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
Common size of retraction cord?
00
technique for retraction cord?
Single cord retraction technique int the sulcus
Two cord extraction technique
Retraction paste
do you leave the retraction cord in for the single cord retraction technique?
no, leave in for a few minutes, remove, dry with3 in one
Place light-bodied silicone around the prep
Put over occlusal surface to minimise drags
two cord retraction technique?
thicker cord into sulcus
Trays in there for the imp
Brand name of retraction paste?
Expasyl
advantages of retraction paste?
Less invasive - less physical displacement of tissues
Advocated riot to digital impressions
Quicker that placement of cord
Provide fluid control
invasive methods of tissue retraction?
Rarely used, large remit of specialists for challenging cases
- electrosurgery
-gingettage - copper ring - historic technique
why take an interocclusal record?
Provide accurate recreation of interocclusal contacts
Must not extend beyond contact point
what material are used for interocclusal contacts?
Beauty wax or occlusal regisarion paste (electromeric extra-hard addiction cured silicone) e.g. futarD
What do you think of this imp?
Light body over the occlusal surface
Buccal flow not great
6 has captured sulcus depth
Palatal of the 7 little thin and slight excess
Error?
Tray toot small
Not all occlusal surfaces until last standing teeth not captured
error?
contact o the tray with soft tissues may cause tray distortion
Error?
Impression tray positioned too anteriorly, missing posterior occlusal contacts
Anterior air blow
Error?
Sectional impression with inadequate capture of adjacent tooth
error?
Distortion of duel arch tray
Error?
Step caused by differential set different materials high did not blend, also sectional impression does not enable full arch articulation
Error?
Set of surface material inhibited leaving to loss of surface detail
error?
Poor marginal detail
Error?
Internal bubbles caused by saliva, air or blood
Error?
Marginal tears
