Dental Ceramics: A Historical Perspective and Classification Guide

Dental Ceramics
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

Keramos: Greek
Keramika: Sanskrit
A material produced by firing or burning
” a combination of one or more metals with
a non metallic element, usually oxygen.”
Gilman 1967.

Phillips. 11th
Ed.
An inorganic compound with nonmetallic properties
typically consisting of oxygen and one or more metallic
or semimetallic elements( Eg: Aluminium, calcium,
lithium, magnesium, potassium, silicon, sodium, tin,
titanium and zirconium) that is formulated to produce
the whole or
part of a ceramic based prosthesis.
Definition: Dental Ceramics

Definition: Dental Ceramics
0’Brien:
Combination of one or more metals with non
metallic elements especially oxygen, larger
atoms of oxygen serving as a matrix with
smaller metal atoms tucked into the spaces
between oxygen.

Ceramics : A historical perspective……
23,000BC
5500BC:
100BC:
1000AD:
White china clay + “Chine stone”
Ceramic so white that it was comparable only to snow,
So strong that vessels needed walls only 2-3 mm thick,
and consequently light could shine through it. So continuous
was the internal structure that a dish, if lightly struck,
would ring a bell. This is Porcelain!
Earthernware:
Stoneware:
Chinese porcelain

Attempts to imitate the Chinese Porcelain……
1717: Pere, Francois Xavier d’ Entrecolles
In less than 60 years, dental restorative material!
1728: Pierre Fauchard.
1774: Alexis Duchateau: Porcelain dentures.
1791: Nicholas Dubois de Chemant of Paris
Paris Faculty of Medicine :
“united the qualities of beauty, solidity and comfort to the
exigencies of hygiene.”

1806: Giuseppangelo Fonzi : Terrometallic teeth.
1817: Antoine Plantou : porcelain teeth to America
1830: Samuel Stockton: produces first porcelain teeth in the US.
1845: SS White : Porcelain teeth on a commercial basis.
1864: Claudius Ash : Tube Teeth
1882: William Herbst : Inlays of pulverized glass.
1884: Charles H Land : Platinum foil technique.
1886 : First successful inlays.
1894: Custer :Porcelain furnace.
1898: Jenkins :low fusing porcelain
1903: Land :porcelain jacket crown
Dental Ceramics :a historical perspective….

1956: Brecker :ceramometal restorations
1962: Patents of Weinstein and Weinsteinand Weinstein et
al( 1962)
1963: First commercial porcelain :Vita Zahnfabrik
1965: Mc lean and Hughes :aluminous porcelain
1968: Mc Culloch Glass ceramic in dentistry.
1984: Grossman and Adair :Dicor
1985: Hobo and Iwata (Kyocera Bioceram group): Cerapearl.
1983: O’ Brien :high expansion magnesia core
1983: Sozio and Riley : Cerestore.
1984: Corning glass Company( Stookey): First commercial glass
ceramic
1988 :Mormann and Brandestini :CADCAM.

1988 : CEREC1
1989: Wohlwend and Scharer : Pressable ceramic
systems.
1991 : Celay copy milling system.
1994: CEREC II
1992: Ultralow fusing ceramic Ducera LFC
:Cerec3

Classification of Dental Ceramics: Phillips’
According to use or indications
Anterior
Posterior
Crowns
Veneers
Post and Cores
FPDS
Stain Ceramic
Glaze Ceramic.

According to firing temperature:
Ultralow fusing< 8500
C
Low fusing 850-11000
C
Medium fusing 11010
C-13000
C
High fusing>13000
C:
High fusing 1200/14500
C.
Medium fusing 1050/12000
C.
Low fusing 850/1050 0
C
High fusing( 850-1100)
Low fusing( < 850)

High fusing:
Minimizing the additives such as sodium or potassium,
Maximizing the silicate cross links.
Low solubility, high strength and high stability.
Hardness exceeds enamel by 30%.
Classification of Dental Ceramics:

Medium fusing:
fired under vacuum with air admitted at the end of
firing
Low fusing:
increasing the amount of additives in porcelain
reducing the number of crosslinks within the silicate network
It helps to avoid overheating the metal framework
slightly weaker and less stable than high fusing
fired under vacuum.

Ultra low fusing:
Coefficient of thermal expansion match titanium
alloys.
Lower firing temperatures -less oxide formation.

According to the
processing method:
Sintering
Partial sintering
Glass infilteration
CADCAM
Copy milling.
According to microstructure
Glass
Crystalline.
Crystal containing glass.

