Definition of ceramic materials:
The word ceramic is derived from the Greek word:
Ceramic materials are inorganic compounds formed of
metallic or semi-metallic & nonmetallic elements, which
are subjected to high heat treatment [firing] for a time
period to achieve desirable properties.
A ceramic material consists of two phases:
Vitreous phase [Glassy phase]:
It is the phase which is responsible for aesthetics only.
It is formed by vitrification, where the molten glass has been cooled
It is amorphous in structure.
2. Crystalline phase:
It is the phase which is responsible for strength & hardness only.
It is formed by de-vitrification, where the crystallization of the glass
occurs at high temperature in the presence of nucleating agents.
It is crystalline in structure.
Dental porcelain is a vitreous ceramic based on silica network.
Powder in different shades mixed with distilled water .
1. Denture teeth.
2. Crown & bridge.
5. Laminate veneer. [Layer of ceramic bonded to the facial surface of
the prepared tooth]
They are an-hydrated potassium & sodium aluminum silicate.
Upon firing at ~12000, they: fuse, become glassy, retain their form without
If potassium aluminum silicate ∆treatment Leucite + Glassy phase
The precipitation of leucite [Crystalline structure] will change the properties
of dental porcelain:
* Increase strength.
* Increase hardness.
* Increase α.
* Decrease aesthetics.
2. Quartz [Crystalline phase]:
It is present as fine crystalline dispersion throughout the vitreous phase.
It remains unchanged during firing.
It acts as strengthening agent.
It is hydrated aluminum silicate.
It becomes sticky during mixing
During firing, it adheres to quartz & shrinks considerably.
.·. Recent dental porcelain does not contain kaolin.
This is known as feldspathic porcelain
It is an alkali metal ion, as sodium, potassium or calcium which can
associate with the oxygen atoms at the corners of the silica tetrahedra
of the vitreous phase, thereby:
Lowering the fusing temperature of the dental porcelain to be
suitable for different applications.
Increasing its α.
Increasing its fluidity.
N.B.: Effect of high concentration of glass modifier:
It reduces the chemical durability of the vitreous phase.
Devitrification [Crystallization] may occur during porcelain firing.
It is a low fusing glass e.g. boron oxide based glass
Its action is similar to glass modifier.
Sugar & starch:
They help in forming workable mix instead of kaolin.
Pigments & fluorescent agents:
They provide different & natural shades.
Blending the components then melting.
2. During melting, the glass modifier & the flux combine with silica
tetrahedra of the vitreous phase. [thermo-chemical reactions]
3. The material, while red hot, is then quenched to obtain frit.
4. The frit contains two principal phases:
The vitreous phase.
b. The crystalline phase.
Pouring of die.
Adaptation of the platinum foil matrix, which retains the
dental porcelain mix in the shape of the tooth preparation.
The tooth shade is produced by three basic shades of the
dental porcelain powder: opaque, dentin & enamel shades;
the following steps (except the glazing) are repeated for each shade
7. Dental porcelain powder, in the selected shade, is mixed with
distilled water to a creamy consistency
8. The mix is applied in excess [~13%oversize] to the platinum foil
matrix to compensate for shrinkage during firing
9. Proper compaction of the mix is done by vibration, spatulation or
addition of dry powder.
Proper compaction to get rid of excess water shrinkage & porosity in
the dental porcelain.
10. The platinum foil matrix with the oversized mix is placed in an opened
preheated electric porcelain furnace to ensure removal of excess water
without steam. [Drying]
Firing of the mix is done at controlled time & temperature under
Firing is done :
*To remove remaining water
*To fuse DP powder particles at their contact areas forming
a continuous mass [sintering] i.e. no melting or chemical
12. Slow uniform cooling should be done to avoid surface cracks, which are
developed due to
*Large α mismatch between vitreous & crystalline phases.
* To produce smooth, shiny & impervious surface.
* To improve aesthetics & strength.
Glazing is performed either by:
It is the flow of the glass from the D.P. restoration to its surface.
- Addition of low fusing glass to the surface of D.P. restoration.
Generally the properties of D.P. are related to:
1. Biological properties:
D.P. is inert. i.e. Tissue friendly & biocompatible
2. Solubility & Disintegration:
D.P. is indestructible in oral fluids.
Only strong chemicals e.g. Hydrofluoric acid can dissolve D.P.
Dimensional changes during firing:
A considerable amount of shrinkage & porosity occurs due to:
Densification as result of sintering.
