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general revision > dental materials > Flashcards

dental materials Flashcards

1
Q

What does an enamel bonding agent consist of?

a. unfilled resin
b. filled resin
c. a mixture of resins, acetone and ethanol
d. wetting agents or resin
e. prime and bond mixture

A

A - unfilled resin

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2
Q

Etched enamel does not need ‘wetting before the enamel bonding agent is applied.
Why is wetting not required?

a. etched enamel has high surface free energy
b. etched enamel has low surface free energy
c. enamel bonding agent has a low surface tension
d. negative charge in the enamel bonding agent is attracted to the positive calcium ions in the etched enamel
e. negative charge in the enamel bonding agent is attracted to the positive fluoride ions in the etched enemal

A

A - etched enamel has a high surface free energy

Surface free energy is the excess ernst that the surface has compared to the bulk of the material.

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3
Q

What is the bond strength achievable using enamel bonding agents on etched enamel?
(1 MPa = 1 kg/mm^2)

a. 0.1 MPa
b. 5 MPa
c. 30 MPa
d. 80 MPa
e. 250 MPa

A

C - 30 MPa

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4
Q

Which one of the following is NOT an advantage of an enamel bonding agent over dentine bonding agent?

a. decreased marginal leakage
b. better colour stability
c. increased bond strength
d. easier to apply
e. decreased moisture sensitivity

A

E - decreased moisture sensitivity

Enamel bonding agents don’t decrease moisture sensitivity as they are extremely moisture sensitive.

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5
Q

Which of the following is correct about a dentine primer?

a. etches dentine
b. increases the surface free energy (wets) dentine
c. removes the smear layer
d. bonds to composure
e. conditions the dentine

A

B - increases surface free energy

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6
Q

Which of the following is true about the resins in a dentine bonding agent primer?

a. hydrophilic
b. hydrophobic
c. viscous
d. high molecular weight
e. high surface tension

A

B - resin is hydrophobic

(reason you have to keep it dry before curing)

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7
Q

What is the percentage of copper in a high copper dental amalgam alloy?

a. 2-12%
b. 12-32%
c. 52-70%
d. 70%+

A

B - 12-32%

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8
Q

Zinc is often used to improve the properties of amalgam.
What happens to a zinc-containing low copper alloy if moisture gets into it?

a. corrodes
b. contracts
c. reduced
d. expands
e. none of the above

A

D - the alloy expands

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9
Q

Why is tin added to amalgam?

a. decreases the reaction rate and gives an adequate working time
b. decreases corrosion
c. scavenges water molecules
d. increases filling strength
e. decreases setting time

A

A - tin decreases the reaction rate and gives an adequate working time.

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10
Q

What is the greatest disadvantage of using amalgam in posterior teeth?

a. mercury toxicity
b. poor aesthetics
c. sound tissue requires removal for retention
d. increased incidence of cusp fracture
e. decreased lifetime of restoration compared with other materials

A

C - requires removal of sound tissue for retention

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11
Q

Which of the following materials should not be used with composites?

a. kalzinol
b. zinc phosphate
c. vitrebond
d. fuji GIC
e. poly-F

A

A - kalzinol

Prevents bonding of composite to enamel and dentine in a cavity.

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12
Q

What is the maximum thickness of composite which can be cured by a curing light?

a. 0.5mm
b. 1mm
c. 2mm
d. 4mm
e. 6mm

A

C - 2mm

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13
Q

Which of the following events does NOT occur as a result of microleakage at the composite margin?

a. secondary caries
b. loss of restoration
c. sensitivity
d. enamel fracture
e. staining

A

D - enamel fracture

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14
Q

Which of the following is not released from GIC when it sets?

a. zinc
b. aluminium
c. fluoride
d. calcium
e. sodium

A

A - zinc

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15
Q

When fluoride ions leach out of glass ionomer, what replaces them?

a. aluminium ions
b. hydroxyl ions
c. sodium ions
d. carbonate ions
e. silicate ions

