Impressions

Question 1

What is required to get a gook impression?

Answer 1

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

Question 2

What is meant by accuracy in terms of impression?

Answer 2

ability to replicate the hard and soft tissues

Question 3

What is meant by the resolution/precision?

Answer 3

ability to reproduce surface detail

Question 4

What is the dimensional stability?

Answer 4

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

Question 5

What are hydrophobic materials?

Answer 5

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

Question 6

What is the order of different impression materials available?

Answer 6

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

Question 7

What are examples of hydrocolloids?

Answer 7

Reversible - agar

Irreversible - alginates

Question 8

What are examples of synthetic elastomers?

Answer 8

Polysulphides
Polyethers
Silicones - addition or condensation

Question 9

What are the ideal properties of impression materials?

Answer 9

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

Question 10

What are the disadvantages of alginate?

Answer 10

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

Question 11

What are the advantages of polysulphides?

Answer 11

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

Question 12

What are the disadvantages of polysulfides?

Answer 12

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

Question 13

What is the by-product in Condensation silicones?

Answer 13

Alcohol

Question 14

What are the advantages of condensation siicones?

Answer 14

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

Question 15

What are the disadvantages of condensation silicones?

Answer 15

Dimensional stability

Hydrophobic

Question 16

What are condensation and addition silicones also known as?

Answer 16

Polyvinyl siloxanes

Question 17

What are the advantages of addition silicones?

Answer 17

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

Question 18

What are the disadvantages of addition silicones?

Answer 18

Expensive

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

Question 19

What are examples of different addition silicones?

Answer 19

Putty
Heavy-bodied silicone 
medium bodied silicone 
Light-bodied silicone
Super light-bodied

Question 20

Why have so many different addition silicones?

Answer 20

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

Question 21

What are polyethers (impregum) used for

Answer 21

fixed prosthodontics

Impressions of implant copings

Question 22

What are the advantages of polyethers?

Answer 22

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

Question 23

What are the disadvantages of polyethers?

Answer 23

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

Question 24

How do you do mechanical soft tissue management?

Answer 24

Retraction cord or retraction paste

Question 25

How do you do chemical soft tissue management?

Answer 25

Haemostatic agents | Electrocautery

Question 26

How do you do surgical management of soft tissues?

Answer 26

Soft tissue laser | Rotary curettage

Question 27

What is gingival retraction?

Answer 27

The downward and outward movement of the free gingival margin

Question 28

What does gingival retraction allow?

Answer 28

Syringe impression material beyond the prep margin

Question 29

What is the problem if have gingival inflammation when taking impression

Answer 29

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

Question 30

What is retraction cord?

Answer 30

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

Question 31

What is the single cor technique?

Answer 31

Cord soaked in aluminium chloride | packed into gingival sulcus and removed before impression is taken

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

What is the onestep impression technique

Answer 34

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

Question 35

What is different in the 2-stage technique?

Answer 35

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

Question 36

What is the risk with the 2-stage?

Answer 36

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

Question 37

What is the problem with 1-stage?

Answer 37

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

Question 38

What do you look for when assessing the impression?

Answer 38

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

Question 39

How can digital impressions be taken?

Answer 39

Intra-oral scans in teeth and preparations