10.Dental Ceramics in restorative dentistry.pptx

DENTAL CERAMICS
Presented by:
Dr. M.Namitha
1

CONTENTS
 Introduction
 Historical background
 Classification
 Composition
 Properties
 Methods of strengthening
ceramics
 Metal-Ceramic Restorations
- Introduction
- Ceramics : requirements
composition
manufacture
- Metals
- Processing : condensation
sintering
glazing
cooling
2
Metal ceramic restorations
• Metal porcelain bonding
• Benefits and drawbacks
• Failure
All ceramic restorations
• Sintered All ceramic
• Heat pressed All ceramic
Slip cast All ceramic
restorations
Machinable All ceramic
• hard and soft machined
• cerec system
• celay system
• procera system
• Castable All ceramic :
dicor
comparison of all systems
All ceramic crowns
Porcelain veneers
- Tooth preparation for veneers
- Porcelain application
Cementation and finishing
•Crown Cementation
- Veneer Cementation
Porcelain inlay
• - Indication &
Contraindication
• - Advantage &
disadvantage
- Fabrication of porcelain
inlays

INTRODUCTION
The term ceramic refers to any product made from a non-
metallic inorganic material usually processed by firing at a
high temperature to achieve desirable properties. (Craig)
Inorganic compounds with non metallic properties typically
consisting of oxygen or one or more semi-metallic elements
like aluminium , potassium, magnesium.(Anusavice)
3

HISTORICAL BACKGROUND
• Ceramics were the first artificial material to be made by man
• During stone age-10,000 years ago ceramics were the most
important materials
4
Phillips’ Science of Dental Materials – 11th edition

Types of ceramics :
1. Earthern ware- fired at low temperature and porous
2. Stone ware- fired at a higher temperature than earthern ware, giving strength and
making it impervious to water.
3. Porcelain- obtained by fluxing white china clay with china stone to produce a white
translucent stone ware in 1000 A.D. This material was stronger than both
earthern ware and stone ware.
CERAMIC VASES AND PAINTINGS
5

• First porcelain tooth material was patented in 1789 by deChemant and Alexis
Duchateau
• In 1808, Fonzi, an Italian dentist, invented “terrometallic” porcelain tooth - held
in place by platinum pin or frame
• Dr. Charles Land introduced one of the first ceramic crowns to dentistry in
1903
DENTURE AND DENTURE TEETH -
ALEXIS
6

• 1940- vaccum firing of porcelain
• In 1950s Metal Ceramic Restorations were introduced.
• First commercial porcelain was developed by Vita Zahnfabrik in
about 1963
• 1965- Mc Lean and Hughes- aluminous core ceramic was used for
improved fracture resistance
• The end of the 20th century saw the introduction of several innovative
systems for fabricating all-ceramic dental restorations
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CLASSIFICATION
OF CERAMICS
8

Dental ceramics are classified according to their :
• Firing temperature
• According to the use
• Processing method
• Type of porcelain
• Substructure material
• Methods of firing
• Methods of fabricating ceramic restorations
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 By their firing temperature:
- high fusing : more than 1300 ◦
C
- medium fusing : 1100-1300◦
C
- low fusing : 850 – 1100◦
C
- ultra low fusing : less than 850◦
C
 According to its use:
- Metal-ceramic crowns and fixed partial prosthesis
- All-ceramic crowns, inlays, onlays, veneers and fixed partial prosthesis
10

 According to Processing method :
• Sintering
• Casting
• Machining
 According to the type of Porcelain:
• Feldspathic porcelain
• Leucite reinforced porcelain
• Aluminous porcelain
• Glass infiltrated alumina
• Glass infiltrated spinel
• Glass infiltrated zirconia
• Glass ceramic
11

 According to Substructure material:
- Cast metal
- Swaged metal
- Glass ceramic
- Sintered glass ceramic
- CAD/ CAM Porcelain
- Sintered ceramic core
 According to Methods of firing:
- Air fired – Firing at atmospheric pressure
- Vacuum fired – Firing at reduced pressure
- In diffusible gases
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 According to the fabrication technique:
- Sintered (metal-ceramics)
- Heat-pressed (IPS Empress)
- Slip-Cast (In-Ceram Alumina)
- Machinable cermics
13

ACCORDING TO ITS FUNCTION WITHIN THE RESTORATION
• Core ceramics - Supports and reinforces the restoration in all-ceramic restorations
• Opaquer ceramics - Masks or hides the metal or underlying core ceramic. Bonds
ceramic to underlying metal
• Veneering ceramics
o body or dentin - Simulates the dentin portion of natural teeth
o incisal - Simulates the enamel portion of natural teeth
o Gingival - Simulates the darker gingival portion of teeth
o Translucent - Simulates translucent incisal enamel
seen sometimes in natural teeth
• Stains - Used to color ceramics to improve esthetics
• Glaze - Imparts a smooth glossy surface to the restoration
Phillips’ Science of Dental Materials – 11th edition 14

