final set
final cure
describe each stage of curing.
initial set
- stiffens the paste
- appears without elastic properties
- material can be manipulated
final set
- appears elastic to a solid rubber mass
- material must be placed in the mouth
final cure
- occurs from 1-24 hrs
- doesn’t affect dimensional stability
what’s the annoying thing about polysulfides and c silicones?
require condensation polymerisation
= there are by products
with polysulfides, what base, cross-linking agent, catalysts (2) and fillers (3) are/can be used?
BASE
mercaptan polysulfide
CROSS-LINKING AGENT
sulfur and/or lead dioxide
CATALYSTS
copper hydroxide or zinc peroxide
FILLERS
zinc sulfate, lithopone or calcium sulphate dehydrate
where may you use polysulfide impression materials?
complete denture
removable fixed partial denture
crown
bridges
give 2 examples of polysulfides used.
permlastic
omni-flex
describe a polysulfide reaction of mercaptan and lead dioxide
mercaptan + lead dioxide
= polysulfide rubber + lead oxide + water
how do you make the polysulfide impression material?
equal lengths of paste
mix thoroughly within a minute
setting time = 8-12 mins
pour within an hour
why may making polysulfide impression material not be favourable?
messy
poor dimension stability
requires custom tray
bad odour
may stain clothing
long setting time
5 pros of Polysulfide.
- cheapest non-aqeuous hydrocolloids
- long working time
- high tear strength
- high flexibility
- good detail reproduction
with polyethers, what base, cross-linking agent, catalyst and filler are used?
BASE
polyether
CROSS-LINKING AGENT
sulfate
CATALYSTS
glycol-based plasticisers
FILLERS
silicone
7 advantages of Polyether
- accurate
- good dimensional stability
- can use stock trays
- good detail
- pour within a week
- multiple casts
- good wettability
6 disadvantages of polyether
- £££
- short working time
- rigid - difficult to remove from undercut
- bitter taste
- low tear strength
- absorbs water - this changes dimension, but u have a week
with C-silicones, what base, cross-linking agents (2), catalyst and filler are/can be used?
BASE
poly dimethyl siloxane
CROSS-LINKING AGENT
alkyl orthosilicate or organo hydrogen siloxane
CATALYST
organo tin compound
FILLER
silica
what is the by-product of C-Silicone?
ethyl alcohol
5 Pros of C-Silicone
- better elastic property
- pleasant for patient
- can use a stock tray
- good working time
- good setting time
4 disadvantages of C-Silicone
- poor dimensional stability
- poor shrinkage
- have to pour within 30 mins
- poor wettability = hydrophobic
describe how a-silicones are supplied.
2 pastes in automixing guns or as putties
one paste = vinyl polydimethylsiloxane prepolymer
other paste = siloxane prepolymer
catalyst = chloroplatinic acid
another name for a-silicones.
polyvinylsiloxanes
what happens is a-silicones are not mixed properly or if there are any impurities?
hydrogen gas given off the impression
= air bubbles in the model
6 pros of a-silicone
- accurate
- good dimensional stability - a week
- stock tray
- multiple casts
- easy to mix
- good odour
cons of a-silicone
- £££
- sulfur inhibits the setting - be careful with latex gloves
- short working time
- poor tear strength
- possible hydrogen gas release - can add palladium to absorb
- working and setting time affected by temperature and moisture
what material is the best for dimensional stability and why?
a-silicone
- pouring can be between 7 and 10 days
- very stiff material