According to composition/Type:
Feldspathic porcelain
Leucite-reinforced
porcelain
Aluminous porcelain
Alumina
Glass-infiltrated alumina
Glass-infiltrated spinel
Glass-infiltrated zirconia
Glass ceramic
According to translucency
Opaque
Translucent
Transparent.

According to application:
Core Porcelain.
Dentin or Body Porcelain
Enamel or incisal porcelain
According to the method of firing
Air fired.
Vacuum fired.

Craig:
All ceramic
Machined
Slip cast
Heat pressed
Sintered.
Ceramic- metal
Sintered.
Denture teeth.
Manufactured.

Silicate ceramics Oxide ceramics Glass ceramics
Principal AMORPHOUS
glass phase with porous
structure i.e. mainly silica
(SiO2)
Principal CRYSTALLINE
phase e.g. Al2O3, MgO,
ZrO2
Principal AMORPHOUS
glass phase
Also contain crystals e.g.
K2O, Al2O3, MgO, ZrO2
None or small glass
phase content
Crystal phase induced
by controlled
crystallization
(feldspathic or
aluminous)
e.g.zirconia (ZrO2)
Pure alumina
e.g. Dicor glass ceramic

Single unit crowns.
Porcelain Jacket Crowns.
Metal Ceramic Crown or PFMcrowns.
Castable glass ceramic crowns.
Veneers for crowns and bridges.
Artificial teeth.
Inlays and Onlays.
Ceramic Brackets used in Orthodontia.
Applications of dental ceramics:

Ceramic V/S Porcelain :
What’s the difference?

Ceramic:
Nonmetallic
Inorganic
Man made objects formed by baking raw materials at high
temperatures.

Porcelain:
Feldspar
Kaolin Quartz
All porcelains are ceramics.www.indiandentalacademy.com

Esthetic alternative to discolored teeth.
Esthetic alternative :grossly decayed carious teeth.
Congenital anamolies
Veneers
Inlays
Onlays
Abutment retainers
Denture tooth materials.
Orthodontics as ceramic brackets.
Indications for ceramics:

Young permanent teeth.
Small short or thin crowns( relative contraindications)
PFM not indicated in high lip line patients.
Teeth round in cross section OR
Teeth more axially tapered than usual.
Abusive bite.
Patient’s lifestyle susceptible to trauma.
Contraindications:

Biocompatibility
Esthetics:
Color and translucency
Capable of being pigmented.
Colour stability.
Stain resistance.
Chamaleon like effect
Durability: Wear resistance and low solubility.
Ability to form precise shapes
High stiffness
High melting point.
Low thermal conductivity
Low electrical conductivity.
Advantages

Brittle: Low fracture toughness.
High firing shrinkage of conventional porcelains.
Attrition of opposing teeth.
More tooth reduction.
Cervical bulge and metal line in case of PFM restoration
Technique sensitive.
Specialized training required.
Expensive equipment required.
Difficult to repair if fails.
Cannot be repaired if the shade is altered.
Patient may complain of crackling sound on biting.
Disadvantages:

Feldspar
Quartz Kaolin

Composition of various porcelains( %)
Material Kaolin Silica
( Quartz)
Feldspar
( Binder)
Glasses
Decorative
porcelain
50 25 25 0
High fusing
dental
4 15 80 0
Low fusing
dental
0 25 60 15

Tile sanitory ware
Porcelain artware
Bone china
dinnerware
Dental
porcelain
Silica
ClayFeldspar

Composition of Dental Porcelain
Feldspar 60-80%( Basic glass former)
Kaolin- 3-5%( Binder)
Quartz- 15-25%( Filler)
Alumina-8-20%( Glass former)
Boric oxide-2-7%(Glass former and fluxes)
Oxides of Na, K and Ca -9-15%(Fluxes or glass
modifiers)
Metallic pigments less than 1%(Color matching)

Naturally occurring double silicate of potassium and
aluminium.K20.Al2O36SiO2
Dentistry: Potash Feldspar:
Increased resistance to pyroplastic flow
Increased viscosity.
Functions of Feldspar:
Basic Glass former.
During firing fuses to form a matrix and the porcelain
powder particles will fuse together by a process of liquid
phase sintering.
Acts as a flux and surface glaze.
Feldspar (60-80%) Basic glass former