15

• Dental Porcelains, to a large extent are glassy
materials
• Glasses are supercooled liquids/ non-crystalline
solids
• During cooling, molten glass solidifies with a liquid
structure instead of a crystalline structure
• Such a structure is called vitreous and the process
of forming it is known as vitrification
16
2-dimensional amorphous structure of
potassium silicate glass

• For high fusing porcelains,
- feldspar 75-85%
- kaolin 4-5%
- quartz 13-14%
• For medium and low fusing porcelains,
- same raw ingredients
- addition of balancing oxides/fluxes (glass modifiers)
- modify the properties by interrupting glass network
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COMPONENT FUNCTION
Feldspar Basic glass former
Kaolin Binder, gives opacity
Quartz Filler
Alumina Glass former and flux
Alkalies (Na, K or Ca oxides) Glass modifiers
Opacifiers(Zirconium oxide) Reduces transparency
Coloring pigments Modifies color
COMPOSITION
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FELDSPAR
• Naturally occuring , composed of potash (K2O), Soda (Na2O), Alumina
(Al2O3), and Silica (SiO2).
• Chemically it is designated as potassium-aluminum silicate, with a
composition of K2O, Al2 O3 6SiO2.
• In its mineral state, feldspar is crystalline and opaque.
19

KAOLIN/ CHINA CLAY
• Hydrated aluminum silicate.
• When mixed with water -- sticky mass – allows unfired porcelain to be
easily worked and moulded.
• Adheres to quartz framework and shrinks considerably during firing.
• White in color ; reduces translucency.
gives opacity to the mass
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Quartz
 Framework for other ingredients.
 Silica can exist in four different forms
• Crystalline quartz
• Crystalline cristobalite
• Crystalline tridymite
• Non-crystalline fused silica
 Remains unchanged at high temperature used in firing porcelain
and thus contributes stability to the mass during heating.
21

Glass modifiers
– Na, K or Ca oxides
– Act as fluxes
– Interrupts silica tetrahedra
– Lower softening temperature of glass
– Increase flow and coefficient of thermal
expansion
– Remove impurities
22

Excess :
- Reduces chemical durability (resistance to attack
by water, acids and alkalis ) of glass
- Devitrification (crystallization) on overheating
- Degradation of ceramics
23

• Intermediate oxides (Al2O3 ):
- lowers softening temperature
- Reduces viscosity of glass
• Boric oxide (B2O3):
- Glass modifier as well as glass former
- Three dimensional arrangement – less stability
- Lower melting point, less viscosity and a higher expansion
• Other additives:
- Lithium oxide
- Magnesium oxide
24

Opacifying Agents
• To increase the opacity in order to simulate natural teeth.
• Generally consists of metallic oxide (between 8% to 15%) ground
to a very fine particle size (<5 m) to prevent a speckled
appearance in porcelain
• Zirconium oxide
• Titanium oxide
• Tin oxide
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Coloring pigments
• Added to the porcelain in small quantities to obtain delicate shades
necessary to simulate natural teeth.
 Metallic oxides
• Titanium oxide – yellowish brown
• Manganese oxide – lavender
• Ferrous oxide or Nickel oxide – Brown
• Cobalt oxide – Blue
• Copper oxide, Chromium oxide – Green
• For fluorescence – uranium oxide
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Stains
• Stains are generally low fusing colored porcelains
used to imitate markings like enamel crack lines,
calcification spots, fluoresced areas,etc
• Internal staining - life like results and prevents direct
damage to stains by surrounding environment
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• color modifiers – less concentrated than stains
- to obtain gingival effects or highlight body colors
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Glazes and Add-on Porcelain
• Dental glazes consists of low fusing porcelains
• Purpose –enamel like luster -
seal the open pores in the surface of fired porcelain.
• Significance – marked increase in strength of porcelain by
preventing crack propagation
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• Self Glaze (natural glaze)
A vitrified layer that forms on the
surface of a dental ceramic
containing a glass phase when the
ceramic is heated to a glazing
temperature for a specified time.
• Over Glaze (add on Glaze)
The surface coating of glass formed
by fusing a thin layer of glass
powder that matures at a lower
temperature than that associated
with the ceramic substrate.
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•Types : Self-glazing and add-on glazing

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• Add-on porcelain - used for simple corrections of tooth contour or
contact points
• Disadvantages : low chemical durability, difficulty in even application,
: higher content of glass modifiers – reduce the resistance of the
applied glazes to leaching by oral fluids
• Overglazing : glassy and greenish hue
• Too high temperatures : pyroplastic flow, roundening of line angles &
loss of surface characteristics

