All Ceramics - Dental

All Ceramics – Dr. Nithin Mathew
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ALL CERAMICS
(Material Aspect)
Dr. Nithin Mathew

CONTENTS
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• Introduction
• History
• Classification
• Composition
• Advantages & disadvantages
• Manufacture
• Fabrication
• Methods of strengthening ceramics
• All Ceramic Systems
• Selection of ceramics
• Conclusion
• References

INTRODUCTION
• Ceramic - First material to be artificially made by humans.
• Ceramic is derived from the Greek word ‘keramos’, which means ‘potter's clay’.
• Earliest techniques consisted of shaping the item in clay/soil and then baking it to fuse the
particles together, which resulted in coarse and porous products.
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• The term CERAMIC refers to any product made essentially from a non metallic inorganic
material processed by firing at a high temperature to achieve desirable properties.
• DENTALCERAMIC (Anusavice)
• A specially formulated ceramic material that exhibits adequate strength, durability and
color that is used intraorally to restore anatomic form and function, and/or esthetics.
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• CERAMICS
Compounds of one or more metals with a non metallic element (usually silicon,
boron, oxygen) that may be used as a single structural component or as one of the
several layers that are used in the fabrication of a ceramic based prosthesis.
(Glossary of Prosthodontic Terms)
• PORCELAIN
A ceramic material formed of infusible elements joined by lower fusing materials.
(Glossary of Prosthodontic Terms)
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Terminologies
• COPY-MILLING
• A process of machining a structure using a device that traces the surface of master
metal, ceramic, or polymer pattern and transfers the traced spatial positions to a
cutting station where blank is cut or ground in a manner similar to key-cutting
procedure.
• SINTERING
• The 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.
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• VITRIFICATION :
• The development of a liquid phase by reaction or melting, which on cooling provides
the glassy phase, resulting in a vitreous structure.
• When the glass begins to crystallize , the process is called DE-VITRIFICATION.
• GREEN STATE :
• A term referred to as pressed condition before sintering.
• SPINEL :
• A crystalline mineral composed of mineral oxides such as magnesium oxide or
aluminium oxide.
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• SLIP CASTING :
• A process used to form “green” ceramic shapes by applying a slurry of ceramic
particles and water or special liquid to a porous substrate, thereby allowing capillary
action to remove water and densify the mass of deposited particles.
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All Ceramics – Dr. Nithin Mathew 10
ADA SPECIFICATION
 Dental ceramic : 69
 Dental porcelain teeth : 45
 Metal ceramic system : 38
ISO SPECIFICATION
 Dental ceramic : 6872
 Dental porcelain teeth : 22112
 Metal ceramic system : 9693

HISTORY
 1728 : Proposed the use of porcelain in dentistry – Pierre Fauchard
 1774 : Made first porcelain denture– Alexis Duchateau
 1789 : First porcelain tooth material patented - de Chemant & Duchateau
 1808 : Terrometallic porcelain tooth – Fonzi
 1817 : Porcelain teeth introduced in the US – Planteau
 1825 : Commercial production of porcelain teeth (SS White Company) – Samuel Stockton
 1837 : Introduced improved version of porcelain- Ash
 1887 : Introduced porcelain jacket crown using platinum foil matrix technique - CH. Land
 1903 : First ceramic crowns introduced to dentistry – Charles Land
 1957 : Introduced Vacuum firing - Vines & Sommelman
 1962 : Formulation of feldspathic porcelain – Weinstein & Weinstein
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 1963 : First commercial feldspathic porcelain developed – Vita Zahnfabrik
 1965 : Aluminous core ceramic – Mclean and Hughes
 1968 : Use of glass ceramics – MacCulloh
 1983 : Bonding composite resin to acid etched porcelain – Simonsen & Calamia
 1983-84 : First castable ceramic – Dicor – Grossman & Adair
 1985 : First CAD/CAM was publicly milled and installed in the mouth – Morman & Brandestini
 1987 : CEREC 1 was introduced
 1989 : First slip cast alumina ceramic- Inceram alumina- Sadoun
 1991 : Pressable glass ceramics- Wohlwent
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 1997 : Sirona CROWN 1.0 program for producing full-ceramic posterior crowns was introduced
 2008 : Sirona released the MCXL milling unit which can produce a crown in 4 mins
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CLASSIFICATION
 Firing temperature
 Use / Indications
 Fabrication techniques
 Crystalline phases
 Microstructure
 Translucency
 According to system
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FIRING TEMPERATURE
 High fusing : > 1300°C
 Medium fusing : 1101 - 1300°C
 Low fusing : 850 - 1100°C
 Ultralow fusing : < 850°C
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USE / INDICATIONS
 Veneers
 All ceramic crowns
 Inlays and onlays
 Ceramic dentures
 Post & Cores
 Orthodontic brackets
 FPD

FABRICATION TECHNIQUE
 Sintered (Metal Ceramics)
 Cast (Dicor)
 Heat pressed (IPS Empress)
 Slip cast (Inceram)
 Machined (Cerec Vitablocs)
 Partial sintering and glass infiltration
 CAD CAM & copy milling
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CRYSTALLINE PHASE
 Alumina based (Optec HSP)
 Feldspar based (Conventional Ceramics)
 Leucite based (IPS Empress)
 Spinel based (Inceram Spinel)

TRANSLUCENCY
 Opaque
 Translucent
 Transparent
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MICROSTRUCTURE
 Glass
 Crystalline
 Crystal containing glass

COMPOSITION
 Pure alumina
 Pure Zirconia
 Silica glass
 Spinelle
 Leucite based glass ceramic
 Lithia based glass ceramic
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APPLICATION
 Core porcelain
 Body porcelain
 Enamel porcelain

According To Systems
• Metal ceramic systems
• Cast metal systems and non cast systems
• All –ceramic systems
• Conventional powder slurry ceramic
i. Alumina reinforced porcelain
ii. Magnesia reinforced porcelain
iii. Leucite reinforced
iv. Zirconia-whisker fiber reinforced
v. Low fusing ceramics
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• Castable Ceramics
i. Flouormicas
ii. Other Glass Ceramics
• Machinable Ceramics
i. Analogus Systems
a. Copymilling
a. Mechanical
b. Automated
b. Erosive Techniques
a. Sono - erosion
b. Spark - erosion
ii. Digital Systems (CAD/CAM)
i. Direct
ii. Indirect
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• Pressable Ceramics
i. Shrink free ceramics
ii. Leucite reinforced ceramics
• Infiltrated Ceramics
i. Alumina based
ii. Spinel based
iii. Zirconia based

