Condensation silicone impression materials Flashcards
What are condensation silicone (C-silicone) impression materials?
elastomeric imp material
extensively used in dentistry
described by the condensation reaction (something given off)… ethyl alcohol given off
hydrophobic
what os gven off in the C-silicone condensation reaction?
ethyl alcohol
c-silicone hydrophobic or hydrophilic?
hydrophobic - doesn’t like water and reacts with it
2 types of c-silicone?
base paste/putty
accelerator liquid/paste
What is the base in c-silicone?
dimethyl siloxane - low molecular weight silicone which has reactive terminal hydroxyl end groups
What is the accelerator liquid/paste?
stannous octate - accelerator
alkyl silicate - accelerator
exothermic on endothermic setting reaction
exothermic
When should you pour the cast into c-silicone imp?
asap
What happens of you have a reduction in alkyl silicate?
reduce cross-linking and therefore:
weaker material
decreased tear resistance
increased permanent set
In what condition is setting inhibited in c-silicone?
alkyl silicate susceptible to hydrolysis so setting inhibited if contaminated with moisture
Shlf life of stannous octate?
has limited shelf life
Why does alkyl octoate have limited shelf-life?
it oxidises
Properties of C-silicones?
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
Forms of c-silicones?
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
putty and light body used for?
fixed impression
What is lab putty mixed with?
putty mixed with low viscosity paste accelerator (catalyst)
kneaded into mass of the putty
paste/paste c-silicone system used for?
realign denture or used to take impression for a metal denture
What is lab putty used for?
in lab for copy denture
Indications of c-silicones?
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)
Why not use c-silicones?
when dimensional stability is absolutely critical
c-silicone used for fixed prosthodontics?
usually a putty and wash (light body) presentation)
Indication for c-silicones and removable prosthodontics?
putty used for first impression (duplicate dentures)
second imp where accuracy is required
wash impression in the duplicate technique
relines/rebases etc
impression decontamination steps?
Use of optosil putty?
crown an dbridge work
Use of xantopren?
metal dentures etc
paste/paste system
Flaws of c-silicones?
not as accurate or dimensionally stable as some other elastomeric imp materials
advantages of c-silicones?
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
weaknesses of c-silicones?
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
