L4 Anterior all ceramic crowns

Question 1

What are the indications for all ceramic crowns?

Answer 1

• Heavily restored tooth requiring a crown, primarily damage to the interproximal regions
• All other less destructive options have failed/not had acceptable outcomes
• Tooth is in the aesthetic zone
• Pt allergic to metals used in metal crowns e.g. Nickel
• Patient preference, cost
• Operator preference/experience

Question 2

What are the 3 broad material options for anterior crowns?

Answer 2

• Composite
• All ceramic
• Metal ceramic

Question 3

What materials are used for all ceramic crown restorations?

Answer 3

• Strong ceramic core with a weaker but more aesthetic veneer (Emax)

OR

• Monolithic (material used in 1 layer) structure featuring a crack resistant microstructure (e.g. lithium disilicate or Zirconia)

Question 4

What types of ceramic are used in the UDH for all ceramic crowns?

Answer 4

• Zirconia: aka zirconium dioxide. Core structure of zirconia and layers of aluminum silicate built on top for aesthetics.
• Emax CAD: milled.
• Emax pressable: cast. For veneers or single crowns, more translucent, better if natural tooth isn;t too dark.

Question 5

How are Zirconia and Emax CAD crowns manufactured?

Answer 5

• Milled from a single block of material
• Monolithic block milling
• Colour of block is the same all the way through
• Reliably reproduced
• Limitation: can only work to the shape of the burs available, impacts the way the tooth needs to be prepared

Question 6

Why is correct preparation imporant for all ceramic crowns?

Answer 6

• Uniform reduction results in optimal ceramic strength
• Adequate reduction = better aesthetics, better longevity
• Smooth edges = lower stress/weak spots
• Lower stress reduces risk of crack propagation and fracture
• Ceramic restorations require a passive fit, preparation must be adequately tapered

Question 7

How does preparation differ for an all ceramic crown compared to a generic crown?

Answer 7

• More tooth reduction
• Must be adequately tapered
• Keep tooth as high/long as possible
• Non-cylindrical prep, rotational stress will cause crown to debond
• Chamfer margin necessary
• More reduction of incisal edge for better aesthetics

Question 8

What are the values of reduction for an all ceramic crown preparation?

Answer 8

• Up to 2mm incisal edge removal for translucency/aesthetics
• Deeper chamfer margin than veneer (1mm)
• 1-1.5mm even axial reduction

Question 9

Describe the preparation order for an all ceramic crown.

Answer 9

1) Incisal edge reduction with chamfer or parallel bur
2) Interproximal reduction (needle then chamfer bur)
3) Margin preparation buccally and then palatally
4) 2-plane reduction of labial surface
5) Reduce palatal concavity with rugby ball
6) Refine any sharp edges

Question 10

What guides for amount of reduction can be used?

Answer 10

• Depth grooves
• Putty matrix

Question 11

How are ceramic crowns fitted to a a tooth?

Answer 11

• Ceramic can be cemented or bonded
• For ceramic that is to be resin bonded to the tooth structure, the ceramic must be thin (0.3-0.5mm) e.g. for veneers
• In order to be bonded, the ceramic needs to be etchable with hydrofluoric acid: glass ceramics are etchable, Zirconia is not (need to ensure a retentive prep)

Question 12

What are the indications for a composite crown?

Answer 12

• Temporary solution/interim crown, can be used as a diagnostic aid whilst we decide what to do with the tooth
• Not to be used for a posterior tooth for a long period of time, high fracture risk

Question 13

What are the benefits of composite crowns?

Answer 13

• Relatively cheap
• Can last 2-3 years without significant deterioration
• Easily adjusted and repaired
• Can be bonded or cemented to the tooth