• Primary constituent
• Minerals composed of potash (K₂O), soda(Na₂O) and silica (SiO₂)
• 75-85%
Feldspar
• 4-5%
• Increases the moldability of the plastic porcelain
• Serves as a binder
• Consists of Al₂O₃ 2SiO₂ 2H₂O (Hydrated Aluminium Silicate)
• Kaolin is opaque and can lower the translucency of porcelain
Kaolin
• Present in concentrations of 13-14%
• Provide strength, firmness and improve translucency of porcelain
• Serves as a framework for other ingredients
Quartz
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Composition of Dental Ceramics

GLASS MODIFIERS
• Potassium, sodium and calcium oxides
• Serve as fluxes
• Lower the viscosity of glass
• Increase thermal expansion
OPACIFYING AGENTS
• Zirconium oxide
• Titanium oxide
• Tin oxide

PIGMENTS
• To obtain various shades to mimic natural tooth colour.
• Made by fusing metallic oxide with fine glass and feldspar & regrinding to a powder.
.
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Metallic oxide Colour
• Iron or nickel oxide ⎼ Brown
• Copper oxide ⎼ Green
• Titanium oxide ⎼ Yellowish brown
• Manganese oxide ⎼ Lavender
• Cobalt oxide ⎼ Blue

ADVANTAGES of Dental Ceramics
 Highly esthetic
 Biocompatibility
 Electrical Resistance
 Thermal Insulation
 Wear resistance
 Can be formed to precise shapes
 Ability to be bonded to tooth structure
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DISADVANTAGES
 Brittleness
 Fabrication : Technique sensitive
 Wear of opposing natural teeth
 Difficult to repair intraorally
 High cost of fabrication
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MANUFACTURING OF CERAMICS
• Pyro-chemical reactions during manufacture of porcelain:
• Ceramic raw materials are mixed together in a refractory crucible and heated to a
temperature well above their fusion temp
• Series of reactions occur.
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CaCO3
P2O5
BaCO3
SiO2
Al2O3
MgO MgF2 CaF2

• After the water of crystallization is lost,
• Flux reacts with the outer layers of silica, kaolin and feldspar
• Feldspar fuses and intermingles with kaolin and quartz
• Feldspar undergoes decomposition to form glass and leucite
• The molten glass begins to dissolve the quartz and kaolin
• Continuous heating results in total dissolution
• Then the fused mass is quenched in water
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CaCO3
P2O5
BaCO3
SiO2
Al2O3
MgO MgF2 CaF2

• Internal stresses within the glass are produced and breaks into fragments frit
• The process of blending, melting and quenching the glass is called FRITTING
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CaCO3
P2O5
BaCO3
SiO2
Al2O3
MgO
MgF2 CaF2
Crucible

Melting
CaCO3
P2O5
BaCO3
SiO2
Al2O3
MgO MgF2 CaF2
Tank with cool water
Quenching
FritSieving

• Ceramics : 2 phases
• Glassy Phase (Vitreous)
• Provides translucency
• Makes ceramic brittle
• Crystalline Phase
• Added to improve the mechanical properties
• Newer ceramics (35-90%)
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DISPENSING
• Conventional dental porcelain kit supplied as a kit containing :
• Fine ceramic powder in different shades of enamel, dentin, core/opaque
• Special liquid or distilled water
• Stains and colour modifiers
• Glazes and add-on porcelain
• Shade guide
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FABRICATION OF CERAMIC RESTORATIONS
• The fabrication of conventional porcelain restoration is by :
• Condensation
• Sintering
• Glazing
• Cooling
CONDENSATION :
• Padding or packing of wet porcelain into position
• The movement of particles is generated by vibration, spatulation or whipping, brush
technique and spray opaquing.
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CONDENSATION :
• Build-up of Cervical Porcelain
• Build-up of Body Porcelain
• Cut-back
• Build-up of Enamel Porcelain
• Condensation methods:
• MANUAL CONDENSATION
• ULTRASONICCONDENSATION
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Advantages of ultrasonic condensation:
• Reduces the fluid content of layered ceramics; resulting in denser and more vibrant porcelain
mass.
• Enhances translucency and the shade qualities of the fired ceramic.
• Shrinkage can be reduced to below 5%
• Time-saving as it reduces the number of compensatory firing cycles
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SINTERING / FIRING :
• Process of heating closely packs particles to achieve interparticle bonding and sufficient
diffusion to decrease the surface area or increase density of the structure.
• Process of partial fusion of compact glass
• Steps:
• Pre-heating the furnace
• Condensed mass placed
• Green porcelain is fired
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Pre-heating (Drying):
• Placing the porcelain object on a tray in front of a preheated furnace at 650C for 5min for low
fusing porcelain and at 480C for 8min for high fusing porcelains till reaching the green or
leathery state.
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• Significance:
• Removal of excess water allowing the porcelain object to gain its
green strength.
• Preventing sudden production of steam that could result in voids
or fractures.
Ceramic particles held together in the “green
state” after all liquid has been dried off

SINTERING / FIRING :
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FIRING
TECHNIQUES
According to
temperature
presetting:
Temperature
controlled
method
Temperature –
time control
method
According to the media
employed for firing:
AIR
FIRING
Porosity due
to air inclusion
VACUUM
FIRING
Reduce
porosity
DIFFUSABLE
GASES
Helium,
hydrogen or
steam are
substituted for
the ordinary
furnace

Stages of Maturity of Porcelain during Firing
Bisque bake
A series of stages of maturation in the firing of ceramic materials depending on the degree of
pyrochemical reaction and sintering shrinkage occurring before vitrification (glazing).
• Low bisque
• Medium bisque
• High bisque
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• Low bisque
• Surface of porcelain is very porous and will easily absorb water.
• Medium bisque
• Surface is still porous but the flow of the glass grains is increased and entrapped air
will become sphere shaped.
• High bisque
• Surface is completely sealed and presents a smooth texture.
• Overfired porcelain become milky or cloudy in appearance – Devitrification.
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STAGES OF MATURITY
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Low bisque stage Medium bisque stage High bisque stage
Characteristics Grains of porcelain start to
soften and coalesce at the
contact points
Flow of glass grains
increase and the residual
entrapped furnace air
becomes sphere shaped
Firing shrinkage is complete,
and has adequate strength, for
any corrections by grinding
prior to glazing
Particle cohesion Incomplete Considerable Complete
Porosity Highly porous and absorbs
water
Reduced although still
porous
Slight/absent depending upon
the material used
Shrinkage Minimal Majority / definite Complete
Strength Weak & friable Moderate High
Surface texture Porous Matte surface Egg shell appearance
Color &
translucency
Opaque Less opaque Color and translucency
developed

