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year 1 > dental materials > Flashcards

dental materials Flashcards

1
Q

which testing method is used for testing hardness of metals?

a) rockwells
b) brinells
c) vickers
d) knoops
e) shore a durometer

A

b) brinells

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2
Q

which static strength test should not be used for ductile materials?

a) diametral (indirect tensile)
b) direct tensile
c) flexure 3 point bend
d) torsion

A

a) diametral (indirect tensile)

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3
Q

name the four testing methods to determine hardness of a material

A
  • brinells : metals
  • rockwells : range
  • knoop : ceramics, composites, hard plastics
  • vickells: ceramics, composites, hard plastics
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4
Q

what does a Shore A durometer test measure?

A

the rubber hardness of a material

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5
Q

on a stress-strain plot, at what point does permanent deformation occur?

A

beyond the elastic limit

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6
Q

what does the yield point on a stress-strain plot determine?

A

the point where beyond it, strain will increase (stretches) without any further stress being applied

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7
Q

what part of the stress-strain curve determines the elastic modulus?

A

the linear region of the curve

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8
Q

what part of the stress-strain plot shows the resilience ?

A

area under the curve before the elastic limit (so in the elastic region)

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9
Q

what part of the stress-strain plot shows the toughness of a material?

A

the area under the entire curve (upto fracture point)

shows how much total energy can be absorbed by the material

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10
Q

what is the difference between a brittle and ductile material in terms of their toughness and resilience ?

A

BRITTLE: high resilience, low toughness

DUCTILE: low resilience, high toughness

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11
Q

which non Newtonian fluid only flows once the yield stress is reached ?

a) pseudoplastic
b) dilatant
c) viscoplastic
d) rheoplastic
e) thixoplastic

A

c) viscoplastic

- once yield stress reached, can behave like any other non-Newtonian fluid or even Newtonian fluid

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12
Q

which non Newtonian fluid increases in viscosity as the shear rate/force increases?

a) pseudoplastic
b) dilatant
c) viscoplastic
d) rheoplastic
e) thixoplastic

A

b) dilatant

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13
Q

what are the five types of wear that can occur to a material?

A
  • abrasive
  • corrosive
  • erosive
  • adhesive
  • fatigue
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14
Q

what is stress relaxation?

A
  • time dependent decrease in stress at constant strain eg orthodontic wires
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15
Q

what is creep?

A

time dependent increase in stress at constant strain eg amalgam restorations

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16
Q

what is an impact test?

A

tests the resistance to fracture following a rapid loading ( eg dropping dentures)

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17
Q

what is fatigue of a material?

A

the failure of a material due to combining of micro-cracks produced by cyclic loading. fracture occurs when critical crack size reached

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18
Q

what is static fatigue?

A

failure of a material at small load after a period of constant loading

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19
Q

what is a newtonian fluid?

A

one at which the viscosity of a fluid remains constant despite shear rate/force

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20
Q

what is a viscoplastic fluid?

A

a fluid that becomes viscous after surpassing yield point

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21
Q

what are viscoelastic materials?

A

materials that show both viscous and elastic properties

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22
Q

what is the difference between fatigue life and fatigue strength?

A

fatigue life: the number of cycles to cause failure at a given stress

fatigue strength: the stress at which failure will occur after a given number of cycles

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23
Q

list the hazards associated with monomers/polymers

A
  • Irritation to skin, eyes, mucous membranes
  • allergic dermatitis
  • asthma
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24
Q

list the issues associated with sodium hypochlorite

A

(used to disinfect -root canal )

  • high concentration can damage living tissue
  • does not wet dentine well
  • depletes organic constituents
  • limited shelf life
  • causes pain/swelling/bleeding if introduced to periapical tissues
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25
Q

who are at most risk to hazards of methacrylates?

a) dentist
b) nurse
c) technician
d) patient
e) none of the above

A

c) technician

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26
Q

who is at most risk to hazards associated with sodium hypochlorite?

a) dentist
b) nurse
c) technician
d) patient
e) none of the above

A

d) patient

sodium hypochlorite used as disinfectant for root canal

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27
Q

what is the hazards associated with ceramics and who are at most risk to those hazards?

A
  • respiratory disorders due to inhalation of dust

- technicians at risk

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28
Q

who are most at risk of the hazards associated with electroplating?

a) dentist
b) nurse
c) technician
d) patient
e) none of the above

A

c) technician

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29
Q

which ones does not pose a hazardous risk to technicians?

a) methacrylates
b) metals
c) ceramics
d) sodium hypochlorite
e) plaster

A

d) sodium hypochlorite

30
Q

list the pre marketing research methods of determining the safety of materials

A

IN VITRO:

  • physio-mechanical properties
  • biological properties tested using tissue cultures
  • genotoxicity
  • estrogenicity

IN VIVO:

  • implants
  • allergy tests
  • animals/clinical testing
31
Q

define biocompatibility

A

the ability of a material to elicit an appropriate biological response in a given application in the body/mouth

32
Q

define biomaterial

A

a material that interfaces with living tissues without causing an adverse reaction

33
Q

how is allergic dermatitis acquired?

A

contact with low molecular weight substances that bind to plasma proteins and develop an antigen. upon next exposure they produce an allergic response

34
Q

why is an adhesive bond necessary for tooth tissue?

A

tooth structure is hydrophilic while most dental materials are hydrophobic

35
Q

what is the difference between adhesion and cohesion?

A

adhesion: attractive forces between two dissimilar materials
cohesion: attractive forces between similar molecules in the same material

36
Q

what are the three stresses that weaken adhesive bonds?

A
  • thermal expansion
  • dimensional changes
  • moisture
37
Q

what are the factors that affect adhesion?