Evaporation of excess water.
Loss of binder(kaolin) if present.
To decrease the shrinkage & porosity, the following should be done:
Use of small & large powder particles for proper compaction.
Firing under vacuum.
High compressive strength. [Strong bond]
D.P. is even harder than enamel causing wear of the opposing natural teeth;
To reduce this risk:
*Use ultra-low fusing ceramic (less abrasive)
*Glazing to produce smooth surface (less abrasive)
Brittle i.e. Low tensile strength, Low fracture toughness. [Ionic bond].·.
Bulk thickness is required necessitates more tooth reduction.
The strength of DP is usually measured in terms of flexure strength.
[Combination of compressive, tensile & shear strength]
D.P. is stiff material [High modulus of elasticity Only limited elastic
deformation(0.1% strain) can be tolerated before fracture..
D.P. is a translucent material.
Three basic shades of D.P. powder are used: opaque, dentin & enamel
shades to recreate the color of the tooth.
Once the exact color is obtained, it is quite satisfactory & stable
Bonding to tooth structure
Since D.P. restorations are of indirect type, thus their bonding
*The type of the used cement.
*The surface treatment of the tooth & restoration
D.P. is electrical & thermal insulator. [No free electrons]
It has low α. [Strong bond]
The strength values of D.P. << the predicted strength values based on the
strength of their primary interatomic bond. Since DP
*Contain unavoidable fabrication defects & surface cracks.
* Is a brittle material & fractures by crack propagation.
These cracks cause the localized stress at their tips; narrow as the interatomic spacing in the material; to increase reaching the theoretical
strength of the material at a relatively low average stress.
These cracks propagate leading to catastrophic failure of the material.
The methods of strengthening:
Reducing the surface defects.
Interruption of crack propagation.
Development of residual compressive stresses within the surface of the
The methods of strengthening:
Designing components of the restoration with no sharp line or
point angles to reduce stress concentration.
Reducing the surface defects [Stress raisers] to reduce stress
Use of powder with large & small particles.
b. Proper proportioning.
d. Proper drying.
Firing under vacuum.
Interruption of crack propagation:
As the D.P. is a brittle material, it fractures by crack propagation.
There are two methods for crack interruption:
a. Dispersion of tough particles to absorb energy from the crack&
deplete its driving force for propagation [Crack deflection] e.g.
b. Crystal structural changes under stress: [Crack healing]
The energy at the crack tip is absorbed to be used for phase
transformation of zirconia from tetragonal to monoclinic structure.
This phase transformation is accompanied by6%volume expansion,
which will close the crack. [Crack healing]
But the refractive index of zirconia >>than that of the surrounding
structure leading to opacity.
Development of residual compressive stresses within the surface
of the material:
These developing compressive stresses should be first negated by
induced tensile stresses before any net tensile stress occurs.
Developed compressive strength
Normal tensile strength
i.e. The material would take a total tensile stress of 100 MPa to fracture.
Development of residual compressive stresses within the
surface of the material:
a. Ion exchange:
It involves the forcing of the larger potassium ion into the place
previously occupied by the smaller sodium ion creating residual
compressive stresses in the surface of the material during the
b. Thermal tempering:
It involves the rapid cooling of the material while it is hot producing
a skin of rigid glass surrounding a molten core which is going to
c. Thermal compatibility:
Ceramometallic restoration consists of metal coping & fired ceramic
It is three times stronger than the ceramic alone.
Strengthening depends on slight mismatch in the coefficient of
thermal expansion & contraction between metal &ceramic i.e. α of
metal>α of ceramic.
1. Fusion temperature.
2. Type of restoration.
The fusion temperature is that temperature, at which the powder
particles of dental ceramic fuse together during firing.
High fusing ceramic
Medium fusing ceramic
Low fusing ceramic
Ultra low fusing ceramic
type of restoration
Any ceramic restoration is divided into two parts:
type of restoration
According to type of restoration:
A. Porcelain fused to metal restoration:
It consists of metal core & sintered ceramic veneer.
It is three times stronger than ceramic alone.
Requirements of ceramic for successful restoration:
Firing temperature of ceramic<Melting temperature of metal to avoid
melting or sag of metal.
α of ceramic < α of metal [Slight mismatch] to develop residual compressive
stresses at their interface for
- Strengthening of ceramic.
- Compressive bonding between
ceramic & metal.
