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CA2 TYS Learning Pts Flashcards

1
Q

(T/F) Type IV gold alloy has the highest tarnish resistance

A

False
- type I highest tarnish resistance, type IV lowest
- type IV: extra hard gold alloy, lowest gold %

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2
Q

(T/F) acrylic soft liners are brittle but become soft when soaked in water

A

True
- soft liners absorbs shock between hard base of denture and gums
- more comfortable

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3
Q

(T/F) passivation is the process of enhancing the titanium oxide layer to increase resistance to ion release and degradation

A

True

Passivation=> enhance oxide layer to minimise release of metal ions => minimise corrosion/improve corrosion resistance
- via immersion in 40% nitric acid/anodisation for titanium based alloys (implant materials)

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4
Q

(T/F) the benefits of APS are fast setting time, no by-product and high molecular weight

A

True

  • addition polymerise silicones
  • notes say it has moderately low mw silicone tho
  • from internet: high mw, higher degree of entanglement, more bonding, can absorb more energy b4 failing
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5
Q

(T/F) CPS setting time is 6-10mins and the setting shrinkage is 0.6% after 24 hours

A

True

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6
Q

(T/F) using amalgam w smaller particles will result in a net contraction

A

True
- smaller particle size => increased SA, G1 grows faster => increased consumption of mercury => more initial contraction (net contraction)
-smaller particles of silver tin

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7
Q

(T/F) resilient liners can be cleaned w a soft brush and hypochlorites

A

False
- using soft brush is correct
- but shd not use hypochlorite (bleach)
- to be cleaned w WATER

Topic: resin based materials

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8
Q

(T/F) flux is added to alloy to increase the melting temperature and dissolve oxides that form during casting

A

False, dosent increase the melting temp (it makes it more fluid so means decrease melting temp?)

Functions of flux:
- prevent O2 in air from contacting hot metal => prevent oxidation
- dissolves oxides that may form when metal heated
- increases fluidity of metal
- minimise porosity

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9
Q

(T/F) cristoballite expands to a greater extent than quartz

A

True

  • cristoballite is a mineral polymorph of silica
  • topic: investment materials, silica-bonded investment
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10
Q

(T/F) the thickness of bonding resin/adhesive does not affect bonding strength

A

False

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11
Q

(T/F) tissue conditioners bond well to metal framework but need to be changed regularly due to intraoral degradation

A

False
- tissue conditioners = ‘acrylic temporary soft liner’ in dentures
- temporary soft-denture liners that help your gums and soft tissue recover from damage caused by old or poorly-fitting dentures
- formed in situ
- i think why this statement is wrong is cuz it doesnt bond well to metal framework??

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12
Q

(T/F) work hardening for ductile materials such as metals decreases corrosion resistance and increases brittleness

A

True
- increases: hardness, tensile strength, brittleness
- decreases: ductility, corrosion resistance

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13
Q

(T/F) the amt of silica is proportional to the amt of thermal expansion of the investment

A

True

  • silica is added as a binder
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14
Q

The decrease in creep from low to high-copper content amalgams is due to..

A

Lower mercury content

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15
Q

(T/F) shape memory is the ability of the alloy to deform to its preheated shape

A

True

  • topic: wrought metal alloys
  • shape memory
    -> the ability to return to previously manufactured shape, induced thermally (oral temp)
    -> deformed when cold, returns to pre-deformed shape when heated
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16
Q

(T/F) elongation is defined as the length over initial length after breakage

A

True

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17
Q

(T/F) modulus of elasticity is a measure of fracture strength, and is found by taking the stress over the resulting elastic deformation

A

False
- fracture strength is measured by UTS, MoE measures only elastic region
- MoE = stress/strain

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18
Q

(T/F) ductility is defined as the ability of the metal to be stretched into a wire

A

True

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19
Q

(T/F) corrosion resistance is influenced by the composition of the alloy and roughness

A

True

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20
Q

(T/F) work hardening decreases corrosion resistance

A

True

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21
Q

(T/F) corrosion of amalgam alloys is always good because the products aid in marginal retention

A

False
- tho corrosion at interface btw tooth & restoration actually forms corrosion products that seal space
- but not ALWAYS good cuz corrosion also causes harm => 1. Wet corrosion: galvanism, short circuit pulp, pain or 2. Mercuorscopic expansion, pushes restoration away from tooth