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PROPERTIES OF CERAMICS
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Properties
1. Color Stability : Most stable tooth colored
material
2. Brittleness: Relatively brittle at oral
temperature, due to low tensile strength.
3. Strength :
• Compressive Strength : 48,000 psi
• Tensile Strength : 3500 - 5000 psi
• Shear Strength : 16,000 psi
4. Elastic Modulus : 10 * 106 psi
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5. Knoop Hardness No : 460 KHN
6. Abrasion Resistance :
• Natural Tooth : 343 KHN
• Porcelain : 460 KHN
( Hence causes wearing of natural tooth)
7. Dimensional Stability :
Linear coeff of thermal expansion : 12* 10-6 /C
8. Specific Gravity : 2.2 – 2.3 gm/cm3
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9. Thermal Conductivity : 0.005◦ C/cm
10. Shrinkage
Volumetric Shrinkage : 35-45 %
Linear Shrinkage
-High Fusing- 11.5%
-Low Fusing- 14%
(Can be minimized by using less binder, proper
condensation, build up of restoration 1/3rd larger than
original size, firing in successive stages)
11. Diffusivity : 0.64 mm2/sec
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12. Degradability : Generally resistant to degradation
- Mechanical Degradation (Brittle fracture)
- Chemical Degradation (Fluoride attack)
13. Refractive Index : 1.52 – 1.54
enamel : 1.655
37

METHODS OF STRENGTHENING CERAMICS
- Brittle material
- Presence of numerous surface flaws and scratches, porosity, roughness which
act as sharp notches
- Microcracks - tensile stresses and high contact angle of ceramic on metal.
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Methods of Strengthening brittle materials
A. Minimize the effect of stress raiser
• Discontinuities in brittle structures
• Abrupt change in shape/thickness in ceramic contour
 Rounded incisal line angles
 Removal of surface flaws
B. Development of residual compressive stresses
• Minimize tensile stress through optimal design of
ceramic prosthesis
• Minimize the number of firing cycle
• Ion exchange (chemical tempering)
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C. Interruption of crack propagation
 Dispersion Strengthening – introducing very hard
crystalline phases before fusing the porcelain
- Forming crystalline phase by devitrification
 Transformation toughening –introducing partially stabilized
zirconia at high temperature –at low temperature, formation of
stable monoclinic phase (harder) with increase in vol.
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METAL-CERAMIC
RESTORATIONS
41

METAL-CERAMIC RESTORATIONS
• It consists of a cast metallic framework on which at least two layers of
ceramic are baked.
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CERAMICS FOR METAL-CERAMIC
RESTORATIONS
43
• REQUIREMENTS :
- Simulate the appearance of natural teeth
- Fuse at relatively low temperatures
- Thermal expansion coefficients compatible with alloys
used for metallic framework
- Low abrasiveness

• COMPOSITION
- Silica network with Feldspar (potash/ soda)
- Glass modifiers , pigments and opacifiers
- Feldspathic porcelains contain a variety of oxides :
SiO2 matrix 52-65% (by weight)
Al2 O3 11-20%
Na2 O 4-15%
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MANUFACTURE OF PORCELAIN
The ground components mixed together in a refractory
crucible
1200◦C
45
Feldspar
Glassy phase with amorphous structure
Crystalline phase consisting of leucite
heating
12000 c

46
Continuous heating results in total dissolution of all
components forming a homogenous glass
Mix of leucite and glassy phase is quenched in water
Formation of FRITS
Frit is ball milled to achieve proper particle size distribution
And Coloring pigments are added

47
Manufactured feldspathic dental
porcelain
Glassy Leucite
( Amorphous phase) (Crystalline Phase)
Typical properties of glass Tetragonal structure at
Room temperature
i.e. - low toughness
- low strength
- high translucency

48

49
Leucite undergoes a reversible crystallographic phase
transformation at 6250C, Temperature above which its
structure becomes cubic
This transformation is accompanied by a thermal
expansion resulting in 1.2 vol% increase of the unit cell
This explains high thermal expansion coeff. associated
with tetragonal leucite

METALS
• Many alloys are available to be veneered with low and ultra-low fusing porcelains.
• Melting temperature higher than the firing temperature of the veneering porcelain
• Adequate stiffness and strength of the metal framework is required
• The composition of these high-noble, noble, predominantly base metal alloys
control
- the esthetics,
- bonding ability to porcelain,
- and the magnitude of stresses that develop in porcelain during cooling after
sintering
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PROCESSING
Condensation
Sintering
Glazing
Cooling
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52
The process of bringing the particles closer and removing the liquid
binder is known as Condensation.
It includes:-Agitation of particles
-Removal of excess water
Aim: Pack particles as close as possible to reduce
amount of porosity and shrinkage during firing.
CONDENSATION

Factors determining effectiveness :
I. Size of the powder
One Sized Particles 45%
Two Sized Particles 25% Leaves Void
Three Sized Particles 22%
Note: System that uses three sizes of powder is known as gap
grading system
II. Shape of the powder
Round particles produces better packing compared to angular
particles
III. Surface Tension
As liquid is withdrawn, surface tension causes powder
particles to pack closely together
53