Strong interfacial bonding between ceramic & metal is obtained by:
- Compressive bonding.
- Ceramic bonds chemically to the surface oxides of the metal [Adhesive bond].
- Ceramic enters into the surface irregularities of the metal[mechanical interlocking].
Ceramic should be strong.
Ceramic should mask the color of the underlying metal
Composition of the ceramic fired to metal:
Leucite [crystalline phase]:
α of ceramic to be slightly < the higher α of metal.
Strength of ceramic.
Firing temperature of D.P. < Melting temperature of metal.
α of ceramic to be slightly < the higher α of metal.
In the opaque shade to mask the color of metal.
B. All ceramic restoration:
It consists of ceramic core & veneer.
The ceramic core consists of a variety of crystalline phases up to 99% by
Factors affecting the properties of all ceramic restoration:
The nature, amount & particle size distribution of the crystalline phase
influence the mechanical & optical properties of all ceramic restoration.
ii. The match between the refractive indices of the crystalline & glassy phases of
the ceramic core controls the translucency of all ceramic restoration.
iii. The α of ceramic core > the α of ceramic veneer to obtain compressive
Types of all ceramic restorations according to the processing techniques:
- Slip casting
- Heat pressing
Sintered all ceramic material:
The all ceramic crowns have been known since 1900s.
However, they were brittle & fractured easily [half moon fractures]
In order to increase the fracture resistance, the content of the
crystalline phase of the ceramic core is increased by:
Heat- Pressed all ceramic material: [High temperature
Heated ceramic ingot is injected under air pressure into a refractory mold.
After solidification & divesting, the ceramic core is ready for veneering.
Glass ceramic + leucite crystals for inlay , onlay, veneer & crown
*IPS Empress 2:
Glass ceramic + lithium disilicate crystals for crown & bridge
iii. Slip-Cast all ceramic material:
It is supplied as one of the three core ceramics:
Inceram Alumina, Inceram Spinell , Inceram Zirconia.
A slurry[slip]of one of these materials is deposited on the refractory die.
The water from the slurry is absorbed by the capillary action of the porous
die leaving a layer of either Alumina , Spinell or Zirconia on the surface.
This fragile layer is dried & fired (sintered) at certain temperature for certain
time according to the used Inceram.
During firing the refractory die shrinks more than the deposited layer so
that it can be separated easily from the die.
This fired porous core is subjected to glass infiltration process ,where
molten glass is drawn into these pores by capillary action at high
The excess glass is trimmed off.
The ceramic core is now ready for veneering.
Alumina Inceram for short span anterior bridge.
[Intermediate translucency & strength]
Spinel Inceram for short span anterior bridge.
[Highest translucency but lowest strength]
Zirconia Inceram for short span posterior bridge.
[Lowest translucency but highest strength]
- High strength
- Luting with any cement except Spinel Inceram
-High opacity except Spinel Inceram
-Long processing time
-Inability to be etched to aid in cementation
-CAD/CAM [Computer assisted design/Computer assisted
It is used to produce ceramic inlay, onlay or veneer in one visit.
-The preparation is optically scanned [Optical impression]
-The image is computerized.
-The restoration is designed by the aid of the computer
-The restoration is then ground from dense ceramic blocks by a computer
controlled milling machine according to the computerized image.
-Early models ground only the internal surface of the restoration and the
external surface is ground manually.
-Recent models grind both surfaces.
Copy milling :
It is used to produce ceramic core for crown & bridge.
Preparation of stone die
Preparation of resin pattern.
The resin pattern is placed on a machine similar to a pantographic
device used for duplicating house keys.
A tracing tool passes over the pattern guiding a milling tool which
grinds a copy of the pattern from Inceram block.
The milled ceramic core is then glass infiltrated.
The glass infiltrated core is built up with veneering porcelain &fired
Type of used ceramic:
Dense Inceram (Alumina, Spinell or Zirconia) block
Advantages of machinable ceramics:
Reduced chair time
Single appointment (in CAD/CAM restoration)
High strength due to less porosity
Disadvantages of machinable ceramics:
Poor marginal accuracy
Advantages of all ceramic restoration:
Better aesthetic, as no metal collar, subgingival
grayish shadow or poor translucency
More hygienic ,as no metallic hypersensitivity or
Disadvantages of all ceramic restoration:
Less strength than ceramometallic restoration
In a bridge, the connectors should be sufficiently
thick to resist the high tensile stresses.