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Fixed Pros I > Metal Ceramic and All Ceramic Preparations > Flashcards

Metal Ceramic and All Ceramic Preparations Flashcards

1
Q

describe a metal ceramic crown

A
  • porcelain fused to metal
  • crown with a metal core with porcelain baked into the metal core
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2
Q

what are the indications for PFM crowns

A
  • when opposing tooth is porcelain/ceramic
  • when a high level of esthetics is needed
  • when preparation is unusual
  • bridges and other long span fixed restorations
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3
Q

what are the advantages of PFM crowns

A
  • natural appearance due to the porcelain baked on to the metal coping
  • more resistant to fracture than all ceramic crowns
  • greater strength due to metal core than all ceramic crowns
  • design flexibility
  • adaptable to multiple types of margin designs
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4
Q

describe the design flexibility of metal ceramic preparations

A
  • can have whole crown layered with porcelain
  • can also have metal occlusal with porcelain facing on buccal only because metal occlusal adds strength
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5
Q

what types of margin design can you used for PFM

A

-chamfer
- shoulder
- and shoulder with bevel

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6
Q

why are we still using PFM

A

it can be used everywhere in the mouth

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7
Q

how does the prep need to be prepared to accomodate the requirements and benefits of PFM crowns

A
  • to accomodate metal and porcelain
  • to provide optimum strength
  • to allow for optimum esthetics
  • to decrease gingival problems associated with PFM crown design
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8
Q

what are the PFM components

A
  • metal: minimum thickness of 0.3-0.5mm
  • porcelain: opaque porcelain, body porcelain, incisal porcelain, shoulder porcelain
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9
Q

how thick is the metal coping

A
  • 0.3-0.5mm in veneered areas
  • 0.8-1.0mm in unveneered areas
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10
Q

how thick is opaque porcelain

A

0.1-0.2mm

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11
Q

how thick is shoulder porcelain

A

0.8mm

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12
Q

how thick is gingival, body and incisal porcelain

A

0.8-2mm

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13
Q

what is the maximum thickness of incisal porcelain

A

3mm

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14
Q

what reduction do you need with metal occlusion

A

1.5mm

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15
Q

what reduction do you need with porcelain occlusion

A

2.0mm

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16
Q

what is the importance of two plane reduction

A
  • allows for even thickness of material
  • could endanger the pulp without it
  • decrease the esthetics with thinner areas which do not allow proper porcelain coverage
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17
Q

what does continuing shoulder margin into and through interproximal areas before thinning to chamfer allow for

A

porcelain esthetics to be carrier into the contact regions for maximum esthetics

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18
Q

what do shoulder finish lines provide

A

greater space for an esthetic thickness of metal and porcelain without having to over contour the crown restoration

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19
Q

a proper shoulder margin with appropriate depth allows the crown margins to be contoured for:

A

optimal gingival health and esthetics

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20
Q

why is a shoulder with a rounded line angle preferred for PFM crowns

A
  • easier to prepare than a sharp 90 degree angle
  • if any part of the crown is milled, a mill cannot create a 90 degree finish line angle
  • less stress on the tooth with a rounded shoulder finish line
  • often referred to as a modified shoulder margin
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21
Q

what are the types of PFM margin designs

A
  • metal collar
  • disappearing metal
  • porcelain margin
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22
Q

describe the metal collar

A

porcelain is stopped with some metal showing at the margin
- use heavy chamfer or shoulder
- margin depth 1.2mm ideally but can accomodate smaller

23
Q

what situations would you use metal collar

A
  • ease of fabrication and precise fit if margin cannot be large enough to accomodate metal and porcelain
  • if margin is sub gingival, metal collar allows for less material and less likely an over contoured crown which would create gingival problems
24
Q

describe disappearing metal

A
  • metal is thinned to a fine line that is barely visible
  • allows for metal burnishing of margin to secure a precise fit just like metal collar
  • use heavy chamfer or modified shoulder margin
  • shoulder margin depth 1.0-1.2mm ideally, but can accomodate smaller
25
Q

when is disappearing metal used

A

when margin depth is not enough to allow for porcelain and metal at the margin

26
Q

describe porcelain margin

A
  • metal and porcelain fill shoulder finish line space. no metal is seen
  • highest esthetics
  • difficult to fabricate requiring excellent lab technician
  • use modified shoulder margin
  • shoulder margin depth 1.2mm required
27
Q

why are crown margins placed sub gingivally

A
  • esthetics
  • to cover dentin
  • when decay has extended below the gingiva
  • when retention/resistance is needed
  • previous restorations extended sub gingival
28
Q

describe sub gingival margins

A
  • placed 0.5mm below gingiva
  • margin should be smooth to ensure well adapted crown can fit without irritating gingiva
  • finish lines need to be deep enough axially to allow for adequate space for crown material
29
Q

what is biologic width

A

2.0mm

30
Q

what happens if crown margin violates biological width

A

gingival inflammation and resorption of bone will occur

31
Q

emergence profile:

A
  • crown and tooth contour which preserves the gingiva health
  • proper emergence profile creates smooth transition from tooth to crown
  • extremely difficult with implant crowns
32
Q

what are the metal ceramic problems

A
  • porcelain is a brittle substance that can fracture if not designed correctly
  • porcelain needs to be less than 3mm thick
  • if not baked correctly porcelain will be weaker and the internal stresses of chewing will likely cause fractture
  • porcelain is abrasive to natural teeth
  • often see wear on opposing dentition
  • require more reduction of tooth structure
33
Q

metal ceramic preparation design is based on:

A
  • fundamentals of tooth prep to achieve resistance and retention
  • material design with metal and porcelain and where those materials are to be placed on the restoration
  • esthetic requirements such as where the porcelain extends
34
Q

what are the advantages of all ceramic crowns

A
  • esthetics
  • can be milled
  • gingival compatability
35
Q

what are disadvantages of all ceramic crowns

A
  • reduced strength
  • substantial tooth reduction required
  • technique sensitive for prep and cementation
  • opposing tooth wear
  • greater fracture potential
  • limited use in bridges
36
Q

what are indications for all ceramic crowns

A
  • highest level of esthetics
  • light occlusal loads
  • tooth preparation is possible
37
Q

what are contra indications for all ceramic crowns

A
  • heavy occlusal loads
  • unfavorable occlusion
  • short preparation with ceramic thickness greater than 3mm
  • margin depth to accomodate ceramic not available
38
Q

how do you prepare all ceramic preps

A
  • incisal reduction: 2-2.5mm
  • facial axial reduction 1.2-1.7mm
  • lingual axial reduction 1.0-1.2mm
  • marginal reduction 1.0–1.2mm
  • modified shoulder or heavy chamfer
39
Q

what are benefits of all ceramic crowns

A
  • with no metal to obscure the translucency and overall esthetics can be the best we have in dentistry
40
Q

why are ceramics susceptible to fracture

A
  • surface flaws and stress concentrations combine to encourage fracture
  • ceramics do not have the ability to absorb the stresses on them and therefore fracture
41
Q

how is the brittleness overcome with all ceramics

A
  • manage occlusal forces
  • restoration and preparation design
  • cement with resin cement
  • reinforce the glass ceramics
42
Q

what is e max made of

A

lithium disilicate

43
Q

when is e max indicated

A

anterior/posterior single crowns
- anterior bridge
- inlay/onlay/veneer

44
Q

describe e max- lithium disilicate

A
  • strength 360-500mpa
  • 90% of the time resin cement is required
  • requires 1mm margin and minimum 1.5mm reduction with ideal around 2mm reduction
45
Q

how strong is enamel

A

300mpa

46
Q

using e max and other glass ceramics on anterior teeth:

A
  • lower occlusal forces favor the use of the ceramics
  • glass ceramics are most esthetic so anterior use is best
  • edge to edge or occlusion in the gingival 1/5 is unfavorbale for ceramics
  • must have adequate tooth support as too much ceramic thickness is easily broken
47
Q

using e max and other glass ceramics on posterior teeth

A
  • higher occlusal forces questioning the use of the ceramics
  • glass ceramics are most esthetic so posterior use is not as important
  • heavy occlusion on the molars leads to increased fracturing. all ceramic crowns are contra indicated in bruxers
  • must have adequate tooth support as too much ceramic thickness is easily broken. often not enough room on 2nd molars for ceramics
48
Q

what is used to help strengthen all ceramic crowns

A

resin cement

49
Q

how much do resin cements increase the strength of these crowns

A

50%

50
Q

what are the preparation design guidelines for all ceramic

A
  • flat plane at right angle to forces
  • modified shoulder or heavy chamfer
  • no sharp line angles
  • adequate length of preparation for support
  • uniform axial reduction with ideal taper
  • round or flatten incisal edge to reduce fracture
  • more than 3mm of porcelain left incisally will result in higher risk of fracture
  • short preps leave too much ceramic and cannot be retained with anterior occlusal forces
51
Q

excessive porcelain bulk:

A

decreases strength

52
Q

what material should be used with a short prep

A

PFM or PFZ

53
Q

what is the most esthetic restoration to date

A

all ceramic

54
Q

describe PFZ

A
  • allows for the full strength zirconia to be used with esthetic porcelain on the facial or covering the whole zirconia core
  • white core eliminates many of esthetic problems we can have with PFMs

Fixed Pros I (13 decks)

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