Dental ceramics/certified fixed orthodontic courses by Indian dental academy

Dental Ceramics
‘Tooth look-alikes’
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

Contents
What are ceramics?
History
Classification
Composition and manufacture
General properties
Processing methods
Methods of strengthening ceramics
Metal ceramic systems
Alloys
Foil bonded
Failures

What are Dental Ceramics?

Indian Dental academy
Leader continuing dental education
Offer both online and offline dental courses

Ceramics
‘Keramos’ – Ceramic
An earthy material usually of a silicate nature
and may be defined as “a combination of one or
more metals with a non- metallic element,
usually oxygen”. (Gilman, 1967)

Types
Silicate
Oxide
Glass
Non-oxide

Dental Ceramics
Consist of silicate, glass and oxide ceramics
An inorganic compound with non-metallic
properties typically consisting of oxygen and one
or more metallic or semi-metallic elements (e.g.
Al, Ca, Li, Mg, K, Si, Na, Sn, Ti and Zr) that is
formulated to produce the whole or part of a
ceramic based prosthesis.
» Philips (11th
Ed.)

History of Dental Ceramics

History of Dental Ceramics
1000 – Porcelain was developed in China
1774 – Alexis Duchateau
1789 – Nicolas de Chemant
1808 – Giuseppangelo Fonzi
1817 – Planteau
1822 – Peale
1825 – Stockton
1903 – Dr. Charles Land

1938 – Dr. Charles Pincus
1962 – Weinstein and Weinstein
Porcelain with high TEC and low sintering temp.
Thermally compatible and bondable alloys
1965 – Mc Lean and Hughes
1980’s – Dr. Horn
1984 – Adair and Grossman: Dicor
1985 – CAD-CAM: Cerec system
1990’s – IPS Empress
1992 – Duceram LFC

Classification of Dental
Ceramics

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
e.g. Dental
porcelains
(feldspathic or
aluminous)
e.g. Pure
zirconia (ZrO2)
Pure alumina
e.g. Dicor glass
ceramic
Philips 11th
Ed.www.indiandentalacademy.com

Philips
Use or indications
Anterior crowns
Posterior crowns
Veneers
Post and Cores
FPDs
Stain ceramic
Glaze ceramic
Denture teeth

Firing temperature
High fusing - 1300˚C
Medium fusing – 1101-1300˚C
Low fusing – 850-1100˚C
Ultralow fusing - < 850˚C
Application
Core porcelain
Dentine or body porcelain
Enamel porcelain

Composition
Feldspathic porcelain
Leucite-reinforced porcelain
Aluminous porcelain
Alumina
Glass-infiltrated alumina
Glass-infiltrated spinel
Glass-infiltrated zirconia
Glass ceramic

Processing method
Sintering
Partial sintering and glass infiltration
CAD-CAM
Copy Milling
Microstructure
Glass
Crystalline
Crystal-containing glass

Translucency
Opaque
Translucent
Transparent
Method of Firing
At atmospheric pressure
At reduced pressure – Vacuum firing

Van Noort
Metal ceramics
Reinforced ceramic core systems
Alumina-reinforced PJCs
Glass infiltrated high strength ceramics
Pure alumina cores
Resin-bonded ceramics
Glass ceramics

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

Composition

Feldspathic Porcelains
A vitreous ceramic based on silica and potash feldspar
(K2O·Al2O3·6SiO2) or soda feldspar (Na2O·Al2O3·6SiO2).
Silicate ceramics
Silicate Glass

Manufacture
Fritting – the combination of blending, melting
and quenching the glass components.
Frit – resultant product after fritting.

Composition
Feldspar
Quartz
Kaolin
Alumina
Boric oxide
Oxides of Na, K and Ca
Metallic pigments
60-80%
15-25%
3-5%
6-20%
2-7%
9-15%
< 1%

Components
Feldspar
Forms glass phase
• Retains shape when fused at high temperature
• Undergoes incongruent melting between 1150-1530˚C to
form leucite.
Potash feldspar (K2O.Al2O3.6SiO2) – increases
viscosity
Soda feldspar (Na2O.Al2O3.6SiO2 – lowers fusion
temperature

Quartz
Refractory skeleton
Strengthens and hardens porcelain
Kaolin (Al2O3.2SiO2.2H2O)
Binder
Gives opacity therefore generally omitted
Al2O3
Strength and opacity
Alters softening temperature
Increases viscositywww.indiandentalacademy.com

Fluxes and Glass
Modifiers
Na, K or Ca oxide
Interrupt silica tetrahedra
Lower fusion temperature
Increase flow
Increase thermal expansion
Remove impurities
Excess :
• Reduced chemical
durability
• Devitrification on
overheating