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22
Q

(T/F) passivation decreases corrosion resistance

A

False
- increases corrosion resistance

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23
Q

(T/F) using too much wetting agent can cause a poor fitting casting

A

False

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24
Q

(T/F) inadequate setting expansion can cause a poor fitting casting

A

True

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25
Q

(T/F) using a sprue with a diameter too wide can cause a poor-fitting casting

A

False

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26
Q

(T/F) hardness is not affected by the water/powder ratio for investment material

A

True
- hardness is the resistance to surface deformation/scratches

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27
Q

(T/F) thermal expansion is not affected by water/powder ratio for investment

A

False
- increase water/powder ratio = decrease thermal expansion

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28
Q

(T/F) setting expansion is not affected by water/powder ratio for investment

A

False

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29
Q

(T/F) fracture strength is affected by water/powder ratio for investment

A

True
- increased w/p ratio = decreased strength
- fracture strength: the amt of force it can take b4 permanent deformation

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30
Q

(T/F) lower colour stability is directly related to insufficient polymerisation time

A

True

  • topic: resin based materials
  • mostly referring to denture acrylics
  • heat cured resins => higher colour stability than autopolymerised resins
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31
Q

(T/F) lower water sorption is directly related to insufficient polymerisation time

A

false

  • topic: resin based materials (denture resins)
  • auto-polymerised resins => higher water sorption than heat cured resins => presence of water affects physical & dimensional properties more
  • water absorbed preferentially into polymer component of CR (increased resin content = increased sorption)
  • if bis-GMA polymerise poorly => more space for water to enter => high water sorption
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32
Q

(T/F) lower volumetric shrinkage is directly related to insufficient polymerisation time

A

False
- seems to be related to the size of the CR molecule, the larger the molecule, the less shrinkage
- topic: CR

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33
Q

(T/F) higher polymerisation shrinkage stress is directly related to insufficient polymerisation time

A

False
- Shrinkage stress is the pressure put on the adhesive and surrounding tooth structure during the polymerization process.
- related to the number of bonded surfaces
- topic: CR

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34
Q

(T/F) CoCr has high ductility and is used as a denture base

A

False
- its used as denture base
- but not ductile

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35
Q

(T/F) silver-palladium is white and has acceptable corrosion resistance

A

True
- silver-palladium precious alloy issa alternative to dental casting gold alloys
- prolly for cast crowns

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36
Q

(T/F) higher gold content indicates higher ductility

A

True

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37
Q

(T/F) Zinc polycarboxylate has chemical bonding to tooth structure

A

True
- topic: zinc cements
- radioopaque cement that can be used to cement crowns, bridges, onlays, inlays
- provides chemical adhesion to tooth structure

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38
Q

(T/F) zinc phosphate has anti-cariogenic properties

A

False
- lacks anti-cariogenic properties
- is brittle w poor tensile strenght
- no chemical adhesion
- but one of the earliest and universal luting cement w high strength & low film thickness

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39
Q

(T/F) GIC can prevent secondary caries effectively

A

False

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40
Q

(T/F) ZOE has low solubility

A

False
- high solubility, eugenol disintegrates cement => thus, used for temporary resto
- but eugenol has sedative effect on pulp! Good

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41
Q

(T/F) ZnOE (provisional cement has high wash out resistance

A

True

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42
Q

(T/F) ZnOE is easily cleaned out from internal surface of provi shell and tooth surface

A

True

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43
Q

(T/F) ZnOE provides a good marginal seal to prevent microbial ingress

A

True

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44
Q

(T/F) ZnOE provides high retention resistance and cohesion

A

False
- used as temporary cement
- no chemical adhesion + high solubility

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45
Q

(T/F) type I cements effectively prevents secondary caries

A

False

  • type I cements =luting cements
    -> small particle size
    -> fast set w early resistance to water uptake
    -> radioopaque
  • topic: GIC
  • other types of cements
  • type 2.1 restorative aesthetic
  • type 2.2 restorative reinforced
  • type 3 lining or base cement/pit & fissure sealant
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46
Q

(T/F) zinc polycarboxylate adheres chemically to tooth structure

A

True

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47
Q

(T/F) zinc phosphate is an adequate anticariogenic

A

False

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48
Q

(T/F) ZOE has limited solubility in oral fluid

A

False

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49
Q

(T/F) ZOE has high tensile strength and can be used for both temporary and permanent restorations

A

False, only used for temporary restorations

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50
Q

(T/F) improved ZOE materials serve as a good temporary restoration pending placement of a permanent restoration because they maintain the opposing and adjacent teeth in their respective positions