METHODS OF CONDENSATION
1. Vibration Method
2. Spatulation Method
3. Dry Brush Method
4. Whipping Method
5. Combination of Vibration and Whipping
54

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- Mild vibrations are used to pack the wet powder
densely on the underlying framework.
Vibrated slowly
Brings excess water on the surface
Blotted away with a clean tissue
Note: Excess Vibrations Slumping of the mass

- Small spatula is used to apply and smoothen the wet
porcelain in incremental layers
- Smoothening action brings the excess water to the surface
which is removed by blotting
Placement of dry powder onto the wet surface
water is drawn towards the dry powder
Wet particles are pulled together
56

57
Whipping method
A large soft brush is moved in a light dusting action over the
wet porcelain
Brings excess water to the surface
Blotted away with a clean tissue
(Blotting occurs towards the blotted area)
Note: The same brush can be used to remove any coarse
surface particle along with the excess water
Combination method
Vibration method followed by Whipping method

SINTERING
Defined as a process of heating closely packed particles to
achieve inter particle bonding and sufficient diffusion to
decrease the surface area or increase density of the structure.
STEPS:
1. Pre heating the furnace.
2. The condensed porcelain mass is placed in front or
below the muffle, to permit remaining liquid binder and
vapor to dissipate (so as to prevent steam formation
when placed inside the furnace)
3. The “Green” porcelain is placed into the hot zone of the
furnace and the firing cycle is initiated.
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SINTERING

I. Loss of water which was added to the powder to form a workable mass
II. With rise in temperature, particles fuse by sintering and cause firing
shrinkage
(32-37% for low fusing and 28-34% for high fusing)
III. Glazing – which occurs at temperatures of 955C-1065C
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AIR FIRING
During firing, partial fusion of particles at their point of contact
Temp sintered glass gradually flows to fill up air spaces
Air becomes trapped in form of voids because fused mass is
too viscous to allow all the air to escape
Porosity

61
How vacuum firing works?
porcelain placed in the furnace –powder particles with air
channel around
Air pressure reduced to 0.1atm –air around particles to this
pressure
Temp until firing temperature – particles sinter –voids formed
Vacuum is then released and furnace pressure returns 1atm
Increase in pressure from 0.1-1atm compresses residual pores
Marked reduction in porosity in vacuum sintered porcelain

62
ADVANTAGES OF VACUUM FIRING
• Improves translucency and decreases surface roughness
• Increases impact strength approximately 50%
• Reduces the amount of porosity to 0.56% (from 5.6%)
in air fired dental porcelain

63
DIFFUSIBLE GAS FIRING
• It is an alternate method which uses the principle of diffusion to secure
improved density in fused porcelain
• A diffusible gas such as helium may be introduced to furnace at low
pressure during sintering stage
• The helium gas is entrapped instead of air in interstitial spaces
• Since its molecular diameter is smaller than porcelain lattice, its diffuses
outward under pressure of shrinking porcelain

64
Low Bisque Medium Bisque High Bisque
Surface very porous Less porous Completely sealed
and smooth
Grains start to soften
and lense at contact
point
Entrapped air
becomes sphere
shaped
A slight shine appears
on the surface
Shrinkage is minimal Definite shrinkage
Body extremely weak
and friable
Body is strong
STAGES IN FIRING

65
GLAZING OF PORCELAIN
After porcelain is cleaned and any necessary stains
are applied, it is returned to the furnace for final glaze firing
Usually, the glazing step is very short
When glazing temperature is reached, a thin glassy
film (glaze) is formed by viscous flow on the porcelain
surface
Natural glaze enhances transverse strength, esthetics
and reduces crack propagation
Over glazing should be avoided

BONDING OF PORCELAIN TO METAL
66

BONDING OF PORCELAIN TO METAL
• It is the primary requirement for the success of PFM prosthesis
• Theories of a metal-ceramic bonding fall into 2 groups
a) Mechanical interlocking
b) Chemical bond
• Alloys forming adherent oxide layer during the degassing procedure forms a
good bond to porcelain
• Some Pd-Ag alloys that do not form any external oxide layer, rather oxidize
internally undergo mechanical interlocking
67

• Clinical fractures of the metal ceramic restorations
may occur along the following zones :
68

PORCELAIN LABIAL MARGINS
• Many patients object to the grayness at the margin associated with
metal-ceramic restorations.
• If esthetics is of prime importance, a collarless metal-ceramic crown
should be considered.
• Collarless crowns have a facial margin of porcelain and lingual and
proximal margins of metal
• Advantages : - better esthetics and better plaque removal
• Disadvantages :- the marginal adaptation of these restorations is
slightly inferior to that of cast metal
69

