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IRS > Impressions > Flashcards

Impressions Flashcards

1
Q

What is required to get a gook impression?

A 
Impression tray choice
Size of tray 
Rigid tray - maintains pressure on teeth and soft tissues, preventing distortion
Good Soft tissue management 
Appropriate technique 
Appropriate choice and use of material
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2
Q

What is meant by accuracy in terms of impression?

A

ability to replicate the hard and soft tissues

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3
Q

What is meant by the resolution/precision?

A

ability to reproduce surface detail

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4
Q

What is the dimensional stability?

A

Maintenance of the material in terms of size and shape over a prolonged time

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5
Q

What are hydrophobic materials?

A

dont like water, lead to bubbles, voids, inaccuracies if inadequate moisture control

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6
Q

What is the order of different impression materials available?

A

1800’s dental plaster
1930’s elastic hydrocolloids: agar and alginates
1950’s synthetic elastomers polysulfide materials
Then condensation silicones - dimensional stability better than hydrocolloids but release condensation byproducts and shrinkage
Special trays and fillers in putty silicone reduced the effect of shrinkage
1965 polyethers - no condensation by-products and better dimensional stability
1975 addition silicones no condensation by-products

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7
Q

What are examples of hydrocolloids?

A

Reversible - agar

Irreversible - alginates

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8
Q

What are examples of synthetic elastomers?

A

Polysulphides
Polyethers
Silicones - addition or condensation

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9
Q

What are the ideal properties of impression materials?

A 
High accuracy 
Good dimensional stability 
Good tear strength 
Elastic
Easy to use 
Good working and setting times
Acceptable taste and smell 
Tolerant to disinfection 
Cheap
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10
Q

What are the disadvantages of alginate?

A

Insufficient reproduce of surface details
Poor dimensional stability
Not suitable for definitive indirect restoration impressions
Do not use it for opposing arch impression

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11
Q

What are the advantages of polysulphides?

A

Long working time if have multiple preps
Flexible, so easy to remove
Good tear resistance
Long shelf life

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12
Q

What are the disadvantages of polysulfides?

A 
Long working time 
Poor dimensional stability 
Sticky to handle 
Unpleasant smell 
Need special tray
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13
Q

What is the by-product in Condensation silicones?

A

Alcohol

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14
Q

What are the advantages of condensation siicones?

A

Easy to use
Good surface detail reproduction
Wide range of material choice and techniques
Good tear resistance

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15
Q

What are the disadvantages of condensation silicones?

A

Dimensional stability

Hydrophobic

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16
Q

What are condensation and addition silicones also known as?

A

Polyvinyl siloxanes

17
Q

What are the advantages of addition silicones?

A 
Excellent dimensional stability
Excellent surface detail reproduction
Wide range of material choice (viscosities) techniques
Biocompatible
Simple mixing 
Reasonable working time
18
Q

What are the disadvantages of addition silicones?

A

Expensive

Hydrophobic - getting better - does lead to poorer wetting of the surfaces and increased air entrapment

19
Q

What are examples of different addition silicones?

A 
Putty
Heavy-bodied silicone 
medium bodied silicone 
Light-bodied silicone
Super light-bodied
20
Q

Why have so many different addition silicones?

A

Putty = not very accurate, but good dimensional stability and viscosity with more filler
Light/medium bodied = high detail reproduction, thermic contraction, setting contraction, lower viscosity and filler

21
Q

What are polyethers (impregum) used for

A

fixed prosthodontics

Impressions of implant copings

22
Q

What are the advantages of polyethers?

A

Excellent dimensional stability
Good surface dtail reproduction
Only one viscosity but undergoes shear-thinning allowing it to flow
Hydrophilic

23
Q

What are the disadvantages of polyethers?

A

Very stiff/rigid so difficult to remove from the mouth and cast - can pull out periodontally involved teeth
Swells with water if kept for a long time in damp environment
Bitter taste

24
Q

How do you do mechanical soft tissue management?

A

Retraction cord or retraction paste

25
Q

How do you do chemical soft tissue management?

A

Haemostatic agents

Electrocautery

26
Q

How do you do surgical management of soft tissues?

A

Soft tissue laser

Rotary curettage

27
Q

What is gingival retraction?

A

The downward and outward movement of the free gingival margin

28
Q

What does gingival retraction allow?

A

Syringe impression material beyond the prep margin

29
Q

What is the problem if have gingival inflammation when taking impression

A

The techniques do not control inflammed or allow us to take an impression when gingivae are inflammed - manage before hand
Need equi- and subgingival prep finish lines

30
Q

What is retraction cord?

A

A cord that is packed into the gingival sulcus to retract the gingivae to improve visibility, access and moisture control

31
Q

What is the single cor technique?

A

Cord soaked in aluminium chloride

packed into gingival sulcus and removed before impression is taken

32
Q

What are retraction pastes, and what are they used for?

A

Viscous agents syringed into gingival sulcus to provide retraction and haemostasis
useful in simple cases with equigingival finish lines

33
Q

What is electro-surgery and soft tissue lasers used for?

A 
Widen or re-contour gingival profile
Widen gingival sulcus
Remove overgrown tissue
Used in combination with cord or paste usually
Haemostasis
34
Q

What is the onestep impression technique

A

Select tray and apply adhesive
Select material - putty, heavy body with light body
Soft tissue management - retraction cord/paste, electrocautery
Remove retraction cord
Dry teeth - silicone hydrophobic
Syringe light-body around the prep
Place some light body onto the heavy in the tray
Seat impression
Remove in one direction
Inspect, if good, rinse and disinfect
Send to lab

35
Q

What is different in the 2-stage technique?

A

Putty or heavy body is mixed
Spacer is places - thin sheet of plastic
Take impression
This creates a special tray
Then remove retraction cord, dry teeth, syringe light body around the prep, reseat impression

36
Q

What is the risk with the 2-stage?

A

Not sitting the tray exactly where placed first time or it will not be accurate

37
Q

What is the problem with 1-stage?

A

with putty which has a high viscosity, a lot of pressure is needed to seat the tray, this can distort or push away the lower viscosity material

38
Q

What do you look for when assessing the impression?

A 
Well defined margins 
Good surface detail
No drags or voids 
No tray exposure
All prep in the appropriate material
Impression adhering to tray
39
Q

How can digital impressions be taken?

A

Intra-oral scans in teeth and preparations

IRS (16 decks)

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