GLAZING :
• Produces smooth, shiny and impervious outer layer, also effective in reducing
crack propagation.
• 2 ways :
• Add-on glazing
• Self glazing – most preferred technique
COOLING :
• Carried out slowly
• Rapid cooling results in cracking or fracture of glass and loss of strength.
• After firing, placed under a glass cover to protect it from air current and
contamination by dirt.
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Porcelain Surface Treatment
 Natural or Autoglaze
• Porcelain has the ability to glaze itself when held at its fusing temperature in air for 1-4
mins.
• Porcelain loses its ability to form a natural glaze after multiple firings
 Applied Overglaze
• Applied overglaze is a low fusing clear porcelain painted on to the restoration and fired at
a fusing temperature much lower than that of the dentin and enamel porcelain.
• An applied overglaze is indicated in large restoration that have numerous corrections.
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Instrumentation for Finishing and Polishing Ceramic Restorations
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Sequence Instruments
1 Medium to fine grit diamond instrument
2 30 fluted carbide burs
3 Rubber, abrasive impregnated porcelain polishing points
4 Diamond polishing paste

Methods of Strengthening Ceramics
• Minimize the effect of stress raisers
• Develop residual compressive stresses
• Minimize the number of firing cycles
• Ion exchange
• Thermal tempering
• Dispersion strengthening
• Transformationtoughening
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1. Minimize the effect of stress raisers
• Stress raisers are discontinuities in ceramic and metal ceramic structure that causes stress
concentration.
• Restoration should be designed in such a way that it avoids exposure of ceramic to high tensile
stresses.
• Use of maximum thickness of ceramic on the occlusal surface.
• Abrupt changes in the shape or thickness in ceramic contour should be avoided.
• Sharp line angles in the preparation can cause stress concentration.
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2. Develop residual compressive stresses
• The coefficient of thermal contraction of metal should be slightly higher than that of porcelain.
• Metal contracts slightly more than the porcelain on cooling from firing temperature to room
temperature
• Leave porcelain in residual compression and provides additional strength for the prostheses.
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3. Minimize the number of firing cycles
• Leucite is a high expansion crystal phase which affects the thermal contraction coefficient of
porcelain.
• Multiple firings increases concentration of crystalline leucite.
• Increasing the no. of firing cycles can increase the LCTE of veneering porcelain. This leads to
stresses on cooling.
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4. Ion exchange/ Chemical tempering
• Effective method of inducing residual compressive stresses.
• Sodium containing glass article is placed in a bath of molten potassium nitrate
• Exchange of ions take place
• Since potassium ion is 35% larger than sodium ion, squeezing of the potassium ion creates
very large residual compressive stresses.
• Potassium rich slurry, applied to ceramic surface and heated
to 450°C for 30 mins.
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5. Thermal Tempering
• Creates residual compressive stresses by rapidly cooling the surface of the object while it is in
the molten state.
• Rapid cooling produces a skin of rigid glass surrounding a molten core.
• The solidifying molten core as it shrinks, creates residual compressive stress within the outer
surface.
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6. Dispersion Strengthening
• Process of strengthening ceramics by reinforcing them with a dispersed phase of a different
material.
• Most dental ceramics are reinforced by dispersion of crystalline substances.
• Ex. Alumina in aluminous porcelain, spinel in In Ceram.
• When crystalline material such as alumina (Al₂O₃) is added to a glass, the glass is
strengthened and crack propagation does not take place easily.
• Resulted in development of aluminous porcelain for porcelain jacket crowns.
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7. Transformation Toughening
• This method also relies on dispersion of a crystalline material within the ceramic.
• Strengthening occurs due to a change in the crystal structure under stress which prevents
crack propagation.
• Dental ceramics based primarily on zirconia crystals when heated to a temperature between
1470°C and 2010°C undergo change in the crystal structure from tetragonal to a monoclinic
phase at approx. 1150°C
• The toughening mechanism results from the controlled transformation of metastable
tetragonal phase to the stable monoclinic phase.
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ALL CERAMIC SYSTEMS
• Classified according to the method of fabrication:
• Conventional (powder – slurry) ceramics
• Infiltrated / Slip Cast Ceramics
• Castable Ceramics
• Pressable Ceramics
• Machinable Ceramics
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CONVENTIONAL CERAMICS
(POWDER – SLURRY)

• Supplied as powders in different shades & translucencies.
• Mixed with water to form slurry
• Slurry build up in layers on a refractory die
58

ALUMINOUS CORE PORCELAIN
• Mc Lean and Hughes developed a PJC with an alumina reinforced
• Significant improvement in fracture resistance
• Consisted of a glass matrix containing between 40-50 wt% of Al2O3.
• Large sintering shrinkage (15-20%)
• Inadequate translucency
• Principle indication: maxillary anterior crown restoration
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DisadvantagesAdvantages
• Improved Fracture Resistance
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• Low CTE : 8 x 10-6/0C.
• Large sintering shrinkage (15-20%)
• Improvement in strength is insufficient to
bear high stresses

MAGNESIA – REINFORCED PORCELAIN
• O’Brien in 1984
• High expansion ceramics
• Core material
• Crystalline magnesia (40-60%) ‘Forsterite’.
• Magnesia crystals strengthen glass matrix by both dispersion strengthening and crystallization
within the matrix .
• Flexural strength is 131 MPa
• Doubled upto 269 MPa by the addition of glaze.
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Advantages
62
• Increased co-efficient of thermal expansion
• Improved strength (glass infiltration of magnesia core)
• High expansion property

LEUCITE-REINFORCED PORCELAIN
• They are feldspathic porcelains, dispersion strengthened by crystallization of leucite crystals
in the glass-matrix.
• The leucite and glassy components are fused during the baking process at 10200C.
• Leucite crystals in the glass - matrix (50%).
• Strength : Nucleation and growth of leucite crystals.
• Translucency : Closeness of the refractive index of leucite with that of the glass matrix.
• Flexure strength : approximately 140 MPa.
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• High strength (leucite reinforcement)
• Good translucency
• Moderate flexural strength
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• Marginal inaccuracy due to sintering
shrinkage.
• Fracture in posterior teeth.
• High abrasive effect on opposing teeth.

