2014 Flashcards
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
Which of the following is thermoplastic?
a) Polyethylene vinyl acetate
a) Polyethylene vinyl acetate
What increases Tg?
long straight chains
and strong interaction between polymers chains
gutta purcha
trans 1,4 polyisoprene (rigid; natural elastomer)
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
What is the activator of addition polymerisation?
BPO
Which one is an inhibitor?
Eugenol
Latex gloves inhibit the polymerisation of?
Addition silicon
What happens if you heat elastomer more than Tg?
a) Soft and ductile
b) Hard
c) Rubbery
c) Rubbery
What causes setting expansion?
a) Crystallization
b) Increase W/P ratio
c) Chemicals
d) Immersion in water
a) Crystallization
Which metal used in dentistry is liquid in room temperature?
a) Hg
b) Ag
c) Au
a) Hg
Which of the following is a characteristic of a metal?
a) Forms positively charged ions in solution
a) Forms positively charged ions in solution
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
According to hall petch, there is a direct proportionality between the grain diameter and the yield of strength.
a) T
b) F
b) F
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
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
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
a) Plaster
Which gypsum products is used for diagnostic casts?
a) Type III
a) Type III
Which gypsum products has the highest compressive strength?
a) Type IV
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
idk
What happens during the third stage of annealing?
a) Strength decreases due to increased grain size
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