Resistance to pyroplastic flow
Incongruent melting (11500
C and 15300
C )
Leucite:
Large coefficient of thermal expansion (20-25 ppm/0
C.)
thermally compatible with dental casting alloys.
Strengthening material.
Incongruent melting( Peritectic transformation)
Feldspar: Properties

Hydrated aluminium silicate.
Functions:
Binder.
Pyrochemical reaction: rigidity.
Opacity to the mass.
Disadvantages:
White :reduces the translucency of porcelain.
added in small amounts.
Starch or sugar.
Kaolin( 3-5%)Binder

O2
Si4+
Si4+
Si4+
Tetrahedral Silica
Quartz/ Silica (15-25%) Filler
Crystalline quartz
Cristobalite
Tridymite
Amorphous fused quartz.
Below 5750
C Alpha quartz
Above 5750
C Beta quartz
Above 8700
C Tridymite
Above 1470o
C Crystobalite

Functions:
Refractory skeleton
Provides strength and hardness to porcelain during fusing.
Unchanged at the usual firing temperatures : stability to the
mass during heating.
Quartz/ Silica (15-25%)
Grinding Pure Quartz

Functions:
Strength and opacity to the porcelain.
Alters softening point
increases the viscosity of porcelain during firing.
Aluminium oxide( 8-20% glass former)

O2
Si4+
Si4+
Si4+
Sodium carbonate
Lithium carbonate
low fusing glasses.
Function:
Lower the sintering temperature
and increase flow of porcelain.
They also absorb and remove
impurities.
Excess flux:
Reduces the chemical durability
Crystallization and devitrification
Fluxes (9-15%)
Interrupts silica network.

Glass modifiers
Lower the softening temperature.
Increase the CTE.
Decrease viscosity.
Oxides : Sodium, Potassium and Calcium oxide( 9-15%)
Boric oxide- 2-7% is also added for the same purpose.
Water is an important but a weaker glass modifier.
When porcelains are exposed to tensile stresses in moist
environment for long periods
H30+ replaces alkali metal ions in porcelain
slow crack growth
New ultra low fusing porcelains : large amount of sodium oxide and
hydroxyl group to lower the fusion temperature to as low as 6600
C.

Pigments
Feldspars are colorless or greyish.
Color frits
Metallic oxides Glass Feldspar
Ferric oxide, platinum Grey.
Chromium oxide, copper oxide Green
Cobalt salts Blue
Ferrous oxide,nickel oxide Brown
Titanium oxide Yellowish brown
Manganese oxide Lavender
Chromium tin, Chromium alumina Pink
Indium Yellow, ivory

Opacifiers:
Oxides of Cerium, titanium, zirconium and tin.
Ground to a particle size of less than 5 µm.
Differenc in the RI between glass and opacifiers cause more
opalescence.
Fluorescing agents:
Cerium oxide ( eg. Fluorescent bulbs and sunlight).
Fluorescence is the phenomenon in which an object emits light
when it is illuminated by a specific light source, in case of teeth, it
gives an appearance of vitality.
Uranium compounds: Health hazard.
Opacifiers and Fluorescing agents.

Fritting:
•Combination of blending, melting and quenching the glass
components
Frit:
•The resultant product after fritting.
•Components are mixed, fused and quenched
•Cracking and fracturing throughout the fused mass.
•Frit then ground to fine powder.
Manufacture

Pyrochemical reaction occurs and much of the shrinkage is
complete
Technician fuses the porcelain powder, he simply remelts the
fluxes without causing significant increase in reaction
between the components.
Glaze:
• Overglaze.
• Selfglaze.

Overglazes :
Ceramic powders containing more glass modifiers
Lower fusion temperatures.
The coefficient of thermal expansion slightly lower than that of
the body porcelain.
Self glaze:
Constituents of porcelain frit completely melted to form a
single phase glass.
Chemical durability is better due to higher fusion temperature.
Glazes

Strengthening of the material perse.
Methods of designing components.
Methods of strengthening porcelain

Introduction of residual
compressive stresses into the
surface of the material
Interruption of crack propogation
Ion exchange
Thermal tempering
Thermal expansion
coefficient mismatch
Polishing
Dispersion of a crystalline phase
Transformational toughening
Hydrothermal porcelain

Introduction of Residual Compressive Stresses:
The restoration will not yield and fracture due to tensile stress.
The residual stresses must first be negated by developing tensile
stresses before any net tensile stress develop.

Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
K+
K+
K+ K+
K+
K+
K+
Na+
Na+
Na+
K+ K+
K+K+
Na+
K+
K+
Before ion exchange After ion exchange
K+
K+
Na+
1.33 Ǻ
0.98 Ǻ
Stuffing

Ion Exchange:
GC’s Tuf Coat.
Internal surface of an all ceramic crown
Not recommended for new high- strength porcelains
( i.e. aluminous porcelain, Procera, In- Ceram)
Major Application:
Anterior porcelain jacket crown made from a feldspathic
porcelain without a core.

Thermal Tempering:
Quench hot molten glass in silicone oils or other liquids so as to
uniformly cool the surface.

Thermal Expansion coefficient mismatch:
Fabrication of glass or ceramic in combination with metal.
Ceramic in combination with metal are heated and cooled
The metal of the MCRs has a slightly higher CTE
It contracts more than the porcelain on cooling after firing.
Residual compressive stresses in porcelain.

Advantage:
No major investments
reduces the surface flaws.
dramatically increases the strength by 50- 100%
Shofu or Soflex finishing disks-Reglazing .
Polishing

Interruption of crack propogation

Dispersion of a crystalline phase
Aluminous Porcelain:
Alumina( Al203) is added in particulate form.
Dicor:
Mica crystals grow in situ when the cast crown in subjected
to heat treatment.
The coefficient of thermal expansion between the crystalline
material and the surrounding glass matrix require a close
match. Eg. Alumina and zirconium.

Transformation Toughening
Transformation toughened Zirconia: a polycrystalline material
Firing temperature:
Tetragonal
Room temperature
Monoclinic( 4.4%)
Stabilization of tetragonal form at room temp.
( 3-8% mass) of calcium and later yttrium or cerium.
Metastable: The trapped energy drives it back to monoclinic under stress

Disadvantages:
Long term instability in the presence of water.
Porcelain compatibility issues
Opacity.
Transformation Toughening
Change in crystal structure under stress to absorb energy from the
crack

Hydrothermal Porcelain
Duceram LFC.
specialized nonfeldspathic composition
forms a plasticized surface layer when hydrated.
Surface hardness is reduced.
Flexural strength is increased.
The increase in strength is due to the plastic nature of
the hydrated surface, which allows for deformation of
surface flaws and prevents them from propogating
through the bulk.

O
Si
O
O
O
O
O
O
Si
Si
Si
Si
O
O
O
O
O
Si
Si
Si
Si
Si
Si
Si
Si
Si
Na+
Na+
Na+
Hydroxyl groups
Hydrothermal Porcelain

The design should not be subjected to tensile stress.
Sharp line angles on the preparation and coping avoided.
The porcelain thickness should be uniform.
In PJC,the tensile stresses avoided by having favorable occlusion
In PFM, metal should be strong and ductile not allowing flexing.
In brigdes, use greater connector height( 4mm) ,broader connctor
Designing of the components:

Esthetic Properties:
Colour, translucency and vitality .
Chemical stability:
Chemically inert
Some form of fluoride can damage porcelain.
1.23 % ( APF)
8% stannous fluoride Dull and rough within min.
Hydrofluoric acid.
Stannous fluoride( 0.4%) or sodium fluoride(2%) :will not etch .
The etching of the interior with hydrofluoric acid: Bonding.
Phosphoric acid, has very little effect on dental porcelain.
Properties of Ceramics.

Shrinkage on heating:
The linear shrinkage : 11.5% for high fusing porcelain
14% for low fusing porcelain.
CTE should match tooth structure to minimize shrinkage and gap
CTE should be slightly lower than that of the casting alloy
keeping the porcelain in residual compression upon cooling from
firing temperatures.
CTE: 12-13X 10-60
C
Thermal shock failure:
Caused by uneven heating or cooling.
More severe on reheating or glazing a crown than cooling.
Thermal properties:

Compressive strength :good.
Tensile strength: Poor.
Unavoidable surface defects like porosities and microscopic cracks.
When porcelain is placed under tension, stress concentrates around
these imperfections resulting in brittle fracture.
Shear strength: low :due to the lack of ductility
Mechanical properties:

Property Value
Strength
Flexure Strength Ground-75.8 Mpa(11,000psi)
Glazed141.1Mpa( 20,465psi)
Compressive Strength 331Mpa(48,000psi)
Tensile Strength( low) 34Mpa( 5000psi)
Shear strength( low) 110 Mpa( 16.000psi)
Modulus of elasticity( high) 60-70 Mpa( 10x106 psi)
Surface hardness 460KHN 611-703VHN( Kg/mm2)

