Posterior Full Coverage Crowns

Question 1

Reason for placing full coverage temporary crowns on compromised teeth?

Answer 1

Restore function and morphology
Restore and improve aesthetic
Preserve remaining tooth structure
Improve confidence = psychology

Question 2

Why are endo tx teeth weak?

Answer 2

Loss structural integrity

1. Prep of access cavity
2. Loss of roof of pulp chamber
3. Fragile due to loss dentine elasticity

Question 3

What are reasons for cusp protection on posterior teeth?

Answer 3

For structural integrity

1. Loss marginal ridge
2. Substantial loss tooth structure
3. Heavily restored teeth

Question 4

What types of restorations are available for posterior teeth?

Answer 4

1. Adhesive
2. Cusp-coverage cast restoration - onlay, 3/4
3. Full-coverage

Question 5

7 points in assessment/ design considerations?

Answer 5

1. Tooth in function
2. Aesthetic considerations
3. Adjacent/ opposing teeth
4. Perio tissue
5. Pulp, RCT, periodical tissue
6. Retention of crown
7. Material

Question 6

What are ideal perio condition?

Answer 6

Optimal plaque control with perio attachment
Alveolar bone levels good
Stabilised perio disease - pocket depth reduction w/ no BOP

If crown placed periodontally compromised tooth may accelerate breakdown perio tissue

Question 7

Reasons why pulp death may occur following crown prep?

Answer 7

1. Aggressive insult to tooth
2. Thermal damage
3. Local anaesthesia - adrenaline reduce blood flow
4. Desiccation - drying creates negative pressure
5. Bacterial contamination - tubules large (older pt more sclerosed)
6. Chemical damage - cements
7. Osmotic pressure

Question 8

How many teeth will become non-vital?

Answer 8

1-2 in 10 preps

10-20%

Question 9

How to reduce chance of pulp death?

Answer 9

Good pre-op assessment inc. vitality

Shoulder prep of 1.2mm result remaining width of 0.7mm dentine in 50% (50% less 0.7mm) - problem if prominent pulp horns

Question 10

What should consider when picking material?

Answer 10

Balance aesthetic and function

Ceramic: less aesthetic (less translucent) - need thicken stronger material

Question 11

Adv and disadv of full gold crown?

Answer 11

Adv:

• conservative - minimal reduction
• gold is strong thin sections
• ideal bruxism pt
• can be adjusted intra-orally

Disadv:
- less aesthetic

Question 12

What are different types of gold and their use?

Answer 12

Type I = soft - hard enough stand biting force - used one-surface onlay

Type II = medium - less burnish able but harder - multiple surface onlay

Type III = hard - most common used - metal crowns

Type IV = extra hard = RPDs , not fixed prosthetics

Question 13

What is the composition of type III gold alloy>

Answer 13

75% gold
10% silver
10% copper 
3% palladium 
2% zinc

Question 14

Survival rates of gold crowns?

Answer 14

97% at 9 years - 94.1% 540 years

Question 15

Why are metal-ceramic crowns used?

Answer 15

Metal core - provide strength
More aesthetic - at cost of tooth tissue

Disadv: extensive buccal reduction, only metal component can be adjusted intra-orally

Question 16

What are 3 different types of PFM alloys used?

Answer 16

1. High-nobel alloy (min 60% noble metal) - contain small amount tin, indium or ion which provide oxide layer needed for bond w/ porcelain
2. Nobel alloy (min 25% noble metal) - high strength, durability, hardness, ductility
3. Base-metal alloy (<25% nobel metal) - less expensive, harder and stronger but less elastic

Question 17

What is noble metal?

Answer 17

Gold, palladium, silver - combo

Question 18

What is survival of PFM?

Answer 18

5 years = 93.3%

Question 19

What posterior crowns have higher survival?

Answer 19

Gold >PFM > all ceramic

Question 20

What/ when all ceramic crown used?

Answer 20

High strength ceramic core -layered w/ translucent porcelain
Aestehtic
Low edge strength - need rounded shoulder
Extensive reduction
Intra-oral reduction not possible

Question 21

What is survival of ceramic crown?

Answer 21

Acceptable 5 year fracture - 4.4%

Molar > premolar - fracture rate
Posterior >anterior - fracture rate

Question 22

What are Shillingburgs 5 principles?

Answer 22

1. Preservation tooth structure
2. Retention - prevent dislodgement axial direction
3. Resistant - resist rotation non-axial direction (lateral load)
4. Structural durability
5. Marginal integrity

PolyRatesRasinSlicedMuffins

Question 23

Ideal features of posterior prep?

Answer 23

1. Well-defined and finished margin
2. Clear finish line
3. Ceramic margin should be butt-joint round shoulder
4. Follow gingival contour
5. Metal margin should be chamfer
6. Prep line angles best rounded - thin/sharp edge can cause fracture (stress point)

Question 24

How should an all ceramic crown be prepped?

Answer 24

Minimal occlusal reduction = 1.5mm (reflect morphology)
Functional cusp reduction = 2mm
Parallel wall for retention - 5 degree taper
Shoulder margin

Question 25

How should PFM crown be prepped?

Answer 25

Buccal shoulder - 1.2-1.4mm (accommodate metal and porcelain) Lingual chamfer- 0.5-0.7mm Occlusal = 2mm Functional cusp bevel - structural durability Where shoulder meet chamfer - wing (chamfer inter proximally) -preserve tooth structure

Question 26

How should full gold crown be prepped?

Answer 26

<1mm reduction all way round Parallel walls - slight taper Even occlusal reduction Bevel functional cusp

Question 27

What are the clinical stages of posterior crowns?

Answer 27

1. Phase I - Pe-op clinical and radiographic assessment - Tx plan and informed consent 2. Phase II - Tooth build up and prep - Impression - Shade selection - Temporisation 3. Phase III - Remove temp and try-in definitive crown - Check occlusion and aesthetic - Cement and check