981. The thickness of the gel between the tray and the tissues for hydrocolloid impressions should always he at least?
A.3 mm
B.1.5 mm
C.6 mm
D.1 mm

982. Commercially pure titanium is the dental implant material of choice as it?
A. has very low density
B.oxidizes upon contact with air or normal tissue fluids
C.has a modulus of elasticity 5 to 10 times higher than that of bone
D.induces bone formation

983. Compared to heat-curing resins, chemically activated resins have increased?
A. strength
B.color stability
C.residual monomer content
D.working time
E.none of the above

984. Which of the following acids is commonly used for etching enamel surfaces?
A. Citric acid
B.Hydrochloric acid
C.Phosphoric acid
D.Picric acid

985. The liquid for glass ionomer cements is similar to that of?
A. zinc phosphate cements
B.resin cements
C.polycarboxylate cements
D.silicate cements

986. The pH of poly-carboxylatecement liquid containing poly-acrylic acid, is approximately

987. A measure of the ductility of a material is its?
A. hardness number
B.percent elongation
C.tensile strength
E.yield strengt

988. Water at 20°C is more suitable for cooling the agar hydrocolloid impression than is ice water because the sol is a good thermal conductor and rapid cooling may cause a concentration of stresses where gelation takes place last.
A. Both the statement and reason are true
B.The statement is true but the reason is false
C.The statement is false but the reason is true
D.Both the statement and reason are false

989. The dentist can decrease the setting expansion of plaster by?
A. increasing the W/P ratio
B.selecting a plaster with a finer particle size
C.reducing the accelerator concentration
D. increasing the mixing time
E. adding powered gypsum to the mix

990. At a temperature of 650°C, when the gypsum investment mold is adequately heated, the colour of the sprue when viewed in a shadow, is?
A. dull red
B.cherry red
C.bright orange
D.light orange

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