Property Value
Coefficient of thermal
expansion
Feldspathic:6.4-7.8x10-60
C.
Reinforced:12.38-16.23 x10-60
C
Thermal conductivity 2.39 Mcal/s(cm2)( 0C/cm)
Specific gravity 2.2-2.3( true is 2.242)

Fabrication of metal fused to ceramic restoration
Fabrication of coping for metal ceramic prosthesis:
Casting a pure metal( Titanium) or an alloy( High noble, noble
or predominantly base meta) through lost wax process.
Electrodeposition of gold or other metal on a duplicate die.
Burnishing and heat treating metal foils on a die.
CAD- CAM processing of a metal ingot.
The platinum foil matrix is a thin sheet of pure platinum 0.001” thick that is
swaged over a die to form a support for firing the porcelain.

Cleaned by air blasting or sandblasting.
Degassing:
Formation of an oxide layer.
Removes impurities, prevents formation of bubbles on the oxide surface
This oxide is responsible for the development of a bond between the
metal and porcelain.
Noble metals: Indium and tin
Base metal: Alloys do not need such additions.
Too thick oxide layer leads to poor bond formation.
Degassing

Building up of porcelain:
A plastic mass : Powder and liquid.
With a brush, the plastic mass is applied over the matrix. It is built
to the shape of a crown in layers of core, dentin and enamel.

Application of Wash Opaque
Powder opaque Paste opaque Spray on method

Application of opaque: Hides color and forms bond.
Dentin Layering: Body porcelain Enamel: Incisal porcelain.

The process of bringing the particles closer and of removing the liquid
binder is known as condensation.
Liquid binder :
Distilled water.
Propylene glycol :alumina core build up.
Alcohol or formaldehyde based liquids :opaque or core build up.
Aim : To pack the particles as close as possible in order to reduce the
amount of porosity and shrinkage during firing.
Factors determining the effectiveness of condensation:
Size of the particles:
One size: void space of 45%
Two sizes : 25%
Three or more sizes:22%. Gap Grading System.
Shape of the particles: Round particles :better packing compared to
angular particles.
Condensation

Methods of Condensation
Vibration
Spatulation
Brush technique
Ultrasonic
Gravitational
Whipping.

creamy
capable of being transferred in small increments.
High quality sable hair brushes
Advantages of wet brush technique:
Maintains the moisture content in the porcelain.
Metal spatulas causes more rapid drying out.
The brush can be used to introduce enamel colors, effect
masses or stains without changing instruments.
Greater control over small increments.
Blending of enamel veneers
Wet brush technique/
Brush additive technique:

Mild vibration to densely pack the wet powder
upon the underlying matrix.
The excess water :blotted with a tissue.
Serrated handle of a porcelain instrument
lightly passed over the model or die pin.
Vibration:

Spatulation:
Spatula used to apply and
smoothen the porcelain
Disadvantages:
Danger of dislodging the porcelain
particles ,may cause invisible cracks.
The sandpaper like effect of
porcelain on metal
Discoloration of the final product.

Dry Brush technique:
Dry powder sprinkled over the wet porcelain
Disadvantage:
It enhances the risk of porcelain drying out
Control of powder :difficult ,time consuming.
Ultrasonic:
Vibrator.
The low amplitude with high rate of vibrations
per second pulls the liquid to the surface with
almost no disturbance in porcelain contour.
This is a final condensing procedure.
Condensation Methods:

A large soft brush moved in light dusting action over the wet porcelain
Brings excess water to the surface,
Same brush can be used to remove any coarse surface particles along
with excess water.
Combination of vibration and the whipping.
Disadvantage:
This method works best with fine grain,
Excess manipulation could allows these fine particles to float away with
liquid during blotting.
Surface tension of water is the driving force for condensation.
Whipping

Internal or External Stains:
Intrinsic Stain Extrinsic Stain.
Built into the succesive layers of
porcelain.
Placed on the surface of
the final layer.
must be stripped completely
and rebuilt if modifications
are found necessary.
Susceptible to dissolution in
oral fluids as the fusion
temperatures of glazes are
reduced by the addition of
glass modifiers, which
unfortunately lower the
chemical durability.

Pre firing procedures:
If directly in a hot furnace:
it will evolve steam rapidly ,crumble or
explode.
Dry the wet structure in a warm atmosphere
before placing into the hot furnace.
At the elevated temperatures of the furnace,
the starch or sugar binder ignites ;
the surface of the structure blackens.
The door of the furnace is slightly left ajar.

