NEET MDS Shorts
704351
Dental MaterialThe working time for a polysulfide impression material can be safely and effectively increased by cooling the mixing slab to a temperature above the dew point
351766
Dental MaterialPhosphoric acid is used for etching enamel
843352
Dental MaterialWarpage of an impression compound occurs when the surface of the compound is hard and inside is soft
283033
Dental Material
Ductility of Base metalalloy increased by Nickel
Cobalt: (35-65%) decrease hardness, strength and rigidity. Chromium: (23 –
30 %) passivity effect, decrease melting point. Nickel: (0-20%) decrease
strength and hardness, increase ductility (Nickel cause sensitivity in some
patients). Molybdenum: (0-7%) increase hardness.
847549
Dental Material
To impart a hardening heat treatment to a dental gold alloy, the best method is to Reheat to 450°C and cool uniformly to 250°C over a period of 15 to 30 minutes
Reheating the casting to 450°C and then allowing it to cool uniformly to 250°C over 15 to 30 minutes is a method known as "solution annealing." This process is indeed used to harden dental gold alloys. Solution annealing involves heating the alloy to a temperature where the primary phase (usually gold) goes into solution with the secondary phase (typically a harder metal like palladium, silver, or copper). This creates a homogeneous structure that, when cooled slowly, leads to the precipitation of the secondary phase and subsequent hardening.
724269
Dental MaterialTypes of expansion that are possible in an investment are
thermal expansion, hygroscopic expansion, and setting expansion
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.
109423
Dental MaterialStrength and hardness of a gypsum model or cast are affected by water-powder ratio and porosity of cast