70
A, A thin metal band provides excellent adaptation but is
very unesthetic unless it can be hidden subgingivally.
rarely used for anterior teeth.
B, "Disappearing" margin, sometimes called a
conventional margin, is commonly used. However, the
metal often causes unacceptable greyness of the gingival
tooth surface.
C to E, Various cut-back designs for labial porcelain
margin restorations. Reducing the metal will provide
better esthetics but makes the laboratory phase more
demanding and may result in margin chipping.
F, A 360-degree porcelain margin provides excellent light
transmission in the gingival area and optimal esthetics;
however, the laboratory fabrication is very demanding
Labial margin designs for metal-ceramic
restorations

71

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Benefits of metal-ceramic
system
• when properly fabricated, stronger and more
durable than all ceramic
• Long span bridges can be fabricated, taking care of
proper prosthetic design and occlusal relationship
• They withstand forces of occlusion without wear
• Long term color stability
• Less tooth preparation required
• No staining along the metal ceramic interface as
seen in acrylic resin veneered structures

73
Drawbacks of Metal- Ceramics:
a) Increased opacity and light reflectivity
b) The fit of long span bridges or splints may be affected by
the creep of the metal during successive bakes of
porcelain.
c) More difficult to obtain good aesthetics than regular or
aluminous porcelain.
d) Porcelains used in the metal-ceramic techniques are
more liable to devitrification which can produce
cloudiness.
73

ALL- CERAMIC RESTORATIONS
74

• In a survey carried out in 1994, metal-ceramic crowns and
bridges- for 90% of the fixed restorations.
• Recent developments with improved fracture resistance and
excellent esthetics increase in the use of all ceramic
products
• Ceramic crowns and bridges came into widespread use
since beginning of 20th century
• The ceramics employed conventionally was – high fusing
feldspathic porcelain.
• McLean and Hughes in 1965 alumina reinforced
porcelain core material
75

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Various methods of fabricating ceramic restoration vary
according to different formulations available
1) Condensed sintered.
• Traditional feldspathic porcelain jacket crown
• Porcelain jacket crown with aluminous core (Hi-Ceram)
• Ceramic jacket crown with leucite reinforced core (Optec HSP).
2) Cast glass ceramics (Dicor)
3) Injection molded (leucite reinforced) glass ceramic (IPS Empress).
4)Slip cast-glass infiltrated ceramics
• Glass infiltrated aluminous core restorations (In-Ceram)
• Glass infiltrated spinell core restorations (In-Ceram Spinell)
• Glass infiltrated zirconia core (In-Ceram Zirconia).
5)Milled ceramic restoration or cores
• CAD/CAM restorations
• Copy milled restorations

PORCELAIN JACKET CROWN
(Condensed sintered)
• These are crowns made entirely of feldspathic porcelain.
• They are constructed on a platinum foil matrix which is subsequently
removed.
TYPES
• Porcelain jacket crown (traditional).
• Porcelain jacket crown with aluminous core (Hi-Ceram).
• Porcelain jacket crown with leucite reinforced core (Optek HISP).

TRADITIONAL PORCELAIN JACKET CROWN
• The all-porcelain crown (PIC) has been introduced around since a century (early
1900s).
• These early crowns are also referred to as traditional or conventional PJCs.
• They were made from conventional high fusing feldspathic porcelains.
• these were very brittle and fractured easily.
• The marginal adaptation was also quite poor.
• Because of these problems they gradually lost popularity and are no longer used
presently.

PORCELAIN JACKET CROWN WITH ALUMINOUS CORE
• The problems associated with traditional PJCs led
to the development of the PJC with an alumina
reinforced core (McLean and Hughes, 1965).
• The increased content of alumina crystals (40 to
50%) in the core strengthened the porcelain by
interruption of crack propagation.
• In spite of the increased strength they were still
brittle and therefore not indicated for posterior
teeth and their use was restricted to anterior teeth.

• The porcelain jacket crowns are made using the platinum foil matrix
technique.
Platinum foil matrix
• A platinum foil is adapted to the die with a wooden point.
• The platinum foil functions as matrix.
• It supports the porcelain during condensation and firing.

Condensation and firing
• The core porcelain is carefully condensed on to the foil.
• The foil with the condensed porcelain is carefully removed from the die.
• It is then placed in the furnace and fired.
• After cooling, the rest of the crown is built up with conventional feldspathic porcelain.
Removing the foil
• After completion of the restoration the platinum foil is gently teased out and discarded.
• This can be quite difficult.

• High modulus of elasticity (350 GPa)
• Relatively high fracture toughness (3.5 – 4MPa)
• Flexural strength – twice that of feldspathic porcelains (139-145MPa)
• Excellent clinical performance for anterior teeth
82

LEUCITE REINFORCED PORCELAIN (OPTEC HSP)
• Optec HSP is a feldspathic porcelain with a higher lucite crystal
content (leucite reinforced).
• Its manipulation, condensation and firing is quite similar to the
alumina reinforced porcelain jacket crowns (using platinum foil
matrix).
Uses
• Inlays, onlays, veneers and low stress crowns.