A

True

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51
Q

(T/F) improved ZOE materials serve as a good temporary restoration pending placement of a permanent restoration because they have thermal insulation qualities comparable to those of dentine

A

True
- yep thermal insulation is about same as dentine
- biological properties, aka pH is also least irritating to pulp at 6.6-8

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52
Q

(T/F) improved ZOE materials serve as a good temporary restoration pending placement of a permanent restoration because they have a therapeutic palliative effect on the dental pulp

A

True

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53
Q

(T/F) improved ZOE materials serve as a good temporary restoration pending placement of a permanent restoration because they have excellent marginal seal

A

True

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54
Q

(T/F) the addition of ortho-ethoxy benzoic acid to ZOE cement decreases the solubility but increases the strength of the cement

A

False
- it increases both the strength and solubility of the cement

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55
Q

(T/F) ZOE can be used on a rigid/flexible tray

A

False
- must use a rigid tray

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56
Q

(T/F) ZOE cannot be used for undercuts

A

True

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57
Q

(T/F) ZOE has low dimensional stabilty

A

False
- high dimensional stability as compared to alginate

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58
Q

(T/F) ZOE is thermoreversible

A

False

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59
Q

(T/F) ZOE has poor detail reproduction

A

False

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60
Q

(T/F) ZOE is most commonly used as temporary cement because of its better tooth sealing properties

A

True

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61
Q

(T/F) ZOE impression paste has low viscosity

A

True

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62
Q

(T/F) ZOE impression paste needs a rigid tray

A

True

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63
Q

(T/F) CoCr is very hard and this facilitates manual polishing

A

False

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64
Q

(T/F) CoCr has a high modulus of elasticity and this allows it to have thin clasps

A

True

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65
Q

(T/F) CoCr is very ductile and this allows for easy manipulation of clasps

A

False

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66
Q

(T/F) work hardening decreases corrosion resistance and brittleness

A

False
- increases corrosion resistance and brittleness

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67
Q

Carbon content of CoCr alloys should not exceed..

A

0.4%
- excess carbide will result in severe brittleness

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68
Q

(T/F) CoCr denture is easy to manipulate and repair

A

False

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69
Q

(T/F) CoCr dentures cannot be used with denture cleansers

A

True
- corrosion will occur if used w hypochlorites or other chlorine containing compounds
- oxygenating denture cleaners will stain alloy
-

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70
Q

(T/F) CoCr has high MOE and high scratch resistance, facilitating manual polishing

A

False
- high MOE
- high hardness, so difficult to polish

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71
Q

(T/F) CoCr has high MOE and demands a high force to elastically deform a wire

A

True
- more rigid and less likely to deform
- stiffer material will have a higher elastic modulus

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72
Q

(T/F) main reason for fracture of partial denture casts made from CoCr alloy during service is the low yield strength of the alloy

A

False
- CoCr has high yield strength

Strength of material can be described by the following properties:
1. Proportional limit
- stress above which stress is no longer proportional to strain
2. Elastic limit
- maximum stress a material can withstand before it becomes plastically deformed
3. Yield strength/proof stress
- stress required to produce a given amount of plastic strain
4. Ultimate tensile strength, shear strength, compressive strength, flexural strength: each of which is a measure of stress required to fracture a material

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73
Q

Proportional limit is..

A

The stress above which stress is no longer proportional to strain

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74
Q

Elastic limit is..

A

The maximum stress a material can withstand before it becomes plastically deformed

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75
Q

Yield strength/proof stress is..

A

The stress required to produce a given amount of plastic strain

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76
Q

What does ultimate tensile strength measure?

A

Stress required to fracture a material

  • so does shear strength, compressive strength, flexural strength
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77
Q

(T/F) Carbon is the most critical component of CoCr alloys in which a small change causes a great variation in physical properties?

A

True

  • carbon variations produces pronounced effects on strength, hardness and ductility
  • it forms carbides w the metallic constituents
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78
Q

(T/F) in CoCr alloys, cobalt contributes to the passivating effects of the alloy

A

False
- chromium contributes to the passivating effects of the alloy by forming a ‘passive’ chromium oxide layer over the surface

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79
Q

(T/F) low density of CoCr allows it to be light and good for denture base

A

True

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80
Q

(T/F) CoCr is easy to maintain and repair

A

False
- difficult to repair

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81
Q

(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in hardness

A

False
- CoCr is very very hard!!