INFILTRATED / SLIP CAST CERAMICS

GLASS INFILTRATED CORE CERAMICS
• Inceram Alumina
• Inceram Spinel
• Inceram Zirconia
• 2 components : Powder & Glass
• Fabrication:
• Powder mixed with water to form suspension called “SLIP”
• SLIP is painted onto refractory die : absorbs water – leaving solid alumina
• Baked at 11200C for 10 hours : opaque, porous core
• Glass powder applied to core and fired at 11000C for 3-4hrs
• Molten glass infiltrates the porous alumina or spinel by capillary action
• Veneering
66

Die preparation
Mixing aluminous powder with water to
produce slip
The slip is painted onto the die
with a brush
The water is removed by
the capillary action of the
porous gypsum, which
packs the particles into a
rigid porous network
Sintering : 10 Hrs 11200C
Porous
network

Glass powder is used to fill the
pores in the alumina core.
Glass Infiltration (4hrs 11000C)
Glass becomes molten and flows into the
pores by capillary diffusion
Removal of excess glass Veneering with esthetic porcelain

• The internal surface is sandblasted (with 50µ A12O3)
• Since the density of In-ceram core makes conventional methods of etching with HF acid
ineffective for bonding with a resin-cement.
69

INCERAM ALUMINA
• Developed by a French scientist and dentist Dr. Michael Sadoun (1980) and first introduced in
France in 1988.
Composition:
Two three-dimensional interpenetrating phases :
• Alumina/ Al2O3 crystalline : 99.56 wt%
• An Infiltration of glass lanthanum aluminosilicate
70

• Lanthanum
• Decreases the viscosity of the glass to assist infiltration
• Increases its refractive index to improve translucency.
Fabrication stages :
• Slip casting
• Veneering of core
71

PROPERTIES
STRENGTH :
• Densely packed crystalline particles (70% alumina) limit crack propagation and prevent
fracture.
• Flexure strength : 450 MPa range
72

PROPERTIES
COLOR :
• Final color : influenced by the color of the alumina core (opaque).
• Colorants used : transitional metal ions incorporated into the glass structure itself
• Spinel ceramic : the core is more transparent and its corresponding infiltration glass is slightly
tinted.
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• Minimal firing shrinkage, hence an
accurate fit.
• High flexure strengths (3 times)
• Aluminous core (opaque) : used to cover
darkened teeth or post/ core.
• Wear of opposing teeth is lesser
• Biocompatible : less plaque accumulation.
74
• Requires specialized equipment.
• Poor optical properties or esthetics
(opaque alumina core)
• Incapability of being etched
• Slip casting is a complex technique
• Considerable reduction of tooth surface

IN-CERAM SPINELL
• Introduced due to the comparatively high opacity of the alumina core.
• Incorporating magnesium aluminate (Mg A12O4) results in improved optical properties
characterized by
• Increased translucency
• About 25% reduction in flexural strength
• Spinel or Magnesium aluminate (Mg A12O4) is a composition containing A12O3 and Mg2O.
75

• Spinel renders greater strength
characteristics.
• Spinell has extended uses (Inlay / Onlay,
ceramic core material and Veneers.)
76
• Incapable to be etched by HF
• 25% reduction in flexural strength.

IN-CERAM ZIRCONIA
• A mixture of zirconium oxide / aluminium oxide is used as a framework material,.
• Physical properties were improved without altering the proven working procedure.
• The final core of ICZ consists of
• 30 wt% zirconia
• 70 wt% alumina.
77

• High flexural strength
• 1.4 times the stability
• 2-3 times impact capacity compared to
ln-Ceram Alumina
• Excellent Marginal Accuracy
• Biocompatibility
78
• Poor esthetics due to increased opacity
• Inability to etch

79
CASTABLE CERAMICS

• Introduced by Mc Culloch in 1968
• Di-Cor
• New types
• Cera pearl
• Canasite glass ceramic
• Optimal pressable ceramic
• Olympus castable ceramics
• Castable phosphate glass ceramic
80

• Supplied as ceramic ingots
• Fabricated using Lost Wax technique and Centrifugal casting technique
• Steps:
• Wax pattern – invested
• Dewaxing
• Molten glass cast into mould using centrifugal casting machine
• Glass core : ceramming (heat treatment process)
• Microscopic plate-like crystals grow within the glass matrix
• Veneeredusing feldspathic ceramics : Dicor Plus
81

DI-COR (Dentsply + Corning Glass Co)
• First commercially available castable ceramic material.
• Non porous, non homogenous, microstructure with uniform crystal size which is derived from
the controlled growth of crystals within an amorphous matrix of glass.
• Dicor composed of:
• Tetrasilicicfluormica crystals : 55 %
• Glass ceramic : 45 %
82

Major Ingredients Minor Ingredients
• SiO2 : 45-70%
• K2O : upto 20%
• MgO : 13-30%
• MgF2 (nucleating agent)
• A12O3 : upto 2% (durability & hardness)
• ZrO2 : upto 7%
• Fluorescing agents (esthetics)
• BaO : 1 to 4% (radiopacity)
Supplied as :
• Special Dicor casting crucibles, 4.1 gm Dicor glass ingot
• Dicor shading porcelain kit.

PROPERTIES
• Flexural strength : 81 ± 6.8 Mpa
• Strength : 440-505 KHN
• Biocompatible
• Less bacterial counts : smooth surface, low surface tension, fluoride content.
84

PROPERTIES
Esthetics :
• Gross man and Adiar
• Hue and chroma of metal ceramics and Castable ceramics matched natural teeth.
• Value of only Castable ceramics matched natural teeth.
• Presence of mica crystals scatter light similar to enamel rods.
• Chameleon effect i.e. the restoration acquires a part of the color from adjacent teeth and
fillings as well as the underlying cement lute.
85

PROPERTIES
Cementation :
• Zinc phosphate, light activated urethane resin
• Etching with ammonium difluoride for 2 min (Bailey & Bennet 1988)
Survival rate :
• Kenneth et al 1999 - 14yr study
• Crowns : 82%
• Cores : 100%
• Inlay and onlay : 90%
• Partial coverage : 92%
• Expenstein et al 2000 : Posterior 70%, anterior 82.7%
86

• Chemical and physical uniformity.
• Excellent marginal adaptation
• Compatibility with lost-wax casting
process.
• Ease of adjustment
• Low thermal conductivity
• Radiographic density is similar to that of
enamel
87
• Requires special equipments
• Veneers failure rate as high as 8%
• Must be stained with low fusing feldspathic
porcelain

CASTABLE APATITE GLASS CERAMIC (CERAPEARL)
• 1985 -Sumiya Hobo & Iwata
• Available as Cera Pearl
• Crystalline microstructure similar to natural enamel
• Mechanical properties superior to enamel
88

Composition
• CaO : 45% - reacts with P2O5
• P2O5 : 15% - Aids in glass formation
• SiO2 : 35% - Forms the glass matrix.
• MgO : 5% - Decreases the viscosity (anti flux)
• Other : Trace elements (Nucleating agents during ceramming)
89

