Phillips Dental Materials Gypsum Products

Question 1

What is gypsum?

Answer 1

CaS04- 2H2O Calcium sulfate dihydrate

Question 2

What form of calcium sulfate hemihydrate is Dental Plaster/Plaster of Paris?

Answer 2

Beta Form

Question 3

What form of calcuium sulfate hemihydrate is Dental Stone?

Answer 3

Alpha Form

Question 4

When plaster is mixed with fillers such as forms of silica what is this called?

Answer 4

Gypsum dental investment

Question 5

What are the characteristics of Beta Form/Dental Plaster?

Answer 5

Large irregularly hsaped crystal particles with capillary pores Absorb more water

Question 6

What are the charachteristics of alpha form or Dental Stone?

Answer 6

Smoother Smaller regularly shaped crystalline particles in forms of rods or prisms Absorb less water

Question 7

Hemihydrate is how many times more soluble in water than dihydrate?

Answer 7

4 times more soluble

Question 8

What do the terms Initial Gillmore, Vicat and Final Gillmore refer to?

Answer 8

Initial Gillmore = time at which a needles does not make an impression Vicat= The time elapsed until the needle no longer penetrates to the bottom of of the mix Final Gillmore= The elapsed time at which this needle leaves only a barely perceptible mark on the surface

Question 9

What does Loss of Gloss refer to ?

Answer 9

The point at which the reaction proceeds and the excess water is taken up in forming the dihydreate so the mix loses its gloss.

Question 10

Does dental stone shrink, stay the same, or expand as it sets? What two factors can influence this?

Answer 10

Expands Lower water/powder ration and a longer mixing time increases the setting expansion

Question 11

How can you decrease setting expansion of dental stone?

Answer 11

Adding potassium sulfate, sodium chloride or borax

Question 12

True or False: Some inorganic salts that are often accelorators can also become retarders?

Answer 12

True! Sodium chloride is an accelorator up to about 2% of the hemihydrate but at a higher concentration acts as a retarder

Question 13

What are the 5 types of Gysum?

Answer 13

1 Impression Plaster 2 Model Plaster 3 Dental Stone 4 Dental Stone–High Stength 5 Dental Stone –High Expansion

Question 14

What is the preferred method of mixing dental stone? A.) Premeasure powder and add water B.) Premeasure water and add powder

Answer 14

B– Premeasure water and add powder