2. Dental Ceramics
is an inorganic material that contains
metallic or semi-metallic elements
with non-metallic elements (usually
oxygen).
Theses elements can be Aluminum,
calcium, titanium ,silicon, zirconium
,magnesium, phosphorous,
potassium, lithium, sodium.
3. Dental ceramics
These materials can be defined by their inherent
properties; they form hard, stiff, and brittle materials
This is due to the type of the atoms present, the nature of
their inter-atomic bonding, which is ionic and covalent
mostly ,& the shape of the atoms packed or held together
Other properties of ceramics are:
Wear resistance, refractory (high melting point), thermal
insulators, non-magnetic, oxidation resistance, prone to
thermal shock and chemically stable
4. Dental ceramics
Ceramics contains a crystalline phase and a glass (continues )
phase depending on structural arrangement of the atoms
In general, the more glassy the microstructure (i.e. non-crystalline)
the more translucent it will appear, and the more
crystalline, the more opaque
With a range from very translucent to very opaque.
This is especially based on the silica structure
a. Silicate Types:
(1) Clays (hydrated alumino-silicates)with water
(2) Feldspars (anhydrous alumino-silicates)no water
(3) Quartz (silica)
b. Non-silicate Types
5. Glass in general
Glass is an amorphous solid (non-crystalline) material that
exhibits a glass transition
Glasses are typically brittle and can be optically transparent
The most familiar type of glass is soda-lime glass, which is
composed of about 75% silicon dioxide (SiO2), sodium oxide
(Na2O) from sodium carbonate (Na2CO3), lime (CaO)
In science, the term glass is defined in a broader sense, encompassing every solid
that possesses a non-crystalline (i.e. amorphous) structure and exhibits a glass
transition when heated towards the liquid state.
Quartz sand (silica) is the main raw material in commercial glass production
Quartz is the 2nd most abundant mineral in the Earth's continental crust, after
feldspar.
It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with
each oxygen being shared between two tetrahedra, giving an overall formula SiO2.
6. Crystalline in general
A crystal or crystalline solid is a solid material which
constituent atoms, molecules or ions etc..,are arranged in
an ordered pattern extending in all three spatial
dimensions at a microscopic level
large crystals are usually identifiable by their
macroscopic geometrical shape, consisting of flat faces
with specific, characteristic orientations
The scientific definition of a "crystal" is based on the
microscopic arrangement of atoms inside it, called the
crystal structure.
A crystal is a solid where the atoms form a periodic
arrangement
7. microstructure
Microscopically, a single crystal has atoms in a near-perfect periodic
arrangement; a polycrystal is composed of many microscopic crystals
(called "crystallites" or "grains"); and an amorphous solid (such as glass)
has no periodic arrangement even microscopically.
crystalline polycrystalline amorphous
8. Feldspars
Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8)
are a group of rock-forming tecto-silicate minerals that
make up as much as 60% of the Earth's crust
in glassmaking, alumina from feldspar improves product
hardness, durability, and resistance to chemical
corrosion, because it can crystallize
In ceramics, the alkalis in feldspar (calcium oxide,
potassium oxide, and sodium oxide) act as a flux,
lowering the melting temperature of a mixture.
Fluxes melt at an early stage in the firing process,
forming a glassy matrix that bonds the other components
of the system together
9. Classification based on the microstructural level
we can define ceramics by the nature of their composition of glass-to-
crystalline ratio to four basic compositional categories, with a
few subgroups:
composition category 1 – glass-based systems (mainly silica)
composition category 2 – glass-based systems
mainly silica + crystalline fillers (typically Lucite, more recently,
lithium disilicate)
composition category 3 – crystalline- based systems
with glass fillers (mainly alumina)
composition category 4 – polycrystalline solids (alumina and
zirconia) (no glass content at all only crystalline)
10. Other classification Systems for Dental Porcelains
1. Classification Based on Fusion Temperatures:
High Fusing: 1288 - 1371 °C (2350 - 2500 °F), Used for :
Denture Teeth, Aluminous Cores
Med Fusing: 1093 - 1260 °C (2000 - 2300 °F), Used for
:Porcelain jacket crowns, Inlays
Low Fusing: 871 - 1066 °C (1600 - 1950 °F)Used for Porcelain
fused to metal Restorations
Classification Based on Application Design:
a. Porcelain Core : Porcelain veneered onto porcelain cores
b. Porcelain Inlays and onlays
c. Cast Porcelain : Cast porcelain crown
d. Porcelain/Metal : Porcelain fused to metal
11. Classification Based on Usage of Low Fusing Porcelains
a. Opaque Porcelains = Low Fusing Glass + Opacifiers
b. Body Porcelains = Low Fusing Glass + Colorants
(1) Incisal or Enamel= Low Fusing Glass +little colorant
(2) Gingival or Dentin=Low Fusing Glass +yellow oxides
(3) Modifiers =Low Fusing Glass + white/gray oxides
c. Stains or Glazes = Low Fusing Glass + Colorants
12. Related Definitions and Terminology
Condensation=Padding &/or packing of porcelain powders into position prior to firing
Biscuit =Cohesive powder compact at particle-to-particle contacts after initial fusion
Frit = An unfused or partially fused powder mass.