CHEMISTRY
90
CaPO4
1460°C
– 1510°C
Amorphous
Mass
750°C
– 870°C
Crystalline
Oxyapatite
Exposed to
moisture
Hydroxy
Apatite
Ceramming
Ceramming :
The ceramming oven is preheated at 750°C for 15 minutes. After the cast glass ceramic is
placed in the oven the temperature is raised at the rate 500C / min until it reaches 870°C and held
for 1 hr.
External staining : Cerastain ( Bioceram )

PROPERTIES
• Cerapearl is similar to natural enamel in Composition
• Density : 2.97 gm/cm2
• Refractive index : 1.66
• Thermal conductivity : 0.002
• Hardness : 343
• Clinical success : (crowns) 2 year success rate –100%
91

92
PRESSABLE CERAMICS

• Supplied as ceramic ingots
• Fabricated using Lost Wax technique and heat pressed into the mould
• Steps:
• Wax pattern – invested in phosphate bonded investment
• Placed in specialized mould with alumina plunger
• After burnout, ceramic ingot is placed under plunger and heated to 11500C
• Veneeredusing feldspathic ceramics
93

CLASSIFICATION
• Shrink free ceramics
• Cerestore
• Al-ceram
• Leucite reinforced glass ceramics
• IPS empress
• Optec/OPC
• Lithia reinforced glass ceramic
• IPS empress 2
• OPC 3G
94

CERESTORE (Shrink Free Ceramics)
• Consists of Al2O3 and MgO mixed with Barium glass frits.
• On firing crystalline transformation produces Magnesium aluminate spinel, which occupies a
greater volume than the original mixed oxides compensates for the conventional firing
shrinkage.
95

• Unfired Cerestore core :
• Al2O3
• MgO
• Glass frit
• Silicone resin
• Fillers
96
• Fired Cerestore core :
• α- Al2O3 (Corrundum)
• MgAl2O4 (Spinel)
• Ba Mg2Al3 (Si9Al2O3) – Barium osumilite

Chemical And Crystalline Transformation
• Silicone Resin SiO SiO2 Alumina Aluminosilicate
(160-8000C)
(900-13000C)
• Al2O3 + MgO MgAl2O4 (decreased shrinkage )
97

PROPERTIES
• Flexural strength : 225 Mpa
• Fit : exceptional fit because of direct moulding process.
• Low thermal conductivity
• Radiodensity similar to enamel
• Biocompatible
98

Advantages
• Dimensional stability of the core material in the molded (unfired) and fired states
• Better accuracy of fit and marginal integrity
• Esthetics
• Biocompatible (inert) and resistant to plaque formation (glazed surface)
• Radio density similar to that of enamel
• Low thermal conductivity; thus reduced thermal sensitivity
• Low coefficient of thermal expansion and high modulus of elasticity results in protection of
cement seal
99

Disadvantages
• Complex
• Specialized laboratory equipment and cost
• Inadequate flexural strength compared to the metal-ceramic restorations
• Poor abrasion resistance, hence not recommended in patients with heavy bruxism or
inadequate clearance
• LIMITATIONS and high clinical failure rates of the Cerestore led to the withdrawal of this
product from the market.
• Improved version : 70 to 90% higher flexural strength - marketed as Al Ceram.
100

IPS-EMPRESS
• Hot pressed ceramics
• 2 types:
• Leucite reinforced (K2O – Al2O3 – 4 SiO2)
• Lithium Disilicate reinforced (SiO2 – LiO2 – P2O5 – ZrO2)
101

COMPOSITION
• Pre cerammed, pre colored : INGOTS
• SiO2 : 63%
• Al2O3 : 17.7%
• K2O : 11.2%
• Na2O : 4.6%
• B2O3 : 0.6%
• CaO : 1.6%
• BaO : 1.6%
• TiO2 : 0.2%
• Contains higher concentration of leucite crystals, which increases the resistance to crack
propagation
102
Leucite
content
Conventional
Porcelain
Dicor
IPS Empress
Pressable ceramic
30-35% 50-60% 80-85%

FABRICATION
Lost-wax technique:
• Wax pattern is invested
• Burnout (at 850°C)
• The ceramic ingot plunger and the entire assembly is
preheated to 11000C
• After 20 minute holding time the plunger presses the ceramic
under vacuum (0.3-0.4 MPa) into the mould
• Held under pneumatic pressure (45-mins) to allow complete
and accurate fill of the mould.
103

PROPERTIES
• Flexural strength : 160-180 Mpa
• The increase in strength has been attributed to :
• Pressing step which increases the density of leucite crystals
• Subsequent heat treatments which initiate growth of additional leucite crystals
• Esthetics : High esthetic value (translucent, fluorescent)
• Clinical survival :
95% survival rate of 2-4 years (Deniz G et al 2002)
• Marginal adaptation : Better marginal adaptation compared to aluminous core material.
104

Advantages
• Lack of metal or an opaque ceramic core
• Moderate flexural strength (160-180 MPa)
• Excellent fit (low-shrinkage ceramic)
• Improved esthetics (translucent, fluorescent)
• Etch-able
• Less susceptible to fatigue and stress failure
• Less abrasive to opposing tooth
• Biocompatible material
105

Disadvantages
• Potential to fracture in posterior areas.
• Special laboratory equipment such as pressing oven and die material (expensive)
• Inability to cover the color of a darkened tooth preparation or post and core, since the crowns
are relatively translucent.
• Compressive strength and flexural strength lesser than metal-ceramic or glass-infiltrated (In-
Ceram) crowns.
106

IPS EMPRESS 2 (IVOCLAR)
• Second generation of pressable materials for all- ceramic bridges.
• Lithium disilicate crystal >60vol%.
• The apatite crystals are layered which improved optical properties (translucency, light
scattering) which contribute to the unique chameleon effect.
107
IPS Empress IPS Empress 2
Flexural
strength
Upto 150 MPa > 400 Mpa

• Other applications :
• Core build-up system with the pre-fabricated zircon oxide root canal posts
Advantages
• High biocompatibility
• Excellent fracture resistance
• High radiopacity
• Outstanding translucency
108

IPS E.MAX PRESS
• Introduced in 2005.
• Considered as an enhanced lithium disilicate press-ceramic material when compared to
Empress II.
• Better physical properties and improved esthetics
109

Strength
110

MACHINABLE CERAMICS

Impression
Casts & Die
Wax Pattern
Investing
Casting
Lost Wax Technique
Camera
Contact
Digitizer
Laser
Machine Sinter
Computerised
Design
CAD / CAM System
Traditional Technique Higher Technology
Data
Acquisition
Restoration
Design
Restoration
Fabrication
Electrical
Discharge
Machine

