Dental Ceramics Flashcards
What are the 3 categories on the ceramic spectrum?
- Glass-Based Systems (Aesthetic)
- Glass-Based Systems with Fillers
- Polycrystalline (Strong Opaque, like Zirconia, no glass)
What are some examples of Glass-Based Systems with Fillers?
- EMAX!
- Empress
- Glass composition similar to glass-based
- Crystals have either been added or grown
What are the 3 sub-categories of Glass-Based Systems with fillers?
- Low-moderate leucite-containing feldspathic glass
- High leucite-containing glass
- Lithium disilicate glass ceramic
Describe sub-category 1 of glass-based systems with fillers…
- Low-moderate leucite containing feldspathic glass
- Known as feldspathic porcelain
- Typically powder/liquid
- Porcelain veneers
Describe sub-category 2 of glass-based systems with fillers…
- High leucite-containing glass
- Also called “glass ceramic”
- Powder/liquid
- Pressable: IPS Empress
- Machinable: Empress CAD (computer aided design)
What is the flexural strength of Empress CAD?
120 MPa
What types of restorations would you use Empress for?
HT: Inlays/Veneers
LT: Onlays/Crowns
Anterior Crowns, Inlays, Onlays, Veneers
What is a contraindication for using Empress?
Bruxism
Describe sub-category 3 of glass-based systems with fillers?
- Lithium-disilicate glass ceramic
- Lithium oxide crystals added (doubles the strength!)
- Pressable: EMAX Press (Ivoclar)
- Machinable: EMAX CAD (computer aided design)(Ivoclar)
What is the flexural strength of lithium disilicate?
500 MPa
Are there lots of opacities for lithium discilicate?
Yes!
HT
MT
LT
MO (Medium opacity for layering)
What process turns EMAX crowns from the blue phase to their porcelain state?
Crystallization
What types of restorations can you use EMAX for?
- Anterior/Posterior Crowns
- Onlays
- Anterior FDPs
What have 6 clinical studies shown about EMAX after 4 years of monitoring 237 restorations?
- 97.9% of the restorations survived!
- Failures attributed to irreparable chipping/fractures
What is the occlusal reduction recommended by the manufacturer for EMAX CAD?
1 mm
What is an example of Polycrystalline Solid material?
Zirconia
Describe Zirconia basics…
- Dense
- Air Free
- Glass Free
How much does Zirconia shrink when being sintered?
20%
What are some indications for Zirconia?
Crowns, FDPs, Implant Abutments
What are the 3 phases of Zirconia?
- Monoclinic
- Tetragonal
- Cubic
What are some concerns about Zirconia?
Chipping of veneering porcelain
- Due to mismatch of coefficient of thermal expansion yields poor support of veneering porcelain
What are 2 elements of Framework Zirconia?
- Zirconia core
2. Lithium disilicate veneer
What is full-contour zirconia?
An all zirconia crown
- Favorable enamel antagonist
- Polished full contoured zirconia crown
- Very Opaque, esthetics issue, kind to opposing teeth when polished
Describe Cubic Zirconia crowns…
What is its flexural strength?
- stabilized 5-mol% yttria oxide
- 53% cubic/47% tetragonal
- Increased translucency
- Flexural strength: 700 MPa
For Ceramic Polymer, what 2 materials make up this restoration?
Ceramics mixed embedded in a highly cross-linked resin matrix
What are 2 positive characteristics of ceramic polymer restorations?
- Less prone to cracking
2. Better edge quality
What is the primary indication for ceramic polymers?
According to Fasbinder…
The product continues to be indicated for inlays, onlays (with an internal retentive design element) and veneer restoratives)
If you were going to choose a material for an inlay, onlay, or veener, what 3 materials could you choose?
- Leucite-Reinforced (Empress)
- Lithium silicates (EMAX)
- Ceramic Polymers
If you were going to choose a material for an anterior crown, what 3 materials would you choose?
- Leucite-Reinforced (Empress)
- Lithium silicates (EMAX)
- Cubic Zirconia
If you were going to choose a material for a posterior crown, what 2 materials would you choose?
- Lithium silicates (EMAX)
2. Full Contour Zirconia
If you were going to choose a material for an anterior 3-init FDP, what 3 materials would you choose?
- Lithium silicates (EMAX)
- Framework Zirconia
- Cubic Zirconia
If you were going to choose a material for a posterior multi-unit FDP, what 2 materials would you choose?
- Full-contour zirconia
2. Framework zirconia
What phase of Zirconia does it mill in?
Monoclinic
Through what process at 1170 C shift Zirconia from Monoclinic to Tetragonal?
Sintering
What percent shrinkage does the sintering process cause?
20%
What is the strongest phase or Zirconia?
What isn’t good about this phase?
Tetragonal is the strongest phase
VERY Opaque
What causes Zirconia to be “metastable” after cooling from the sintering process?
Ytria in between crystals allows the Zirconia to stay in the Tetragonal phase
What does chewing/wear and tear/cyclic loading do to Tetragonal Zirconia?
