FP - impression techniques Flashcards

(36 cards)

1
Q

name the 2 hydrophillic impression materials

A

alginate (irreversible)
agar Van R (reversible)

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2
Q

name the 3 hydrophobic elastomeric impression materials

A

silicones
polysulphides (permlastic)
polyethers (impregum)

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3
Q

why are hydrophobic impression materials not ideal?

A

gingival crevicular fluid - but they are used for crown and bridge

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4
Q

name the types of silicone impression materials

A

addition cured - aquasil/ president/ affinis
condensation cured - Xantopren/ optosil

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5
Q

what is alginate impression material used for?

A

removable pros - chromes

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6
Q

when must alginate impressions be poured?

A

less than 24 hours after impression taken

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7
Q

what type of tray does agar require?

A

tray with cooling mechanism

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8
Q

what is the crucial requirement for sillicone impressions?

A

dry prep

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9
Q

what are the advantages of agar impressions?

A

very accurate and stable (2 years)
can be disinfected

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10
Q

what must you do when pouring an addition cured silicone impression?

A

leave for over an hour

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11
Q

what must be done to pour a condensation cured silicone impression?

A

leave for 24 hours before pouring

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12
Q

what type of impression is more accurate, addition or condensation cured silicone?

A

addition

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13
Q

what type of silicone (putty) do we have at DDH?

A

Affinis

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14
Q

what are properties of polyethers (Impregum)?

A

very accurate
rotten taste
stiff on removal - perio pt!!

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15
Q

what are properties of polysulphides (permlastic)?

A

long working time
great for undercuts (used in RP)
smelly

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16
Q

what polyether impression material is used in DDH?

17
Q

what types of trays are a must for any fixed pros imp?

A

rigid tray - made from cold cure acrylic

18
Q

what is the issue with rim-lock trays?

A

cant cut them out of the mouth

19
Q

would you use a special tray with polyether?

A

no, it is too stiff

20
Q

what impression technique is used for cast post and core?

A

putty/ wash - 1 stage

21
Q

general rules for impression technique in fixed pros?

A

dry prep
block out undercuts
firm seating then NO pressure (support only)

22
Q

explain the putty wash 1 stage technique?

A

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

23
Q

what is used for mixing of the wash in the one stage putty wash technique?

A

double helix mixer tip

24
Q

explain the mono phase impression technique

A

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

25
what is the average biological width?
2.04mm
26
what does the biological width consist of?
epithelial attachment supracrestal connective tissue attachment
27
what happens if you violate the biological width?
inflammation of gingival tissues inflammation of periodontal tissues bone loss = recession
28
what distance do we want between the gingival papilla and alveolar crest to base of proximal contact point?
5mm
29
how are soft tissues managed pre operatively?
sort perio pre-operatively surgically lengthen crown
30
how do you manage soft tissues before impression?
temporarily displace gingival margin retraction with braided cord with astringent, or injectable material (3M-ESPE/ Expasyl)
31
how can you remove the gingivae in soft tissue management?
electrocautery scalpel high-speed (troughing)
32
what can retraction cord be soaked in for haemostasis?
ferrous sulphate/ aluminium chloride
33
what patients can you not carry out electrosurgery on?
pts with pacemakers
34
what should be considered doing when there is inadequate occluso-gingival height?
surgical crown lengthening
35
what is the local regime for disinfecting impressions?
10 x 1.7g Actichlor tabs per 1 litre water - 3 mins
36
when would you use pick-up impressions?
if you fail to get a good impression of one or two preps