• Application of CAD/ CAM techniques was actively pursued by three groups of researches
• Group supported by Henson International of France.
• Combined group effort between the University of Zurich and Brains, Brandestini
Instruments of Switzerland.
• University of Minnesota, supported by the U.S. National Institute of Dental Research.
113

FRENCH SYSTEM
• Optical impression – Laser scanner
• Data processing – By Shape recognition software
• It has a library (memory) describing theoretical teeth.
• The system uses:
• 3-D probe system based on electro-optical method
• Surface modelling and screen display
• Automatic milling by a numerically controlled 4-axis machine
114

SWISS SYSTEM
• Optical impression - Optical topographic scanning using a 3-D oral camera
• Data processing - By an interactive CAD unit
• The system uses:
• A desk top model computer
• Display monitor permitting visual verification of quality of data being acquired
• Electronically controlled 3-axis milling machine
115

MINNESOTA SYSTEM
• Optical impression - Photograph based system using a 35-mm camera with magnifying lens.
• Data processing - Data obtained in the dental office is sent to another location for processing
and machining.
• 3-D Reconstruction uses :
• Direct line transformation and an alternative technique proposed by Grimson
• Milling with a 5-axis milling machine
116

CLASSIFICATION - Machinable Ceramics
117
ANALOGOUS SYSTEM DIGITAL SYSTEMS
I. Direct
II. Indirect
i. 3-D scanning
ii. CAD modelling
iii. Fabrication
I. Copy milling
i. Fabrication of prototype for scanning
ii. Copying and reproduction by milling
II. Erosive techniques
i. Sono Erosion
ii. Spark Erosion

FINE SCALE FELDSPATHIC PORCELAIN
I. CEREC VITABLOC MARK I:
• Feldspathic porcelain
• Larger particle size (10-50 micron)
II. CEREC VITABLOC MARK II:
• Feldspathic porcelain reinforced
with aluminium oxide (20-30%)
• Fine grain size (4 micron)
GLASS PORCELAIN
I. DICOR
Flurosilica Mica Crystals Plates (2 microns)
II. MGC F
Tetrasilica mica
(enhance fluorescence, machinability)
III. PRO CAD
Leucite - Reinforced Glass Ceramic
(high strength)
118
• 2 Classes of Machinable Ceramics

DIGITAL SYSTEMS
CAD-CAM:
• Uses digital information about the tooth preparation or a pattern of the restoration to provide
a computer-aided design (CAD) on the video monitor for inspection and modification.
• The image is the reference for designing a restoration on the video monitor.
• Once the 3-D image for the restoration design is accepted, the computer translates the image
into a set of instructions to guide a milling tool [CAM] in cutting the restoration from a block of
material.
119

STAGES OF FABRICATION
All systems ideally involve 5 basic stages:
1. Computerized surface digitization
2. Computer - aided design
3. Computer - assisted manufacturing
4. Computer - aided esthetics
5. Computer - aided finishing
• The last two stages are more complex and are still being developed for including in
commercial systems.
120

Scanning 3D Miniature Camera
• Microprocessor unit stores the pattern
• Video display serves as a format for manual construction
• Final 3-D restoration is developed from above again by
microprocessor
CAD-CAM Procedure (10-15mins)

• Electronic information is transferred to miniature multiple axis milling device
• Milling device generates a precision fitting restoration from a standard ceramic block

CEREC SYSTEM
• Brains. A. G, Switzerland in 1980
• Manufactured in West Germany, Siemens group
• Consists of:
• 3-D video camera (scan head)
• Electronic image processor with memory unit
• Digital processor
• Miniature Milling machine
123

• Translucency and color of porcelain very
closely to natural dental tissues
• Quality of ceramic is not changed during
processing
• Can be placed in one visit
• Prefabricated ceramic is wear resistant
124
• Occlusal anatomy to be developed
• Inaccuracies in fit
• Poor esthetics systems

CEREC 2 SYSTEM
• Morman & Brandestini in 1994
• Constant further development
• Major changes include:
• Enlargement of grinding unit from 3 to 6 axes
• Sophisticated software technology : occlusal surfaces
• Minor technical innovations:
• Magnification factor increased from 8x to 12x
• Improved grinding precision by 24 times
• Improved accuracy of fit
125

CEREC 3 SYSTEM
• Operator can record multiple images in seconds
• Creates a virtual cast for entire quadrant
126

OTHER DIGITAL SYSTEMS
• DURET SYSTEM
• Francois Duret : produced by Sopha (France)
• CICERO SYSTEM
• COMET SYSTEM
127

ADVANTAGES : Machinable Ceramics
• Single visit
• Good patient acceptance
• Eliminates procedures like impression model making and fabrication of temporary prosthesis
• Void free porcelains without firing shrinkage
• Better adaptation
• Inlay,onlay can be fabricated chair side
• Eliminates asepsis
• Since its computer assisted crowns of correct dimensions can be obtained
• Glazing is not required : can be polished
• Less abrasion of tooth structure : homogenous material
128

DISADVANTAGES : Machinable Ceramics
• Limitations in fabrication of multiple units
• Inability to characterize shades and translucency
• Inability to image in wet environment
• Techniquesensitive
• Expensive
• Limited availability
129

ANALOGUS SYSTEMS : COPY MILLING
CELAY SYSTEM
• Switzerland in 1992
• High precision manually operated
• Key duplication
• Advantage : Recreation of all surfaces.
130
COPYING SIDE
• Various size probes represent
size of diff milling burs is run
over surface of pattern
MILLING SIDE
• At same time matched rotary
instru-mills same shape out of
restorative block

ANALOGUS SYSTEMS : EROSIVE TECHNIQUES
SONO EROSION:
• Based on ultrasonic methods.
• The ceramic blank is surrounded by an abrasive suspension of hard particles, such as boron
carbide, which are accelerated by ultrasonics, and thus erode the restoration out of the
ceramic blank.
131

ANALOGUS SYSTEMS : EROSIVE TECHNIQUES
SPARK EROSION:
• 'Electrical Discharge Machining' (EDM)
• Metal removal process using a series of sparks to erode material from a workpiece in a liquid
medium under carefully controlled conditions.
• Liquid medium : light oil called the dielectric fluid.
132

CERCON & LAVA ZIRCONIA CORE CERAMICS
133
• Fabrication
Tooth
preparation
Impression
made
Wax pattern
made on
model
Anchored on
to the Cercon
Brain
Presintered
zirconia blank
attached on other
side of brain unit
Unit activated
Pattern
scanned
Milled prosthesis then removed
from unit and placed in the
cercon furnace (13500C for 6 hrs)
Trimming
Finished
ceramic core
framework
Veneering

