FP - impression techniques Flashcards
name the 2 hydrophillic impression materials
alginate (irreversible)
agar Van R (reversible)
name the 3 hydrophobic elastomeric impression materials
silicones
polysulphides (permlastic)
polyethers (impregum)
why are hydrophobic impression materials not ideal?
gingival crevicular fluid - but they are used for crown and bridge
name the types of silicone impression materials
addition cured - aquasil/ president/ affinis
condensation cured - Xantopren/ optosil
what is alginate impression material used for?
removable pros - chromes
when must alginate impressions be poured?
less than 24 hours after impression taken
what type of tray does agar require?
tray with cooling mechanism
what is the crucial requirement for sillicone impressions?
dry prep
what are the advantages of agar impressions?
very accurate and stable (2 years)
can be disinfected
what must you do when pouring an addition cured silicone impression?
leave for over an hour
what must be done to pour a condensation cured silicone impression?
leave for 24 hours before pouring
what type of impression is more accurate, addition or condensation cured silicone?
addition
what type of silicone (putty) do we have at DDH?
Affinis
what are properties of polyethers (Impregum)?
very accurate
rotten taste
stiff on removal - perio pt!!
what are properties of polysulphides (permlastic)?
long working time
great for undercuts (used in RP)
smelly
what polyether impression material is used in DDH?
pentamix
what types of trays are a must for any fixed pros imp?
rigid tray - made from cold cure acrylic
what is the issue with rim-lock trays?
cant cut them out of the mouth
would you use a special tray with polyether?
no, it is too stiff
what impression technique is used for cast post and core?
putty/ wash - 1 stage
general rules for impression technique in fixed pros?
dry prep
block out undercuts
firm seating then NO pressure (support only)
explain the putty wash 1 stage technique?
2 viscosities (putty and wash)
syringe wash around tooth, load impression tray with putty at the same time
seat putty in impression tray over wash before starts setting
what is used for mixing of the wash in the one stage putty wash technique?
double helix mixer tip
explain the mono phase impression technique
one viscosity - polyether/ med viscosity silicone
place some material in syringe
tray is loaded with same material
insert tray with impression material over syringed material
what is the average biological width?
2.04mm
what does the biological width consist of?
epithelial attachment
supracrestal connective tissue attachment
what happens if you violate the biological width?
inflammation of gingival tissues
inflammation of periodontal tissues
bone loss
= recession
what distance do we want between the gingival papilla and alveolar crest to base of proximal contact point?
5mm
how are soft tissues managed pre operatively?
sort perio
pre-operatively surgically lengthen crown
how do you manage soft tissues before impression?
temporarily displace gingival margin
retraction with braided cord with astringent, or injectable material (3M-ESPE/ Expasyl)
how can you remove the gingivae in soft tissue management?
electrocautery
scalpel
high-speed (troughing)
what can retraction cord be soaked in for haemostasis?
ferrous sulphate/ aluminium chloride
what patients can you not carry out electrosurgery on?
pts with pacemakers
what should be considered doing when there is inadequate occluso-gingival height?
surgical crown lengthening
what is the local regime for disinfecting impressions?
10 x 1.7g Actichlor tabs per 1 litre water - 3 mins
when would you use pick-up impressions?
if you fail to get a good impression of one or two preps
