lecture 5- all ceramic and metal ceramic crown Flashcards
crown that has a metal core with porcelain baked onto metal core
-takes strength of metal and combines tooth matching esthetic ability of porcelain
metal-crown
aka PFM (porcelain fused to metal crown)
indications for PFM crown
- when opposing tooth is porcelain/ceramic
- when high level of esthetics is needed
- when prep is unusual
- bridges and other long span fixed restorations
adv of PFM crown
- natural appearance due to porcelain baled on metal coping
- more resistant to fracture than all-ceramic crowns
- greater strength bc of metal core
- design flexibility
- adaptable to multiple types of margin designs
design flexibility of of PFM
-can have whole crown layered with porcelain
-can also have metal occlusal with porcelain facing on buccal only.
metal occlusal adds strength!
what margin designs can PFM do
- chamfer
- shoulder
- shoulder with bevel (not commonly used)
to accommodate the requirements and benefits of using a PFM crown, the preparations need to be designed in particular ways. so criteria is:
- to accommodate metal and porcelain
- provide optimum strength
- allow for optimum esthetics
- to decrease gingival problems associated with PFM crown design
PFM components
porcelain:
metal minimal thickness:
opaque porcelain
body porcelain
incisal porcelain
shoulder porcelain
metal: minimal thickness of 0.3-0.5mm
porcelain thickness to maximize:
esthetics
metal coping
in veneered areas=
in unveneered areas=
in veneered areas=0.3-0.5mm
in unveneered areas=0.8-1.0mm
opaque porcelain:
0.1-0.2mm
shoulder porcelain:
0.8mm
gingival, body, and incisal porcelain:
0.8-2mm
metal-ceramic preparation
metal occlusion:
porcelain occlusion:
metal: 1.5mm occlusal reduction
procelain: 2mm occlusal reduction
metal ceramic prep importance of two plane reduction:
what happens without two planes?
allows for even thickness of material
without two planes: can endanger pulp
can also decrease esthetics with thinner areas which do not allow proper porcelain coverage
continuing shoulder margin into and through interproximal areas before thinning to chamfer, allows for
porcelain esthetics to be carried into the contact regions for max esthetics
this provides greater space for an esthetic thickness of metal and porcelain without having to over-contour the crown restoration
shoulder finish lines
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 crown is milled(metal coping), a mill cannot create a 90 degree finish line
- less stress on tooth with rounded shoulder finish line (especially for RCT treated tooth or small teeth/teeth under heavy occlusal load)
- often referred to as a modified shoulder margin
3 types of PFM crown margin designs
- metal collar
- disappearing metal
- porcelain margin
porcelain is stopped with some metal showing at the margin
metal collar
why use metal collar?
- ease of fabrication and precise fit if margin cannot be large enough to accommodate metal and porcelain
- also if margin is deep subgingival, this allows for less material and less likey an over-contoured crown (which would create gingival problems)
- use heavy chamfer or shoulder
- margin depth 1.2mm ideally, but can accommodate smaller
metal is thinned to a fine line that is barely visible
disappearing metal
why use disappearing metal
- metal is thinned to fine line that is barely visible
- allows for metal burnishing of margin to secure precise fit (like metal collar)
- when margin depth is not enough to allow for porcelain and metal both at margin
- use heavy chamfer or modified shoulder margin
- shoulder margin depth 1-1.2mm ideally, but can accommodate smaller
why use porcelain margin?
- highest esthetics
- difficult to fabricate requiring excellent lab
- use modified shoulder margin
- shoulder margin depth 1.2 required
metal and porcelain fill should finish line space. no metal is seen
porcelain margin
new PFM’s placed with margins slightly ____and with porcelain margin design
subgingival
why are crown margins placed subgingivally?
- esthetics
- cover dentin
- when decay has extended below gingiva
- when retention/resistance is needed
- previous restorations extended sub-gingival
sub-gingival margins:
- placed 0.5mm below gingiva
- margin 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
if your crown margin violates this, gingival inflammation and resorption of bone will occur
biological width
emergence profile for metal-ceramic prep
- crown and tooth contour which preserve the gingiva health
- proper emergence profile creates smooth transition from tooth to crown
- extremely difficult with implant crowns. one of the biggest challenges we face today with implants
metal ceramic problems
- porcelain is a brittle substance that if not designed correctly can fracture
- porcelain needs to be less than 3m thick
- if not baked correctly, porcelain will be weaker and the internal stresses of chewing etc, will likely cause fracture
this is abrasive to natural dentition, so often we see significant wear on opposing dentition
porcelain
what are required to do more reduction of tooth structure than all metal crowns but have greater esthetics than all metal crowns
PFM
prep design for metal-ceramic 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
advantages of all ceramic crowns
- ESTHETICS- most realistic restorations we have
- can be milled
- gingival compatibility
disadvantages of all ceramic crown
- reduced strength
- substantial tooth reduction required
- technique sensitive for prep and cementation
- opposing tooth wear
- greater fracture potential
- limited use in bridges
indications for all ceramic crowns
- highest level of esthetics
- light occlusal loads
- tooth prep is possible (enough tooth remains)
contra-indications for all ceramic crowns
- heavy occlusal loads
- unfavorable occlusion(end to end)(bruxer)
- short prep with ceramic thickness greater than 3mm
- margin depth to accommodate ceramic not available
all ceramic preparation
incisal reduction:
facial axial reduction:
lingual axial reduction:
marginal reduction:
incisal reduction: 2-2.5mm
facial axial reduction: 1.2-1.7mm
lingual axial reduction: 1-1.2mm
marginal reduction:1-1.2mm
what chamfer is required for all ceramic prep
modified shoulder or heavy chamfer
benefits of all ceramic crowns
- with no metal to obscure, the translucency and overall esthetics can be the best we have in dentistry
what are susceptible to fracture
ceramics
these combine to encourage fracture in all ceramic prep
surface flaws and stress concentrations
-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
e.max- lithium disilicate inductions
anterior/posterior single crown
anterior bridge
inlay/onlay/veneer
strength of e.Max-lithiu, disilicate
360-500mpa (enamel around 300 mpa)
what cement is required for all ceramic crowns 90% of the time
resin cement
e.Max-lithium disilicate requires ___mm margin and minimum ___mm reduction with ideal around ___mm reduction
1mm margin
minimum 1.5 reduction
ideal around 2mm
using e.Max and other glass ceramics on anterior teeth…
- lower occlusal force favoring the use of ceramics
- glass ceramics are most esthetic, so anterior use is best
- edge to edge or occlusion in the gingival 1/5 is UNFAVORABLE 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 question use of ceramics
- glass ceramics are most esthetic, so posterior use 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
to help strengthen all-ceramic crowns, this is used. increases strength of ceramic crowns by up to 50%
-stronger than other conventional cements
resin cement
all ceramic prep design guidelines:
- flat plane at right angle to forces
- modified shoulder or heavy chamfer
- no sharp line angles
- adequate length of prep for support
- uniform axial reduction with ideal taper
rather than sharp incisal edge, do this to the incisal edge to reduce fracture.
more than ___mm of porcelain left incisally will result in significantly higher risk of fracture
round or flattened
3mm
all ceramic prep.
short preps:
excessive porcelain bulk:
short: leave too much ceramic and also cannot be retained easily with anterior occlusal forces
excessive: decreases strength
where all ceramic crown would not be preferred, this could be used.
esthetic porcelain on facial or covering the whole ___core.
PFZ- porcelain fused to zirconia
zirconia core