A
  • wettability
  • contact angle
  • surface energy/tension
  • surface roughness
  • viscosity
38
Q

how does surface energy/tension affect adhesion?

A 
high surface energy of solid 
=  high wettability of liquid 
= small contact angle
= greater surface area covered by adhesive
= good adhesion
39
Q

how does the viscosity of an adhesive affect its properties?

A

the wettability of a liquid is resisted by its viscosity

the more viscous = the poorer the wettability = the poorer the adhesive properties

40
Q

which type of adhesion is better?

solid-to-solid

solid-to-liquid

A

solid-to-liquid

41
Q

what are the three main types of adhesion?

A
  • MECHANICAL (interlocking)
  • PHYSICAL (van der Waals)
  • CHEMICAL (covalent/ionic bonds) - eg Glass Ionomer Cements
42
Q

what is molecular entanglement?

A

the combination of mechanical, physical and chemical adhesion
it is very strong

43
Q

how are methyl methacrylates formed

a) condensation reactions
b) addition reactions

A

b) addition reactions

44
Q

how are free radicals formed in dentistry?

A
  • heat
  • light curing
  • self-curing with two paste systems (at room temp)
45
Q

what are thermosetting polymers?

A

initially rubbers that become rigid with increased cross-links

46
Q

what is vulcanisation?

A

formation of sulphur cross links in polymers

47
Q

what is the difference between elastomers and hard resins?

A

ELASTOMERS:

  • deform easily
  • low intermolecular forces
  • reversible deformation due to cross links

HARD RESINS:

  • high intermolecular forces
  • difficult to deform
  • also known as thermoplastics
48
Q

what is the ‘glass transition temperature’?

A

the temperature at which a rigid material becomes soft and rubbery (Tg)

49
Q

if a polymer is naturally elastomeric at room temperature, what does this tell you about its Tg?

A

the Tg (glass transition temperature) is LESS than the room temperature

50
Q

how do plasticisers make a material more rubbery/compliant?

name an example

A

plasticisers work by DEPRESSING the Tg due to MOLECULAR LUBRICATION

phthalates are plasticisers

51
Q

what are copolymers and their types?

A

co polymers are polymers formed with more than one type of monomer

  • RANDOM COPOLYMER: random arrangement of monomers
  • BLOCK COPOLYMER: blocks of monomer groupings along the polymer chain
  • GRAFT COPOLYMER: main chain of one type of monomer, with branches of a different type of monomer
52
Q

all dental material polymers are..?

a) atactic
b) isotactic
c) syndiotactic

A

a) atactic

53
Q

what are the different stereochemistry arrangements of polymers?

A

ATACTIC: random arrangement of head and tail configurations

ISOTACTIC: all substituents re on the same side of polymer chain (all monomer units have same stereochemistry)

SYNDIOTACTIC: alternating head-tail linkages (repeating monomers have alternating stereochemistry)

54
Q

alginate is water soluble or insoluble?

A

soluble

55
Q

name crystalline polymers and their use in dentistry

A

polyethene - used to reinforce denture bases

polypropylene- instrumental trays

56
Q

what are denture base materials made out of?

A

poly methyl methacrylates - PMMA

57
Q

which polymer is not water soluble?

a) HEMA
b) PMMA
c) poly acrylic acid
d) alginate

A

b) PMMA

58
Q

how does fast and slow cooling rates affect grain size of metal/alloy crystals?

A

fast cooling = small grain size

slow cooling = large grain size

59
Q

what are the different types of corrosions metals can under go?

A
  • chemical (between metal and non metal)
  • electrochemical/galvanic (between two dissimilar metals)
  • localised galvanic (between two different phases of same alloy (eg solution/sold))
  • crevice corrosion: difference in surface oxygen levels ( due to plaque covering)
  • pitted corrosion : difference in oxygen levels due to damage of oxide layer
  • stress corrosion: under sustained force in corrosive environment
60
Q

what makes metals easy to deform?

A

crystal defects

61
Q

what causes permanent deformation of metals?

A

the movement of dislocation as a result of an applied force above yield stress

62
Q

what stops dislocations during metal deformation?

A
  • grain boundaries
  • impurities
  • point deflects
  • another dislocation
63
Q

for solid solution alloys, what happens when you cool down too quickly?

A

coring

64
Q

how do you prevent coring from happening to solid solution alloys?

A

homogenisation

65
Q

what is solution hardening?

A

the mixture of two different metals = different atomic radii sizes which creates point deflects that prevent dislocation movements thus making the material harder

66
Q

what is order hardening ?

A

quickly cooling (quenching) then reheating the metal to form allow the formation of a superlattice

67
Q

what is homogenisation?

A

heating the alloy to allow diffusion of atoms to give a homogenous composition

68
Q

what is coring and how do you fix it?

A

coring is the rapid cooling of a solid solution alloy resulting in layers of solid forming that have different compositions .

you can fix it by homogenisation

69
Q

what is work strain hardening and what can reverse it?

A

work strain hardening is the constant strain being applied to a wrought alloy casuing existing dislocations to stack up at the grain boundaries and the formation of new dislocations. this causes the alloy to become brittle

this can be undone by the process of annealing (reheating the alloy)

70
Q

what is annealing?

A

a process to undo the hardening caused by work strain hardening

it involves heating the alloy
with increasing temp you get:
1) recovery
2) recrystallisation
3) grain growth
71
Q

what is the difference between a eutectic binary alloy and a solid solution alloy?

A

solid solution alloys are two metals completely soluble in one another. their solid is a mixture of the two metals

eutectic alloys consist of metals that are NOT soluble in one another and solidify as separate metals

year 1 (8 decks)

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