Condensation silicone impression materials

Question 1

What are condensation silicone (C-silicone) impression materials?

Answer 1

elastomeric imp material

extensively used in dentistry

described by the condensation reaction (something given off)… ethyl alcohol given off

hydrophobic

Question 2

what os gven off in the C-silicone condensation reaction?

Answer 2

ethyl alcohol

Question 3

c-silicone hydrophobic or hydrophilic?

Answer 3

hydrophobic - doesn’t like water and reacts with it

Question 4

2 types of c-silicone?

Answer 4

base paste/putty

accelerator liquid/paste

Question 5

What is the base in c-silicone?

Answer 5

dimethyl siloxane - low molecular weight silicone which has reactive terminal hydroxyl end groups

Question 6

What is the accelerator liquid/paste?

Answer 6

stannous octate - accelerator

alkyl silicate - accelerator

Question 7

exothermic on endothermic setting reaction

Answer 7

exothermic

Question 8

When should you pour the cast into c-silicone imp?

Answer 8

asap

Question 9

What happens of you have a reduction in alkyl silicate?

Answer 9

reduce cross-linking and therefore:

weaker material

decreased tear resistance

increased permanent set

Question 10

In what condition is setting inhibited in c-silicone?

Answer 10

alkyl silicate susceptible to hydrolysis so setting inhibited if contaminated with moisture

Question 11

Shlf life of stannous octate?

Answer 11

has limited shelf life

Question 12

Why does alkyl octoate have limited shelf-life?

Answer 12

it oxidises

Question 13

Properties of C-silicones?

Answer 13

alkyl silicate is not complelety stable in presence of ester

minimal shrinkage as the bulk material is filler

shrinkage proportional to amount of polysiloxane present

Question 14

Forms of c-silicones?

Answer 14

putty + accelerator - lab putty

putty and light body +accelerator - fixed impression

paste/paste + accelerator - realign denture or used to take impression for a metal denture

Question 15

putty and light body used for?

Answer 15

fixed impression

Question 16

What is lab putty mixed with?

Answer 16

putty mixed with low viscosity paste accelerator (catalyst)

kneaded into mass of the putty

Question 17

paste/paste c-silicone system used for?

Answer 17

realign denture or used to take impression for a metal denture

Question 18

What is lab putty used for?

Answer 18

in lab for copy denture

Question 19

Indications of c-silicones?

Answer 19

where dimensional stability is not critical

fixed prosthodontics

removable prosthodontics

primary impression to construct wax replicates of the existing denture
- putty presentation used
(could also use alginate)

Question 20

Why not use c-silicones?

Answer 20

when dimensional stability is absolutely critical

Question 21

c-silicone used for fixed prosthodontics?

Answer 21

usually a putty and wash (light body) presentation)

Question 22

Indication for c-silicones and removable prosthodontics?

Answer 22

putty used for first impression (duplicate dentures)

second imp where accuracy is required

wash impression in the duplicate technique

relines/rebases etc

Question 23

impression decontamination steps?

Answer 23

Question 24

Use of optosil putty?

Answer 24

crown an dbridge work

Question 25

Use of xantopren?

Answer 25

metal dentures etc

paste/paste system

Question 26

Flaws of c-silicones?

Answer 26

not as accurate or dimensionally stable as some other elastomeric imp materials

Question 27

advantages of c-silicones?

Answer 27

More accurate than alginate
High elasticity
Adequate tear strength – better than addition silicone
Adequate working time (2:30 seconds) and setting time (8-9 minutes)
Hydrophobic – not susceptible to imbibition (swelling) or syneresis (shrinking)
Tasteless and no odour
Less messy than alginate
Less expensive than a-silicone
Biodegradable

Question 28

weaknesses of c-silicones?

Answer 28

Releases an alcohol by-product that can cause shrinkage
Not as accurate as addition silicone
Hydrophobic – excellent moisture control is required
Higher priced than alginate