L5 Metal ceramic crowns Flashcards

1
Q

What is the strongest crown type?

A

All metal crown

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2
Q

List the 4 crown types.

A
  • Full veneer metal crown/all metal crown
  • Metal ceramic crown
  • All ceramic crown
  • Composite crown
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3
Q

How can ceramic crown strength be improved?

A
  • Using a reinforced ceramic core system
  • Using a metal substructure (MCC)
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4
Q

Describe reinforced ceramic core systems.

A
  • Glass infused ceramics
    -Almunious substructure (porcelain jacket crown)
  • Pressable material e.g. emax
  • Machined cermaics
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5
Q

How is a metal substructure used to improve the strength of a ceramic crown?

A
  • Metal substructure, opaque layer of ceramic on top, outer layers of porcelain on top of this
  • Metal gives strength to the overlying ceramic
  • Metal has a rough surface which ceramic can easily adhere to
  • Chemical bond forms between the oxidised metal and the porcelain base layer
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6
Q

Describe the bonding of ceramic to metal in MCCs.

A
  • Mechanical interlock: sandblasted metal surface
  • Chemical bonding: oxide layer on metal can bond to ceramic
  • Compression fit: difference in co-efficient of thermal expansion between metal and ceramic, ceramic shrinks onto metal, provides compression of ceramic and tension of the metal base layer to provide tight compression fit
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7
Q

Does the metal alloy of an MCC have a high or low melting point?

A
  • Metal alloy has high melting point (higher than ceramic)
  • Means the metal substructure doesn’t melt as the ceramic is fused on top
  • High melting point achieved as palladium and platinum are added to the gold alloy substructure, or cobalt chromium is used as a base metal alloy
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8
Q

What are the advantages of MCCs?

A
  • Metal is strong in thin sections so less tooth needs to be removed
  • Metal margin may allow a shallower preparation if aesthetics is less important e.g. posterior tooth, low lip line
  • Metal is better in parafunction
  • Cheaper to produce
  • Metal margins are easier to adjust than ceramic
  • Metal margins can be polished more eaily than ceramic
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9
Q

What are the disadvantages of MCCs?

A
  • Metal needs to be hidden so the ceramic has to be thicker, therefore more tooth is removed compared to an all ceramic crown
  • Opacity requires good ceramic work, more technically challenging
  • Crown failure causes metal to be exposed, very unaesthetic
  • Potential metal allergy issues
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10
Q

How do the principles of crown preparation differ for an MCC compared to the generic crown principles?

A
  • Increased tooth reduction, higher risk of pulpal damage (doesn’t apply to posterior teeth as aesthetics not as significant)
  • Taper and prep height equally important
  • Shoulder margin for metal and ceramic, chamfer for metal only
  • Occlusal reduction for posterior teeth depends on if surface is made of ceramic or metal, more removal needed for ceramic
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11
Q

Describe the order of preparation for an anterior MCC.

A

1) Incisal edge reduction
2) Interproximal reduction with thin needle bur and hand instruments
3) Chamfer bur interproximally
4) 2 planes of reduction buccally
5) Margin preparation: chamfer all around, then shoulder bur just on buccal surface
6) Rugby bur for palatal reduction
7) Refine sharp edges

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12
Q

What are the measurements for a MCC?

A
  • Buccal shoulder margin = 1-1.2mm
  • Palatal chamfer margin = 0.5mm (half bur width)
  • 1.5-2mm occlusal reduction (2mm functional cusp)
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13
Q

What variations are there for MCC coverage?

A

Occlusal coverage:
- Fully covered occlusal surface
- Partial coverage with ceramic only buccally (aesthetic)
- Metal palatal surface or ceramic palatal surface

Inform patients of risks and benefits of taking more or less tooth structure.
What is best for the patient functionally e.g. bruxism- metal for longevity.

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