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82
Q

(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in specific gravity

A

True
- specific gravity = relative density!
- CoCr is not that dense! Thats why it can be light and used for dentures

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83
Q

(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in casting shrinkage

A

False

Casting shrinkage is (for Co-Cr: 2.3%, Ni-Cr: 2.0%, gold: 1.25 +/- 0.1%)
- so casting shrinkage is larger in CoCr than in gold

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84
Q

(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in fusion temperature

A

False

(Co-Cr: 1250-1500 deg celcius, gold: 870-950 deg)
- fusion temp for CoCr is higher than for gold

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85
Q

(T/F) type IV partial denture gold alloy exceeds a base-metal partial denture alloy in modulus of elasticity

A

False

(Co-Cr: 200 X 10^3 N/sq mm, which is twice that of gold)

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86
Q

(T/F) passivating effect CoCr -nickel alloy is due to the formation of chromium carbide

A

False
- due to formation of chromium oxide

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87
Q

(T/F) gold content decreases from gold I to IV

A

True

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88
Q

(T/F) ductility decreases from gold I to IV

A

True

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89
Q

(T/F) MOE decreases from gold I to IV

A

False
- MOE decreases, the alloy gets stronger

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90
Q

(T/F) type IV gold alloy has the highest tarnish resistance

A

False
- cuz less gold, so less tarnish resistance

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91
Q

(T/F) localised shrinkage porosity generally occurs at the region of the sprue and the restoration

A

True
- localised shrinkage porosity is caused by a lack of molten metal during solidification, which occurs when 1. Sprue diameter is too small 2. Investment is not sufficiently heated
- the porosity occurs at the region of the ingot

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92
Q

(T/F) solid solutions: solute in random positions in solvent lattice structure, single phase

A

True

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93
Q

What are the alternatives to dental casting gold alloys?

A
  1. Low gold alloys
    - noble metal content is below 60%=> lower tarnish resistance
  2. Silver-palladium precious alloys
    - 60-70% silver & 25% palladium
  3. Non-precious alloys (Ni-Cr-Be)
    - consists mainly of nickel and chromium
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94
Q

(T/F) Type IV gold alloys in hardened condition have a lower MOE than chromium-nickel alloys (in partial denture framework)

A

True

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95
Q

(T/F) Type IV gold alloys in hardened condition are heavier than chromium-nickel alloys (in partial denture framework)

A

True

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96
Q

(T/F) Type IV gold alloys in hardened condition are lower density than chromium-nickel alloys (in partial denture framework)

A

False
- cobalt nickel is lower density than type IV

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97
Q

(T/F) Type IV gold alloys in hardened condition have a higher hardness than chromium-nickel alloys (in partial denture framework)

A

False
- cobalt nickel is harder than type IV gold framework

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98
Q

(T/F) zinc is added to dental casting alloys to improve corrosion resistance of alloy

A

False
- zinc is added to increase hardness (w palladium) & improve castability and reduce melting temp

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99
Q

(T/F) zinc is added to dental casting alloys to improve castability of alloy

100
Q

(T/F) zinc is added to dental casting alloys to serve as an oxide scavenger

101
Q

(T/F) zinc is added to dental casting alloys to reduce coring

A

False
- copper is added to reduce coring, it reduces difference between solidus and liquidus temp
- coring is basically segregation of different metals in an alloy?

102
Q

(T/F) chromium is present in a type IV gold alloy

103
Q

(T/F) palladium is present in a type IV gold alloy

104
Q

(T/F) indium is present in a type IV gold alloy

105
Q

(T/F) copper is present in a type IV gold alloy

106
Q

(T/F) gold alloy does not shrink due to presence of palladium

A

False
- palladium is there to increase 1. Tarnish resistance 2. Corrosion resistance 3. Hardness

  • higher melting temp/range correlates to higher shrinkage
107
Q

(T/F) type I gold alloy is considered a noble alloy because of high gold %>90%

A

True
- noble alloys are those w >25% wt noble

108
Q

(T/F) increase in gold content => decrease in ductility and corrosion resistance

A

False
- more gold = more ductile n more corrosion resistance

109
Q

(T/F) type IV is the hardest because it has the highest gold content

A

False
- least gold content thats why hardest

110
Q

type IV gold alloys are usually utilized for

A

Partial denture frameworks or complete denture bases

111
Q

Type I & II gold alloys are usually utilized for..

A

Restorations which are not subjected to great amounts of stress
- prolly direct gold fillings
- class III & class Vs & inlays (type I) & onlays (type II)

112
Q

Type III gold alloys are usually used for..

