Dr. Brantley (Die and Investment Materials)

Question 1

for investment materials, what is responsible for the 2% shrinkage and 2% expansion

Answer 1

• gold alloy setting causes shrinkage

- casting investment of gypsum particles pushing each other away causes expansion

Question 2

what are the starting and ending materials in gypsum calcining process

Answer 2

• starting: calcium sulfate dihydrate
• ending: hemihydrate (product)

*the end product is gypsum

Question 3

what are the three gypsum products and what are their water-to-powder ratios?

Answer 3

• plaster (.4-.5)(high porosity and surface area)
• stone (.3-.4)(lower porosity and SA than plaster)
• high-strength stone (.2-.3)(lowest)

Question 4

what are the two chemical modifiers and what do they do?

Answer 4

• accelerators (reduce setting time)

- retarders (inc setting time)

Question 5

what type of die stone has high strength and the lowest setting expansion and contain larger amounts of modifiers

Answer 5

type IV

Question 6

what type of die stone has high strength AND high expansion?

Answer 6

type V

Question 7

more modifiers cause more/less expansion?

Answer 7

less

Question 8

gypsum products are stronger in wet/dry conditions?

Answer 8

dry

Question 9

what temperature casting investment is used with gold-based alloys for all-metal restorations?

Answer 9

low-heat

Question 10

what temp casting investment is used with metal-ceramic restorations

Answer 10

(phosphate bonded) HIGH - heat

Question 11

what temp casting investment is used with additional metals other than gold or ceramics?

Answer 11

(silicate-bonded) HIGH - heat

Question 12

what are the two main roles for casting investments?

Answer 12

• provide mold cavity for restoration alloy

- compensating expansion for cast shrinkage when alloy cools

Question 13

three ways of expansion of investment mold cavity

Answer 13

• normal expansion
• hygroscopic expansion (highest expansion)
• thermal expansion

Question 14

keeps components together and provides structural framework

Answer 14

binder

*calcium sulfate hemihydrate

Question 15

does NOT participate in the setting reaction and provides THERMAL expansion during the burnout stage

Answer 15

refractory (quartz)

Question 16

the relative amount of expansion is greater for ____ than ____ (in reference to thermal expansion)

Answer 16

• cristobalite

- quartz

Question 17

two types of techniques for burnout stage

Answer 17

• low-heat (hygroscopic)(what we do)

- high-heat (thermal)

Question 18

two ways to increase the strength and expansion of gypsum bonded investment

Answer 18

• inc P/W ratio

- inc spatulation (mixing)

Question 19

in phosphate bonded investments, the REFRACTORY amount is more/less than the BINDER amount

Answer 19

more

Question 20

special liquid provides what?

Answer 20

-higher setting expansion in a hygroscopic setting

Question 21

can you have too much special liquid?

Answer 21

yes, too much may reduce setting expansion and lead to issues