LEUCITE- REINFORCED CERAMIC
(Optec HSP)
• Contain up to 45% by vol. tetragonal leucite
• Greater leucite content
- higher flexural strength (104MPa) and Compressive
strength
- high thermal contraction coefficient
84

Advantages
• They are more esthetic because, the core is less opaque (more
translucent) when compared to the aluminous porcelain.
• Higher strength.
• No need of special laboratory equipment.
Disadvantages
• Fit is not as good as metal ceramic crowns.
• Potential marginal inaccuracy.
• Not strong enough for posterior use.

CASTABLE GLASS CERAMICS(DICOR)
• The castable glass ceramic is quite unlike the other porcelains.
• Its properties are more closer to that of glass and its construction is quite different.
• This is the only porcelain restoration made by a centrifugal casting technique.
• The subsequent 'cramming process is also quite unique to this porcelain.
• Ceramming enhances the growth of mic crystals within the ceramic.

SUPPLIED AS
• The first commercially available castable glass-ceramic for dental
use was 'Dicor' developed by Corning glass works and marketed
by Dentsply.
• They are supplied as glass ingots.
• A precrystallized form called Dicor MGC is also available as
machinable blanks for CAD/CAM.

COMPOSITION
• Dicor glass-ceramic contains 55 vol% of tetrasilicic fluormica crystals.
FEATURES
• The Dicor glass-ceramic crown is very esthetic. This is because of its greater
translucency (unlike some other porcelains which have more opaque core).
• It also picks up some of the color from the underlying cement. Thus the color
of the bonding cement plays an important role.
USES
• Inlays, onlays, veneers and low stress crowns.

FABRICATION OF A DICOR CROWN
1. The pattern is first constructed in wax and then
invested in refractory material like a regular
cast metal crown.
2. After burning out the wax, nuggets of Dicor glass are
melted and cast into the mold in a centrifugal casting
machine.
3. The glass casting is carefully recovered from the
investment by sandblasting and the sprues are
gently cut away.
4. The glass restoration is then covered with an
embedment material to prepare it for the next stage
called ceramming.

5. Ceramming is a heat treatment process by which the glass is
strengthened. Ceramming results in the development of microscopic
crystals of mica, which
- Improves the strength and toughness of glass
- Improves the esthetics of the restoration (it reduces the transparency of
the glass making it more opaque and less glass-like).
6. The cerammed glass can be built up with special veneering porcelain
and fired to complete the restoration. Surface stains may be applied to
improve the esthetics.

ADVANTAGES
1. Ease of fabrication.
2. Good esthetics (greater translucency and chameleon effect).
3. Improved strength and fracture toughness.
4. Good marginal fit.
5. Very low processing shrinkage.
6. Low abrasion of opposing teeth.
DISADVANTAGES
1. Inadequate strength for posterior use.
2. Internal characterization not possible. Has to be stained externally to improve
esthetics.

HEAT PRESSED ALL – CERAMICS
• Heat pressing relies on the application of external pressure at high
temperatures to sinter and shape the ceramic
• During heat pressing , ceramic ingots are brought to high temperatures
in a PO4 bonded investment mold
92
IPS Empress Ingots

• Pressure (0.3-0.4MPa) is then applied
through a refractory plunger.
• This allows filling of the mold with soft
ceramic
• The temperature is held for 10-20 min.
• Mechanical properties are
maximized with excellent crystal dispersion, higher
crystallinity, and smaller crystal size, compared to
sintered all ceramics
93

LEUCITE- BASED CERAMICS (IPS Empress I)
• Heat pressing temperatures for this system are between 1150 – 1180C
for 20 minutes
• The final microstructure : 1-5 um sized leucite crystals dispersed in a
glassy matrix
• Porosity : 9% by vol.
94

• Advantages :
- Excellent fit and esthetics
- Moderate flexural strength
• Main disadvantages :
- Initial cost of the equipment (pressing oven and die material)
- Relatively low strength compared with other all-ceramic
systems.
- Potential to fracture in posterior areas.
• Uses:
- Indicated for single anterior crowns, inlays, onlays and veneers
95

LITHIUM DISILICATE BASED MATERIALS
(IPS Empress II)
• The second generation of heat-pressed ceramics
contain lithium disilicate (Li2Si2O5) as a major
crystalline phase.
• Heat-pressed at 890° to 920° C
• Later veneered with ceramics.
96

• Compared to first-generation leucite-based ceramics, the main advantage is
- enhanced flexural strength (300 MPa) and
- fracture toughness (2.9 MPa ).
• Several studies have reported that heat-pressing promotes- crystal alignment
along the direction of pressing because of the high aspect ratio of the
crystals.
• This leads to an even higher resistance to crack propagation in the direction
perpendicular to crystal alignment.
97

Slip-Cast All-Ceramic Materials
• Introduced in dentistry in the 1990s.
• Three types of ceramics are available for slip-casting:
- alumina-based (Al2O3)
- spinel-based (MgAlO4),
- zirconia-toughened alumina (12Ce-TZP-Al2O3).
98