A
  • have generally replaced type I n II for general use
  • indicated for crowns or bridge/abutments
113
Q

(T/F) type IV gold alloys are heavier than chromium-nickel alloys

114
Q

(T/F) gold alloys have less resistance to fracture than chromium-nickel alloys

115
Q

(T/F) back pressure porosity can result from low investment permeability

A

True

  • back pressure porosity occurs because air in the mold space cannot escape
  • if density of investment is too high ( too low W/P ratio) => can lead to insufficient porosity
116
Q

(T/F) back pressure porosity can result from insufficient wind-up of the casting machine

A

True
- i think the it means not enough casting pressure cuz the machine nvr spin fast enough

117
Q

(T/F) back pressure porosity can occur due to sprue being too narrow

A

True

  • metal cant flow in easily enough so the space is occupied by air
118
Q

(T/F) back pressure porosity can occur because pattern is too far from ring opening aka sprue too short

119
Q

(T/F) type IV gypsum has the lowest water/powder ratio

120
Q

(T/F) dental plaster causes a higher temperature rise during setting per unit volume than improved stone (densite)

A

True
- conversion of hemihydrates to dihydrate is exothermic
- greater conversion in plaster than in stone, so plaster setting releases more heat

121
Q

(T/F) dental plaster has higher setting expansion than improved stone (densite)

A

False
- the lower the W/P ratio, the higher the setting expansion
- stone expands more than plaster

122
Q

(T/F) in mixing of dental plaster, W/P ratio can influence setting time

123
Q

(T/F) in mixing of dental plaster, W/P ratio can influence setting expansion

124
Q

(T/F) in mixing of dental plaster, W/P ratio can influence hygroscopic expansion

125
Q

(T/F) in mixing of dental plaster, W/P ratio can influence strength

126
Q

(T/F) plaster powder differs from the powder of dental stone in that plaster is the hemihydrate of calcium sulphate and stone is the dihydrate of calcium sulphate

A

False
- unreacted powder always contains only hemihydrates
- dihydrates form when powder is mixed w water

  • in plaster, theres a greater conversion of hemihydrate to dihydrate due to higher w/p ratio
127
Q

(T/F) stone particles are smaller & more regular than plaster particles which are big and irregular

128
Q

(T/F) plaster is less porous than stone

A

False

  • plaster is more porous than stone
129
Q

(T/F) stone has greater dimensional accuracy than plaster

130
Q

(T/F) the higher dry strength and hardness of die stone (type IV) as compared to plaster (type II) is due to the addition of modifiers to die stone

131
Q

(T/F) the higher dry strength and hardness of die stone (type IV) as compared to plaster (type II) is due to the difference in chemical composition of these materialsf

132
Q

(T/F) the higher dry strength and hardness of die stone (type IV) as compared to plaster (type II) is due to lesser amt of water required by densite for its chemical reaction

133
Q

(T/F) the higher dry strength and hardness of die stone (type IV) as compared to plaster (type II) is due to lesser amt of water required for solution and wetting during mixing

134
Q

(T/F) upon setting, class I dental laboratory stone will exhibit contraction

A

False
- expansion, due to outward thrust of the growing crystals against one another

135
Q

(T/F) upon setting, class I dental laboratory stone will exhibit loss in compressive strength

A

False
- it will gain strength

136
Q

(T/F) setting expansion of gypsum investment material compensates for casting shrinkage

137
Q

(T/F) gypsum-bonded investments are not recommended for metal-ceramic alloys cuz they decompose when heated to the temperature needed for casting these alloys

A

True
- idky tho

138
Q

(T/F) accelerators decrease the setting time of plaster and retarders decrease the setting expansion

A

True
- but both accelerators and retarders generally reduce setting expansion

139
Q

(T/F) within practical limits, when the w/p ratio is increased beyond the recommended amt in mixing plaster, the setting time is increased

140
Q

(T/F) within practical limits, when the w/p ratio is increased beyond the recommended amt in mixing plaster, the setting expansion is increased

A

False
- setting expansion will decrease, cuz got more water

141
Q

(T/F) within practical limits, when the w/p ratio is increased beyond the recommended amt in mixing plaster, the compressive strength increases

A

False
- compressive strength will decrease, cuz w/p ratio increases
- so more empty space left behind when the water evaporates

142
Q

(T/F) within practical limits, when the w/p ratio is increased beyond the recommended amt in mixing plaster, surface hardness is decreased

A

True
- surface becomes easier to scratch
- hm? Another anki said surface hardness not affected by w/p ratio tho that doesnt make sense but which is true?

