The porosity formed due to simultaneous nucleation of solid grains and gas bubbles at the first moment that metal freezes at the mold walls is called__________?

Related Mcqs:

1. Air bubbles formed on the surface of casting is probably due to________________?

   A. Improper casting pressure
   B. Improper heating of the investment
   C. Improper angulation of sprue
   D. Improper wetting of the wax pattern by the investment

2. In processing methyl methacrylate, the resin may show porosity if the flask is placed too soon porosity most likely occur_____________?

   A. Throughout the denture
   B. Near the borders
   C. In the thickest part
   D. On the denture surface

3. Suck back porosity is due to_________________?

   A. Attached impurities on undersurface of casting
   B. Hot spot
   C. No rapid cooling
   D. Inadequate melting temperature

4. Subsurface porosity is due to_____________?

   A. Thermal changes
   B. Thickness of the resin
   C. Lack of temperature
   D. Packing past the dough stage

5. Subsurface porosity is due to_____________?

   A. Thermal changes
   B. Thickness of the resin
   C. Lack of temperature
   D. Packing past the dough stage

6. Porosity of denture base is due to_______________?

   A. Packing at dough stage
   B. Curing at 160°F for 9 hrs
   C. Inadequate pressure
   D. All of the above

7. The castability of chromium-cobait base metal alloys when compared to gold based noble metal alloys is_______________?

   A. More
   B. Less
   C. Equal
   D. Depends on the alloy type

8. Linear coefficient of thermal expansion of metal used for metal caramic restoration range from________________?

   A. 11.5-12.5×10-6/°C
   B. 10.5-11.5×10-6/°C
   C. 13.5-14.5×10-6/°C
   D. 16.5-17.5×10-6/°C

9. Sub surface porosity can be decreased by_______________?

   A. Decreasing the sprue length
   B. Decreasing the sprue thickness
   C. Increasing the melting temperature
   D. Increasing the mould temperature

10. Back pressure porosity can be avoided by________________?

    A. Using asbestos linear
    B. Placing the sprue at least one quarter inch away form the end of casting ring
    C. Preventing rapid heating the investment in burnout oven
    D. Using a short and wide sprue