Deck 9: Model and Die Materials

Question 1

What is a good way to determine the final setting time of gypsum material?

A) Loss of surface gloss
B) Dissipation of the heat of reaction
C) When the material can no longer be poured
D) When the conversion of hemihydrate to dihydrate is complete

Answer 1

When the conversion of hemihydrate to dihydrate is complete

Question 2

Which of the following model and die materials are derived from the mineral gypsum?

A) Dental stone
B) Model plaster
C) High-strength dental stone
D) A, B, and C
E) A and C

Answer 2

A, B, and C

Question 3

Which of the following statements is true of the production of dental stone?

A) It is produced by heating gypsum in an open kettle.
B) The hemihydrate produced is b-calcium sulfate hemihydrate.
C) The hemihydrate produced is a-calcium sulfate hemihydrate.
D) A and B are true statements.
E) A and C are true statements.

Answer 3

The hemihydrate produced is a-calcium sulfate hemihydrate.

Question 4

If the temperature of the water used to mix gypsum materials is raised up to body temperature (37.5° C), the setting time decreases. However, if water temperature is raised above 37.5° C, the setting time will increase.

A) Statement 1 is correct; statement 2 is correct.
B) Statement 1 is correct; statement 2 is incorrect.
C) Statement 1 is incorrect; statement 2 is correct.
D) Statement 1 is incorrect; statement 2 is incorrect.

Question 5

When gypsum is mixed by hand, the mass is stirred with a spatula at a rate of about _____ revolution(s) per second for _________.

A) five; about 5 minutes
B) two; about 2 minutes
C) two; about 1 minute
D) one; about 2 minutes
E) one; 30 seconds

Question 6

Gypsum model and die materials exhibit ________ in contrast to epoxy model and die materials.

A) excellent compatibility with impression materials
B) excellent abrasion resistance
C) slight expansion
D) both A and C
E) both B and C

Question 7

How should gypsum powder and water be added to the mixing bowl?

A) Water should be added first.
B) Powder should be added first.
C) The second material added should be sprinkled in slowly over a period of about 30 seconds.
D) Both A and C
E) Both B and C

Question 8

Which of the following statements is true of the compressive strengths of gypsum materials?

A) Die stone has the lowest compressive strength, because it has the least excess water.
B) Die stone has the lowest compressive strength, because it has the most excess water.
C) Die stone is almost four times as strong in compression as plaster, because the excess water is minimized.
D) Die stone is almost four times as strong in compression as plaster, because the excess water is maximized.

Question 9

Which form of dental gypsum product is created by boiling gypsum in a 30% solution of calcium chloride?

A) Dental stone
B) Model plaster
C) High-strength dental stone
D) A and B
E) B and C

Question 10

The ________ and ______ dense the crystal of the hemihydrate, the less excess water required to get a workable mass.

A) larger; more
B) larger; less
C) smaller; more
D) smaller; less

Question 11

For high-strength die materials, reproduction of detail is not critical because a precision casting will be fabricated on the gypsum die. Reproduction of detail is measured by pouring the gypsum material against a metal die with lines of decreasing depth scribed on it.

A) Statement 1 is correct; statement 2 is correct.
B) Statement 1 is correct; statement 2 is incorrect.
C) Statement 1 is incorrect; statement 2 is incorrect.
D) Statement 1 is incorrect; statement 2 is correct.

Question 12

Which of the following materials will accelerate the setting reaction of gypsum products?

A) Agar
B) Blood
C) Saliva
D) Terra alba
E) Unset alginate

Question 13

________ are highly accurate replicas of a single tooth and generally are used to make metal crowns or inlays.

A) Models
B) Casts
C) Dies
D) A and C
E) B and C

Question 14

Orthodontic plaster is a mixture of what two compounds?

A) Model plaster and dental stone
B) Impression plaster and dental stone
C) Impression plaster and model plaster
D) High-strength/low-expansion and high-strength/high-expansion dental stone

Question 15

Accelerators are chemicals that ________ the rate of setting and ________ the time of setting.

A) increase; increase
B) increase; decrease
C) decrease; increase
D) decrease; decrease

Question 16

Which of the following chemicals is an effective accelerator for gypsum materials?

A) Borax
B) Calcium sulfate
C) Potassium sulfate
D) B-calcium sulfate hemihydrate
E) A-calcium sulfate hemihydrate

Question 17

When a model or die is wet, its compressive and tensile strength is approximately ____________ its strength when dry.

A) four times
B) twice
C) one-half
D) one-quarter
E) one-sixteenth

Question 18

What occurs if an excessive amount of water is used to prepare gypsum materials?

A) A reduction in the setting time
B) Increased setting expansion
C) A reduction in strength
D) A, B, and C
E) A and C

Question 19

Which of the following types of dental stones and dental plasters requires the least amount of excess water?

A) Dental stone
B) Model plaster
C) High-strength dental stone

Question 20

Which of the following types of gypsum products is also known as die stone?

A) Dental stone
B) Model plaster
C) Impression plaster
D) High-strength/low-expansion dental stone
E) High-strength/high-expansion dental stone

Question 21

The inherent roughness limits the ability of gypsum materials to capture the finest details of impressions. Reproduction of detail is sufficient for most applications.

