Posterior Full Coverage Crowns I and II

Question 1

Why restore a compromised tooth?

Answer 1

Restoring function and aesthetics
Restore structural integrity and resisting fracture
Integrity with other prosthesis

Question 2

Why crown root filled teeth?

Answer 2

Weakened tooth due to access cavity prep
Loss of structural integrity associated with loss of roof of the pulp chamber
Loss of dentine elasticity

Question 3

When is cuspal protection of posteriors needed?

Answer 3

Loss of marginal ridges
Loss of substantial tooth structure
Heavily restored teeth

Question 4

How to achieve cuspal protection?

Answer 4

Adhesive restorations (direct resin composite)
Cusp coverage cast restorations (onlay, 3/4 crown)
Full coverage restoration (crown)

Question 5

When are crowns used to achieve integrity with other structures (example)?

Answer 5

Place crowns on abutment teeth to incorporate the RPD

Question 6

What design considerations are made with posterior crowns?

Answer 6

Is the tooth in function
Appearance
Adjacent teeth
Periodontal tissues
Pulp
Retention of the crown to the tooth
Materials
Cost

Question 7

What to consider with periodontal tissues with posterior crowns?

Answer 7

Plaque control
Periodontal attachment
Alveolar bone levels
Status of periodontal disease
Mobility

Question 8

Pulpal death following crown preps due to?

Answer 8

Aggressive insult to tooth, dentine and odontoblasts
Thermal damage
LA
Desiccation
Bacterial contamination

Around 10-20% of pulps necrose after crown prep - warn pt before of loss of vitality

Question 9

What does a 1.2mm shoulder crown prep on a posterior tooth leave?

Answer 9

1.2mm shoulder crown prep on a posterior tooth leaves less than or 0.7mm remaining dentine thickness

Question 10

Posterior crown materials?

Answer 10

Metal
Metal ceramic
Ceramic

Question 11

Features of metal (full gold) crowns?

Answer 11

Minimal tooth reduction as strong
Least aesthetic
Can be adjusted intraorally (occlusion)

Question 12

Gold alloy types?

Answer 12

Type 1 - soft gold

• can withstand biting forces
• soft enough to burnish against margins of cavity
• main use - one surface inlays

Type 2 - medium gold

• less burnishable
• hard enough to stand up in small
• multiple surface inlays that do not include buccal or lingual surfaces

Type III - hard gold

• Most common for all metal crowns and bridges
• Gold 75%, silver 10%, copper 10%, palladium 3% and zinc 2%

Type IV - extra hard
- Used for partial denture frameworks but not used in fixed prosthetics

Question 13

Survival of a gold crown?

Answer 13

97% at 9 yrs

94.1% for >40 yrs

Question 14

Metal-ceramic crown features?

Answer 14

Metal core
Extensive buccal tooth reduction
Aesthetics at the cost of tooth tissue
Only the metal component can be adjusted intra-orally

Question 15

PFM alloy types?

Answer 15

High noble alloys have a minimum of 60% noble metals and min of 40% by weight of gold  
Noble alloys (gold, palladium, silver) contain at least 25% by weight noble metal - high strength, durability, hardness and ductility

Base metal alloys

• Contain less than 25% noble metal
• Much harder, stronger and twice the elasticity of high noble and noble metal alloys
• Casting can be made thinner - still rigid and can support porcelain
• Contain nickel and beryllium - allergic reactions

Question 16

Metal ceramic and all ceramic crown survival?

Answer 16

Systematic review:
5 yr survival 93.3% of all ceramic crowns
95.6% for metal ceramic crowns

Question 17

All ceramic crown features?

Answer 17

High strength ceramic core
Most aesthetic
Low edge strength
Requires extensive reduction
Intra-oral adjustment not possible

Question 18

All ceramic crowns survival rate?

Answer 18

5 yr fracture rate of 4.4%

Molars - higher fracture rate than premolar crowns

Question 19

Principles of tooth preparations for crowns?

Answer 19

Preservation of tooth structure
Retention and Resistance
Structural durability
Marginal integrity
Preservation of periodontim

Question 20

Retention form of retention?

Answer 20

Prevents dislodgement of the crown in an axial direction

Question 21

Resistance form of retention?

Answer 21

Prevents dislodgement of the crown due to rotation from a lateral load

Question 22

What should the tooth prep design be?

Answer 22

Well defined and well finished
Clear finish line visible
Ceramic margins should be a butt-joint rounded shoulder
All prep line angles and point angles are best rounded

Question 23

What should the tooth prep be for all ceramic crowns?

Answer 23

Minimal occlusal reduction - 1.5mm
>2mm in areas of stress
5 degree taper
Shoulder margin

Question 24

What should the occlusal reduction reflect?

Answer 24

The morphology of the tooth and the functional pathways of the occlusion

Question 25

Features of a PFM crown prep?

Answer 25

Chamfer
Lingual axial reduction
Wing
Functional cusp bevel
Planar occlusal reduction
Facial axial reduction
Shoulder
Gingival bevel

Question 26

Posterior crowns - stage 1 of clinical stages?

Answer 26

Pre-op clinical and radiographic assessment
Further investigations, study models, diagnostic wax up
Tx planning
Informed consent

Question 27

Clinical stage 2 - posterior crowns?

Answer 27

Tooth build up and preparation
Impression
Occlusal record
Temporisation
Fabrication (lab stage)

Question 28

Posterior crowns - clinical stage III?

Answer 28

Removal of temp crown
Try in of definitive crown
Cementation of definitive crown
Occlusal check 
Review