Colouring pigments
Metallic oxides
‘Colour frits’
• Titanium oxide Yellow -→
Brown Shade
• Indium Yellow / Ivory→
• Iron oxide / Nickel oxide
Brown→
• Cobalt salt Blue→

Opacifying agents
To mask oxide layer
Metal oxide 8-15% : ZrO, CeO, TiO, SnO
Stains and color modifiers
Low fusing coloured porcelain
Other additives
Boric oxide
Lithium oxide
Magnesium oxidewww.indiandentalacademy.com

Glazes
To seal the open pores
Self-glaze or Auto-glaze
High temperature
Add-on glaze
Higher glass modifiers
Lower temperature
Less durable

General Properties
Including Advantages and
Disadvantages

Advantages
Biocompatibility
Esthetics
Colour and Translucency
Long term colour stability
Durability
Wear resistant
No Solubility
Ability to be formed into precise shapes

Disadvantages
Brittle
High shrinkage of conventional porcelains
Technique sensitive
Specialized training required
Costly equipment
More tooth reduction
Attrition of opposing tooth
Difficult to repair
Expensive

Good Properties
Translucency like enamel (Refractive index – 1.52-1.54)
High Stiffness (Elastic modulus – 10 x 106
psi)
Low thermal conductivity (0.0050˚C/cm)
Low electrical conductivity
High melting point
Low solubility

Strength
Compressive strength
350-550 MPa
Tensile strength
20-60 MPa
Brittle
Critical strain – 0.1%
Low fracture toughness

Bad Properties
Very low tensile strength
Low fracture toughness
Extremely sensitive to the
presence of surface
microcracks.
Difficult to machine
(KNH 460)

Coefficient of thermal expansion
Feldspathic porcelains
Dependent on leucite content
Metal ceramics – 13.5-15.5 ppm/˚C
All ceramics – 5.5-7.5 ppm/˚C
Pressed Leucite systems – 16 ppm/˚C

Processing
Condensation
Firing
Glazing

Compaction/Condensation
The process of packing the particles together and of
removing the liquid binder is known as condensation.
The main driving force involved in condensing dental
porcelain is surface tension.
Liquid
Distilled water
Propylene glycol
Alcohol
Special liquid

Methods
Wet brush technique/
Brush additive
technique
Brush application
method
Vibration
Spatulation
Whipping
Mechanical
Ultrasonic vibration

Layers

Firing
Sintering - A process of heating closely packed particles
to achieve interparticle bonding and sufficient diffusion
to decrease the surface area or increase the density of the
structure.
Liquid phase sintering

Furnace
Horizontal muffle
Vertical muffle
Temperature method
Temperature-time
method

Types
Air fired
Slow maturation period
Vacuum fired
Dense, pore-free mass
Shorter firing time
Diffusible gas firing procedure
Helium, hydrogen or steam

Stages
Low bisque
Porous
Minimal shrinkage
Weak
Medium bisque
Flow of glass
Shrinkage
High bisque
Sealed surface
Strong

Glazing
Advantages
Increased strength (40-46%)
Wear resistance
Lower solubillity
Less abrasive to opposing dentition

Methods of strengthening
ceramics

Why do Ceramics have a Low
Fracture Toughness?
Actual strength 100 times lower than theoretical
strength
Why?
Defects and flaws on surface or bulk of restorations

F
F
a
Surface flaw/crack acted on
by a tensile force F

The crack tip
Crack tip radius ρ

2
1
2 





=
ρ
σσ
a
tip
Where σtip = stress at the crack tip
σ = applied stress
a = crack size (diameter of the ellipse)
ρ = crack tip radius
Johnathan Knowles

ρσ
1
∝tip
As crack tip radius decreases,
stress at the crack tip increases
(Sharp corners!)
atip
∝σ As crack diameter increases,
σσ ∝tip
As the applied stress increases,
This shows that once a crack starts to propagate, the
stress required to continue the propagation falls and the
crack accelerates rapidly (spontaneous propagation).
This is the major cause for failure.