143
Q

compared to calcium sulphate dihydrate, the solubility of hemihydrate calcium sulphate at 20 degrees is…

A

Higher
- hemihydrate is 4x more soluble in water than dihydrate near room temp

144
Q

(T/F) vigorous mixing of gypsum will decrease setting time

145
Q

What is hygroscopic expansion?

A
  • expansion that occurs when the setting process is allowed to occur under water
  • on air, the superficial tension of water limits crystal expansion
146
Q

(T/F) hygroscopic expansion increases w a higher w/p ratio

A

False
- hygroscopic expansion decreases w a higher w/p ratio

147
Q

(T/F) increase w/p ratio leads to increase in porosity, expansion and decrease in setting time

A

False
- increased porosity
- decreased expansion
- increased setting time

148
Q

(T/F) more vigorous mixing of gypsum multiplies nuclei, leading to faster setting

149
Q

(T/F) dental stone is harder than dental plaster because the particles of stone are harder

A

False
- particles are the same
- stronger, cuz less water added during mixing, since its easier to wet stone particles which are smaller and more regular

150
Q

How does accelerator affect gypsum setting time?

A
  • increase rate of dissolution of hemihydrate => saturates solution form faster => crystallise faster

Some accelerators:
NaCl, Na2SO4, K2SO4

151
Q

The setting of gypsum is least affected by
1. Spatulation time
2. Room temp
3. W/P ratio
4. Chemical accelerators
5. Chemical retarders

152
Q

Gypsum primarily occurs in nature as

A

Di-hydrate
- then gotta dry it out into a hemihydrate

153
Q

Gypsum products shd be kept in airtight containers to prevent..

A

Airborne dust from reducing the setting time of w/p mix by providing too many nuclei of crystallization

154
Q

(T/F) wax reservoir should be larger than the sprue to alloy easy flow of molten alloy

155
Q

(T/F) 6mm of investment above position of wax pattern is to prevent investment breakage

156
Q

(T/F) wax pattern that is sprued w a diameter too large may result in casting w rounder margins

157
Q

(T/F) surface irregularities on casting can be caused by too high casting pressure

158
Q

(T/F) surface irregularities on casting can be caused by too rapid elimination of wax/too rapid heating

159
Q

(T/F) surface irregularities on casting can be caused by inadequate wetting agent

160
Q

(T/F) surface irregularities on casting can be caused by too short sprue

161
Q

(T/F) boron can be used as an antiflux

A

False
- boron is used as a flux in casting

162
Q

(T/F) graphite can be used as an antiflux

163
Q

(T/F) flux is added to alloy to increase the melting temperature and dissolve oxides that form during casting

A

False
- increases fluidity of metal (decreases melting temp)
- but yes, dissolve oxides that form during heating

164
Q

(T/F) the oxidising part of the flame has no colour and a low temperature, thus, it should be kept away from the alloy during casting

165
Q

The metal constituent that helps reduce oxide formation during the casting of (crown) alloy is..

166
Q

The major reason for pickling a casting is to..

A

Remove oxides or carbonaceous residues

167
Q

(T/F) Greatest amount of alloy shrinkage occurs when the molten alloy cools from solidus to room temp

A

False

  • when molten alloy cools to solidus
168
Q

(T/F) in type II gypsum-bonded investment, hygroscopic expansion is used for compensation of alloy casting shrinkage

169
Q

(T/F) silicone, which is used as a refractory in inlay investment material, helps to prevent the contraction of the gypsum binder when the investment is heated

A

False

  • silica, not silicone, provides a refractory during the heating of the investment
    -> provides for high temp strength and also expands when heated due to a change in crystalline form (a-form to b-form)
  • modifiers like boric acid and NaCl are responsible for preventing shrinkage of the gypsum when it is heated above 300 deg celsius
170
Q

(T/F) It is an ideal property of investment material for the microstructure to not have porosities

171
Q

(T/F) it is an ideal property for investment material to have high mechanical strength in room temp and high temp>400

172
Q

(T/F) in type II investment materials, the finer the particle size of the silica, the more the hygroscopic expansion

173
Q

(T/F) modifiers such as boric acid and sodium chloride are added to gypsum bonded investment material to prevent most of the shrinkage of gypsum when it is heated above 300 deg

