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1. CONTENTS:
•
INTRODUCTION
•
GYPSUM
•
CLASSIFICATION
•
MANUFACTURE
•
SETTING PROCESS
•
PROPERTIES
•
MANIPULATION
•
COMPATIBILITY
•
INFECTION CONTROL
•
RECENT DEVELOPMENTS
•
CONCLUSION
•
REFERENCES

2. INTRODUCTION
• Auxiliary dental material.
• Glossary of Prosthodontic terms:
• Model: Facsimile used for display purposes, a miniature
representation of something.
• Dental Cast: A positive life size reproduction of a part or parts of
the oral cavity.
• Die: The positive reproduction of the form of a prepared tooth in
any suitable substance.
• Direct link between the clinical phase of treatment and the technical
laboratory procedures.
• Contributes significantly to the ultimate success of the prosthesis.
GYPSUM:
• Originates from the Greek word ‘Gypos’ which means chalk.
• Dihydrate of calcium sulfate.
• Chemical formula CaSO4.2H2O.
• Sulfate mineral most commonly found.
• Usually white to yellowish white in color.
• Large beds of gypsum were formed when seawater evaporated, leaving dissolved
Calcium and Sulfate ions to form deposits of gypsum.
• United States is the largest producer as well as the biggest consumer of gypsum.
Others are Canada, France, Japan and Iran.
Gypsum mineral can be found in various forms:
1. ROCK–GYPSUM: widely occurring massive dull coloured rocks.
2. ALABASTER: Large fine-grained white stones. Often used for carving into
vases and ornaments. Also used in building of King Solomon’s Temple
3. SELENITE: as transparent crystals
4. SATIN SPAR: as fibrous crystals.
SYNTHETIC GYPSUM:
•
•
Also produced as a by-product of manufacture of phosphoric acid.
CHEMICAL GYPSUM.
3 H2SO4(l) + Ca3(PO4)2(s) + 6 H2O(l)
2 H3PO4(s) + 3 CaSO4·2H2O(s)

3. PROPERTIES:
 Found as prismatic, curved or twisted monoclinic crystals of vitreous luster.
 Specific gravity: 2.3
 It cleaves perfectly in one direction.
 Moh hardness no: 2, which means that it can be scratched by a fingernail.
USES:
1. As a raw material for making Plaster of Paris. Plaster of Paris is called so,
because the gypsum that was used to manufacture it came from a village called
Montamarte, near Paris. It is used extensively in construction purposes.
2. Grounded gypsum (land plaster) is sometimes used as a fertilizer for soil that
needs calcium.
3. Raw gypsum is also used to keep Portland cement from hardening too quickly.
4. It is also used to make paint (as a filler), filters, insulation and wall plaster.
5. Alabaster is used for carving ornaments and vases.
6. Selenite is sometimes used as an optical material.
Gypsum produced for dental application is nearly pure calcium sulfate dihydrate.
DENTAL USES OF GYPSUM PRODUCTS:
• Impression plaster is used to make the impression of the edentulous mouth.
• For preparation of study models of oral and maxillofacial structures.
• To form cast and dies on which dental prosthesis are constructed.
• As a mold material for processing complete dentures.
• For mounting of casts on the articulator.
• Also used as a binder for silica, gold alloy casting investment, soldering
investment and investment for low melting point nickel-chromium alloys.

4. GYPSUM PRODUCTS:
• Refers to the various forms of calcium sulfate, hydrous and anhydrous.
• Manufactured by the calcination of calcium sulfate dihydrate.
• Calcination can be controlled to produce partial or complete dehydration.
ADA No: 25.
ISO No: 6873.
Gypsum products can be classified into five types:
GYPSUM PRODUCTS
IMPRESSION PLASTER
( ISO TYPE I )
PLASTER
( ISO TYPE II )
HIGH STRENGTH PLASTER
STONE
( ISO TYPE III )
STONE, HIGH STRENGTH,
LOW EXPANSION
( ISO TYPE IV )
STONE, HIGH STRENGTH,
HIGH EXPANSION
( ISO TYPE V )

5. CHEMISTRY OF GYPSUM:
In the temperature range of 20º to 700ºC that is important in dental manipulation of
gypsum products, three phase changes occur in the CaSO4-H2O system.
40º – 50ºC
1) CaSO4.2H2O
CaSO4.1/2H2O + Water
(Calcium Sulfate
Hemihydrate)
90º – 100ºC
2) CaSO4.1/2H2O
γ-CaSO4
+ Water
(Hexagonal Form)
(Soluble anhydrite)
300º – 400ºC
3) γ-CaSO4
CaSO4
(Orthorhombic CaSO4)
(Insoluble anhydrite)
MONOCLINIC
HEXAGONAL ORTHORHOMBIC
Calcium Sulfate Hemihydrate Soluble anhydrite Insoluble anhydrite
Calcium Sulfate Dihydrate

6. MANUFACTURE:
From the conversion temperature given before, it can be seen that calcium sulfate
hemihydrate would be produced by heating gypsum to temperatures in the range of 50o
to 90 oC. However, at these temperatures the reaction is slow; even at 90oC substantially
complete conversion takes about 12 hours (Khalil et. al., 1971). Therefore, in
commercial processes temperatures higher than this are used, for shorter times.
The stable phase at these higher temperatures is hexagonal calcium sulfate, so the initial
product of calcination is partly of very largely this anhydrous form. However, on cooling
to temperatures below 85 oC and exposure to atmospheric moisture, the hexagonal
calcium sulfate rehydrates to form the hemihydrate.
In the production of plaster, the gypsum is ground to a fine powder, impurities such as
sulphur (S) and quartz (SiO2) are removed, and then it is subjected to calcination.
dehydration by heat
or other means
Mineral Gypsum
Plasters
Synthetic Gypsum
formulation
Dental plaster
Hydrocal
Densite
Dental Stone
High strength
dental stone

7. MANUFACTURE:
From the conversion temperature given before, it can be seen that calcium sulfate
hemihydrate would be produced by heating gypsum to temperatures in the range of 50o
to 90 oC. However, at these temperatures the reaction is slow; even at 90oC substantially
complete conversion takes about 12 hours (Khalil et. al., 1971). Therefore, in
commercial processes temperatures higher than this are used, for shorter times.
The stable phase at these higher temperatures is hexagonal calcium sulfate, so the initial
product of calcination is partly of very largely this anhydrous form. However, on cooling
to temperatures below 85 oC and exposure to atmospheric moisture, the hexagonal
calcium sulfate rehydrates to form the hemihydrate.
In the production of plaster, the gypsum is ground to a fine powder, impurities such as
sulphur (S) and quartz (SiO2) are removed, and then it is subjected to calcination.
dehydration by heat
or other means
Mineral Gypsum
Plasters
Synthetic Gypsum
formulation
Dental plaster
Hydrocal
Densite
Dental Stone
High strength
dental stone