BONDING OF PORCELAINS
RESIN–CERAMIC BONDING
• Function of the silane primer between porcelain and the composite resin plays an important
role.
• Etching of ceramic surface with 7.5 to 10% hydrofluoric acid for 2-10mins and then followed
by silanization increased the bond strength to porcelain (Peremuter and Montagonon, 1981)
134

METAL-CERAMIC BONDING
1. Chemical bonding across the metal-porcelain interface:
• Diffusion between surface oxide on the alloy and ceramic
2. Mechanical interlocking:
• Due to surface irregularity of the alloy
• Air abrasion with aluminium oxide particles
3. Residual compressive stresses:
• Core has slightly higher CTE than porcelain
• Porcelain draws towards the coping on cooling : residual compressive forces
135

REPAIR OF CERAMIC RESTORATIONS
1. PORCELAIN REPAIR :
• Fracture is totally in porcelain
• Simplest repair
• Preparation of porcelain surface by bonding :
• Surface roughening by using diamond burs, air abrasion and acid etching
with 9.5% HF acid
• Application of silane coupling agent & allowed to dry for 1 min.
• Application of bonding agent
• Shade matched composite
136

2. MIXED (PORCELAIN/METAL ) REPAIR :
• Involves exposed metal
• More complicated
• If remaining porcelain:
• Adequate : exposed metal and remaining porcelain is veneered with composite
opaquer & subsequently with layers of shade matched composite.
• Inadequate : exposed metal surface is used as an adhesive substrate after
preparation for bonding with composite opaquer layer followed by shade matched
composite.
137

3. METALREPAIR:
• Involves the exposed metal with or no remaining porcelain
• Most difficult
• 2 methods :
• Veneering exposed metal surface with direct bonding of shade matched composite
after preparation of exposed metal surface for bonding.
• Fabrication of an over casting: small areas of remaining porcelain are removed if
present. Crown / pontic is reduced circumferentially to provide room for both
porcelain and metal, & provide margin for the laboratory technician and a thin metal
overcasting with fused porcelain veneer is fabricated.
138

OTHER APPLICATIONS OF CERAMICS
• ALL CERAMIC POST & CORES
DRAWBACKS of conventional Metal Post & Core
• Decrease depth of translucency of restoration
• Shine through in cervical root, altering appearance of thin gingival tissue
• Corrosion products
139

ADVANTAGES of All-ceramic Post & Core
• All ceramic restoration transmits certain percentage of incident light to ceramic core & post .
• Color of final restoration will be derived from an internal shade
• Depth of translucency in cervical root area
• Biocompatible
MATERIALS USED
• In–ceram
• Dense – sintered alumina ceramic
• Zirconium oxide ceramics
140

CERAMIC-DENTAL IMPLANTS
• Ceramic oxides : resistant to corrosion
• Tissue grow into surface porosity
• Ceramic Coating for Implant
• Bioactive Ceramics : High density Alumina, TriCalcium Phosphate, High Alumina polymer
composite
• Inert Ceramics : Alumina, Zirconium Oxide
141

CERAMIC INSERTS
• Megafillers for direct posterior composite restorations
• Reduce bulk of composite resin
• Decrease shrinkage
• Minimize wear
Composition
• Glass inserts
• Lithium – alumino-silicate glass (heat treated & silanated)
eg: Beta –Quartz Glass –ceramic inserts
142

CEROMERS
• Ceramics + Polymers = Ceromers
• Ceramics:
• Abrasion resistance
• High stability
• Esthetics
• Composites
• Ease of final adjustments
• Excellent polishability
• Bonding with luting cement
• Possibility of repair
143

ZIRCONIA IMPLANTS
• A radical new solution to immediate dental implant placement.
• Patient’s extracted tooth is laser scanned and modified in CAD
software
• Machined out of zirconium
• Implanted in the still healing socket
• Provides incredibly natural looking results.
144

• An increase of the crystalline content as seen in the pressable materials and the fully sintered
zirconia generally corresponds to an improvement of the mechanical properties.
• An increase of crystalline content of a glass–ceramic is accompanied with an increase of the
strength and fracture toughness.
146
Strength, Fracture Toughness and Microstructure of a Selection of All-Ceramic
Materials. Part I. Pressable and Alumina Glass-Infiltrated Ceramics
Part II. Zirconia-based dental ceramics
Guazzatoa, Mohammad Albakrya, Simon P. Ringerb, Michael V. Swain
Dental Materials (2004) 20, 441–448

• Vita Inceram crowns exhibited significantly higher fracture strength than conventional all-
ceramic crowns.
147
An Evaluation of Two Modern All-Ceramic Crowns and their comparison with
Metal Ceramic Crowns in terms of the Translucency and Fracture Strength
Girish Nazirkar, Suresh Meshram
International Journal Of Dental Clinics 2011:3(1):5-7

• The fracture strength of monolithic high translucent zirconia crown is considerably higher
than that of porcelain-veneered zirconia crown cores, porcelain-veneered high translucent
zirconia crown cores and monolithic lithium disilicate crowns.
148
Fracture strength of monolithic all-ceramic crowns made of high translucent yttrium
oxide-stabilized zirconium dioxide compared to porcelain-veneered crowns and
lithium disilicate crowns
Camilla Johansson, Gratiela Kmet, Johnny Rivera, Christel Larsson & Per Vult Von Steyern
Acta Odontologica Scandinavica 2014; 72: 145-153

• Lithium Disilicate glass-ceramic restorations had higher fracture resistances than leucite
reinforced glass-ceramic restorations.
149
Dynamic fatigue and fracture resistance of non-retentive all-ceramic full-coverage
molar restorations. Influence of ceramic material and preparation design
Jan-Ole Clausen, Milia Abou Tara∗, Matthias Kern
Dental Materials 26 (2010) 533–538

• Observations regarding zirconia-based all ceramic restorations compared with PFM restorations:
• Better esthetically than typical PFM restorations
• Long-term color stability probably will be the same as that with PFM restorations
• Margins of the restorations have a more acceptable appearance than those of PFM.
• Strength and service record of PFM restorations and zirconia based restorations in three-unit
prostheses is similar.
• Gingival sensitivity to metal will be reduced or eliminated with use of zirconia-based.
150
Choosing an all-ceramic restorative material
Porcelain-fused-to-metal or zirconia-based?
Gordon J. Christensen
JADA, Vol. 138; May 2007