Methods of Strengthening
Strengthening of the brittle material
Development of residual compressive stresses within
the surface of the material.
Interruption of crack propagation through the
material.
Methods of designing components to minimize
stress concentrations and tensile stresses

Development of Residual
Compressive Stresses
The residual stresses must first be negated by
developing tensile stresses before any net tensile
stress develops.
Ion exchange/ chemical tempering:
Introduces larger ions into smaller ion vacancies
A molten KNO3 bath is used
Residual compressive stresses = 700 MPa
All types of ceramics are not amenable to ion-
exchange

Thermal tempering
Rapid cooling/quenching of the surface of the object
while it is in molten/softened state
Hot glass-phase ceramics are quenched in silicone oil
or other special liquids to uniformly cool the surface

Thermal compatibility
TEC alloy > TEC porcelain
Core shrinks more putting veneer in compression
Difference not > 0.5-1 ppm/˚C
Core
Veneer
Higher TEC
Radial tensile stresses
Axial compressive stresses

Interruption of crack
propagation
Dispersion of a crystalline phase
Alumina (e.g. In Ceram)
Mica (Dicor)
Transformation toughening
Partially Stabilised Zirconia (PSZ)
Contains 3mol% Yttria which causes the zirconia to form in the
metastable tetragonal form
On crack approaching, the tetragonal -ZrO2 inverts to
monoclinic-ZrO2
There is a volume expansion
This hinders crack propagation
Ceramic steel

Optimal prosthesis design
Minimise tensile stress
Minimise stress raisers e.g. sharp corners
Uniform thickness of porcelain
Use fine grit abrasive
Do not use all-ceramic restorations in high occlusal stress regions
In all-ceramics
Use greater connector height (4 mm)
Broader connector

Minimize number of firing cycles
Multiple firings
Increase in leucite content
Increase in thermal contraction coefficient of
porcelain
May cause mismatch with metal
Immediate or delayed crack formationwww.indiandentalacademy.com

MaterialMaterial
FlexuralFlexural
strengthstrength
(MPa)(MPa)
FractureFracture
toughnesstoughness
(MPa/m(MPa/m22
))
Porcelains Feldspathic
Leucite
60-110
120-180
1.1
1.2
Glass ceramics Cast/
cerammed/
premade/ hot
pressed
140-220 2.0
Alumina
Spinel
Pure/ glass
infiltrated
Glass infiltrd.
400-600
325-410
3.8-5.0
2.4
Zirconia PSZ 900 9
Tooth structures Dentin
Enamel
16-20
65-75
2.5
1
Ironside and Swain

Metal Ceramic Systems

Advantages
High strength values due to metal
reinforcement. More fracture resistant.
Improved fit on individual crowns provided by
cast metal collar.
Less tooth structure removal compared to all
ceramic restorations.
Permanent esthetics

Disadvantages
Difficult to obtain good esthetics due to increased opacity of metal
substructure.
Porcelains used in metal ceramic techniques are more liable to
devitrification.
More difficult to create depth of translucency because of dense
opaque porcelain
Preparation for metal ceramic requires significant tooth reduction to
provide sufficient space for the materials when compared to all
metal restoration.
Patients may be allergic to the metal

Indications
Discolored teeth
Grossly decayed carious teeth
Congenital anomalies
Abutment retainers
Splinting mobile teeth
Occlusal corrections
Alignment corrections

Contraindications
Patients with active caries or untreated periodontal disease.
In young patients with large pulp chambers due to high risk of pulp
exposure
Teeth where enamel wear is high and there is insufficient bulk of
tooth structure to allow room for metal and porcelain.
High lip line
Anterior teeth where esthetics is of prime importance
Short and thin crowns
Round cross section or axially tapered teeth

Feldspathic Porcelain
Leucite is a potassium aluminium silicate (KAlSi2O6)
One of the most important phases in dental ceramics
Leucite tends to form readily from feldspars
Importance:
Increases thermal expansion
Gives strength
Drawbacks:
Greater tendency to devitrify due to alkali content
Changes in thermal contraction on repeated firing
Shoulder porcelain: used with or without a knife edge metal margin
to avoid metal collar.

Types of veneering ceramics
Low fusing ceramics (850-1100˚C)
Feldspar based porcelains
Ultra low-fusing ceramics (< 850˚C)
Porcelains and glasses
E.g. Duceram LFC
• Hydrothermal glass
• Well distributed small crystal particles (400-500 nm)
• Reduced enamel wear
• No of sag of alloy
Glazes
Self-glaze
Add-on
Stains www.indiandentalacademy.com

Classification of MC alloys
(Naylor 1986)
Alloys divided into 2 systems:
A. Noble (Precious) metal alloys
B. Base-metal (Non-noble/non-precious) alloys
Each system further divided into constituents

SYSTEM GROUP
A) NOBLE METAL ALLOYS
1) Gold-platinum-palladium
2) Gold-palladium-silver
3) Gold-palladium
4) Palladium-silver
5) High palladium
High silver
Low silver
B) BASE METAL ALLOYS
1) Nickel-chromium
2) Cobalt-chromium
3) Other systems
Beryllium
Beryllium free

