FIXED PROS - Elastomeric Impression Materials

Question 1

why are impressions taken?

Answer 1

• study the case
• diagnose the case
• help plan treatment
• educational tool for the patient
• construct indirect restorations

Question 2

what is considered when choosing the impression material? CDFES

Answer 2

• consistency
• • dimension stability - does it keep accurate shape
• ease of handling
• flowability
• setting time

Question 3

what is an elastomer?

Answer 3

natural or synthetic rubber which can undergo deformation under force and regain its original shape when force is removed

e.g. rubber band

Question 4

when is a elastomeric material used?

Answer 4

when a accurate impression is essential

Question 5

what are 11 ideal properties of a impression to be used in a patient?

Answer 5

• 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

Question 6

what are the 2 types of elastic materials? give examples of them.

Answer 6

Aqueous Hydrocolloids
- Agar - reversible
- Alginate - irreversible

Non-aqueous Hydrocolloids
- Polysulfide
- Silicones - Condensation and Addition (A silicones and C silicones)
- Polyether

Question 7

why is alginate not used? its irreversible?

Answer 7

• tears easy
• dimensionally unstable - immediate pour and single caste
• low detail reproduction
• difficult to disinfect

Question 8

2 components used in making the impression material.

Answer 8

using a base and catalyst

Question 9

what is another name for the catalyst?

Answer 9

accelerator

Question 10

what are the different types of flowability/viscocity you can have for the impression material?

Answer 10

light bodied
regular/medium bodied
putty

Question 11

what determines the viscosity?

Answer 11

how much filler there is

Question 12

what is a light bodied impression material known as? why is it used?

Answer 12

syring type
wash type

• flowable
• good details

Question 13

what are medium/regular bodied impression materials also known as? why would it be used?

Answer 13

tray type

• so stiff
• helps to force light-bodied in close contact with prepared tooth and surrounding tissue
  = more accurate impression

Question 14

how is a putty made?

Answer 14

must be manually kneaded

Question 15

what are the 3 steps of curing?

Answer 15

initial set
final set
final cure

Question 16

describe each stage of curing.

Answer 16

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

Question 17

what’s the annoying thing about polysulfides and c silicones?

Answer 17

require condensation polymerisation
= there are by products

Question 18

with polysulfides, what base, cross-linking agent, catalysts (2) and fillers (3) are/can be used?

Answer 18

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

Question 19

where may you use polysulfide impression materials?

Answer 19

complete denture
removable fixed partial denture
crown
bridges

Question 20

give 2 examples of polysulfides used.

Answer 20

permlastic
omni-flex

Question 21

describe a polysulfide reaction of mercaptan and lead dioxide

Answer 21

mercaptan + lead dioxide
= polysulfide rubber + lead oxide + water

Question 22

how do you make the polysulfide impression material?

Answer 22

equal lengths of paste
mix thoroughly within a minute
setting time = 8-12 mins
pour within an hour

Question 23

why may making polysulfide impression material not be favourable?

Answer 23

messy
poor dimension stability
requires custom tray
bad odour
may stain clothing
long setting time

Question 24

5 pros of Polysulfide.

Answer 24

• cheapest non-aqeuous hydrocolloids
• long working time
• high tear strength
• high flexibility
• good detail reproduction

Question 25

with polyethers, what base, cross-linking agent, catalyst and filler are used?

Answer 25

BASE
polyether

CROSS-LINKING AGENT
sulfate

CATALYSTS
glycol-based plasticisers

FILLERS
silicone

Question 26

7 advantages of Polyether

Answer 26

• accurate
• good dimensional stability
• can use stock trays
• good detail
• pour within a week
• multiple casts
• good wettability

Question 27

6 disadvantages of polyether

Answer 27

• £££
• short working time
• rigid - difficult to remove from undercut
• bitter taste
• low tear strength
• absorbs water - this changes dimension, but u have a week

Question 28

with C-silicones, what base, cross-linking agents (2), catalyst and filler are/can be used?

Answer 28

BASE
poly dimethyl siloxane

CROSS-LINKING AGENT
alkyl orthosilicate or organo hydrogen siloxane

CATALYST
organo tin compound

FILLER
silica

Question 29

what is the by-product of C-Silicone?

Answer 29

ethyl alcohol

Question 30

5 Pros of C-Silicone

Answer 30

• better elastic property
• pleasant for patient
• can use a stock tray
• good working time
• good setting time

Question 31

4 disadvantages of C-Silicone

Answer 31

• poor dimensional stability
• poor shrinkage
• have to pour within 30 mins
• poor wettability = hydrophobic

Question 32

describe how a-silicones are supplied.

Answer 32

2 pastes in automixing guns or as putties

one paste = vinyl polydimethylsiloxane prepolymer
other paste = siloxane prepolymer

catalyst = chloroplatinic acid

Question 33

another name for a-silicones.

Answer 33

polyvinylsiloxanes

Question 34

what happens is a-silicones are not mixed properly or if there are any impurities?

Answer 34

hydrogen gas given off the impression
= air bubbles in the model

Question 35

6 pros of a-silicone

Answer 35

• accurate
• good dimensional stability - a week
• stock tray
• multiple casts
• easy to mix
• good odour

Question 36

cons of a-silicone

Answer 36

• £££
• 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

Question 37

what material is the best for dimensional stability and why?

Answer 37

a-silicone
- pouring can be between 7 and 10 days
- very stiff material