Dental materials 4

An optimal proportioning of gypsum powder and water is achieved by

Powdering

Using the powder/water ratio

Vibrating the mixing bowl

Using distilled water

Which casting investments are non-porous

Gypsum-bonded

Phosphate-bonded

Silicate-bonded

All of the above are porous

The setting expansion of phosphate-bonded casting investments is a result of:

The expansion of cristobalite

The polymerization of the binding component

The formation of crystallohydrate

The heating of the mold

Co-Cr alioys for model casting/ precision casting can be cast using:

Gypsum bonded investments

Phosphate bonded

Ethyl silicate bonded

Air bubble formation is avoided by

Accurate proportioning of the powder and liquid

Use of a vacuum mixing machine

Slow drying of the mold

Use of a vibrating table

Expansion of casting investments compensates for

Aggregate shrinkage of alloys

Shrinkage of the molten emtal

He volumetric changes of the alloys occurring during the transition from their solidus temperature to room temperature

Spherical reservoirs are used to avoid the consequences of:

Aggregate shrinking of alloys

Shrinkage of molten metal

The volumetric changes of the alloys occurring during the transition from their solidus temperature to room temperature

Cristobalite as a component of the casting investment materials accounts for their:

Setting expansion

Thermal expansion

Mechanical strength

Porosity

Which of the following statements are true?

All casting investments for precision casting contain cristobalite

The refractory component of the casting investments accounts for their mechanical strength

Ni-Cr alloys are cast using gypsum-bonded investment materials

Noble alloys can be cast using gypsum-bonded or phosphate-bonded investments

A dental casting alloy with solid shrinkage of 1.42% and casting temperature - 900°C is cast using:

Casting investment materials for noble metal alloys

Gypsum-bonded investment containing quartz

Phosphate-bonded investment

Gypsum-bonded investment containing cristobalite

Dental materials 4

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