Sintering/ Firing Procedure of Dental Porcelain:
The temperature raised to the firing temperature of the porcelain
10660
C : aluminous core porcelain
9820
C :opaque porcelains.
Densification : Sintering
Partial fusion and bonding of adjacent surfaces of particles rather
than complete melting.

Firing shrinkage: 30-40% by volume.
32-37% :low fusing
28-34% :high fusing. Due to loss of water and sintering.
Porcelain is built up of a larger size before firing.
Porosity:
Air inclusion during firing: Reduce the translucency.
Firing Shrinkage and Porosity:

Firing Methods:
9800
c
Temperature method: Temperature- Time method

Electrically heated muffle
Pyrometer :indicates the temperature.
Most furnaces :firing under vacuum.
Reduction in porosity: 4.6% to about 0.5%.
1 Horizontal muffle:
2.Vertical muffle:
Porcelain Furnace:

Air firing :
Voids or bubbles
Inclusion of air during firing
Byproduct of vitrification of feldspar.
Reduced translucency and strength.
Coarse porcelain particles are air fired.
Vacuum:
Dense pore free mass.
Reduced firing temperature.
Diffusible glass:
Diffusible gas like helium, hydrogen or steam.
Media used for firing:

Surface appearance of an unglazed porcelain : “bisque”.
Low Bisque:
Rigid and porous.
Little shrinkage.
Particles lack cohesion
Do not have translucency or glaze.
The grains begin to lense at their contact points.
Medium Bisque:
Cohesion between the particles.
Still porous, lacks translucency and high glaze.
Definite shrinkage.
High Bisque stage:
Shrinkage is complete ,mass exhibits a smooth surface.
Slight porosity.
The body does not appear to be glazed.
Stages in maturity:
Lesser firing: Higher strength and esthetics.www.indiandentalacademy.com

First dentin firing
Second dentin firing

Finishing Glazing
Completed restoration.
Glazing:
Improves appearance.
Removes surface imperfections.
Improves mechanical properties

Advantages:
High strength.
Ideal for long span bridges.
Excellent fit.
Disadvantages:
Appearance of metal margins.
Discoloration by metals.
Difficulty in producing an appearance of translucency.
Bond failure with metals.
Possible disadvantages of alloys used.
Extensive tooth reduction( 1.75 mm).
Porcelain- Fused- to Metal Alloys:

Indications for metal ceramic restorations.
Discolored teeth.
Grossly decayed carious teeth.
Congenital anamolies.
Abutment retainers.
Splinting mobile teeth.
Occlusal corrections.
Contraindications:
Active caries or untreated periodontal disease.
In young patient with large pulp chambers.
Enamel wear is high and there is insufficient room for M and P.
High lip line.
Where esthetics is of prime importance.
Short and thin crowns.
Metal Ceramic Restorations.

Requirements for alloys for porcelain bonding.
Coefficient of thermal expansion of alloy close or nearly the same
as that of porcelain. High tensile stresses will otherwise develop.
Fusion temperature of the alloy higher than that of the porcelain
so that it resists melt or sag at the firing temperature of porcelain.
The modulus of elasticity: should be high to prevent flexing of metal
framework and hence avoid fracture of porcelain.
Capable of forming bond with porcelain.
Oxide formation which provide a chemical bond.
Capable of wetting porcelain :mechanical bonding.
Should not contain copper or silver.
Should have a high proportional limit, to avoid excess stress on the
porcelain, which is brittle.

Changes in alloys for PFM Restorations.
Platinum
Palladium
Copper
Silver
Melting temperature
1200-13000
C.
Higher elastic properties.
Greater sag resistance.
CTE matching the porcelains.
Poor castability.

Noble metal alloy systems:
High gold: Gold platinum palladium
Low gold: Gold palladium silver
Gold free: Palladium silver
Palladium Copper.
Base metal alloys:
Nickel Chromium alloys without beryllium.
Nickel Chromium alloys with beryllium.
Co- Cr based alloys.
Foil copings
Bonded platinum foil coping.
Swaged gold alloy foil coping.
Cast metal ceramic alloys:

Typical composition for alloys for PFM restorations
% Au Pt Pd Cu Ag Others
High gold 86 9 5 - - -
Low gold 52 38 - - - 9% In
Pd Ag - - 65 - 35 -
Pd Cu - - 80 15 - 5% others
Ni Cr - - - - - 65%Ni,17%Cr

Composition of ceramic for metal ceramic restoration.
Increased CTE.
Tendency to devitrify and appear cloudy.
Should not be subjected to repeated firing cycles.
Soda
Potash

Nature of the metal ceramic bond:
Chemical bonding:
•Primary bonding mechanism for most dental ceramics.
•Adherent oxide layer is essential for good bond formation.
•Precious metal alloy: tin and iridium oxide
•Base metal alloys :chromium oxide.
For good chemical bonding:
•Sandblasting,
•Ultrasonic cleaner
•Oxidation.

