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Fixed Prosthodontics II > Quiz 2 > Flashcards

Quiz 2 Flashcards

1
Q

what is the consistency of type 1 inlay wax?

A

medium to hard

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2
Q

what is type 1 inlay wax used for?

A

generally used with the direct technique for making patterns in the oral cavity

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3
Q

what temperature is type 1 inlay wax solid at?

A

37 degrees celcius

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4
Q

between type 1 and type 2 inlay wax, which shrinks more?

A

type 1 shrinks more than type 2

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5
Q

what is the consistency of type 2 inlay wax?

A

softer than type 1

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6
Q

what is type 2 inlay wax used for?

A

more commonly used in the indirect technique

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7
Q

what temperature is type 2 inlay wax solid at?

A

25 degrees celcius

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8
Q

what is “suck-back”? how can a reservoir help avoid suck-back?

A
  • can happen during casting of gold crowns
  • cools last at the greatest bulk of molten area (at the sprue) and sucks away from the thinner areas (metal that has filled the mold)
  • reservoir - molten alloy stays molten longer so that suck-back occurs at the bottom instead of the crown
    • compensation for shrinkage that occurs during the solidification of the casting alloy
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9
Q

why are refractory materials added to investments?

A

it is a material that doesn’t burn, so when the investments are put in the oven, the refractory materials will prevent the investment from burning up

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10
Q

what is the refractory material that is used in investments?

A
  • SiO2
  • also silica, quartz, and cristobalite
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11
Q

what is the absolute minimum chamfer width?

A

0.5mm (used with gold)

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12
Q

why do we want to avoid a smaller chamfer width than 0.5mm?

A
  • any smaller can cause problems with:
    • difficult casting
    • reading the margin
    • too thin
    • labs are forced to overcontour to compensate
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13
Q

what are the problems with under-reducing occlusally on a gold crown preparation?

A

it can cause thin spots in the crown and make it more difficult for the lab

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14
Q

what are the problems with over-reducing occlusally on a gold crown preparation?

A

it will interfere with retention and resistance

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15
Q

during casting, which of the following expands, and which contracts?

wax pattern, stone, investment, cooling alloy

A
  • contracts - wax pattern and cooling alloy
  • expands - stone and investment
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16
Q

do you want your casting to be slight oversized or undersized?

A

oversized - it is advantageous for accurate seating

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17
Q

what are factors that influence resistance?

A
  • magnitude and direction of dislodging forces
  • geometry of the tooth preparation
  • physical properties of the luting agent
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18
Q

what components of tooth preparation geometry can increase resistance?

A
  • decreased preparation diameter
  • decreased axial wall taper
  • increased crown height
  • proximarl grooves and boxes
  • definite line and point angles (not rounded)
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19
Q

what are 4 factors that influence retention?

A
  • magnitude of dislodging forces
  • geometry of the tooth preparation
  • roughness of the intaglio surface of the fixed restoration
  • material being cemented or bonded
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20
Q

what components of tooth preparation geometry can increase retention?

A
  • increased axial surface area
  • increased preparation height
  • decreased taper of axial walls
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21
Q

T or F:

retentive features must be anchored in enamel

A

false

they must be anchored in dentin

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22
Q

what are some geometrical features that increase resistance and retention?

A

grooves, box forms, isthmus

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23
Q

2nd molars tend to have short clinical crowns. how can you increase resistance and retention?

A
  • build the resistance and retention form into the preparation
  • if the prep is less than 4mm in height, consider other features to augment the retention
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24
Q

what two techniques can you utilize when using a die to make a crown?

A

scanning and lost wax technique

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25
Q

know the process of how to set up a die, and the order of application of materials when doing a wax-up

A

prep tooth → PVS impression → pour up stone model in articulator (don’t forget silicone separator) → cut die → mark the margin with a red pencil → you can either scan at this point, or if you are doing a wax up, place 2 coats of die sealer → 2 coats of die spacer/relief (1st coat farther from the margin than 2nd coat) → die lube → dip in hot wax → add inlay wax and prepare wax-up → remove wax-up from die → add sprue → investment → put investment in oven for 45 minutes → cast

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26
Q

what is the most effective place on an instrument to apply heat?

