661. The cross linking agent of polysulphide rubber base impression material is______________?
A. Stannous octate
B. Aromatic sulfonate esters
C. Platinum salt catalyst
D. Lead dioxide

662. When making a polysulphide impression for a caste crown, custom trays are usually preferred over stock trays for all of the following reasons except_______________?
A. Custom trays require less impression material
B. Custom trays facilitate uniform contraction of impression material
C. Stock trays may be short in the flange area
D. Impressions made n the custom trays are easier to remove from the mouth

663. Name the accelerator used in Zinc oxide eugenol paste______________?
A. Linseed oil
B. Olive oil
C. Zinc acetate
D. All of these

664. Linear contraction of elostomeric impression with passage of time is highest in______________?
A. Polysulphide
B. Addition silicone
C. Polyetner
D. Condensation silicone

665. Which of the following is true about Agar hydrocolloid impression material ?
A. Liquefies between 71 – 100°C
B. Facilitates fabrication of metal dyes
C. Solidfies between 50 – 70°C
D. Cannot register fine surface details

666. Which one of the following increase the strength and reduce viscosity of agar hydrocolloid impression material_____________?
A. Borax
B. Sulfates
C. Water
D. Carbonates

667. The water powder ratio of alginate is______________?
A. 40 ml of water to 40 gms of powder
B. 100 ml of water to 60 gms of powder
C. 40 ml of water to 15 gms of powder
D. 15 ml of water to 40 gms of powder

668. Best impression material to be used for securing impression after crown preparation_______________?
A. Agar
B. Alginate
C. Elastome
D. Zno paste

669. Which of the following is correct glass transition temperature of Impression compound ?
A. 65°C
B. 39°C
C. 43.5°C
D. 100°C


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