NEET MDS Shorts
881501
Dental Material
It is not possible to construct successive stone dies or casts with Silicon Rubber Impression Materials
186297
Dental MaterialFins or spines may be produced on a casting because of
1.cracks in the investment
2. too rapid heating of the mold
3. steam production which causes the walls of the mold to flake off
447284
Dental MaterialZinc phosphate cement powder contains zinc oxide, magnesium oxide, bismuth oxide
236599
Dental MaterialCobalt in a cast chromium-cobalt-nickel alloy contribute to strength, rigidity, and hardness
342289
Dental Material
Heating a gypsum cast to a temperature above 90°C will remove water of
crystallization and strengthen it. This process is called "burning out" the
gypsum, and it is used to remove the remaining moisture and improve the cast's
stability and accuracy.
Gypsum casts are made by mixing plaster of Paris (calcium sulfate hemihydrate)
with water. When the material sets, it forms calcium sulfate dihydrate crystals
with water molecules trapped within the crystal lattice, known as water of
crystallization. Heating the cast above 90°C causes the water of crystallization
to be released, which results in the cast becoming stronger and more rigid. This
process does not cause the cast to expand but rather to shrink slightly as the
water is removed. Excess gauging water is typically removed during the initial
setting process.
324107
Dental MaterialCobalt is the alloying element that decreases the hardenability of steel, but it can still sustain hardness during tempering
615220
Dental MaterialFerrite and austenite are soft and ductile
244991
Dental MaterialAddition-type silicone rubber impression materials are characterized by their
very low dimensional change, which means they exhibit minimal shrinkage or
expansion upon setting. This is a highly desirable property in dental
impressions as it ensures that the casts or models produced from these
impressions will be accurate representations of the patient's oral structures.
their setting reaction involves the addition of a cross-linking agent to the
base material, which forms a stable polymer without the by-products that can
cause significant dimensional changes