2014 Flashcards by G K

What is correct about metals ?

a) Only in group I and II of periodic table  
b) Reacts with non metal only  
c) Forms positive ions in solutions  

c) Forms positive ions in solutions  

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Which of the following is thermoplastic?  

a) Polyethylene vinyl acetate

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What increases Tg?

long straight chains

and strong interaction between polymers chains

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gutta purcha

trans 1,4 polyisoprene (rigid; natural elastomer)

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What is true about the proprieties of a thermosetting material?

highly cross linked, cannot be reheated and reshaped, infusible but decompose instead, insoluble, superior abrasion resistance compared to thermoplastics; e.g. cross-linked PMMA

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What is the activator of addition polymerisation?

BPO

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Which one is an inhibitor?

Eugenol

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Latex gloves inhibit the polymerisation of?

Addition silicon

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What happens if you heat elastomer more than Tg?

a) Soft and ductile  
b) Hard  
c) Rubbery

c) Rubbery

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What causes setting expansion?

a) Crystallization
b) Increase W/P ratio  
c) Chemicals  
d) Immersion in water  

a) Crystallization

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Which metal used in dentistry is liquid in room temperature?
 a) Hg  
b) Ag
c) Au  

a) Hg

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Which of the following is a characteristic of a metal?

a) Forms positively charged ions in solution

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If a dental gold alloy at 1040 C degree is poured into cylinderical mold at 590 C degree, the first solid formed will be?

a) Small grain size  
b) Homogeneous nucleation  
c) Both

a) Small grain size  

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According to hall petch, there is a direct proportionality between the grain diameter and the yield of strength. 
a) T
 b) F  

 b) F  

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To make wrought metals from a cast metal, it should be?

a) Stressed at a temperature below its melting point  
b) Stressed to a level above its elastic limit but below its tensile strength  
c) Stressed to a level above its tensile strength  
d) Both a & b

d) Both a & b

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In a binary alloy, how many thermodynamic variables are needed to know the physical state at atmospheric pressure? a) 1 
b) 2
 c) 3

b) 2

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Which of the following is one of the base metals that is anticorrosive ? 
a) Chromium 
 b) Cobalt 
c) Nickel 
d) Silver

a) Chromium

If type II gold alloy is quenched, what is increased? a) Strength  

b) Ductility 
c) Hardness 
d) None of the above (because it’s type II)

d) None of the above (because it’s type II)

Which gypsum products is used for mounting casts?

a) Plaster

Which gypsum products is used for diagnostic casts?

a) Type III

Which gypsum products has the highest compressive strength?

a) Type IV

Which of the following doesn’t change?

a) Elastic modulus  
b) Elastic limit  
c) Ductility  
d) Hardness

a) Elastic modulus  

What happens in the second stage of annealing ?

a) Hardness and strength return to their values prior to annealing  
b) Nucleation of new grains  
c) Both a & b

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What happens during the third stage of annealing?  

a) Strength decreases due to increased grain size

Which of the following is not a major component of porcelain? a) CaO b) Si  c) Al d) K2O

c) Al

Which impression material when sets yields a by product and has the largest dimensional change? a) Polysulfide   b) Addition silicone   c) Condensation silicone  

c) Condensation silicone  

If you decide pd to late pour the cast, what would you do to the impression material? a) Expose it to air   b) Store it in water   c) Cover it with very wet towel d) Cover it with moist towel and put it in a closed container

d) Cover it with moist towel and put it in a closed container

Which of the following is the gypsum made with dry heat? a) Plaster b) Plaster of peris

a) Plaster

Which of the following is the gypsum made with heat and steam? a) Alpha hemihydrate   b) Beta hemihydrate

a) Alpha hemihydrate  

What is a property exhibited by most ceramics? | a) High compressive strength

a) High compressive strength

When ceramic is bonded with ceramic, the thermal expansion of ceramic is? a) Slightly lower than metal   b) Significantly lower

a) Slightly lower than metal

Which of the following can be safely used to prolong setting time of impression material? a) Change W/P ratio   b) Lowering water temperature c) Over mixing   d) Under mixing

b) Lowering water temperature

The proper amount of time to separate gypsum & alginate is? a) 20 min   b) 10 min   c) 1hr   d) 24 hr

c) 1hr

Why is ceramic brittle ? 

Low fracture toughness

``` Which physical properties cause shrinkage of hydrocolloids impression? a) Evaporation  b) Syneresis  c) Imbibition  d) a&b ```

 b) Syneresis

Which of the following is a cross linking agent?  

Ethelene glycol dimethacrylate

What is the accelerator for polysulfide?

Lead dioxide

What is the catalyst for addition silicone?

Platinum

The compressive strength of gypsum increases when? a) Water increases   b) Water decreases   c) Powder decreases   d) All of the above

b) Water decreases

Increasing the W/P ratio? a) Increases porosity   b) Weaken it   c) Increases setting time   d) Decrease setting expansion e) All of the above

e) All of the above