SELECTION OF CERAMIC MATERIALS
• Four broad categories or types of ceramic systems:
 Category 1: Powder/liquid feldspathic porcelains
 Category 2: Pressed or machined glass-ceramics
 Category 3: High-strength crystalline ceramics
 Category 4: Metal ceramics
151
Ceramics: Rationale for material selection, Cosmetic Dentistry:2,2013

Clinical Parameters To Evaluate :
• Individual teeth evaluated for specific material selection
• Assessing four environmental conditions in which the restoration will function
1. Substrate
2. Flexure risk assessment
3. Excessive shear and tensile stress risk assessment
4. Bond/seal maintenance risk assessment
Ceramics: Rationale for material selection, Cosmetic Dentistry:2,2013

1. Substrate
• Is it enamel?
• How much of the bonded surface will be enamel?
• How much enamel is on the tooth?
• How much of the bonded surface will be dentine?
• What type of dentine will the restoration be bonded to? Is it a restorative material (e.g.
composite, alloy)?
• High bond strength : Enamel
• Dentine surfaces/composite : Less predictable
• More stress - between dentine and composite - more damage to the restoration and
underlying tooth structure

• Each tooth and existing restorations are evaluated for signs of past overt tooth flexure.
• Signs
• Excessive enamel crazing
• Tooth and restoration wear
• Tooth and restoration fracture
• Micro-leakage at restoration margins
• Recession
• Abfraction lesions

• Low risk
• Low wear; minimal to no fractures or lesions
• Patient’s oral condition is reasonably healthy
• Medium risk
• Signs of occlusal trauma
• Mild to moderate gingival recession along with inflammation
• Bonding mostly to enamel is still possible
• There are no excessive fractures

• High risk
• Evidence of occlusal trauma from parafunction;
• More than 50 % of dentine exposure exists
• Significant loss of enamel due to wear of 50 % or more
• Porcelain must be built up by more than 2 mm.

3. Excessive shear and tensile stress risk assessment
• All types of ceramics (especially porcelains) are weak in tensile and shear stresses.
• Ceramic materials perform best under compressive stress
• If a high-stress field is anticipated : Stronger and tougher ceramics are needed
• The substructure should reinforce the veneering porcelain by utilising the reinforced-
porcelain system technique

• Glass-matrix materials : powder/liquid porcelains and pressed or machined glass-ceramics,
require maintenance of the bond and seal for clinical durability.
• If the bond and seal cannot be maintained, then high-strength ceramics or metal ceramics are
the most suitable, since these materials can be placed using conventional cementation
techniques.

• Clinical situations in which the risk of bond failure is higher are
• Moisture control problems
• Higher shear and tensile stresses on bonded interfaces
• Variable bonding interfaces (different types of dentine)
• Material and technique selection of bonding
• The experience of the operator

Category 1: Powder/Liquid Feldspathic Porcelains
Aesthetic Factors • 0.2–0.3 mm is required for each shade change
Substrate Condition • 50 % or more remaining enamel on the tooth
• 50 % or more of the bonded substrate is enamel
• 70 % or more of the margin is in enamel
Flexure risk assessment • Higher risk and more guarded prognosis when bonding to dentine
• Increased enamel, prognosis improved
• Depending on the dentine/enamel ratio, the risk : low to moderate
Tensile and shear stress risk
assessment
• Low to low/moderate risk.
• Large areas of unsupported porcelain, deep overbite or overlap of
teeth, bonding to more-flexible substrates : Increase the risk of
exposure to shear and tensile stresses
Bond/seal maintenance risk
assessment
• Absolute low risk of bond/seal failure
Indications • Indicated for anterior teeth

Category 2: Pressed or Machined Glass-ceramics
Aesthetic Factors • Minimum working thickness of 0.8 mm
• 0.2–0.3 mm for each shade change is required
Substrate Condition • Less than 50 % of the enamel on the tooth
• Less than 50 % of the bonded substrate is enamel
• 30 % or more of the margin is in dentine
Flexure risk assessment • Risk is medium for Empress, VITABLOCS Mark II and Authentic-type
glass-ceramics and layered IPS e.max
assessment
• Flexure risk is medium to high (and full crown preparation is not
desirable)
• Monolithic IPS e.max has been 100 % successful for as long as 30
months in service.
assessment
• Risk is medium for Empress, VITABLOCS Mark II and Authentic-type
glass-ceramics, and layered IPS e.max.
• Medium to medium/high for bonded monolithic IPS e.max
Indications • Thicker veneers, anterior crowns, and posterior inlay and onlays
• Only indicated in clinical situations in which long-term bond and seal
can be maintained.

Category 3: High-strength Crystalline Ceramics
Aesthetic Factors • Minimum working thickness of 1.2 mm is required.
Substrate Condition • Substrate is not critical, since a high-strength core supports veneering
material.
Flexure risk assessment • Risk is high or low
• For high-risk situations, core design and structural support for
porcelain become more critical
assessment
• Risk is high or low
• High-risk situations : Preparations should allow for a 0.5 mm core
plus 1 mm of porcelain
• Anteriors: There should not be more than 2 mm of unsupported incisal
porcelain.
• Molars : Better to use zirconia cores rather than alumina cores
• High risk molar : Full-contour zirconia restorations recommended.
assessment
• If the risk of obtaining or losing the bond or seal is high, then zirconia
is the ideal all-ceramic to use.
Indications • When significant tooth structure is missing
• Unfavourable risk for flexure and stress distribution is present
• It is impossible to obtain and maintain bond and seal

Category 4: Metal ceramics
Aesthetic Factors • 1.5–1.7 mm is required for maximum aesthetics
Substrate Condition • Substrate is not as critical, since the metal core supports the
veneering material.
Flexure risk assessment • Risk is high or low
assessment
• Risk is high or low
assessment
• If the risk of obtaining or losing the bond or seal is high, then metal
ceramics are an ideal choice for a full-crown restoration.
Indications • Indicated in all full-crown situations, esp when all risk factors are
high.

CONCLUSION
• Dental ceramic technology is one of the fastest growing areas of dental material research and
development. The past decades have seen the development of several new groups of ceramics.
• Each system has its own merits, but may also have shortcomings.
• Combinations of materials and techniques are beginning to emerge which aim to exploit the
best features of each.
• Glass-ceramic and glass-infiltrated alumina blocks for CAD-CAM restoration production are
examples of these.
• The diversity and sophistication of the CAD-CAM systems may prove to be influential in the
future.
164

REFERENCES
• Philips science of dental materials - Anusavice
• Craig’s restorative materials
• Dental materials & their selection - William ’O’ Brien
• Clinical operative dentistry - principles and practice - Ramya Raghu
• Textbookof Dental materials – Mahalekshmi
• Theory and practice of fixed prosthodontics - Tylmann
166

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