A

shank

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27
Q

at what point is the flame the hottest?

A

top of the meniscus

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28
Q

what is a sufficient amount of Au alloy for casting a posterior gold crown?

A

2 pennyweights and a button

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29
Q

is dipping wax softer or harder than inlay wax?

A

softer

this can be problematic because the wax can more easily be pulled or stretched away from the margins while carving

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30
Q

why is it important to insert the die into the dipping wax at a 45 degree angle and then to rotate it vertically and remove?

A

you will avoid entrapment of air within the central fossa of the preparation

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31
Q

wax flows __(to/away from)__ heat, and __(shrinks/expands)__ as it cools

A
  • away from
  • shrinks
32
Q

overheated or burnt wax leaves a ___ residue

A

carbon

33
Q

why should you broaden, smooth, and shape the proximal contact of the tooth adjacent to your die before doing your waxup?

A

helps ensure that you will have sufficient material for an appropriate proximal contact

34
Q

when working on your waxup, why should you not carve away all of the dipping wax that extends apical to the margins?

A

it helps keep the wax on the die

when you are ready to remove the wax pattern from the die, it is helpful to remove the wax that extends beyond the margin

35
Q

T or F:

proximal contacts should be broad in all directions

A

true

36
Q

what are appropriate places to have occlusal contacts on posterior teeth?

A
  • marginal ridges
  • cusp TIP to flat receiving area (like a marginal ridge or flat fossa)
  • no contacts on inclines
37
Q

if you cannot finish your wax-up in one sitting, you will need to remelt your margins prior to investing. why?

A

because wax shrinks

38
Q

what material can be helpful in removing the wax pattern from the die? what is the proper technique for removing the wax pattern from the die?

A
  • rubber dam material
  • as you gently squeeze your finger pads, thumb toward forefinger, your hands will push in opposite directions, pulling the wax pattern off the die
39
Q

how many occlusal contacts per posterior tooth should you have?

A

2-4

40
Q

the sprue allows ___ to escape from the mold, and allows ___ to flow into the mold

A
  • molten and volatile wax
  • molten metal
41
Q

what type of sprue material allows for better escape of the wax during burnout?

A

hollow plastic

42
Q

what is the sprue size for molars? what about for premolars and partial coverage castings?

A
  • molars - 10 gauge (2.5mm diameter)
  • premolars and partial coverage castings - 12 gauge (2.0mm diameter)
  • in general, larger is better (better reservoir)
43
Q

where should sprues be attached to the wax pattern and what are two important concepts related to sprue placement?

A
  • at the bulkiest, non-critical part of the pattern (usually the largest cusp tip)
  • visualize “flow of molten metal” into the pattern
  • creates the path of least resistance and turbulence
44
Q

the ___ is usually made of rubber for easy separation from the investment and casting ring, attaches to the other end of the sprue, and creates the funnel shape through which the molten metal flows

A

crucible former

45
Q

the ___ surrounds the wax pattern and confines the investment material to create the mold

A

casting ring

  • fits into the rubber crucible former
  • ring liner allows for investment expansion
46
Q

when investing, how far should the top of the wax pattner be from the top of the plastic clear ring? how much of the top of the investment will you trim off after it is set?

A
  • 6mm from the top of the clear plastic ring
  • top 2-4mm of the investment will be trimmed
47
Q

what are 3 types of investment?

A
  • gypsum bonded
  • phosphate bonded
  • ethyl-silica bonded
48
Q

which type of investment material is softer, making it easier to retrieve castings, and is also more porous, which facilitates mroe complete mold filling?

A

gypsum bonded

49
Q

which type of investment material produces the best surface reproduction, resulting in smoother castings, and is also (probably) the easiest to work with?

A

gypsum bonded

50
Q

what are 6 factors that increase expansion in gypsum bonded investments?