A) Statement 1 is correct; statement 2 is correct.
B) Statement 1 is correct; statement 2 is incorrect.
C) Statement 1 is incorrect; statement 2 is correct.
D) Statement 1 is incorrect; statement 2 is incorrect.

Question 22

If a 2% solution of borax is added to the gypsum powder, what will happen to the setting time?

A) Reduced slightly
B) Reduced significantly
C) Extended slightly
D) Extended significantly

Question 23

How is the final setting time of gypsum defined?

A) The point where the gypsum can be removed without distortion
B) The point where the gypsum can be removed without fracture
C) The point where the exothermic reaction is complete
D) All of the above
E) Only A and B

Question 24

Which of the following statements is true of the handling of an alginate impression?

A) The heat produced is the result of an endothermic reaction.
B) Any residual water in low places of the impression should not be removed.
C) The poured impression may be kept moist by storing it in a humid environment.
D) An alginate impression should be rinsed completely and disinfected after pouring.

Question 25

What is the purpose of the vibrating table?

A) Helps remove any bubbles that formed during mixing
B) Ensures a smooth mix of the materials
C) Wets the gypsum powder particles
D) Initiates the setting reaction

Question 26

The impression should not be removed from the gypsum for _______ minutes.

A) 3 to 5
B) 5 to 10
C) 10 to 20
D) 20 to 40
E) 45 to 60

Question 27

Which of the following is not a method for pouring a gypsum model base?

A) Pile mound onto a smooth, non-stick surface.
B) Wrap the impression with boxing wax.
C) Over-pour the impression and invert.
D) Fill a base former.

Question 28

Proper wetting occurs when gypsum is poured against a _____-based impression material such as ________.

A) water; alginate
B) water; addition silicone
C) non-water; alginate
D) non-water; addition silicone

Question 29

What are gypsum casts used for?

A) Inlays
B) Crowns
C) Retainers
D) All of the above

Question 30

Which of the following statements is true regarding disinfection of a gypsum model?

A) The model may be sterilized in an autoclave.
B) Disinfecting the impression rather than the model is preferable.
C) Disinfecting the model rather than the impression is preferable.
D) A and B are true statements.
E) A and C are true statements.

Question 31

Which statement(s) is (are) correct about making models, casts, and dies?

A) Fine detail is not significant.
B) Gypsums are not dimensionally stable.
C) The material does not need to be strong.
D) A, B, and C are all correct.
E) A, B, and C are all incorrect.

Question 32

Dies of epoxy for use in fabrication of crowns, bridges, and inlays can be poured into alginate. Epoxy dies are tougher and more abrasion resistant than high-strength stone dies, and they are more accurate and stable dimensionally.

A) Statement 1 is correct; statement 2 is correct.
B) Statement 1 is correct; statement 2 is incorrect.
C) Statement 1 is incorrect; statement 2 is correct.
D) Statement 1 is incorrect; statement 2 is incorrect.

Question 33

Epoxy materials are compatible with most of the elastomeric impression materials. Epoxy materials can be used with alginates.

A) Statement 1 is correct; statement 2 is correct.
B) Statement 1 is correct; statement 2 is incorrect.
C) Statement 1 is incorrect; statement 2 is correct.
D) Statement 1 is incorrect; statement 2 is incorrect.

Question 34

Why do high-strength stone crystals require the least amount of excess water?

A) Large and dense
B) Large and sparse
C) Small and dense
D) Small and sparse

Question 35

What happens if alginate dries out before the gypsum is poured?

A) The alginate will rob the gypsum mix of some of its water.
B) The edges of the alginate may tear off.
C) The impression will be distorted.
D) A, B, and C are correct.
E) A and C are correct.

Question 36

Which of the following represents the time period designated for the initial set of gypsum?

A) Pour begins until the pour is complete.
B) Powder is added to the water until mixing is complete.
C) Powder is added to the water until the pour is complete.
D) Powder is added to the water until the material cannot be used.

Question 37

Which use of gypsum is hardness and abrasion resistance especially important for?

A) Orthodontic models
B) Study models
C) Dies
D) Casts

Question 38

If gypsum materials are not adequately spatulated, _______________ suffers.

A) strength
B) accuracy
C) abrasion resistance
D) dimensional change

Question 39

If the mixing water temperature ___________ the hemihydrate will not set.

A) is above 37.5° C
B) is below 37.5° C
C) reaches 100° C

Question 40

Water-powder ratio is defined as the amount of water in ___________ added to the amount of powder in _______.

A) ounces; ounces
B) ounces; grams
C) milliliters; ounces
D) milliliters; grams

Question 41

Once the impression is removed from the mouth, list the steps for loading the impression tray.

Question 42

Dies can be constructed using digital data. Gypsum dies cannot be scanned for milling procedures.

A) Statement 1 is correct; statement 2 is correct.
B) Statement 1 is correct; statement 2 is incorrect.
C) Statement 1 is incorrect; statement 2 is correct.
D) Statement 1 is incorrect; statement 2 is incorrect.

Question 43

Which statement is correct regarding epoxy dies?

A) Works best with alginate
B) Low resistance to scratches
C) They are dimensionally stable.
D) They are a two-component system.

Question 44

Explain the differences between a study model, a cast, and a die. List the different types of materials associated with each.