381. A rough / Chalky surface of the cast is due to_______________?

A. Not waiting for 20 min before pouring
B. High speed accelerator
C. Air incorporation in the mix
D. All of the above

382. The setting expansion of gypsum products can be reduced by________________?

A. Increased spatulation
B. Adding potassium sulfate
C. Less water powder ratio
D. Allowing setting under water

383. Most commonly used retarder in gypsum_____________?

A. Na2 So4
B. Nacl
C. Citrales
D. K2So4

384. Gypsum product having least expansion_____________?

A. Impression plaster
B. Model plaster
C. Stone plaster
D. Die stone

385. Gillmore needle is used for_______________?

A. Testing the strength of plaster of paris
B. Evaluating the setting time of plaster of pris
C. Testing the metal hardness
D. Testing the purity of noble metals

386. Hysteresis in a hydrocolloid gel is______________?

A. Moisture absorption
B. Temperature lag between gelation and liquefaction temperature
C. Phenomenon of conversion of gel into sol
D. All of the above

387. All of the following can be used to slow down the setting of Zinc oxide eugenol impression paste EXCEPT_________________?

A. Adding a small amount of glycerine
B. Adding a small amount of water
C. Altering the amounts of the two pastes used
D. Cooling mixing slab

388. All of the following statements about Type II silicon impression material are true EXCEPT_______________?

A. They evolve hydrogen when cast if they are not fully cured
B. They exhibit a very low setting shrinkage
C. They have a lower tear resistance than polysulphide rubbers
D. They set by condensation polymerisation

389. The Zinc oxide-eugenol impression pastes harden by________________?

A. Chemical reaction
B. Cold
C. Heat
D. Pressure

390. Plaster mix____________?

A. Rapid spatulation results in decreased setting time
B. 2% potassium sulphate is accelerator
C. Citrates are retarders
D. All of the above


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