Induces tiny surface cracks - causes energy in crack to shift from tetragonal to monoclinic - which is bigger - expands 4% - not clinically detectable…talking microns
What is transformation toughening?
Yes!
In some cases, the tetragonal phase can be metastable. If sufficient quantities of the metastable tetragonal phase is present, then an applied stress, magnified by the stress concentration at a crack tip, CAN CAUSE THE TETRAGONAL PHASE TO CONVERT TO MONOCLINC, WITH THE ASSOCIATED VOLUME EXPANSION (4%).
This phase transformation can then put the crack into compression, retarding its growth, AND ENHANCING THE FRACTURE TOUGHNESS
The mechanism is known as transformation toughening, and significantly extends the reliability and lifetime of products made with stabilized zirconia.
As a result, COMPRESSIVE STRESS ARE GENERATED around the crack tips.
Note that stress are higher near cracks. Consequently, the transformation takes place around cracks. The transformed material (monoclinic crystal) is SQUEEZED by the non-transformed crystal (tetragonal) that is farther from the crack.
What is the minimum strength in MPa for an Inlay, Onlay or Veneer?
50 MPa
What is the minimum strength requirement in MPa for an Adhesively Cemented Single Crown?
100 Mpa
What is the minimum strength requirement for a single crown in MPa?
300 MPa
What is the minimum strength requirement for an Anterior FDP?
300 MPa
What is the minimum strength requirement for a 3 unit posterior FDP?
500 MPa
What is the minimum strength requirement for a long span FDP?
800 MPa
What is the good and bad with PFMs?
Opacity of metal coping used in metal-ceramic restorations limits their ability to mimic the natural tooth. Good mechanical properties though.
What is the good and bad with high strength crystalline ceramics?
- Higher strength ceramics are predominantly crystalline
- More opaque
- As a result, they are often used as a framework in a bilayer restoration with a feldspathic porcelain veneer
Which has least to greatest flexural strength? Feldspathic, Glass-ceramics, Zirconia?
Greatest: Zirconia
Middle: Glass Ceramics
Lowest: Feldspathic porcelain
What has the best translucency? Feldspathic, Glass-ceramics, Zirconia?
Best: Feldspathic
Middle: Glass Ceramics
Lowest: Zirconia
What are the 3 phases of zirconia?
- Monoclinic
- Tetragonal
- Cubic
A common form in dentistry is yttria - stabilized zirconia, in which the tetragonal phase is stabilized at room temperature by adding yttria.
What are indications for Framework Zirconia?
- Multi unit FDP anterior and posterior
- Alternative to PFM and full metal restorations
What makes framework zirconia opaque?
High alumina content (0.25%)
Relative to Full-Contour and Cubic Zirconia which has Alumina content of 0.05%
How do you make framework zirconia more esthetic?
Veneer it with a more translucent feldspathic porcelain or glass-ceramic to create a more natural appearance
What makes zirconia so tough?
Transformation Toughening!
A unique process where upon application of external stress, the material expands in volume, which inhibits crack propagation and enhances the toughness of the material.
Indications for Full Contour Zirconia?
- Single Molar Crowns
- Posterior FDPs
- Alternative to PFM and Gold
What makes Full Contour more translucent?
- Lower alumina content at 0.05%
- Monolithic material unlike framework zirconia (bi-layer restorations)
Does Full Contour Zirconia have transformation toughening?
Yes!
What can even be more translucent then Full Contour Zirconia?
Cubic Zirconia
What makes Cubic Zirconia more esthetic?
Increased levels of yttria > 5 % and a high proportion of cubic phase give it more translucency.
What are some indications for Cubic Zirconia?
- Single Unit Crowns
- Anterior FDPs
Does Cubic Zirconia have transformation toughening?
No!
- High cubic phase makes it more brittle
- Easier crack propagation
What is nicer to opposing teeth, polish or glaze in regards to monolithic zirconia?
Polished zirconia results in less of wear of antagonist enamel versus glazed zirconia
What is the best way to bond Zirconia if you lack axial wall height?
- Mechanical roughening via sandblasting
- Primer containing MDP
The roughening increases the surface area for bonding, while MDP improves the resin cement’s chemical bonding.
What are indications for Feldspathic CAD/CAM material?
Excellent esthetic properties
Mainly indicated for veneers and inlays
What material is more translucent then all the Zirconias and stronger than other glass-based ceramics?
Lithium Discilicate
What are indications for Resin-Ceramic Composites?
Inlays
Onlays
Veneers
What has more predictable bonding, zirconia or LDS?
LDS, improved bonding, better esthetics
What types of restorations would you consider using Framework Zirconia for?
Posterior FDPs
What types of restorations would you consider using Full-Contour Zirconia for?
- Posterior FDPs
- Single Unit Crowns
What types of restorations would you consider using Cubic Zirconia for?
- Single Unit Crowns (can be posterior)
- Anterior FDPs
What types of restorations would you consider using LDS for?
HT: Veneers, Onlays
LT: Single unit crowns, Anterior FDPs
What types of restorations would you consider using Resin-Ceramic Composites?
Veneers, Inlays, Onlays