A

B - hydroxyl ions

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16
Q

The slow plastic deformation that occurs with application of force over time.

a. coefficient of thermal expansion
b. creep
c. fatigue
d. hardness
e. thermal conductivity
f. thermal diffusivity
g. wear

A

B - creep

17
Q

The ability of a material to transmit heat.

a. coefficient of thermal expansion
b. creep
c. fatigue
d. hardness
e. thermal conductivity
f. thermal diffusivity
g. wear

A

E - thermal conductivity

18
Q

The fractional increase in length for each degree of temperature rise.

a. coefficient of thermal expansion
b. creep
c. fatigue
d. hardness
e. thermal conductivity
f. thermal diffusivity
g. wear

A

A - coefficient of thermal expansion

19
Q

Resistance to penetration.

a. coefficient of thermal expansion
b. creep
c. fatigue
d. hardness
e. thermal conductivity
f. thermal diffusivity
g. wear

A

D - hardness

20
Q

Abrasion resistance of a substance.

a. coefficient of thermal expansion
b. creep
c. fatigue
d. hardness
e. thermal conductivity
f. thermal diffusivity
g. wear

A

G - wear

21
Q

The rate at which temperature changes spread through a material.

a. coefficient of thermal expansion
b. creep
c. fatigue
d. hardness
e. thermal conductivity
f. thermal diffusivity
g. wear

A

F - thermal diffusivity

22
Q

When cyclic forces are applied, a crash may nucleate and grow by small increments each time the force is applied.

a. coefficient of thermal expansion
b. creep
c. fatigue
d. hardness
e. thermal conductivity
f. thermal diffusivity
g. wear

A

C - fatigue

23
Q

Which of the following statements are correct?

a. thermal diffusivity is the ability of a material to conduct heat
b. wear is abrasion (with or without chemical) of a substance
c. resilience is a measure of how hard it is to bend a material
d. creep is the slow dimensional change under load
e. stress is the internal force per unit cross-sectional area acting on a material

A

B, D and E

  • wear is abrasion of a substance (with or without chemicals)
  • creep is the slow dimensional change under load
  • stress is the internal force per unit cross-sectional area acting on a material
  • thermal diffusivity is the rate at which temperature changes spread through materials.
  • thermal conductivity is the ability to conduct heat
  • resilience is the energy absorbed by a material undergoing elastic deformation.
  • stiffness is how hard it is to bend a material
24
Q

Dental Amalgam:

a. is a mixture of silver alloy and mercury
b. can be composed of spherical particles, irregular particles or a mixture of the 2
c. Gamma-2 is the name given to the silver-mercury product formed during amalgamation
d. dimensional change is said to be negative if an amalgam expands during setting
e. titration is the process of mixing the silver alloy and mercury

A

A and B - mix of silver alloy and mercury and can have spherical/irregular/both particles.

25
Q

Acid Etching:

a. creates a microscopically rough enamel surface
b. following etching, the etch and should be washed away with saline
c. enamel of deciduous teeth should be etched for a shorter time than permanent teeth
d. the etch and is usually 20% phosphoric acid etch
e. the enchant is usually applied for 15-30 seconds

A

A and E - microscopically rough enamel surface, applied for 15-30 seconds.

(enamel on deciduous teeth may need longer etching time)

26
Q

Which material should be placed if you see the pink blush of pulp?

A

Biodentine or MTA

27
Q

What are filler particles usually made from?

A

silica

(average size is 0.05 micrometers)

28
Q

What reaction does composite undergo to set?

A

free radical addition polymerisation

29
Q

Whcih reaction sets GIC?

A

acid-base reaction

30
Q

What affect would using a high copper alloy have on the amalgam?

A

it would strengthen it

31
Q

What is the cave surface angle for amalgam?

A

90 º

32
Q

What is creep?

A

the movement of amalgam to unsound margins of the cavity causing ditching

33
Q

What is the main component of alginate?

A

sodium alginate

34
Q

Which component of MTA can cause tooth discolouration?

A

bismuth oxide

general revision (11 decks)

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