A
  • decreased water/powder ratio
  • prolonged spatulation
  • water bath set - 100*F for 1 hour immediately after setting
    • “hygroscopic expansion”
  • dry ring liner
  • two ring liners
  • ringless investment technique
51
Q

what are two factors that reduce expansion with gypsum bonded investments?

A
  • add water to the mix
  • eliminate the casting ring liner
52
Q

which type of investment material is suitable for metal-ceramic alloys which typically fuse around 2550*F?

A

phosphate bonded

53
Q

which investment material has more silical refractory material which creates more expansion in the burnout oven (this compensate for additional shrinkage of metal as it cools from a higher casting temperature)?

A

phosphoate bonded

54
Q

what investment material is used for high-melting base metal alloys and partial denture frameworks?

A

ethyl-silica bonded

55
Q

___ is when the casting is placed in water when the button no longer has a red glow?

A

quenching

56
Q

quenching interferes with the crystalline lattice of the alloy, which results in ___

A

a softer, more malleable alloy

57
Q

which type of casting alloy is soft and used for simple inlays?

A

type I

58
Q

which type of casting alloy is medium in hardness and is used for complex inlays, onlays, and single unit crowns?

A

type II

59
Q

which type of casting alloy is hard and is used for crowns and fixed dental prostheses?

A

type III

60
Q

which type of casting alloy is extra hard and is used for partial denture frameworks?

A

type IV

61
Q

___ is the melting point of the alloy

A

fusing temperature

62
Q

is 9 or 20 karat gold more yellow?

A
  • 9 karat (37.5% Au) is more yellow (jewelry gold)
  • 20 karat (85% Au) is not very yellow (dental gold)
  • in general: more gold, less tarnish and more biocompatible
  • avoid Ni (allergies)
63
Q

what are the best locations for sprue placement for a maxillary premolar? maxillary molar? mandibular premolar? mandibular molar?

A

usually on the functional cusps

  • maxillary premolar - L cusp
  • maxillary molar - ML cusp
  • mandibular premolar - B cusp
  • mandibular molar - MB cusp
64
Q

when placing a sprue, you should try not to involve the ___ area

A

proximal contact area

65
Q

T or F:

you can use the sprue as a handle when pulling the wax pattern off the die

A

false

the sprue only becomes the handle once the pattern is safely off the die

66
Q

what is the main reasoning for making all wax connections fluid when adding the sprue to the wax pattern as well as the curcible former?

A

to reduce turbulence

67
Q

what is the purpose of trimming the top of the investment?

A

it allows the escape of hot gasses from the mold, ahead of the incoming molten metal

68
Q

do gypsum bonded or phosphate bonded investments produce a rougher surface on the casting?

A

phosphate bonded investments

69
Q

what is the order of surfaces you should finish your casting?

A

zones 1-7

  1. internal margin
  2. intaglio surface
  3. sprue area
  4. proximal contacts
  5. occlusal surface
  6. axial walls
  7. external margin
70
Q

what is the most critical area of the entire casting?

A

zone 1 - internal margin

71
Q

you should not try your casting onto the die until the entire ___ area is free of irregular areas

A

intaglio surface (zone 2)

72
Q

what is the width that the uniform space between the casting and the die should be?

A

25-35um

73
Q

the marginal area of the casting should create a tight seal at the die margin, with a gap of what width?

A

10um or less

74
Q

when finishing a gold cast, what is the issue with progressing too rapidly to a finer grade abrasive?

A

wastes time

75
Q

why is it important to create a highly polished axial wall surface of a gold casting?

A

it enables the patient to carry out optimum plaque control (under-finishing/polishing results in rough surfaces that harbor plaque)

76
Q

what are two benefits of crown-master pliers being non-metallic?

A
  • will not scratch polished surface of the crown
  • will not conduct frictionally induced heat
77
Q

when polishing a gold cast, which direction should the poliching brush be rotating?

A

in an apical direction

Fixed Prosthodontics II (4 decks)

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