Question 1

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

Accepted Answer

Gypsum materials, despite their inherent roughness, can capture sufficient detail for most dental applications, making both statements correct.

Question 2

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

Accepted Answer

Adding a 2% solution of borax to gypsum powder acts as a retarder, which means it slows down the chemical reaction that causes the gypsum to set. Therefore, the setting time of the gypsum will be extended slightly.

Question 3

How is the final setting time of gypsum defined?

Accepted Answer

The final setting time of gypsum is defined as the point where the gypsum can be removed without distortion or fracture. It is not necessarily related to the completion of the exothermic reaction, which can continue even after the gypsum has set. Therefore, only options A and B are correct.

Question 4

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

Accepted Answer

Keeping the poured alginate impression moist by storing it in a humid environment can prevent distortion, as the impression can dry out and shrink over time. Options A and B are incorrect as the heat produced during the setting reaction of alginate is exothermic, not endothermic, and residual water should be removed from the impression surface to prevent distortion. Option D is incorrect as only the poured model needs to be disinfected, not the impression itself.

Question 5

What is the purpose of the vibrating table?

Accepted Answer

The answer of What is the purpose of the vibrating...

Question 6

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

Accepted Answer

The answer of The impression should not be removed from...

Question 7

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

Accepted Answer

Pouring a gypsum model base typically involves methods that create a uniform and stable base for the dental impression. Over-pouring the impression and inverting it is not a standard method for creating a base. This technique could lead to an uneven and potentially unstable base, which is not desirable for accurate dental models.

Question 8

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

Accepted Answer

Proper wetting occurs when gypsum is poured against a water-based impression material such as alginate. Alginate is a water-based material, which allows for better wetting and adherence of the gypsum product used to create dental models or casts.

Question 9

What are gypsum casts used for?

Accepted Answer

The answer of What are gypsum casts used for?
...

Question 10

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

Accepted Answer

Disinfecting the impression rather than the model is preferable because it helps to prevent the potential distortion or damage that could occur to the gypsum model during the disinfection process. Disinfecting the impression can effectively reduce the microbial load before the model is poured, thus indirectly disinfecting the model as well. Autoclaving a gypsum model is not recommended as the high heat and pressure can cause damage or distortion to the model.

Question 11

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

Accepted Answer

All three statements are incorrect. Fine detail is significant in making models, casts, and dies, especially in dentistry and other areas where precise reproduction of the original is critical. Gypsums, such as dental stone and plaster, are dimensionally stable once set, and can accurately reproduce the model's shape. The material used must be strong enough to withstand the stresses of the process and the forces applied during use.

Question 12

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.

Accepted Answer

The answer of Dies of epoxy for use in fabrication...

Question 13

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

Accepted Answer

Statement 1 is correct as epoxy materials are compatible with most elastomeric impression materials including polyethers, addition silicones, and condensation silicones. 
However, statement 2 is incorrect as epoxy materials should not be used with alginates, as they may react with the calcium sulfate present in alginates, leading to an incomplete setting reaction and inaccurate impressions.

Question 14

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

Accepted Answer

High-strength stone crystals are typically made up of large and dense particles, which require less water to fill the gaps between them and achieve optimal bonding. This results in a more compact and durable structure, as well as reduced shrinkage and cracking during curing.

Question 15

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

Accepted Answer

If alginate dries out before gypsum is poured, it will absorb water from the gypsum and cause the gypsum to have less water available for proper setting. This can result in a distorted impression. Additionally, the edges of the alginate may tear off, further distorting the impression. Therefore, options A and C are the correct choices. Option B is a possible consequence, but it is not as significant as the other two. Therefore, the best choice is E, as it includes the two most significant consequences.

Question 16

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

Accepted Answer

The initial set time for gypsum is the period from when the powder is added to the water until the material reaches a state where it can no longer be used or manipulated.

Question 17

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

Accepted Answer

Hardness and abrasion resistance are especially important for dies as they need to withstand the pressure and wear during the casting process to create accurate and precise restorations.

Question 18

If gypsum materials are not adequately spatulated, _______________ suffers.

Accepted Answer

If gypsum materials are not adequately spatulated, dimensional change suffers. Inadequate spatulation can result in air entrapment, which can lead to inaccuracies in the dimensions of the final product.

Question 19

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

Accepted Answer

The answer of If the mixing water temperature ___________ the...

Question 20

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

Accepted Answer

Water-powder ratio is typically measured in milliliters and grams. Milliliters are used to measure water because it is a liquid, while grams are used to measure powder because it is a solid. Therefore, the correct option is D, milliliters; grams.

Quiz 9: Model and Die Materials