Alumina and Spinel-Based Slip-Cast Ceramics
(In Ceram)
• The alumina content of the slip for alumina based ceramics is more than 90%.
 Steps in fabrication :
• Prepare teeth with an occlusal reduction of 1.5-2mm and a
circumferential chamfer of 1mm
• Make an impression and pour 2 dies
• Alumina powder+ water –slurry
• Slurry painted on an absorbent refractory die
99

• drying at 120° C for 6 hours and sintering for 2 hours at 1120°C
and 2 hours at 1180° C,
the porous alumina coping is infiltrated with a lanthanum-containing
glass during a third firing at 1140° C for 2 hours.
100

• Removal of the excess glass
• the restoration is veneered using similar-expansion
veneering ceramic.
leads to a high-strength material because of the
presence of densely packed alumina particles.
101
68% alumina
27% glass by vol.
5% porosity

• The flexural strength is around 600 Mpa
• Excellent fit, comparable with metal ceramics
• Uses : single unit anterior and posterior crowns and
anterior three unit bridges
• Spinel-based slip-cast ceramics (MgAl204) are
- more translucent, because the spinel phase allows better
sintering
- but the flexural strength is slightly lower (378 MPa) than
that of the alumina based system
- Use : Anterior crowns, Anterior single unit inlays,
onlays Veneers
102

Zirconia-Toughened Alumina Slip-Cast
Ceramics
• The combination of alumina and zirconia allows two types of strengthening
mechanisms.
• The stress-induced transformation of ceria and the associated increase in
volume produces compressive stresses within the zirconia grains.
• Additionally, the large alumina grains promote crack deflection.
• The flexural strength of this system has been reported at 630 MPa.
103

• The main advantage - high strength
• Disadvantages high opacity
- long processing times.
• USES:
- Posterior crown’s and Fixed partial prosthesis
104

CAD/CAM CERAMICS
• Constructing a dental ceramic restoration is technique sensitive, labor intensive and
time consuming. Machined ceramics were introduced to overcome some of these
problems. They are also known as milled or machined ceramics.
• Machinable ceramic systems can be divided into two categories
1. CAD/CAM systems
2. Copy milled systems

HISTORY OF CAD/CAM
• The major development in the field of dental CAD/CAM took place in the 1980s.
They were influenced by three important pioneers.
The first was Duret who fabricated
crowns through a series of processes
starting with an optical impression of
the prepared tooth.
The milling was done by a numerically
controlled milling machine (the
precursor of modern CAM/CAM).
The second pioneer was Mörmann,
developer of the CERE system at the
University of Zurich.
A compact chair-side machine milled the
crown from measurements of the
preparation taken by an intraoral camera.
At the time, the system was innovative as it
allowed'same-day restorations.
With the announcement of this system, the
term CAD/CAM spread rapidly to the dental
profession.
The third was Anderson,
the developer of the
Procera system in the
1980s.

• The early systems had to overcome many problems including limited computing
power, poor marginal accuracy,etc.
• Current CAD/CAM systems have come a long way.
• With improvements in technology material and software, restoration fabrication is
considerably more accurate and operator friendly as well.
• CAD/CAM systems are now part of everyday dentistry.

Commercially available CAD/CAM systems
• Many systems are currently available using a variety of techniques and materials.
• Some examples of commercially available CAD/CAM systems are –
1. Cere (Sirona),
2. Sirona Inlab Everest (Kavo),
3. Cercon (Dentsply),
4. Lava (3M ESPE),
5. Zeno (Weiland),
6. 5-tec (Zirkonzahn)

Tooth preparation
Wax pattern
Conventional
impression and
die fabrication
Contact probes or
optical scanning
Further processing - ranges form
simple glazing and staining to
post-sintering and build up with
veneering ceramics
Restoration or
framework milling
(CAM process)
Restoration or
framework design
(CAD process)

Scanner or digitizer
• The dimensions of the prepared tooth (or die or wax pattern) are picked up
and digitized in order to create a 3 dimensional image of the prepared tooth
in the computer.
• This is achieved by scanning of the preparation or the die.
• The 2 types of digitizers currently employed are
1. Contact probes - Physically contacts the die as it moves along its surface while
transmitting the information to the computer. E.g. Procera Forte contact
scanner.

2. Scanners - Unlike contact probes, scanners are optical devices.
These include
Intraoral hand-held wands
• These are chairside scanners. The intraoral scanner reflects light (visible light, laser or LED) and
captures it with a camera to create an optical impression of the prepared tooth and adjacent
structures. Multiple images have to be captured to stitch together a composite 3D image in the
computer. In some systems a special powder is dusted to reduce reflection and improve readability.
Laboratory scanners
• These are larger devices that scan the cast or die using different technologies. Some use a camera to
capture multiple images similar to the intraoral scanner (white light optical scanner). Others use 2
cameras to capture the obiect from multiple angles using white light (e.g. Kavo Everest) or laser
planes projected in a grid pattern. The Procera optical scanner uses a laser beam to measure
distances (conoscopic holography).

