971. All of the following are grain refiners of noble metal casting alloys, except?
A. rhenium
D.all of the above
E.none of the above

972. The commonly used composite restorative materials have a matrix based upon?
A. vinyl resins
B.epoxy resins
C.alkyl resins
D.ester resins

973. Which substance is usually adsorbed onto the surface of gold foil by manufacturers, to act as a protective film?
A.Chromium oxide
D.Sulfur dioxide

974. Bonding agents improve the bond strength of composite resins to the tooth structure by?
A. chemical adhesion to enamel
B.forming complex chelateswith the inorganic portion of tooth structure
C.decreasing the surface tension of composite resin
D.improved wetting and penetration into the enamel irregularities
E.all of the above

975. The principal factor in minimizing the firing shrinkage of porcelain is the?
A. amount of hydrated aluminium silicate present
B.fusion temperature
C.uniformity of particle size
D.thoroughness of condensation
E.ratio of silica and alumina

976. Liquids which become more rigid as the rate of deformation increases are termed
A. thixotropic

977. The setting time of zinc oxide -eugenol paste will be decreased by?
A. cooling the glass slab employed for mixing
B.using a very short mixing time
C.adding a small amount of petrolatum to the mix
D.increasing the ratio of base paste to the catalyst paste
E.none of the above

978. Cohesion of direct filling gold at room temperature Is an example of the principle of?
A. homogenization
C.atomic attraction

979. The primary role of modifiers in dental plasters is to?
A. increase strength
B.reduce porosity
C.regulate the setting time
D.control the hygroscopic expansion
E.increase hardness

980. After plaster is mixed, which of the following is the first to occur?
A.Gillmore needle -final setting time
B.Loss of gloss
C.Vicat needle -setting time
D.Gillmore needle -initial setting time

Leave a Reply