2. Gypsum Flashcards
Desirable Properties • \_\_\_\_ • Dimensional stability • \_\_\_\_ • Abrasion resistance
accuracy
strength
Gypsum or Epoxy?
• Different ____
• Epoxy > some labs use epoxy; but most of dentistry is gypsum
properties
What Is Gypsum?
• Naturally occurring mineral that formed as the result of evaporating ____ in massive prehistoric basins
• Chemically, it is ____
• Primary ingredient in ____ and ____
• Two parts \_\_\_\_
sea water hydrous calcium sulfate (CaSO4-2H2O) wallboard plaster water
Food Grade Gypsum
• Necessary in the manufacture of ____ and ____
• Used in the food, beverage and pharmaceutical industries as an ____
source of supplemental calcium.
tofu
beer
economical
Types of Gypsum Products
• ____ plaster - used to mount models on articulators
• All these products are ____ identical, but difference is how they’re ____
mount
chemically
manufactured
Die Stone
• Used to pour up dies for ____, removable PD
• ____
crown/bridges
velmix
Manufacture of Gypsum Products
CaSO4.2H2O + heat CaSO4.1⁄2H2O + 11⁄2H2O
calcium sulfate ____ calcium sulfate ____
Effect of Heating Environment Open air — ____
Steam autoclave — ____
Salt bath — ____
* Mined out of earth, in a heating process water is driven out * Calcium sulfate hemihydrate (\_\_\_\_ in wet lab)
dihydrate
hemihydrate
beta hemihydrate
alpha hemihydrate
alpha hemihydrate
powder
Types of Gypsum Products • Impression Plaster
– Calcium sulfate ____ hemihydrate: Type ____
• Model Plaster
– Calcium sulfate ____ hemihydrate: Type ____
– ____ casts
– Orthodontic casts
• Dental Stone
– Calcium sulfate ____ hemihydrate: Type ____ – ____ casts
* Used in edentulous patients; simple oral anatomy (can be taken out in pieces though) * Dental stone > harder model
beta
I
beta
II
diagnostic
alpha
III
denture
Types of Gypsum Products
• High-Strength Dental Stone: Type ____ (____)
– ____ stone
– Hard surface resistant to abrasion
– ____ hardening solutions
• High Strength/High expansion: Type ____ (____)
– ____ casting
• Synthetic Gypsum
– By-product of ____ manufacture
IV alpha die gypsum V alpha basemetal phosphoric acid
Types of Gypsum Products
Type I/II \_\_\_\_, porous Irregular \_\_\_\_ volume of water \_\_\_\_ hemihydrate
Type III/IV/V
____ & Regular shapes, ____ vol. of water
____ hemihydrate
spongy
high
beta
prismatic
lower
alpha
Setting Reaction
11⁄2H2O + CaSO4.1⁄2H2O CaSO4.2H2O
Calcium sulfate hemihydrate calcium sulfate ____
Model plaster — ____ ml
Dental stone — ____ ml
High-strength dental stone — ____ ml
dihydrate
45
30
19-24
Manipulation of Gypsum
• Add water ____ then weighed powder
• Mix ____ to a smooth mix
• Mechanical mixing ____
• Mix on vacuum that \_\_\_\_ the air out - much better mix
first
vigorously
recommended
pulls
The Setting of Gypsum
• ____ formation
• ____ formation
• ____ Expansion
11/2H2O + CaSO4+1/2H2 —> CaSO4*2H2O
• Have model set in more water - \_\_\_\_ setting conditions • Add powder to the water (best way) • Initial crystal growth > \_\_\_\_ contact > expansion > termination • Allow to set in more water, then you much more \_\_\_\_ ○ In presence of water, less \_\_\_\_ > can expand a whole lot more
nuclei crystal setting hydroscopic solid phase expansion surface tension
Properties of Gypsum
Products
• Mixing time
– Mechanical - ____ sec – Hand spatulation - ____ min
• Working time – ____ min
• Setting time
– From start of mixing to hardened material – Measured with a ____ test
20-23
1
3
penetration
Methods of Determining Setting Time • \_\_\_\_ needle – Initial and final setting time • Vicat needle – Initial \_\_\_\_ time • Loss of Gloss – Few minutes before \_\_\_\_ setting time • Temperature rise
• Penetration test • By putting amount of \_\_\_\_ as sets > determines when it reaches a full set ○ Or, loss of gloss, leave it alone until it undergoes a full set
gillmore
setting
vicat needle
pressure
