Chapter 17- Impressions

Question 1

Why are impressions made?

Answer 1

In order to make a cast

Question 2

What are casts used for?

Answer 2

To make preparations

Question 3

An impression for cast should meet what 3 requirements?

Answer 3

1. Exact duplicate of the prepared tooth along with unprepared tooth structure beyond the prep
2. Other teeth and tissue adjacent to the cast should be accurately produced to permit proper articulation of the cast
3. Free of bubbles

Question 4

In terms of wet ability, impression materials can be described as?

Answer 4

Hydrophilic or hydrophobic, hydrophobic cannot become wet

Question 5

Greater contact angle increases the probability of?

Answer 5

Air entrapment during pouring

Question 6

What can repel materials with a large contact area?

Answer 6

Hemorrhage or fluid in the gingival sulcus

Question 7

Which materials are the least viscous?

Answer 7

Light bodied polysulfide and condensation silicone

Question 8

Which materials are the most viscous?

Answer 8

Heavy bodied polysulfide

Question 9

Does viscosity increase or decrease following mixing?

Answer 9

Increase

Question 10

How does shear rate affect viscosity?

Answer 10

Lower pressure means less viscosity.

Question 11

What conditions would this be seen in?

Answer 11

A syringe

Question 12

What is the term for a material that becomes more fluid as flow rate increases?

Answer 12

Thixotropic

Question 13

Shear rate for mixing material is how many times greater than mixing?

Answer 13

100x

Question 14

What are the cheapest impression materials?

Answer 14

Hydrocolloid

Question 15

Most expensive?

Answer 15

polyvinyl siloxane

Question 16

What is reversible hydrocolloid made of?

Answer 16

Agar or seaweed

Question 17

What is added to reversible hydrocolloid to accelerate setting and increase rupture strength?

Answer 17

K+ sulfate

Question 18

What does tempering do to reversible hydrocolloid?

Answer 18

Increase its viscosity so its more easily managed

Question 19

What are the 3 stages in the conditioning sequence?

Answer 19

Liquifying bath, storage bath, tempering bath

Question 20

What do you do in the liquefying bath?

Answer 20

Boil for 10 minutes at 212 degrees

Question 21

What about the storage bath?

Answer 21

Store at 150 degrees for 10 minutes

Question 22

Tempering bath?

Answer 22

110 degrees for 5-10 minutes

Question 23

What is the laminate technique?

Answer 23

Combining reversible and irreversible hydrocolloid

Question 24

Custom resin trays provide accuracy for?

Answer 24

Single tooth restorations

Question 25

How is polysulfide better than hydrocolloid?

Answer 25

Better dimensional stability

Question 26

Is polysulfide hydrophilic or phobic?

Answer 26

Phobic

Question 27

Polyvinyl siloxane has good or bad dimensional stability?

Answer 27

Excellent, casts can be poured from it one week after impression is taken