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Fixed Pros II > Lecture 4- Metal Ceramics > Flashcards

Lecture 4- Metal Ceramics Flashcards

1
Q

what does a PFM crown consist of

A

a metal casting or coping which fits over the prepared tooth and has ceramic fused to the metal

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2
Q

how thick does the metal coping need to be with noble metal

A

0.3-0.5mm thick

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3
Q

how thick does the metal coping need to be with base metal

A

0.2mm

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4
Q

how thick does the metal coping need to be where porcelain is not overlayed

A

0.8-1.0mm thick

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5
Q

how thick is the opaquing porcelain

A

0.2-0.3mm thick

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6
Q

what is the order of body porcelain laid down in

A

dentin -> enamel -> translucent -> modifiers

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7
Q

how thick is the body porcelain

A

0.8-2mm thick

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8
Q

what is the goal of the high fusing shoulder porcelain

A

decrease shrinkage that happens when you fire

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9
Q

what is the metal coping designed to support

A
  • with thickness to support the porcelain
  • to support occlusal and proximal contacts
  • with extensions to support porcelain
  • margin design to adapt perfectly to margins and support the porcelain if porcelain margins are placed
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10
Q

describe the design of the coping

A
  • convex, rounded angles
  • ledge of metal to support a 90 degree metal-ceramic finish
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11
Q

what happens if there is less than a 90 degree angle between the metal and porcelain

A

cracking, fracture

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12
Q

assuming metal coping is at least 0.3-0.5mm thick, the metal coping should provide:

A
  • an even porcelain thickness needed to provide optimum strength
  • from 0.5-2mm of porcelain thickness
  • provide support in stress bearing areas like cusp tips, incisal edges, marginal ridges
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13
Q

describe the thickness that is desired with porcelain

A

a thin uniform thickness

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14
Q

if porcelain is more than 2mm thick, what becomes a high risk

A

fracture

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15
Q

what is the ideal thickness of porcelain

A

1-1.5mm

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16
Q

where do we need adequate thickness for rigidity to prevent porcelain fracture while trying to optimize esthetics

A

in the pontic and connectors

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17
Q

how is a PFM made

A
  • start with wax up
  • design metal coping
  • metal is cast at 2300-2600 degrees or milled
  • porcelain is then stacked onto coping in layers
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18
Q

what does the opaque porcelain layer do

A
  • masks the metal
  • forms the oxide bond with oxide layer of metal coping
  • silica oxide from ceramic to oxide layer of metal
  • van der waal forces exist here
  • acts as the base for the eventual shade of the crown
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19
Q

what colors are included in the body porcelain

A
  • dentin
  • enamel
  • translucent
  • shoulder porcelains
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20
Q

what are stains and glazes used for

A

final color match

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21
Q

when do you do color modification

A

once crown is complete

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22
Q

stains and glazes have a ____ fusing temperature than body porcelains

A

lower

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23
Q

what are the types of metal substructure

A
  • Au-PT-Pd (gold- platinum - palladium)
  • Pd-Ag (gold- palladium- silver)
  • Ni-Cr- Be (nickel- chromium - beryllium)
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24
Q

what are the classes of the metal substructure

A
  • high noble
  • noble
  • base metal
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25
Q

what are the desirable characteristics of metal ceramic alloys

A
  • biocompatibility
  • accuracy of fit
  • high modulus of elasticity and high yield strength
  • high resistance to deformation
  • easily soldered
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26
Q

what are high noble metals made of

A

noble metal content greater than or equal to 60% with at least 40% of content being gold

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27
Q

describe the gold- platinum - palladium formulation

A
  • this formulation is up to as much as 88% gold
  • this much gold makes this formulation softer and susceptible to sag
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28
Q

describe the gold- palladium-silver formulation

A

the silver used to discolor some porcelain in a process called greening
that problem is mostly gone and overcome with new formulations

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29
Q

describe the gold- palladium formulations

A
  • gold 44%-55%
  • palladium 35-45%
  • resistant to sag with excellent working properties
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30
Q

what formulation of high noble metals do we use at UMKC

A

gold-palladium

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31
Q

what is sag

A

resistance to deformation at high temperatures with good yield strength and a high modulus of elasticity

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32
Q

what are noble metals made of

A

at least 25% of noble metals but doesnt have to be gold

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33
Q

what are the formulations for noble metals

A
  • palladium- silver
  • palladium- copper
  • palladium- cobalt
  • palladium-gallium
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34
Q

noble metals are a compromise between the high noble metals and the base metals in terms of:

A

cost and in density

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35
Q

what factors of noble metals are similar to high noble metals

A

workability and fabrication

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36
Q

because of less gold, noble metals tend to have a:

A

higher strength and greater resistance to deformation

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37
Q

what are the formulations of base metal

A
  • nickel- chromium
  • nickel- chromium- beryllium
  • cobalt-chromium
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38
Q

describe base metals

A
  • stiffer metal
  • harder metal
  • greater sag resistance
  • lowest density
  • lowest cost and lowest quality
  • higher likelihood of reaction if pt has metal allergy
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39
Q

what is the down side to lowest density in base metal

A

more difficult to cast and therefore more difficult to finish in preparation for the porcelain and not able to create strong solder joints
- can also lead to high oxide formation and thus problems with bonding

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40
Q

because of the nickel and beryllium in the base metals what two possible issues arise:

A
  • allergic reaction
  • toxicity to the lab tech
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41
Q

PFM crowns are layered with what type of porcelain

A

feldspathic

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42
Q

describe feldspathic porcelain

A

relatively weak material
- wears opposing teeth at a very high rate

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43
Q

what are the properties of ceramic

A
  • excellent esthetic properties
  • biocompatible
  • excellent insulator and protection against heat and electricity
  • shrinks as it is fired
  • brittle
44
Q

what are the results of ceramic being brittle

A
  • crack propagation
  • porosities in the porcelain act as crack initiators
  • there is a stress dependent reaction between water vapor and crack tips in porcelain that cause growth and further fracture even with comparatively low occlusal loading over long periods
45
Q

in ceramics the compressive strength is _____ than the tensile strength

A

better

46
Q

what are the types of ceramics

A
  • predominately glass
  • particle filled glass ceramic
  • polycrystalline ceramicd
47
Q

describe the predominately glass form of ceramics

A
  • etchable
    -optical properties include most translucent
  • weakest strength
  • most esthetic
  • feldspathic porcelain
48
Q

describe the particle filled glass ceramic

A
  • etchable
  • increased strength
  • less translucent than feldspathic
  • lithium disilicate
49
Q

describe the polycrystalline ceramic

A
  • not etchable
  • highest strength possibilities
  • lowest translucency
  • zirconia
50
Q

what are the components to feldspathic porcelain

A
  • feldspar - 75-85%
  • quartz
  • alumina
  • glass modifiers
  • leucite - 10-20%
51
Q

what does feldspar do

A

responsible for forming the glass matrix

52
Q

what does quartz do

A

framework around which other components flow

53
Q

what does alumina do

A
  • hard strong oxide which increases strength
  • increases the viscosity of the melt when firing
54
Q

what do glass modifiers do

A
  • alkali fluxes ( mostly potassium and sodium oxides)
  • increases the coefficient of thermal expansion
  • includes opacifiers and colorants
55
Q

what does leucite do

A

key ingredient to increase coefficient of thermal expansion to bring ceramic closer to the coefficient of thermal expansion in the metal

56
Q

where does the strength of the PFM come from

A
  • the bond between the ceramic and the. metal substructure
  • the compatability of the metal and the porcelain
  • design and rigidity of the metal coping or framework
57
Q

the metal- porcelain bond is accomplished with:

A
  • mechanical interlocking of materials
  • vander waals forces
  • chemical bonding
  • compressive forces
58
Q

describe the mechanical interlocking in the metal- porcelain bond

A
  • microabrasions from metal finishing or from air abrasion create a surface that allows for the interlocking of porcelain and metal
  • these microabrasions also clean the surface
  • these microabrasions also increase the surface area of the metal
  • the microabrasions increase the wettability of the metal meaning the porcelain will flow over the metal material better and therefore flow into the abraded surface
59
Q

describe the mechanism of the metal-porcelain bond

A
  • an oxide layer is formed as the metal coping is fired in the heating treatment
  • traces of gallium, tin, indium and iron move to the surface
  • base metal alloys readily oxidize
  • gases are released from the metal
  • this oxidation stage after firing is critical and requires no contamination
  • the oxide layer of the metal bonds to similar oxides in the opaque layer of the porcelain
60
Q

when done correctly this oxide bond is so strong that the _____ will break before the bond gives away

A

porcelain

61
Q

after the opaque layer is placed what layers are placed next

A

shoulder porcelain -> body dentin porcelain -> enamel porcelain

62
Q

why is the coefficient of thermal expansion matched with dental porcelain

A

to reduce ceramic fracture in response to heating and cooling

63
Q

is porcelain CTE higher or metal

A

porcelain

64
Q

is the melting temperature of metal higher or lower than the fusing range of the veneering porcelain and what temp is it

A

higher at 1600-1900 degrees

65
Q

the melting temperature of metal must be high enough so as to __________. usually needs a difference of at least ______ degrees F.

