Gypsum Products (properties) Quiz 2

Question 1

tensile and compressive strengths increase rapidly as?

Answer 1

the gypsum hardens following the initial set

Question 2

Why is there wet strength and dry strength?

Answer 2

Because free water decreases strength. When dry, small crystals anchor larger ones. When wet, small crystals go on a watery holiday

Question 3

tensile strength is less affected by high W/P ratios than?

Answer 3

compressive strength

Question 4

tensile and compressive strengths decrease with?

Answer 4

high W/P ratios

Question 5

tensile strength of gypsum is lower than ________ strength? What percent lower?

Answer 5

compressive (10-25% of the value for compressive strength)

Question 6

increased spatula time above one minute causes strength to?

Answer 6

decrease

Question 7

List gypsum material in order of weakest to strongest

Answer 7

plaster < stone < die stone < high strength die stone

Question 8

CaO and gum arabic are used to?

Answer 8

enhance particle wettability and reduce the amount of gauging water required

Question 9

How many categories of gypsum are there?

Answer 9

5

Question 10

Type 1

Answer 10

impression plaster -modifiers are added to control setting time

Question 11

Type 2

Answer 11

model plaster - low strength, used for flasking dentures

Question 12

Type 3

Answer 12

dental stone- used for study models and master casts for fabricating full dentures

Question 13

Type 4

Answer 13

high strength dental stone -due stone

Question 14

Type 5

Answer 14

high strength, high expansion dental stone -high expansion is to compensate for shrinkage of base metal alloys; “Maryland” bridges

Question 15

How should you wet a gypsum cast?

Answer 15

by soaking it in a water bath with gypsum debris on the bottom. AVOID running water

Question 16

What temp should you store gympsum casts in?

Answer 16

high temps. 190-230F

Question 17

How should you store gypsum powder?

Answer 17

sealed containers in cool dry places.

Question 18

don’t store gypsum powder in high humidity, why?

Answer 18

can cause plaster to initiate a setting reaction. *initially as a decrease in setting time, after a while hemihydrate will participate causing further retardness :)

Question 19

surfactants are often in what form? Do what?

Answer 19

a liquid or a spray used on hydrophobic impression materials in order to enhance the wetting of gypsum product during pouring

Question 20

Why is disinfection of casts important?

Answer 20

prevent cross-contamination among patients, dental office staff, lab personal (disinfected casts compare physically to non, but improvements still needed)

Question 21

disinfection policy at UNMC

Answer 21

Remove contamination, spray with phenol, set for 10 minutes in bag, rinse in water

Question 22

Why do you need a clean bowl and spatula?

Answer 22

dirt provides seeds for nucleation of crystals and increases the setting rate