impression materials

Question 1

what do you do if the impression detaches from the tray

Answer 1

throw it away and redo it. it will be too distorted

**use adhesive on tray!

Question 2

any degree of viscoelasticity can cause

Answer 2

certain degree of distortion

Question 3

if VPS and polyether are compressed more than 1/3 of original thickness, then

Answer 3

elastic recovery will not be 100%

-will get plastic deformation

Question 4

why should we not use plastic impression materials

Answer 4

grossly distorted during removal and will not record any undercut

Question 5

trays must be wide enough so that the wall is at least

Answer 5

twice the depth of the undercut

Question 6

heavy body properties

Answer 6

• support light body because it has good dimensional stability
• high viscosity
• low wettability

Question 7

reasons for poor detail

Answer 7

• low temp (longer setting time and more viscosity)

- too much pooled liquid (saliva, blood, water)

Question 8

the only accurate impression material

Answer 8

elastomers

Question 9

criteria for good impression

Answer 9

1. uniform, homogenous mix
2. tray adhesive applied
3. rigid tray
4. no void or pulls on margin
5. details margin with no tears
6. no burn-through of the tray
7. strong bond between light and heavy bodies

Question 10

light body properties

Answer 10

• very accurate
• low dimensional stability
• low viscosity
• great wettability

Question 11

3 most important characteristics of final impression

Answer 11

• accuracy
• tear resistance (to withstand compressive and tensile stress when removing)
• dimensional stability

Question 12

impression material used to record undercuts should be

Answer 12

perfectly elastic