A

True
- consider borax as a constituent of AE sol
- shrinkage happens due to loss of water
- boric acid and sodium chloride prevent most of the shrinkage of gypsum when it is heated above 300 deg

174
Q

(T/F) the refractory in dental investments serve to increase the setting expansion of the material

A

False
- refractory material here refers to the silica (quartz & cristoballite)
- a refractory investment material is one that is high temp resistant

175
Q

(T/F) refractory in dental investments serve to increase the thermal expansion of the material

A

True

  • silica provides refractory in investment material
    -> regulates thermal expansion
    -> we use quartz and cristobalite
  • heating of silica causes change in crystalline from at transition temp
    -> from α to β-form => decreases density => increases volume (thermal expansion)
176
Q

(T/F) gypsum-bonded investments are generally not used for casting metal-ceramic alloys because of their lower strength as compared to phosphate-bonded investments

177
Q

(T/F) in type II investment materials, the finer the particle size of the silica, the more the hygroscopic expansion

178
Q

During inversion, the expansion of cristoballite is..

A

Greater than quartz and tridymite

  • inversion refers to the conversion from α to β forms of quartz/cristoballite
  • inversion comes w expansion
179
Q

What is the inversion temp of quartz?

A

575 degrees celsius

180
Q

What is the inversion temp of cristobalite?

A

200-270 degrees celsius

181
Q

Strength of dental investment for gold alloys is dependent on the amount of..

A

Hemihydrate gypsum

  • investment for gold alloy is commonly gypsum-bonded
  • gypsum-bonded means gypsum is the binder used, thus hemihydrates gypsum determines the strength!
182
Q

(T/F) Largest hysteresis looks like the one with the most deviation from the linear graph

A

True
- think the blue line qns

183
Q

(T/F) an investment material used for casting of gold alloys cannot be used as a soldering investment because it does not possess adequate strength

A

false
- a material strong enough and able to withstand high enough temperature to cast a gold alloy is good enough for soldering

184
Q

The refractory in dental investments serve to..

A

Increase the setting expansion of the material

185
Q

(T/F) w/p ratio of investment material will not affect the hardness

186
Q

(T/F) the larger monocyclic phase of Y-TZP will arrest crack propagation but increases low temp degradation

187
Q

(T/F) passivation increases fracture strength

A

False
- only increases corrosion resistance

188
Q

(T/F) YTZP has high fracture strength

189
Q

(T/F) YTZP ceramic arrests crack propagation because of high brittleness of YTZP

190
Q

How does YTZP resist crack propagation?

A
  1. Crack propagation => tetragonal to monoclinic transformation at surface => substantial increase in volume
  2. Induce surface compressive stresses => crack tip closes => enhance resistance to further propagation
191
Q

What is low temperature degradation?

A
  • slow surface transformation of metastable tetragonal to stable monoclinic structure, in presence of water/water vapour
  1. Stress corrosion mechanism => transformation at surface
  2. Transformation of one grain => increase in volume => stress neighbouring grains
  3. Generate microcracking => enable further water penetration, crack propagation & phase destabilisation
  4. Cycle repeats as stressed neighbouring grains also transform => further increase in volume & stress
192
Q

What are 2 other properties of YTZP other than high flexural/fracture strength?

A
  • excellent corrosion & wear resistance
193
Q

What is shape memory?

A

E.g. martensite to amtensite, return to original shape when exposed to heat

194
Q

(T/F) ortho wires hysteresis is different between final & initial length

195
Q

(T/F) twinning allows permanent deformation w/o breaking of atomic bonds

196
Q

(T/F) NiTi has high fatigue life & corrosion resistance

A

True

  • nickel titanium => wrought metal alloys
  • used for orthodontic wires, crowns, clasps, root canal reamers and surgical instruments
197
Q

(T/F) NiTi work hardening decreases corrosion resistance and increases brittleness

198
Q

(T/F) austenite is converted to martensite by heating

A

False

  • austenite to martensite transition is induced by stress (superelasticity)
199
Q

(T/F) austenite is converted to martensite by force application

200
Q

(T/F) parent form is martensite

A

false
- shd be austenite

201
Q

(T/F) austenite allows permanent deformation

202
Q

(T/F) austenite form has superelasticity

203
Q

(T/F) Ti6Al4V has shape memory

A

false

  • issa implant material
204
Q

(T/F) Ti6Al4V is less brittle than ceramics

205
Q

(T/F) Ti6Al4V has high corrosion resistance

206
Q

(T/F) presence of dissolved oxygen, proteins, pH changes may cause corrosion in implants

207
Q

(T/F) YTZP has high fracture strength but limited designs

208
Q

(T/F) titanium implants fracture uncommonly but fracture due to high impact

A

False
- fracture from inappropriate implant design
- manufacturing defects
- non-passive fit of framework/physiological & biochemical overload

  • main mechanism: metal fatigue from high cyclic occlusal loading
209
Q

Work hardening of NiTi..

