891. When restoring the posterior teeth in a child patient with amalgam, if it is difficult to keep theregion dry, it is preferable to?
A. use zinc free alloys
B. fill the cavity in small increments
C. use automatic condensers
D. all of the above
892. The ability of a direct filled gold restoration to withstand the stresses present can be best explained by which physical characteristic of gold?
A. Dendritic microstructure
B. Transverse strength of about 39,000 psi
C. Apparent density of about 15 gm/cm3
D. Knoop hardness number of 60 to 75
893. prior to investing the casting ring is lined with asbestos to?
A. prevent sliding of the investment mold
B. prevent confinement of mold expansion
C. permit easy retrieval of the casting
D. preventcracking of the mold
E. reduce the amount of investment required for investing
894. Which of the following forms of iron are soft and ductile?
A. Cementite and martensite
B. Martensite and ferrite
C. Ferrite and austenite
D. Austenite and cementite
895. Type II noble metal alloys are appropriate for casting ?
A. pontics, full crowns. thick 3/4 crowns, inlays subject to moderate stresses
B. full crowns, ponlics, inlays, partial frame-works
C. small inlays, long span budges, saddle bars
D. short span bridges. 3/4 crowns. thin cast backing abutments
896. A method of imparting hardening heat treatment to dental gold alloys, is to?
A. Heat the alloy to 450°C and gradually cool to 225°C in half an hour
B. heat the alloy to 700*C and quench in cold water
C. heat the alloy to 500-C and bench cool for 2 days
D. heat the alloy to 200°C, hold for 20 minutes and then further heat to 600°C and quench in cold water
897. Strength of an amalgamrestoration will be more if?
A. a slight excess of mercury is left in the restoration
B. lower condensation pressures are applied
C. porosity is less
D. trituration time is increased
E. none of the above
898. A wrought metal?
A.is resistant to corrosion or attack by acids
B. formed by working on a cast metal
C. formed by pouring molten metal into a mold
D. cannot he heat treated
E. none of the above
899. The most effective method of preventing distortion of the wax pattern is?
A.by holding the WAX under equal pressure, from all Sides while it solidifies
B.to invest the pattern as soon as possible
C.to dip the die repeatedly in molten wax
D.By adding molten wax In small increments
900. The ability of an alloy to withstand mechanical stresses without permanent deformation, is reflected by it?
A.resilience
B.yield strength
C.hardness
D. fatigue resistance