Fixed prosthodontics impressions: material and techniques Flashcards
Factors to consider when taking an imp?
- Impression material for working and opposing casts
- Tray selection
- Adhesive selection (must be effective for impression material
chosen) - Handling properties
- Tissues to be recorded
- Soft tissue management
- Patient tolerance
- Interocclusal record
3 cateogeois of imp materials?
Non-elastic
Synthetic elastomers
Hydrocolloids
why are non elastic imp material no suitable for fixed pros?
Inability to accurately record undercuts
what imp material for fixed pros?
Synthetic elastomers
Polysulphides
Polyether
Silicones
reversible hydrocollid?
Agar
Not see today due to need for expensive water cooled trays
irreversible hydrocolloids?
Alginate
pros f hydrocolloid?
Mean suitable for opposing imps
Hydrophilic, good record of surface detail
Alginate cheap
cons of hydrocolloids?
Unsuitable for crown imps
Poor dimensional stability because of water loss of imbition
Low tear strength unsuitable for recording gingival sulcus
setting time for polysulphides?
Slow over 10 mins
polysulphides still used in dentistry
no
Due to
- slow set
- messier
- unpleasant door
- impression shrinkage
- special tray 4mm spacing
- 48 hours maximal storage time prior to casting
advantages of polysulphides?
Long working time and excellent tear resistance
properties of polyether?
Developed specifically for dentistry
Fast set time under 5 mins
When stored dry, good dimensional stability
Earn auto-mixed optimal material qualities and ease
Rigid when set, can be difficult to remove in case of undercuts
Adequate tear strength
More hydrophilic that silicones
properties of c-silicone (lab putty)?
Setting produces the by-product alcohol
Less dimensional stability that a-silicones
More dimensional stability that alginate
Rick of sensitisation reactions therefore only used for imp/duplication out the mouth
properties of a-silicones?
Widely used for corn and bidet work imps
Available in light, medium and heavy bodes and also putty
Neutral taste
Bet elasticity of the elastomers
Adequate tear strength
Hydrphophic
name 3 imp techniques?
One stage
Two stage unspaced
Two stage spaced
one stage impression for a-silicone?
Either putty and wash or heavy and light bodied material beware of recoiled
Two stage unspaced imp material for a-silicones?
More dense material recorded frst followed by lightbodied material beware material can be separate
Apart from a plastic tray what other tray can be used for one stage a-silicone imp?
Metal - prevent recoil
Not normally go to tra, use f struggling with imp distortion
two stage spaced imp technique for a-silicone?
Can be spaced by polyethylene separator over teeth, recording putty imp before preparation or by gouging away part of the putty to enable space for lightbodied material
Beware increased complexity and grater opportunity for incorporation of errors
why is one stage technique more popular?
easier and more predictable
do we normally use a special tray in fixed pros?
No
techniques for gingival retraction?
retraction cord
Why would you want to retract the gingiva at the margin?
pick up the margin
what is retraction cord?
Knitted interlocking chains of cotton
Can be used with epinephrine hydrochloride
May be used with stringent e.g. 20% ferric sulphate, 15.5% ferric sulphate, aluminium chloride
