IMPRESSIONS

Question 1

how to get a good impression

Answer 1

impression tray choice
appropriate technique
management of soft tissue
choice and use of materials

Question 2

impression tray choice

Answer 2

size (try in)
rigid tray (supports material)
retention (adhesives, perforations, rim lock tray)

Question 3

accuracy defintion

Answer 3

ability to replicate hard and soft tissues

Question 4

resolution/provision

Answer 4

ability to reproduce surface detail

Question 5

dimensional stability

Answer 5

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

Question 6

ideal properties of impression materials

Answer 6

• high accuracy
• good dimensional stability
• elastic
• good tear strength
• easy to use
• good working and setting times
• tolerant to disinfection
• acceptable taste and smell
• cheap

Question 7

classifying impression materials

Answer 7

1) hydrocolloids
- reversible ie agar
irreversible alginates
2) synthetic elastomers
- polysulphides, polyethers, silicones (addition or condensaiton)

Question 8

alginate

Answer 8

irreversible hydrocolloid
- good for variety of impressions
insufficient reproduction of detail for indirect
poor dimensional stability
not sutible for definitve restoration impressions

Question 9

polysulphides dis and ad

Answer 9

ad
- long working time, mutilpe preps
flexible easy to remove
good tear resistance
long shelf life

disavantages
- long working time
poor DStability
sticky to handle
unpleasant smell
need special tray

Question 10

condensation silicones

Answer 10

by product as condensation
poorer DS than additional

easy to use
good surface detail reproduction
wide range of material choice
good tear resistant

Hydrophobic
dimensionally unstable

Question 11

addition silicones

Answer 11

used for indirect restorations
can have high or low viscosity
catalyst and base mixed
hydrophobic

ad 
- good DS
good surface detail
biocompatible
simple mixing

dis
- spenny
hydrophobic
setting time affected by temp
can be difficult to remove casts

Question 12

polyethers

Answer 12

used for prosthodontics
ad
good DS
good SD
hydrophilic
undergos shear thinning allowing it to flow

dis
- rigid so hard to remove (esp with undercuts)
swells with water
bitter taste

Question 13

soft tissue management types and how

Answer 13

1) mechanical
- retraction cord
- retraction paste
2) chemical
- haemostatic agents
3) surgical
- electrocautery
- soft tissue laser
- rotatory curettage

Question 14

gingival retraction

Answer 14

downward and outward movement of the free gigival margin

allows impression material beyond the prep margin

Question 15

retraction cord use

Answer 15

soaked in haemostatic sol eg AlCl or epinephrine
double cord technique
- useful for subgingival margins, more technique sensitive

Question 16

retraction paste

Answer 16

agent syringed into giggival sulcus to provide retraction and haemostasis

Question 17

impression techniques for indirect restorations

Answer 17

additon silicones
twin mix or one stage - two viscosites seated in mouth together
two stage
- first impression taken in putty/heavy body with spacer
reline with lower

Question 18

when to know which impression technique to use

Answer 18

if you dont have a rigid tray and can see the lower viscosity material is being pushed from the prep margin you can chose the two stage technique

Question 19

assessing the impression

Answer 19

• well defined margins
• good surface detail
• no drags or voids
• no tray exposure
• all preparation in appropriate material (light body)
• impression adhering to tray

Question 20

why may an impression have airbubbles/voids or drags

Answer 20

ensure tooth is try
keep tip of syringe within the material and starting from finish line and end occlusally
select correct try size
whole impression needs to be filled with material so its impression is supported in all directions