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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
who are at most risk to hazards of methacrylates? a) dentist b) nurse c) technician d) patient e) none of the above
c) technician
26
who is at most risk to hazards associated with sodium hypochlorite? a) dentist b) nurse c) technician d) patient e) none of the above
d) patient | sodium hypochlorite used as disinfectant for root canal
27
what is the hazards associated with ceramics and who are at most risk to those hazards?
- respiratory disorders due to inhalation of dust | - technicians at risk
28
who are most at risk of the hazards associated with electroplating? a) dentist b) nurse c) technician d) patient e) none of the above
c) technician
29
which ones does not pose a hazardous risk to technicians? a) methacrylates b) metals c) ceramics d) sodium hypochlorite e) plaster
d) sodium hypochlorite
30
list the pre marketing research methods of determining the safety of materials
IN VITRO: - physio-mechanical properties - biological properties tested using tissue cultures - genotoxicity - estrogenicity IN VIVO: - implants - allergy tests - animals/clinical testing
31
define biocompatibility
the ability of a material to elicit an appropriate biological response in a given application in the body/mouth
32
define biomaterial
a material that interfaces with living tissues without causing an adverse reaction
33
how is allergic dermatitis acquired?
contact with low molecular weight substances that bind to plasma proteins and develop an antigen. upon next exposure they produce an allergic response
34
why is an adhesive bond necessary for tooth tissue?
tooth structure is hydrophilic while most dental materials are hydrophobic
35
what is the difference between adhesion and cohesion?
adhesion: attractive forces between two dissimilar materials cohesion: attractive forces between similar molecules in the same material
36
what are the three stresses that weaken adhesive bonds?
- thermal expansion - dimensional changes - moisture
37
what are the factors that affect adhesion?
- wettability - contact angle - surface energy/tension - surface roughness - viscosity
38
how does surface energy/tension affect adhesion?
``` high surface energy of solid = high wettability of liquid = small contact angle = greater surface area covered by adhesive = good adhesion ```
39
how does the viscosity of an adhesive affect its properties?
the wettability of a liquid is resisted by its viscosity the more viscous = the poorer the wettability = the poorer the adhesive properties
40
which type of adhesion is better? solid-to-solid solid-to-liquid
solid-to-liquid
41
what are the three main types of adhesion?
- MECHANICAL (interlocking) - PHYSICAL (van der Waals) - CHEMICAL (covalent/ionic bonds) - eg Glass Ionomer Cements
42
what is molecular entanglement?
the combination of mechanical, physical and chemical adhesion it is very strong
43
how are methyl methacrylates formed a) condensation reactions b) addition reactions
b) addition reactions
44
how are free radicals formed in dentistry?
- heat - light curing - self-curing with two paste systems (at room temp)
45
what are thermosetting polymers?
initially rubbers that become rigid with increased cross-links
46
what is vulcanisation?
formation of sulphur cross links in polymers
47
what is the difference between elastomers and hard resins?
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
what is the 'glass transition temperature'?
the temperature at which a rigid material becomes soft and rubbery (Tg)
49
if a polymer is naturally elastomeric at room temperature, what does this tell you about its Tg?
the Tg (glass transition temperature) is LESS than the room temperature
50
how do plasticisers make a material more rubbery/compliant? name an example
plasticisers work by DEPRESSING the Tg due to MOLECULAR LUBRICATION phthalates are plasticisers
51
what are copolymers and their types?
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
all dental material polymers are..? a) atactic b) isotactic c) syndiotactic
a) atactic
53
what are the different stereochemistry arrangements of polymers?
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
alginate is water soluble or insoluble?
soluble
55
name crystalline polymers and their use in dentistry
polyethene - used to reinforce denture bases polypropylene- instrumental trays
56
what are denture base materials made out of?
poly methyl methacrylates - PMMA
57
which polymer is not water soluble? a) HEMA b) PMMA c) poly acrylic acid d) alginate
b) PMMA
58
how does fast and slow cooling rates affect grain size of metal/alloy crystals?
fast cooling = small grain size slow cooling = large grain size
59
what are the different types of corrosions metals can under go?
- 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
what makes metals easy to deform?
crystal defects
61
what causes permanent deformation of metals?
the movement of dislocation as a result of an applied force above yield stress
62
what stops dislocations during metal deformation?
- grain boundaries - impurities - point deflects - another dislocation
63
for solid solution alloys, what happens when you cool down too quickly?
coring
64
how do you prevent coring from happening to solid solution alloys?
homogenisation
65
what is solution hardening?
the mixture of two different metals = different atomic radii sizes which creates point deflects that prevent dislocation movements thus making the material harder
66
what is order hardening ?
quickly cooling (quenching) then reheating the metal to form allow the formation of a superlattice
67
what is homogenisation?
heating the alloy to allow diffusion of atoms to give a homogenous composition
68
what is coring and how do you fix it?
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
what is work strain hardening and what can reverse it?
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
what is annealing?
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
what is the difference between a eutectic binary alloy and a solid solution alloy?
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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