Computer (CAD process)
• The restoration or the core is designed in the computer. Most manufacturers have their own software for the
CAD process.
• The CAD process aids in designing either the restoration, coping or the FDP substructure. The computer can
automatically detect the finish line.
•
• Some use a library of tooth shapes that is stored on the computer to suggest the shape of the proposed
restoration.
• A recording of the bite registration is also added to the data.
• The combined information together with the 3D optical impression of the prepared tooth establishes the
approximate zone in which the new restoration can exist.
• The proposed restoration can then be morphed to fit into this zone in an anatomically and functionally correct
position.
• The dentist can make corrections or modify the design if required and then send it to the milling unit for
completion.

MILLING STATION
• Milling stations have evolved considerably since they were first introduced into the market.
• The earlier models ground only the internal surface. The external surface had to be manually ground.
• Current CAD/CAM machines can grind the external surface also.
• Signals from the computer control the milling tool which shapes the ceramic block according to the computer
generated design.
• To begin the process the ceramic block is attached to the machine via a frame or built-in handle(s).
• Milling is performed by a diamond or carbide milling tool.
• The Cere station uses 2 diamond burs to grind the internal and external surface simultaneously.
• Other machines use a single tool that moves along multiple axis (3 to 5 axis) and performs the milling action.
• The Everest (Kavo) Engine is an example of a 5 axis milling action.
• Some machines (Kavo Everest) can mill both ceramic and titanium.

Ceramic blanks
• A variety of ceramic blanks in various sizes, shades and shapes are available for
milling.
• Multiple units can be produced from the larger blocks.
• The smaller blanks may produce only a single coping or restoration.
• The blank is attached via a frame to the machine or by one or more handles on the
blank itself.

Classification of machinable ceramic blanks
1. Feldspathic porcelain blanks [Vitablocs Mark II (Vita)1.
2. Glass ceramic blanks
• Tetrasilicic fluormica based glass ceramic [Dicor MGC (Dentsply)]
• Leucite based [ProCad (Ivoclar), Everest G (Kavo)]
• Lithia disilicate glass ceramic [IPS e max CAD (Kavo)I.
3. Glass infiltrated blanks
• Alumina (Vita In-Ceram Alumina)
• Spinell (Vita In-Ceram Spinell)
• Zirconia (Vita In-Ceram Zirconia).
4. Presintered blanks
• Alumina (Vita In-Ceram AL)
• Ytria stabilized Zirconia (Vita In-Ceram YZ).
5. Sintered blanks
• Ytrria stabilized Zirconia (Everest ZH blanks).

COPY MILLED (CAM) SYSTEMS
• Some systems use a copy milling technique to produce ceramic cores or
substructures for FDPs.
• In copy milling a wax pattern of the restoration is scanned and a replica is milled out
of the ceramic blank.
CAD/CAM COPY MILLING
Scan preparation Scan pattern
Restoration designed virtually Restoration designed manually
Object milled from virtual pattern Restoration mills replica of pattern

Commercial systems available
• Examples of commercially available copy-milling systems are
1. Celay (Mikrona AG, Spreitenbach, Switzerland).
2. Cercon (Degudent, Dentsply). Cercon has both CAD/CAM and copy-milling systems.
3. Ceramill system.

Fabrication of a copy-milled restoration
substructure
• A stone die is prepared from the impression of the preparation.
• A pattern of the restoration is created using wax.
• The pattern is fixed on the left side of the milling machine (Cercon
Brain).
• A presintered zirconia blank is attached to the right side (milling section)
of the machine. The machine reads the bar code on the blank which
contains the enlargement information.

• On activation the pattern on the left side is scanned (noncontact optical
scanning) while the milling tool on the right side mills out the enlarged replica
(30% larger) of the patter from the attached ceramic blank.
• The milled structure is removed from the machine and sectioned off from the
frame. Any remaining attachment stubs are trimmed and final adjustments are
made.
• The zirconia structure is then placed in a sintering furnace (Cercon Heat) and
fired for 6 hours at 1350 °C to complete the sintering process.
• The restoration is completed using compatible veneering porcelains.

121
Fabrication of a zirconia restoration with
the Cercon system.
(A) Cercon brain (milling unit).
(B) Zirconia blanks.
(C) Wax pattern.
(D) Blank in position.
(E) Milling.
(F) Separating.
(G) Sintering (cercon heat).
(H) A completed substructure.
(I) A completed prosthesis.

REFERENCES
• Phillips’ Science of Dental Materials – 11th edition
• Science of Dental Materials with clinical applications, V.Shama Bhat, 3rd
edition.
• Art and Science of Operative Dentistry, Sturdevant’s, 7th edition.
122

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