A

Increases hardness + decreases ductility + corrosion resistance

210
Q

(T/F) NiTi has high fatigue strength & excellent corrosion resistance

211
Q

(T/F) self etching primer is 37% phosphoric acid and primer in definite amounts

A

False
- iirc self etching primer it itself is a weak acid
- no additional phosphoric acid added to it

212
Q

(T/F) hybrid layer is the layer where exposed collagen from demineralised dentin is embedded in adhesive resin

213
Q

(T/F) water primer must be used when using the dry technique to expand the collagen network

214
Q

(T/F) mechanical agitation of collagen by the primer allows impregnation of the collagen with the amphiphilic molecules

215
Q

(T/F) alcohol primer is a versatile material that cannot be used for the dry technique

216
Q

(T/F) acid etching of dentine will remove both the smear layer and collagen from the dentine

A

False
- wont remove the collagen

217
Q

(T/F) water and acetone-based primers are applied to dry dentine to ensure adequate permeation of the collagen matrix w monomers

A

False
- acetone based primers shd be applied on wet dentine

218
Q

(T/F) impregnation of primer into porous dentine forms hybrid layer

219
Q

(T/F) etching is done to produce microporosities in enamel and to increase surface area for bonding

220
Q

(T/F) water-based primer on wet dentine promotes impregnation of collagen

A

False
- has to be dry dentine

221
Q

(T/F) primer has no effect on enamel

222
Q

(T/F) 37% phosphoric acid removes smear layer & doesnt demineralise dentine

223
Q

(T/F) bonding to enamel depends on micromechanical interlocking w unfilled resin & acid-etched enamel

224
Q

(T/F) dry technique w dentine can usewater/alcohol based primer

A

False
- dry dentine technique=> only for water based

225
Q

(T/F) bonding to dentine depends on chemical bonding (major) & micromechanical bonding (minor)

A

False
- its mostly micromechanical bonding

226
Q

(T/F) over drying of dentine causes the collapse of collagen fibres

227
Q

(T/F) tin in dental amalgam reduces strength

228
Q

(T/F) tin in dental amalgam reduces hardness

229
Q

(T/F) tin in dental amalgam increases expansion

A

False
- tin reduces expansion in amalgam

230
Q

(T/F) tin increases flow when added to amalgamt

231
Q

(T/F) dental amalgam best withstand forces of tension

A

False
- best withstand forces of compression!

232
Q

(T/F) Hg increases fracture resistance

233
Q

(T/F) amalgam reinforces tooth structure

234
Q

(T/F) Cu and Ag decrease corrosion resistance in amalgam

235
Q

(T/F) when polishing a dental amalgam restoration, heat generation shd be avoided as this will bring free mercury to the surface

236
Q

The phase in dental amalgam that is considered most noble is..

A

Gamma I and gamma

237
Q

(T/F) water contamination of dental amalgam will result in excessive expansion

238
Q

(T/F) the creep value in a high copper content amalgam is lower than that in the conventional amalgam

239
Q

delayed expansion of dental amalgam is caused by the formation of..

A

H2

  • due to moisture contamination, zinc gets corroded & H2 is produced => expansion from within
240
Q

The amount of mercury present in amalgam after condensation directly affects

A
  1. Creep
  2. Flow
  3. Compressive strength
241
Q

(T/F) amt of mercury in amalgam aft condensation affects the creep

242
Q

(T/F) amt of mercury in amalgam aft condensation affects the porosity

243
Q

(T/F) amt of mercury in amalgam aft condensation affects the flow

244
Q

(T/F) amt of mercury in amalgam aft condensation affects the surface finish

245
Q

(T/F) amt of mercury in amalgam aft condensation affects the compressive strength

246
Q

(T/F) in dental amalgam, zinc serves as an oxide scavenger as well as increases the plasticity of the amalgam

A

True

Zinc:
- decreases brittleness of alloy
- increases plasticity
- acts as oxide scavenger
- responsible for delayed expansion on moisture contamination

Y2 DM (14 decks)

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