Crowns Flashcards
(31 cards)
What extra-oral features should you assess when planning for a crown?
Smile line
Symmetry
Incisal show
Speech
Skeletal pattern
OVD/RVD/FWS
TMJ Palpation
What intra oral features should you assess when planning for a crown?
Occlusion
Alignment of teeth
Guidance (canine or group)
Perio/caries status
Interocclusal space
Gingival contour
Shade and shape
What are the benefits of fitting a crown on a patient?
Good coronal seal of tooth
Reinforces the structual integrity of the tooth
Encourages occlusal stability
Good aesthetics from porcelain
Resistant to toothwear
What are the drawbacks of fitting a crown on a patient?
Preperation of healthy tooth can be required
Tooth has a 20-30% chance of going non-vital
What are the typical survival rates for crowns?
Porcelain (Lithium disilicate): 5-15 years
All ceramic: up to15 years
PFM: 10-15 years
Gold: 20 years or more
Zirconia: 20 years or more
All estimates and depend on OHI and other factors.
Define PFM, and outline the features/issues surrounding them.
Porcelain fused metal crown
- Porcelain laminate over the top of a metal alloy core
- Moderate flexural strength
- Metal cervical areas can become obvious if recession
- Posterior teeth
What is a zirconia crown? Outline the features/issues surrounding them.
Durable ceramic material, which is milled from a single block.
- Good flexural strength
- More abrasive than metal
- Avoid in bruxists as may damage opposing teeth/bridgework
What is a Lithium Disilicate crown? Outline the features/issues surrounding them.
Glass-cermaic material, fabricated by pressing or CAD-Milling techniques.
- Low flexural strength, similar to tooth tissues
- Good aesthetics
- Anteriors only
What is a gold crown? Outline the features/issues surrounding them.
Type III gold alloy (16 karat) gold.
- Very good flexural strength
- Less abrasive than Zirconia
- Good survivability
- Unsuitible for aesthetic cases
What are non-precious metal crowns? Outline the features/issues surrounding them.
Silver coloured crowns, typically made of CoCr.
- Very good flexural strength
- Less abrasive than zirconia
- Good survivability
- Unsuitible for aesthetic cases
What preparation principles are indicated for all crown types?
Flat pulpal floor
4-6 degree tapered walls
No undercutes
Rounded line angles
What are the preparation reduction requirements for all ceramic crowns?
Functional cusp: 2mm
Non-functional cusp: 1.5mm
Axial: 1mm rounded chamfer
What are the preparation reduction requirements for gold crowns?
Functional cusp: 1mm
Non-functional cusp: 0.5mm
Axial: 0.5-1mm chamfer
What are the preparation reduction requirements for PFM crowns?
Functional cusp: 2mm
Non-functional cusp: 1.5mm
Buccal shoulder: 1.5mm
Lingual chamfer: 1mm (where only metal required)
What are the main considerations when prescribing a crown?
Aesthetics
Least destructive option for the tooth
Is least destructive to opposing teeth
Whether it is suited for bruxists
Outline the stages in crown prep.
Occlusal reduction
Separation
Buccal reduction
Palatal or lingual reduction (Occlusal reduction if not already completed)
Shoulder and chamfer finish
Check occlusal surface and clearance
Outline the main principles for crown preparation.
Preservation of tooth structure
Retention and resistance
Structural durability
Marginal integrity
Preservation of the periodontium
Aesthetic considerations
How do you create retention and resistance form?
Taper
Length of walls
Path of insertion
Grooves and slots
What is deep margin elevation?
Can be used in place of surgical crown lengthening.
Basically a deep subgingival composite can be placed using a self etching primer. This gives you a good margin that is well clear of gingiva.
What is the purpose of providing a provsional restoration between appointments?
Maintains seal of tooth
Maintains structural integrity of tooth
Aesthetic concerns for patient
What potential risks is there is a poor marginal fit of a crown or fixed bridge retainer?
Plaque retention
Secondary caries
Localised perio
Cemenent dissolution
Poor aesthetics
What are the potential risks of a crown/bridge retainer not seating fully?
Patient discomfort
Plaque retention
Secondary caries
Localised perio
Unintended occlusal adjustments
What are the potnetial risks of occlusal interferences from the bridge/crown?
Post op pain on biting
Occlusal trauma
Restoration fracture
Oposing tooth fracture
Decementation
Bruxism
What erros can be comitted by the dentist leading to crown errors?
Under/over prep
Inacurate impression
Poor gingival retraction
Poor contact point on temp, leading to drifiting
Poor treatment planning
Insufficent taper of axial walls
