All ceramic crown Flashcards
What are the limitations of PFM crowns?
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
How can PFM crown be made more similar to the tooth? What are the problems with doing this?
Metal must be opaqued
Opaque layer might affect the overall appearance (High value and unnatural appearance)
What are the advantages of a PFM crown?
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.
What are dental ceramics made of?
Ceramic is generally a mixture of glass and crystals components
They vary in composition of the microstructure, fabrication method, and clinical application.
What possible restorations are made from dental ceramics?
Laminate veneers
All ceramic crowns
Inlays
Onlays
FPD
What are the advantages to an all ceramic crown?
Superior aesthetics
Biocompatibility
Chemically inert
Insulating properties (Thermal and electric)
High hardness
What are the disadvantages to an all ceramic crown?
Inferior mechanical properties (tensile/flexural strength)
Brittle
Technique sensitive
Technique demanding
What are the indications and contraindications to using all ceramic crowns?
Indications:
High aesthetic demand
Patient request
Metal allergy
More conservative than PFM
Contraindications:
Heavy occlusal forces (bruxism and parafunctional habits)
Deep overbite
What causes fracture?
Fabrication defects (causes stress localization for crack initiation and material failure)
internal surface cracks
What factors increase likelihood for full ceramic crown failure?
Microcracks development during firing and cooling.
Structure weakening after adjustment
Voids are created during processing and sintering
What are the types of CAD-CAM Ceramic?
Glass-based ceramics
Glass-based ceramics with crystalline fillers
Crystalline-based systems with glass fillers
Glass-free ceramics (Polycrystalline ceramics)
Hybrid ceramics
What is crystalline reinforcement?
Addition of crystalline phase with better mechanical properties (metal oxides, leucite crystals, lithium disilicate crystals)
What are the benefits of using crystalline reinforcement?
Greater mechanical properties with increased proportion of crystalline phase
Resist crack propagation.
What are the types of glass ceramics and what is their flexural strength?
Feldspathic = 100MPa
Leucite-reinforced = 160MPa
Lithium disilicate reinforced ceramics = 350 - 450 MPa
Zirconia-reinforced lithium silicate ceramic (10% zirconia) = 460 MPa
How is zirconia reinforced lithium dislicate better than normal lithium disilicate?
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
What are the crystalline based systems with glass fillers and what is their flexural strength?
Glass infiltrated Alumina and zirconia ceramics: 450 - 600 and 700MPa respectively
What are the types of glass free ceramics and what is their flexural strength?
Alumina based polycrystalline ceramics = 600 MPa
Zirconia based polycrystalline ceramics = 900 - 1200 MPa
What are the advantages to Vita YZ HT ceramic and what are the indications for them? What type of crown is it?
It is a glass-free ceramic crown
It has a high translucency
It is tooth coloured or white
Indication = Monolithic bridge restorations.
What are hybrid ceramics used for?
Dual-network structure: Ceramic and polymer
Different shades and 2 levels of translucency
Flexural strength is 150 -160MPa
What are the types of all ceramic based on fabrication method?
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
What are the types of fabrication methods for all-ceramic crowns?
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
What are the advantages and disadvantages to using the traditional method of all ceramic crown fabrication?
Advantages:
Highly translucent
Aesthetic
Added in multiple stages (controlled stage)
Disadvantages:
Weak
Excessive shrinkage
Microporosities
Inhomogeneity
What is the function of the inner core of an all ceramic crown?
The core will strengthen the veneering ceramic
The core has stronger mechanical properties and is much superior than veneering ceramic properties
How is a durable core produced?
Slip casting
Heat pressing
Milling (CAD/CAM)
When are case ceramics used?
For inlays, onlays, and anterior crowns.
They should be adhesively cemented this method is hardly used today.
What are the advantages and disadvantages to heat-pressed ceramics?
Advantages:
Improved mechanical properties
Less risk of shrinkage
Translucent
Aesthetic
Disadvantages:
Requires additional equipment and is time consuming
What are the indications for using heat-pressed ceramics?
Crown
Core materials
Veneer
Inlay
Onlay
What are the advantages to milled CAD/CAM method of ceramic design?
Simpler fabrication method
More durable material application
Homogenous material
Different aesthetic options
Superior accuracy
Chair-side option is available
What are the indications for using CAD/CAM milling fabrication?
All types of restorations
How is CAD-CAM ceramic characterized?
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.
How are ceramic limitations overcome?
Strengthening mechanisms
Improved fabrication methods
Adhesive cementation
How is adhesive cementation conducted?
Using resin cements
How does cementation help reduce failure rate of crowns?
Reduces internal crack propagation
Acid etch and bond techniques allow inherent strength of tooth to be imported to the ceramic restoration.
What are the steps to attaching a ceramic restoration to a tooth?
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
What is the Incisal reduction for an all ceramic crown on an anterior tooth?
1.5mm
How wide is the margin for an all ceramic crown?
Shoulder is 1mm wide and must be supragingival/equigingival
What should the axial reduction be for an all ceramic crown?
1 - 1.5mm
