Dent 1.4 gypsum products

Question 1

The ________ is the basis for all gypsum used in dentistry

Answer 1

Hemihydrate

Question 2

what is the gypsum rock

Answer 2

CaSO4-2H2O (calcium sulfate dyhydrate)

Question 3

what three types of materials are derived from partial dehydration of gypsum rock

Answer 3

Plaster
Stone
High Strength Stone

Question 4

List the final products of the following

1) Plaster
2) Hydrocal
3) densite

Answer 4

1) model lab
2) Dental stone
3) High strength stone

Question 5

what three things Characterize Nucleated re-crystallization

Answer 5

1) Continuous solution of hemimydrate
2) diffusion of calcium and sulfate ions to nucleated centers
3) precipitation of microscopic gypsum crystals

Question 6

Less water = _________

Answer 6

Less Porosity

Question 7

Less porosity =

Answer 7

More strength

Question 8

what causes thick mixes (low W/P ratio) to harden more quickly

Answer 8

Nucleated centers are concentrated in a smaller volume.

The interaction of growing solids occurs earlier and is more effective

Question 9

decreased W/P = _________

Answer 9

denser cast

Question 10

Increased W/P ratio = __________

Answer 10

decreased strength (more porosity)

Question 11

Gypsom is used as a _______ in materials commonly employed in castin of dental _____ _____ and is generally not hated above 700 degrees celsius

Answer 11

Binder, Gold alloys

Question 12

what provides expansion to compensate for gold shrinkage

Answer 12

Refractrory

Question 13

what are two types of Binders

Answer 13

Calcuim sulfate hemihydrate (Gold)

Phosphate, ethyl silicate (high temp alloys)

Question 14

what are the two phases that exist in Silica

Answer 14

Low temperature phase (Alpha)

High temperature phase (Beta)

Question 15

within practical limits increasing amount of silica…(4)

Answer 15

1. increased manipulation time
2. Increased setting expansion
3. increased thermal expansion
4. Decreased compressive strength