Ceramic Restorations Flashcards by Michael McMahan

Enhanced esthetics due to the absence of metal
and improved light transmission.
-Looks like a tooth!
-Most beneficial for teeth with normally colored
dentin as the dentin color can affect restoration
through it

Ceramics

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Most realistic restoration that
looks like a tooth!
HIGH esthetic capabilities

Ceramics

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(3 ways) Why and How does ceramic look so much like a real tooth?

Color Replication
-Ceramics can be tinted/colored to produce 
nearly any tooth shade
Refraction
-Ceramics reflect and absorb light rays 
simulating enamel
Translucency
-Type of porcelain (incisal/dentin/opaque)

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Are ceramics tough or brittle?

Brittle

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Defined as the strength of a material in bending

- Stress on the outermost fibers of a bent test specimen, at failure

Flexure strength

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-Defined as the resistance to fracture when crack present
-Metals –high FT due to plasticity at tip of crack, absorbs energy, making crack
propagation more difficult
-Ceramics –low FT –little plasticity

Fracture toughness

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Ceramics _____ as they are fired

shrink

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Are ceramics more of conductors or insulators?

Thermal insulators

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Do ceramics have low or high fracture strength?

Low fracture strength

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(why ceramics fail at lower than
expected stress)
-Crack will propagate through material, or until a particle
is met which stops the crack growth.

Crack propagation

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Increase in number and size of particles does what for crack propagation?

Decreased crack propagation

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-Strength is reduced in moist environment.
-Stress-dependent chemical reaction between water
vapor and crack tip, causing crack growth and
fracture with comparatively little occlusal loading
(over long periods).

Stress Corrosion

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-Ceramic powder/liquid is built up and molded (feldspathic porcelain)
-Process of heating ceramic powder once molded
-Called “Firing” the ceramic
-Sintering is the reduction of porosities between particles as the ceramic
becomes more rubbery.

Sintering:

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This is a range of temperature where porcelain starts to become molten.
A transition from solid to rubbery.
This is typically between 540 and 610 degrees Celcius.
This is below the ceramic melting point.

Glass Transition Temperature: (Tg)

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What temp range do ceramics start to become rubbery?

540-610 C

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Relies on external pressure to sinter and shape the ceramic at high temperature
Restoration is made from a Wax pattern (lost wax technique)
Also known as High Temperature Injection Molding

Heat Pressing:

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-Hard Milling
-Already densely sintered material
-Silicate, glass ceramics, resin-based
ceramics

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\_\_\_\_ Milling
-Partially sintered material
-Zirconia and Lithium Disilicate (e.Max)
-Sintering to be completed in oven AFTER
manufacture

-Soft milling

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_____ Milling
-Already densely sintered material
-Silicate, glass ceramics, resin-based
ceramics

-Hard milling

_____ ceramics

Most translucent optical properties
Weakest material
Feldspathic porcelain
Can ETCH

Predominately Glass (veneers)

_____ ceramics

Less translucency
increased strength
Lithium Disilicate
Can ETCH

Particle filled Glass Ceramic (eMax)

_____ ceramics

Low translucency
Highest strength
Alumina, Zirconia
Cannot ETCH

-Polycrystalline Ceramic (zirconia)

-Can bond tooth to ceramic with the
etchable ceramics
-Use of a “coupling agent” Silane enhances
bond strength
-Resin cement used – either light cure or dual
cure

Resin bonding

-Dispersed Crystalline phase
– Higher strength
and fracture resistance
-Lithium Disilicate

Reinforcement of the crystalline structure

of the ceramic

-Stress induced transformation -Unique to zirconia -Compressive forces at crack tip retard crack propagation

Transformation Toughening

Resin bonding is a high strength cementation procedure, so bonding ceramics will _____ the ability of the ceramic to flex. Therefore, adds strength.

decrease

___% increase in glass ceramic crown strengthHF Etched ceramic surface (retention) Silane coupling agent (bifunctional monomers form a chemical bond) Resin Composite Cement Etched enamel / dentin –adhesive layer

50%

-Very thin “sheet” of porcelain as thin as 0.3 to 0.5 mm (minimal thickness) -Tooth preparation is specific and is aimed at providing aesthetics and physical support for the veneer. -Veneers are not under heavy occlusal loads. -These are resin bonded to enamel -Can be the most esthetic dental restoration possible -Can be so thin, underlying tooth color can affect optical properties. -Most technically difficult to fabricate

Veneers

-Enamel flexural strength is around 300 MPa -Feldspathic Porcelain flexural strength is much lower at 60-70 MPa -We discussed how to strengthen the porcelain material previously. One additional method to strengthen this porcelain is to add a metal substructure. -Yes! The PFM (porcelain fused to Metal crowns)! -