A

-NOT sag or melt when porcelain is applied
- 300

66
Q

higher amount of gold in the allow the _____ the melting temperature

A

lower

67
Q

what does adding platinum and palladium do to the melting temperature

A

raises it

68
Q

what does adding base metals do to the alloy melting temperature

A

raises it

69
Q

because some porcelains fuse at a higher temperature than the melting temperature of the metal, what type of ceramic is used

A

low fusing

70
Q

metal flexure can cause porcleain to:

A

fracture

71
Q

where should occlusion be in anteriors

A
  • not on the finish line
  • preferable to be at least 1.5mm away
72
Q

why should you not use lingual porcelain on a maxillary anterior

A
  • will cause wear on opposing teeth
  • contraindicated in deep vertical overlap
  • lingual metal collar to support porcelain
  • more tooth reduction would be required
73
Q

what are the advantages of a metal lingual on maxillary anterior

A
  • easier to form anatomy
  • easily polished
  • less wear on opposing teeth
  • less tooth reduction is requried
74
Q

should there be metal or porcelain on contacts and why

A

porcelain for esthetics

75
Q

if there is no contact can the lab tech add on porcelain

A

yes

76
Q

what are the possible occlusal surface designs on posterior teeth

A
  • full porcelain
  • full metal
  • combination
77
Q

when would you do a metal occlusal surface on a posterior tooth

A

if the oppposing tooth is either:
- enamel
- gold
- resin

78
Q

when would you do a porcelain occlusal on a posterior tooth

A

if the opposing tooth is porcelain

79
Q

a metal finish line on posterior teeth is best placed at ______ away from occlusal contacts

A

1.5mm

80
Q

for mandibular posteriors what occlusal design is recommended

A

full porcelain or full metal

81
Q

second molars almost always get _____ occlusal design

A

full metal

82
Q

what is the necessary reduction is porcelain is on the occlusal

A

2mm

83
Q

ideal to have ____ metal collar on the lingual of maxillary teeth to support occlusal forces

A

3mm

84
Q

why is it ideal to make occlusal metal on maxillary posterior teeth

A
  • prevent fracture
  • less reduction on an already short tooth
85
Q

describe the design on mandibular posterior teeth

A
  • full coverage porcelain often used for esthetics
  • 2.0mm reduction
  • metal support under lingual cusps and marginal ridges of 3mm
86
Q

how do you decide on your porcelain design

A
  • patients concern for esthetics
  • clinical crown height
  • opposing occlusal surfaces
  • bruxism
  • possibly add a night guard at the end of tx
87
Q

what is the ideal margin type and why

A

porcelain shoulder because strength

88
Q

when would you use the metal collar

A

only used when you can only have a small margin

89
Q

what is the disadvantage of disappearing metal

A

can chip and break because of occlusion and flexing

90
Q

where is the best placement of porcelain shoulder margins

A

slight subG

91
Q

what are the special considerations when using shoulder porcelain

A
  • uses high fusing aluminous porcelain
  • need a good ceramist
  • need 2 additional firings at a higher temperature
  • 90 degree angle for strength and sealed finish line
92
Q

describe the metal collar margin

A
  • design is a more conservative tooth preparation in cervical area
  • restoration design is easier for the lab to fabricate
  • great for molars that have margins deep subG
  • allows for multiple types of preparation finish lines
93
Q

when is the disappearing margin indicated

A

for areas that the margin cannot be hidden under gingiva

94
Q

what is the common design flaw in disappearing margins

A

metal copings are over contoured and thick at gingival area

95
Q

what is bond failure due to

A

trauma or heavy occlusion

96
Q

what is adhesive fracture and what causes it

A
  • the de-lamination of the porcelain from the metal
  • due to a failure of the manufacture process where there occurs an incorrect oxidation process or contamination of oxide surface
97
Q

what happens if the cooling rate after firing is too rapid

A

the porcelain will compress too rapidly and fracture

98
Q

when will fracture occur in an issue with firing

A
  • if the porcelain is too thick or thin
  • if the metal has deformed during the firing process
99
Q

where would be poor placements of metal ceramic finish line

A
  • lingual for mandibular finish line too close to centric occlusion points or incisal edge
  • too close to incisal edge
100
Q

how is porcelain repairs in fractured PFMs

A
  • can be repaired with composite or amalgam
  • if porcelain is intact it is bonded back together
101
Q

are porcelain repairs strong

A

no

102
Q

what is the #1 reason for PFM fracture and #2

A
  • # 1: poor design
  • # 2: occlusion
103
Q

how can you be successful with PFM crowns

A
  • strength comes from bond between metal and ceramic
  • the type of porcelain and metal enhance or detract from the bond
  • design of the metal coping for proper support of the more fragile porcelain
  • a preparation design that allows for good resistance and retention
  • know what kind of margin you desire
104
Q

what porcelain is used in PFZ crowns

A

3Y on the lingual and feldspathic on the buccal

105
Q
A

Fixed Pros II (13 decks)

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