Procedure recommended to clean the metal of organic debris and
remove entrapped surface gases such as hydrogen.
Advantage:
Removes volatile contaminants not eliminated by Steam or air abrasion.
Allows specific oxides to form on the surface which help in bonding.
Post oxidation treatment:
To reduce oxide layer:
Acid treatment: Hydroflouric, Hydrochloric or dilute sulfuric acids.
Non acid treatment: Air abrasion with pure 50 μm aluminium oxide.
Oxidation or degassing:

Oxide layer is permanently bonded to the metal substructure
on one side while dental porcelain remains on the other.
Oxide layer sandwiched between the M and P.
Surface oxides dissolve or are dissolved by the opaque layer.
Porcelain is brought into atomic contact with the metal
surface for enhanced wetting by the metal, and direct
chemical bonding by sharing of electrons between porcelain
and metal.
Both covalent and ionic bonds are thought to form, but only a
monomolecular layer of oxide is thought to be responsible for
bonding.

A layer of pure gold is deposited onto the cast metal,
short flash deposition of tin.
Cobalt chromium, stainless steel.
Palladium silver, high and low gold content alloys
Titanium.
Advantages:
Improved wetting of the metal by porcelain.
Electrodeposited layer acts as a barrier to inhibit ion penetration by
the metal
Gold color of the oxide film :vitality and esthetics.
Color control of the oxidated surface from gray to reddish brown to gold
Deposited layer acts as a buffer zone to absorb stresses.
The maturation time and temperature of the porcelain is reduced :highly
reflective surface of the gold layer, and the infrared radiation emitted by
the gold on heating.
Bonding using electrodeposition:

Mechanical interlocking:
Presence of surface roughness
Wettability is important for bonding.
Smaller the contact angle: better is the wetting efficiency.
3. Vanderwaals Forces:
Secondary forces generated by a physical attraction between the
charged particles rather than by actual sharing of electrons
4. Compressive Forces:
Ceramic is strongest under compression and weakest under tension
Hence if the coefficient of thermal expansion of the metal substrate is
greater than the porcelain fired over it, porcelain is under compression.
Nature of the metal ceramic bond

Bond failure classification:
Type I: Metal porcelain:
When the metal surface is totally depleted of
oxide prior to firing porcelain, or
When no oxides are available( Gold alloys).
Also on contaminated porous surface.
Type II: Metal oxide- porcelain:
Base metal alloy system.
The porcelain fractures at the metal oxide
surface
leaving the oxide firmly attached to the metal.
Type III: Cohesive within porcelain:
Tensile fracture within the porcelain when the
bond strength exceeds the strength of the
Metal
Porcelain
Metal
Porcelain
Metal oxide
Metal
Porcelain
Porcelain
Metal oxide

Type IV: Metal- metal oxide:
Base metal alloys
Due to the overproduction of Ni and Cr oxides
The metal oxide is left attached to ceramic.
5.Type V: Metal oxide- Metal oxide
Fracture occurs through the metal because of
the overproduction of oxide causing a sandwich
between porcelain and metal
6. Type VI :Cohesive within metal
Unlikely in individual metal ceramic crowns.
Connector area of bridges.
Metal
Porcelain
Metal oxide
Metal
Porcelain
Metal oxide
Metal oxide
Metal
Porcelain
Metal oxide

Improved bonding on the bondable surface of the metal
can be achieved by the following ways:
•Grit blasting with 30-50µm alumina particles at an air pressure of
0.4 to 0.7 Mpa .
•Electrochemical etching.
•Naturally formed oxides on the base metal surface also contributes
to the bonding when MDP or 4 META based resins are used.
•In noble metals :electrochemically deposit a thin layer of tin( 0.5µm)
on noble metal and heat it to an appropriate temperature to
form metal oxide.
A silica coating can be used to improve bonding to noble and
base metal alloys
Bonding of metallic prosthesis