Feldspathic porcelain

-Enamel flexural strength is around 300 Mpa -Leucite reinforced ceramic flexural strength is 120-160 MPa -Would you use this material on a posterior tooth? -Crown – No -Onlay/Inlay – maybe (only where occlusal force is low) -Would Resin bonding help strengthen this material? -Yes. It can be etched and therefore retention and strength is increased with resin bonding. -Indications – anterior crowns, veneers

-Leucite reinforced Ceramic (Empress)

-Enamel flexural strength is around 300 Mpa -Flexural strength for e.Max is 360-500 Mpa -Finally stronger than tooth alone! -Due to its increased strength, Lithium Disilicate is used for: Veneers Anterior and Posterior crowns Anterior bridges (particular cases) Inlays/Onlays with low occlusal forces -Can use resin bonding AND other cements like Resin Modified Glass Ionomer (RMGI)

-Lithium Disilicate Ceramic (e.Max)

``` has a Polycrystalline structure-This provides increased strength -This provides a surface that is not abrasive like porcelain, but instead is gentle on opposing dentition. -Resin Bonding will not increase the strength of Zirconia-Resin bonding will do what for zirconia? -Retention! -Zirconia needs the internal restoration surface to be roughened since it cannot be etched. (Zirconia contains no glass to etch)-Air abrasion -diamond bur ```

Zirconia

Does porcelain or zirconia need to be roughed on the internal surface nor will resin bonding work on it?

Zirconia

-Original crown was from Glidewell Lab 10 years ago.-3Y zirconia crown called Bruxir -Horrible translucency aesthetic early on -Poorly defined occlusal anatomy -3Y Bruxir flexural strength around 1200 Mpa -Because of its toughness, any cement can be used. -Crown has to be ”fired” and will shrink to fit. Shrinks about 25% during firing.

Zirconia

-Stress induced transformation -Unique to zirconia -Compressive forces at crack tip retard crack propogation Phase transformation from tetragonal (T) to monoclinic (M) has associated volume increase (3-5%) →high internal stresses. -Crack initiated; tensile stress at crack tip causes tetragonal→monoclinic shape change -Volume increase with associated compressive stresses in vicinity of crack tip leading to crack closure

-Transformational Toughening

What is the phase transformation that occurs in zirconia during transformational toughening?

tetragonal→monoclinic shape change

-Adding more _____increases translucency -This results in decreased strength

Yttria

``` A _____ crown is a porcelain fused to Zirconia. -Early candidates in this market were not very successful. Lots of porcelain fractures. However, newer formulations are finding greater success and ethetics! -Monolithic options were/are not very esthetic but are much stronger and do not fracture easily. If they were esthetic, were they likely to be strong? ``` - can mask dark dentin cores

PFZ

Can ceramic or zirconia be cemented with any type of cement?

Zirconia

If you want the most esthetic anterior restoration, what material would you choose? - Veneer – ? - Crown – ?

- Veneer – Feldspathic Porcelain | - Crown – e.Max or Empress

-If you want the most esthetic posterior restoration, what material would you choose? -Crown – ? -Crown - ?

- Crown – e.Max | - Crown - 5Y Zirconia

- If you have a bruxing patient, what posterior restoration material would you use? - Crown – ? - Crown – ?

- Crown – 3Y Zirconia | - Crown – Gold

-Only adjust after seated and bonded with resin cement (too fragile to adjust outside the mouth predictably. -Use fine diamonds with a little water -Polish with diamond impregnated polishing paste -Internal surface should not be adjusted if at all possible

Glass Ceramic Veneers

- Adjustment outside the mouth is acceptable - Fine diamond with a little water - Polish with diamond impregnated polishing paste - Internal surface should not be adjusted if at all possible

e.Max (Lithium Disilicate)

-Adjustment outside the mouth is acceptable -Fine diamond with a little water -Polish with diamond impregnated polishing paste -Internal surface needs either air abrasion or diamond bur roughing prior to cementing!

-Zirconia

``` ____ cements -Requires moisture free environment -Required for low strength ceramics -Why? -Requires silane coupling agent for etched ceramics -Primer containing MDP (methacryloyloxydecyl dihydrogen phosphate) placed on zirconia can enhance the chemical bond to cements containing resin. ```

Resin Cements

-Contraindicated in low strength ceramics -Water absorption with setting of cement leading to slight expansion and possible fracture of ceramic at thin margin area -Acceptable for Zirconia

Resin Modified Glass Ionomer