Requirements of MC alloys
Must be able to produce surface oxides for chemical bonding with
dental porcelains.
Co-efficient of thermal expansion should be slightly greater (0.5-1
ppm/˚C) than that of the porcelain veneer to maintain the metal-
porcelain attachment.
Melting range considerably higher than the fusing range of the
dental porcelain fired on it.
The alloy must have high temperature strength or sag resistance →
that is the ability to withstand exposure to high temperatures
without undergoing dimensional change.
Processing should not be too technically demanding.
A casting alloy should be biocompatible.www.indiandentalacademy.com

Nature of Metal-ceramic Bond
Van der Waals forces
Mechanical retention/entrapment
Compressive forces
Direct chemical bonding

Direct Chemical Bonding
Formation of surface oxides which bond to porcelain
Mechanisms:
Oxide layer permanently bonded to the metal
Surface oxides dissolved by the opaque layer. Enhanced wetting
of metal surface.
Techniques:
< 1% of Fe, Sn or In added to alloy. Bond strength increases 3
times
Direct oxide production in base metal alloys (Ni and Cr)
Electrodeposition of tin on platinum (0.2-2 µm)

Oxidation or Degassing
This high temperature processing allows specific oxides
to form on the metal surface which are responsible for
forming a mature, stable oxide layer for the porcelain
metal attachment
Also recommended for cleaning the metal of organic
debris and remove entrapped surface gases such as
hydrogen
Post oxidation treatment:
To reduce oxide layer or contaminants
Acid treatment: HF, HCl, H2SO4.
Non-acid treatment

Proprietary agents
Available for application to metal surface before
condensation of opaque layer.
Applied as thin liquid and fired like opaque layer.
Functions:
Improve bonding by limiting build-up of oxide layer on the base
metal surface during firing
Improve esthetics by helping to block the color of the dark metal
oxide

Copings for MC prostheses
Electrodeposition of Au or other metal on a
duplicate die
Burnishing and heat-treating metal foils on a die
CAD-CAM processing of a metal ingot
Casting of CP Ti or an alloy through lost wax
process

Bonding to Platinum foil
Platinum Bonded Alumina Crown
0.025 mm Pt foil burnished onto die
Coated with 2 µm layer of Sn and oxidized
Advantages
• Reduces subsurface porosity and micro cracks in the
porcelain
• Increases the strength of the unit

Twin Foil Technique (Mc Lean et al, 1976)
Inner foil of 0.025mm platinum provides a matrix for the baking
of the porcelain
Outer foil which forms the inner skin to the crown is tin-plated
and oxidized to achieve strong chemical bond with aluminous
core porcelain
Inner foil removed after firing by soaking in water
Avoids dark shadow of metal collar

Advantages
Reduction of metal and labor costs in construction.
Provision of a porcelain butt fit on the labial/buccal
surface of the crown, eliminating the dark shadow of a
metal collar.
Improvement in strength of aluminous porcelain crown
by reducing internal microcracks and subsurface
porosity
Reduction of stresses at the porcelain-metal interface
during cementation procedures.

Disadvantages
The shrinkage of porcelain makes it difficult to achieve
an accurate fit of the core porcelain in one bake
Therefore, important to allow for shrinkage and prevent
the fired porcelain from lifting the platinum skirt and
spoiling the fit
The cervical contact technique.
The cervical ditching technique

Bonding to Gold foil
1979, Rojers
Pure gold
Renaissance system
Laminated gold-palladium
alloy coping 0.05mm thick
Coping is umbrella shaped
and corrugated
All gold foil techniques
require the use of metal
bonding porcelains

CAPTEK system (Capillary
Casting Technology)
Schottlander and Davis
Captek P: wax strip impregnated
with gold-platinum-palladium
powdered alloy
Captek G: metal strips with 97.5 wt
% Au and 2.5 wt% Ag.
Thickness 0.25 mm
Bonding through interlocking and
residual stresses www.indiandentalacademy.com

Advantages
• Thinner coping
• Improved marginal fit
• Enhanced esthetics
• Biocompatibility (since 88% of the alloy is non-oxidizing)
Indications
• Single crowns
• FPDs with maximum span length of 18 mm

Indications for Foil bonded MC
restorations
Porcelain veneer crowning of adolescent teeth where
minimal tooth preparation is necessary.
Anterior teeth, when metal reinforcement is essential.
Complete porcelain cantilever bridges on anterior teeth
replacing lateral incisors
In heavily worn teeth, thin or short teeth where
minimal occlusal clearance present (not less than
0.8mm)
Repair of fractured metal- ceramic bridges, when
removal of bridge or splint is undesirable.

Contraindications
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

Failure of MC prostheses
Metal oxide-porcelain
Metal oxide-metal oxide
(Cohesive)
Metal - metal oxide
Metal - porcelain
Cohesive within metal
Cohesive within porcelain

Thank You

Dental ceramics/certified fixed orthodontic courses by Indian dental academy

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