Bonded platinum foil coping:
Defects originating from the internal
surface of the crown:
Fracture of porcelain.
Tinplating the platinum foil.
Laying down 2 platinum foils in close
approximation with each other.
Inner foil: 0.025 mm platinum
provides a matrix for baking ceramic
Outer foil: forms the inner skin to the crown
tin plated and oxidized
strong chemical bond with aluminous
porcelain crown.
Bonded alumina crown/ twin foil technique: Mc Lean and Sced( 1976)
The inner foil is then removed after porcelain firing.
Bonded gold foil coping: Rogers 1979. UMK68www.indiandentalacademy.com

To prevent porcelain from lifting the platinum skirt and spoling the fit:
Cervical Contact technique:
Application of a layer of porcelain on the shoulder area to shrink first.
The second bake will then shrink towards the cervical porcelain and
maintain the fit.
Cervical ditch technique:
Porcelain is removed from the shoulder area after the initial build up is
complete, such that a thinnest ditch possible is made to expose the
cervical platinum at the shoulder.

Removal of platinum foil:
Soaking the crown in water.
A fine pointed tweezer is used to lift the skirt away from the edge.
Peel the platinum away from the entire circumference without
damaging the fine porcelain edge (internally towards the incisal
edge).

Porcelain veneer crowning of adolescent teeth where
minimal tooth preparation is necessary.
Anterior teeth, when metal reinforcement is essential.
In heavily worn teeth, thin or short teeth where minimal
occlusal clearance present (not less than 0.8mm), porcelain
crowning of all anterior teeth is indicated.
Repair of fractured metal- ceramic bridges, when removal of
bridge or splint is undesirable.
Coping jacket crowns on unit built bridge -work
Indications for bonded alumina crowns

In periodontally involved teeth, where preparations extend
deeply into root- face and no shoulder preparations are
possible.
Posterior teeth where large areas of tooth are missing and
uneven bulk of porcelain is inevitable.
If lingual shoulder preparations are impossible particularly in
molar region.
Contraindications for bonded alumina crowns

Dr. Itzhak Shoher and Mr. Aaron Whiteman in Europe
Fabrication of PFM restorations without waxing, investing or casting.
Pleated gold and palladium foil consisting of four layers.
Technology of Clad metals:
4 layers clad in a sandwich fashion under high pressure.
Renaissance Crown( Non cast metal ceramic
system)
0.997 Pure palladium
Gold ceramic alloy
Gold ceramic alloy
24k Pure gold.
The pleats are folded, crimped , burnished and swagged.
Heat treated to permit diffusion of the layers to form a interfacial
material.

Initial adaptation:
The form is placed on the die until it
touches the occlusal or incisal surface
The pleats of the form are then closed
with crimping forceps.
Cutting the folds:
The midpoint of each pleat is determined
Cut is made through the pleat with the
crown scissors provided.
Simultaneously twisted to allow for the
final alloying of the metal during
alloying process.
Renaissance Crown fabrication:

Folding the pleats:
Pleats are then folded in the same direction
with the crimping forceps.
Burnishing the form:
Burnished and closely adapted
Swagging:
After appropriate die spacing,
form and the die and placed in a swagger

Alloying:
Propane torch for 4-6 Sec.
Glow brightly , gold will diffuse through the cuts
Interfacial alloy:
It is a metal ceramic solder in powder form
produced by precipitation,
mixed into a creamy paste
applied onto the form.

“Capillary casting technology”.( Captek, Davis
Schottlander and Davis, Letchworth, UK)
Principle of capillary attraction to produce a gold
composite metal.
Elimination of casting process .
Procedure:
Adaptation of a wax strip, impregnated with a
gold- platinum- palladium powdered alloy, to a
refractory die. ( Captek P)
Firing procedures produce a rigid porous layer
which is then infilled with gold from a 2ND
wax strip
( Captek G) by capillary action
The finalized metal coping is then veneered
with porcelain.
CAPTEK

Fig shows the metal coping after firing.
The shear bond strength values atleast equal to PFM.
Composite
Gold matrix reinforced with small particles of Pt-Pd- Au
alloy
The inner and outer surfaces contain approximately
97% Au. The grain size of the foil is 15-20µm.
High melting temperature
Capillary effect when ceramic is applied.
Advantages of CAPTEK:
Improve marginal fit(capillary cast, rather than lost wax )
Enhanced esthetics.
Biocompatibility.

Dental Ceramics: A Historical Perspective and Classification Guide

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