Which of the following is not correct about dental stone?
A. High strength low expansion dental stone contains some additive to reduce expansion.
B. Dental stone is manufactured by heating at temperature 110°- 120° C in an open auto clave.
C. Dental stone is much harder and stronger than B-hemihydrate.
D. Microscopically it is seen as cleavage fragments and crystals in the form of rods and prisms.
A. High strength low expansion dental stone contains some additive to reduce expansion.
B. Dental stone is manufactured by heating at temperature 110°- 120° C in an open auto clave.
C. Dental stone is much harder and stronger than B-hemihydrate.
D. Microscopically it is seen as cleavage fragments and crystals in the form of rods and prisms.
Ans. (B) Dental stone is manufactured by
heating at temperature 110°-120° C in an open autoclave.: Gypsum when heated at 110-130° → Plaster or stone, heated at 130-200°C → Hexagonal anhydrite, heated at 200- 1000°C → Orthorhombic anhydrite. If gypsum is heated to
temperature in the first part of the reaction in an open kiln or an open
autoclave a
• Hemihydrate is produced which is irregular and
spongy. But in the question it was asked about dental stone which is an
• Hemihydrate which is produced by calcining CaSo4.2H20 in
a closed autoclave this leads to significant difference between
• Hemi-hydrate
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