Crowns

Question 1

What extra-oral features should you assess when planning for a crown?

Answer 1

Smile line
Symmetry
Incisal show
Speech
Skeletal pattern
OVD/RVD/FWS
TMJ Palpation

Question 2

What intra oral features should you assess when planning for a crown?

Answer 2

Occlusion
Alignment of teeth
Guidance (canine or group)
Perio/caries status
Interocclusal space
Gingival contour
Shade and shape

Question 3

What are the benefits of fitting a crown on a patient?

Answer 3

Good coronal seal of tooth
Reinforces the structual integrity of the tooth
Encourages occlusal stability
Good aesthetics from porcelain
Resistant to toothwear

Question 4

What are the drawbacks of fitting a crown on a patient?

Answer 4

Preperation of healthy tooth can be required
Tooth has a 20-30% chance of going non-vital

Question 5

What are the typical survival rates for crowns?

Answer 5

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.

Question 6

Define PFM, and outline the features/issues surrounding them.

Answer 6

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

Question 7

What is a zirconia crown? Outline the features/issues surrounding them.

Answer 7

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

Question 8

What is a Lithium Disilicate crown? Outline the features/issues surrounding them.

Answer 8

Glass-cermaic material, fabricated by pressing or CAD-Milling techniques.
- Low flexural strength, similar to tooth tissues
- Good aesthetics
- Anteriors only

Question 9

What is a gold crown? Outline the features/issues surrounding them.

Answer 9

Type III gold alloy (16 karat) gold.
- Very good flexural strength
- Less abrasive than Zirconia
- Good survivability
- Unsuitible for aesthetic cases

Question 10

What are non-precious metal crowns? Outline the features/issues surrounding them.

Answer 10

Silver coloured crowns, typically made of CoCr.
- Very good flexural strength
- Less abrasive than zirconia
- Good survivability
- Unsuitible for aesthetic cases

Question 11

What preparation principles are indicated for all crown types?

Answer 11

Flat pulpal floor
4-6 degree tapered walls
No undercutes
Rounded line angles

Question 12

What are the preparation reduction requirements for all ceramic crowns?

Answer 12

Functional cusp: 2mm
Non-functional cusp: 1.5mm
Axial: 1mm rounded chamfer

Question 13

What are the preparation reduction requirements for gold crowns?

Answer 13

Functional cusp: 1mm
Non-functional cusp: 0.5mm
Axial: 0.5-1mm chamfer

Question 14

What are the preparation reduction requirements for PFM crowns?

Answer 14

Functional cusp: 2mm
Non-functional cusp: 1.5mm
Buccal shoulder: 1.5mm
Lingual chamfer: 1mm (where only metal required)

Question 15

What are the main considerations when prescribing a crown?

Answer 15

Aesthetics
Least destructive option for the tooth
Is least destructive to opposing teeth
Whether it is suited for bruxists

Question 16

Outline the stages in crown prep.

Answer 16

Occlusal reduction
Separation
Buccal reduction
Palatal or lingual reduction (Occlusal reduction if not already completed)
Shoulder and chamfer finish
Check occlusal surface and clearance

Question 17

Outline the main principles for crown preparation.

Answer 17

Preservation of tooth structure
Retention and resistance
Structural durability
Marginal integrity
Preservation of the periodontium
Aesthetic considerations

Question 18

How do you create retention and resistance form?

Answer 18

Taper
Length of walls
Path of insertion
Grooves and slots

Question 19

What is deep margin elevation?

Answer 19

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.

Question 20

What is the purpose of providing a provsional restoration between appointments?

Answer 20

Maintains seal of tooth
Maintains structural integrity of tooth
Aesthetic concerns for patient

Question 21

What potential risks is there is a poor marginal fit of a crown or fixed bridge retainer?

Answer 21

Plaque retention
Secondary caries
Localised perio
Cemenent dissolution
Poor aesthetics

Question 22

What are the potential risks of a crown/bridge retainer not seating fully?

Answer 22

Patient discomfort
Plaque retention
Secondary caries
Localised perio
Unintended occlusal adjustments

Question 23

What are the potnetial risks of occlusal interferences from the bridge/crown?

Answer 23

Post op pain on biting
Occlusal trauma
Restoration fracture
Oposing tooth fracture
Decementation
Bruxism

Question 24

What erros can be comitted by the dentist leading to crown errors?

Answer 24

Under/over prep
Inacurate impression
Poor gingival retraction
Poor contact point on temp, leading to drifiting
Poor treatment planning
Insufficent taper of axial walls

Question 25

What type of cements can be used for PFM crowns?

Answer 25

GI
RMGIC
Resin (self or dual cure)
Zinc phosphate
Zinc polycarboxylate

Question 26

What type of cements can be used for a metal crown?

Answer 26

GI
RMGIC
Resin (self or dual cure)
Zinc phopshate
Zinc polycarboxylate

Question 27

What type of cements can be used for a porcelain veneer?

Answer 27

Resin (light cure only)

Question 28

What type of cements can be used for inlays and onlays?

Answer 28

Resin (light, self, and dual cure)

Question 29

What type of cement can be used for an all ceramic crown?

Answer 29

Resin (self or dual cure)

Question 30

What steps can be taken to make a ceramic crown more retentive?

Answer 30

Sandblasting and etch/primer
HF acid etch followed by etch/primer

Question 31

What is dental primer?

Answer 31

Silane coupling agent