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DMD2 sem 2 > All ceramic crown > Flashcards

All ceramic crown Flashcards

1
Q

What are the limitations of PFM crowns?

A

Invasive tooth preparations (1.2 - 1.5mm for metal and ceramic accommodate the required materials for durability and aesthetics)

Limited aesthetics (translucent nature of teeth allows transmission of light. Metal coping prevents light transmission)

Biocompatibility

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2
Q

How can PFM crown be made more similar to the tooth? What are the problems with doing this?

A

Metal must be opaqued

Opaque layer might affect the overall appearance (High value and unnatural appearance)

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3
Q

What are the advantages of a PFM crown?

A

Limitations and dimensions of milling systems, cast metal produces a more precise internal fit than milled all-ceramic crowns

Metal is better able to withstand higher stress concentrations from more abrupt line angles in the tooth preparations.

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4
Q

What are dental ceramics made of?

A

Ceramic is generally a mixture of glass and crystals components

They vary in composition of the microstructure, fabrication method, and clinical application.

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5
Q

What possible restorations are made from dental ceramics?

A

Laminate veneers

All ceramic crowns

Inlays

Onlays

FPD

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6
Q

What are the advantages to an all ceramic crown?

A

Superior aesthetics

Biocompatibility

Chemically inert

Insulating properties (Thermal and electric)

High hardness

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7
Q

What are the disadvantages to an all ceramic crown?

A

Inferior mechanical properties (tensile/flexural strength)

Brittle

Technique sensitive

Technique demanding

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8
Q

What are the indications and contraindications to using all ceramic crowns?

A

Indications:

High aesthetic demand

Patient request

Metal allergy

More conservative than PFM

Contraindications:

Heavy occlusal forces (bruxism and parafunctional habits)

Deep overbite

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9
Q

What causes fracture?

A

Fabrication defects (causes stress localization for crack initiation and material failure)

internal surface cracks

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10
Q

What factors increase likelihood for full ceramic crown failure?

A

Microcracks development during firing and cooling.

Structure weakening after adjustment

Voids are created during processing and sintering

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11
Q

What are the types of CAD-CAM Ceramic?

A

Glass-based ceramics

Glass-based ceramics with crystalline fillers

Crystalline-based systems with glass fillers

Glass-free ceramics (Polycrystalline ceramics)

Hybrid ceramics

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12
Q

What is crystalline reinforcement?

A

Addition of crystalline phase with better mechanical properties (metal oxides, leucite crystals, lithium disilicate crystals)

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13
Q

What are the benefits of using crystalline reinforcement?

A

Greater mechanical properties with increased proportion of crystalline phase

Resist crack propagation.

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14
Q

What are the types of glass ceramics and what is their flexural strength?

A

Feldspathic = 100MPa

Leucite-reinforced = 160MPa

Lithium disilicate reinforced ceramics = 350 - 450 MPa

Zirconia-reinforced lithium silicate ceramic (10% zirconia) = 460 MPa

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15
Q

How is zirconia reinforced lithium dislicate better than normal lithium disilicate?

A

Higher resistance to dynamic load compared to lithium dislicate

Different shades and 2 levels of translucency (HT and T)

Higher flexural strength 460MPa vs 350 - 450 MPa

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16
Q

What are the crystalline based systems with glass fillers and what is their flexural strength?

A

Glass infiltrated Alumina and zirconia ceramics: 450 - 600 and 700MPa respectively

17
Q

What are the types of glass free ceramics and what is their flexural strength?

A

Alumina based polycrystalline ceramics = 600 MPa

Zirconia based polycrystalline ceramics = 900 - 1200 MPa

18
Q

What are the advantages to Vita YZ HT ceramic and what are the indications for them? What type of crown is it?

A

It is a glass-free ceramic crown

It has a high translucency

It is tooth coloured or white

Indication = Monolithic bridge restorations.

19
Q

What are hybrid ceramics used for?

A

Dual-network structure: Ceramic and polymer

Different shades and 2 levels of translucency

Flexural strength is 150 -160MPa

20
Q

What are the types of all ceramic based on fabrication method?

A

Monolithic crowns: Include leucite reinforced, lithium disilicate, zirconia.

Bilayer crowns: 2 layers; a core and a veneer. Core or copping can be lithium dislicate, glass-infiltrated alumina or zirconia, alumina, and zirconia based

21
Q

What are the types of fabrication methods for all-ceramic crowns?

A

Traditional method: Moistened powder application followed by sintering (Feldspathic ceramics) In this method moistened porcelain powder is placed over an inner core.

Cast ceramics: Wax pattern fabrication followed by casting with molten ceramics

Heat-pressed ceramics: Softened ingot pressed in lost wax space under vacuum

Milled (CAD/CAM): Computer Aided Design and Computer Aided Manufacturing

22
Q

What are the advantages and disadvantages to using the traditional method of all ceramic crown fabrication?

A

Advantages:

Highly translucent

Aesthetic

Added in multiple stages (controlled stage)

Disadvantages:

Weak

Excessive shrinkage

Microporosities

Inhomogeneity

23
Q

What is the function of the inner core of an all ceramic crown?

A

The core will strengthen the veneering ceramic

The core has stronger mechanical properties and is much superior than veneering ceramic properties

24
Q

How is a durable core produced?

A

Slip casting

Heat pressing

Milling (CAD/CAM)

25
Q

When are case ceramics used?

A

For inlays, onlays, and anterior crowns.

They should be adhesively cemented this method is hardly used today.

26
Q

What are the advantages and disadvantages to heat-pressed ceramics?

A

Advantages:

Improved mechanical properties

Less risk of shrinkage

Translucent

Aesthetic

Disadvantages:

Requires additional equipment and is time consuming

27
Q

What are the indications for using heat-pressed ceramics?

A

Crown

Core materials

Veneer

Inlay

Onlay

28
Q

What are the advantages to milled CAD/CAM method of ceramic design?

A

Simpler fabrication method

More durable material application

Homogenous material

Different aesthetic options

Superior accuracy

Chair-side option is available

29
Q

What are the indications for using CAD/CAM milling fabrication?

A

All types of restorations

30
Q

How is CAD-CAM ceramic characterized?

A

It imitates the features that make each tooth individual

Internal shading: Direct colour material is applied in the inner surfaces of the restoration after etching and silanating and then light cured

External shading: The outer surfaces of crowns and veneers are conventionally stained and the application can be combined with glazing.

Cut-back and layer: The most aesthetic technique involves layering porcelain allowing a range of translucencies and colours to be produced.

Polish and glaze: The restoration can be finished by polishing and glazing.

31
Q

How are ceramic limitations overcome?

A

Strengthening mechanisms

Improved fabrication methods

Adhesive cementation

32
Q

How is adhesive cementation conducted?

A

Using resin cements

33
Q

How does cementation help reduce failure rate of crowns?

A

Reduces internal crack propagation

Acid etch and bond techniques allow inherent strength of tooth to be imported to the ceramic restoration.

34
Q

What are the steps to attaching a ceramic restoration to a tooth?

A

Etch the internal surface of the ceramic using HF acid (glass ceramic) or sandblasting (glass-free ceramic)

Silane treatment. In this process a covalent bond is established between the ceramic surface and the composite resin and this improves the wetting of ceramic by composite resin cement

35
Q

What is the Incisal reduction for an all ceramic crown on an anterior tooth?

A

1.5mm

36
Q

How wide is the margin for an all ceramic crown?

A

Shoulder is 1mm wide and must be supragingival/equigingival

37
Q

What should the axial reduction be for an all ceramic crown?

A

1 - 1.5mm

DMD2 sem 2 (97 decks)

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