Metal Ceramic and All Ceramic Preparations Flashcards
describe a metal ceramic crown
- porcelain fused to metal
- crown with a metal core with porcelain baked into the metal core
what are the indications for PFM crowns
- 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
what are the advantages of PFM crowns
- 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
describe the design flexibility of metal ceramic preparations
- can have whole crown layered with porcelain
- can also have metal occlusal with porcelain facing on buccal only because metal occlusal adds strength
what types of margin design can you used for PFM
-chamfer
- shoulder
- and shoulder with bevel
why are we still using PFM
it can be used everywhere in the mouth
how does the prep need to be prepared to accomodate the requirements and benefits of PFM crowns
- to accomodate metal and porcelain
- to provide optimum strength
- to allow for optimum esthetics
- to decrease gingival problems associated with PFM crown design
what are the PFM components
- metal: minimum thickness of 0.3-0.5mm
- porcelain: opaque porcelain, body porcelain, incisal porcelain, shoulder porcelain
how thick is the metal coping
- 0.3-0.5mm in veneered areas
- 0.8-1.0mm in unveneered areas
how thick is opaque porcelain
0.1-0.2mm
how thick is shoulder porcelain
0.8mm
how thick is gingival, body and incisal porcelain
0.8-2mm
what is the maximum thickness of incisal porcelain
3mm
what reduction do you need with metal occlusion
1.5mm
what reduction do you need with porcelain occlusion
2.0mm
what is the importance of two plane reduction
- 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
what does continuing shoulder margin into and through interproximal areas before thinning to chamfer allow for
porcelain esthetics to be carrier into the contact regions for maximum esthetics
what do shoulder finish lines provide
greater space for an esthetic thickness of metal and porcelain without having to over contour the crown restoration
a proper shoulder margin with appropriate depth allows the crown margins to be contoured for:
optimal gingival health and esthetics
why is a shoulder with a rounded line angle preferred for PFM crowns
- 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
what are the types of PFM margin designs
- metal collar
- disappearing metal
- porcelain margin
describe the metal collar
porcelain is stopped with some metal showing at the margin
- use heavy chamfer or shoulder
- margin depth 1.2mm ideally but can accomodate smaller
what situations would you use metal collar
- 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
describe disappearing metal
- 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
when is disappearing metal used
when margin depth is not enough to allow for porcelain and metal at the margin
describe porcelain margin
- 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
why are crown margins placed sub gingivally
- esthetics
- to cover dentin
- when decay has extended below the gingiva
- when retention/resistance is needed
- previous restorations extended sub gingival
describe sub gingival margins
- 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
what is biologic width
2.0mm
what happens if crown margin violates biological width
gingival inflammation and resorption of bone will occur
emergence profile:
- crown and tooth contour which preserves the gingiva health
- proper emergence profile creates smooth transition from tooth to crown
- extremely difficult with implant crowns
what are the metal ceramic problems
- 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
metal ceramic preparation design is based on:
- 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
what are the advantages of all ceramic crowns
- esthetics
- can be milled
- gingival compatability
what are disadvantages of all ceramic crowns
- reduced strength
- substantial tooth reduction required
- technique sensitive for prep and cementation
- opposing tooth wear
- greater fracture potential
- limited use in bridges
what are indications for all ceramic crowns
- highest level of esthetics
- light occlusal loads
- tooth preparation is possible
what are contra indications for all ceramic crowns
- heavy occlusal loads
- unfavorable occlusion
- short preparation with ceramic thickness greater than 3mm
- margin depth to accomodate ceramic not available
how do you prepare all ceramic preps
- 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
what are benefits of all ceramic crowns
- with no metal to obscure the translucency and overall esthetics can be the best we have in dentistry
why are ceramics susceptible to fracture
- surface flaws and stress concentrations combine to encourage fracture
- ceramics do not have the ability to absorb the stresses on them and therefore fracture
how is the brittleness overcome with all ceramics
- manage occlusal forces
- restoration and preparation design
- cement with resin cement
- reinforce the glass ceramics
what is e max made of
lithium disilicate
when is e max indicated
anterior/posterior single crowns
- anterior bridge
- inlay/onlay/veneer
describe e max- lithium disilicate
- strength 360-500mpa
- 90% of the time resin cement is required
- requires 1mm margin and minimum 1.5mm reduction with ideal around 2mm reduction
how strong is enamel
300mpa
using e max and other glass ceramics on anterior teeth:
- 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
using e max and other glass ceramics on posterior teeth
- 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
what is used to help strengthen all ceramic crowns
resin cement
how much do resin cements increase the strength of these crowns
50%
what are the preparation design guidelines for all ceramic
- 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
excessive porcelain bulk:
decreases strength
what material should be used with a short prep
PFM or PFZ
what is the most esthetic restoration to date
all ceramic
describe PFZ
- 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