Firing = Heating of porcelain powder or biscuits to eliminate the porosity and form a
completely solid mass
Soaking = Holding at a fixed firing temperature.
coefficient of thermal expansion= The degree of expansion divided by the change in
temperature
Thermal expansion= the tendency of matter to change in volume in response to a
change in temperature, through heat transfer
13. Feldspathic porcelains
Technically it is a glass rather than true porcelain( translucent)
But since we want a crystalline phase with the amorphous phase
in dental porcelain we add feldspar
feldspar is the main component in it ,feldspar has a tendency to
form a crystalline phase (leucite)
Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8)
In addition feldspathic porcelains contain kaolin as a binder
(Al2Si2O5(OH)4)
Quartz as a filler and strengthen agent
Metallic oxides for opacity and color
Some oxidative elements most present(tin, indium ,gallium) for
the porcelain to bond to the alloy
Used in porcelain fused to metal restorations
14. Leucite
Leucite is a rock-forming mineral composed of potassium and
aluminum tecto-silicate K[AlSi2O6]
Leucite occur as a crystalline phase
It has a large coefficient of thermal expansion compared to
glass
• Feldspar tend to form leucite when
melted
• Feldspathic porcelain contain leucite
crystalline phase
• Note : There is another type of glass
based ceramic reinforced with
luecite crowns used in all ceramic
restorations
15. Porcelain fused to metal restorations
fixed restorations composed of a substructure metal layer and
covered with 3 layers of feildspathic porcelain
The metal alloy part is composed of Noble metals ( gold
platinum, or palladium) they can be classified to :
High noble alloys :contain 40 % or more noble metals
Noble alloys :contain 25 % to 40 % noble metal
Base metal alloys: contain less than 25 % noble metals
The metal coefficient of thermal expansion should be higher
than that of porcelain to place the porcelain in slight
compression when cooled (which gives it a stronger state); the
alloy part should expand more than porcelain when they are
heated to the same temperature
Porcelain is stronger under compressive forces than under
tensile forces
16. PFM
• The alloys should have high yield strength that minimize their permanent
deformation under occlusal surface
• They should be stiff ( high modulus of elasticity ) that minimize their flexure
especially their long span bridges
• Note: porcelain may fracture secondary to flexure or deformation of the metal
substructure ,because of its low ductility
• Advantages of the added Metal substructure :
• High strength. withstand stresses. Thermal compatibility. Less crack
propagation. High resistance to fracture. Give good marginal fit
Bonding porcelain to metal :
Occurs via mechanical and chemical bonding
Mechanical bonding : interdigitating between the opaque layer of porcelain and
the alloy which increases with surface roughness & wetting of the metal
Chemical bonding: occur via the oxide mixing layer (metal-oxide-porcelain)
from the opaque layer and the metal; oxidation of metal is accomplished by
heating the metal structure in a furnace before adding the porcelain
17. Porcelain fused to metal design
The metal part is the substructure
and should be 0.5 mm in thickness
The metal-porcelain junction should
be at least 1.5 mm away from the
occlusal contact
All internal angles should be
rounded to prevent stress
concentration
The metal-porcelain junction should
be at right angle to avoid porcelain
fracture
the porcelain 1 to 1.5 mm (thickest at
the occlusal contact ) build from 3
layers
The 3 layers of porcelain are :
1- the opaque layer: masking the metal and the
dark oxide layer, with minimum thickness of
0.1 mm
2- body or dentine layer : the thickest used to
build most of the crown gives the color and
shade
3- incisal or enamel porcelain : the most
translucent layer to give a natural appearance
18. PFM failure
Mechanical or chemical
failures
1- Metal failure:
. Incomplete degassing
. Incorrect metal conditioner
. Reused metal alloy
2-Porcelain-to-Metal Fractures:
(Most common site for short-term failures to occur. Most common for base metals.)
a. (adhesive failure modes )
Contamination of metal surface (oxide-metal interface failure )
Contamination of oxide surface (oxide-porcelain interface failure)
Porcelain metal interface failure : oxide layer wasn’t formed
b. (Cohesive failure modes )
Oxide- oxide failure : the oxide layer is too thick, Thick oxide layers should be
sandblasted prior to porcelainizing to minimize the oxide thickness
19. Porcelain failure
A- porcelain fracture: (Most common site for long-term
failures to occur. Design or fatigue problems.)
1. Design or procedural errors:
a. Too little bulk of metal
b. Sharp angles in porcelain
c. Improper margin design
D. Inadequate framework design
2. Malocclusion or impact stresses
3. Thermal contraction incompatibility:
a. Built-in stresses generate cracks at pores
b. Thermal fatigue propagates cracks
20. Porcelain failure
B- Intra-Porcelain Failures:
1. "Gray or Black" shades in porcelain color:
a. Insufficient opaque porcelain
b. Improper opaque firing
d. Porcelain oven contamination
2. Porcelain surface cracks:
a. Improper cooling rate
b. Thermal cycling
c. Over-glazed or under-fired porcelain
d. Improper porcelain selection
3. Porcelain surface roughness:
a. Improper finishing and polishing agents
b. Acid dissolution (topical fluorides)
21. REPAIR SYSTEMS:
A. Silane + Acrylic (e.g., FUSION, George Taub Products, Inc.)
B. Silane + Composite (e,g., PULPDENT Porcelain Repair Kit)
C. Silane + Composite (e.g., MIRAGE PFM Repari)
22. Drawbacks of PFM restorations
Inadequate structure for ceramics - thickness of metal
coping.
More occlusal clearance required
Transparent metallic hue - anterior teeth
Metal exposed in case of gingival recession
Patients allergy to metals especially base metal alloys
Casting procedural errors with metals
The extra bonding failures at porcelain-metal interface
23. All- ceramic restorations
In some hand-layered porcelain restorations , feldspathic porcelain
is fused to aluminum oxide, glass-infiltrated aluminum oxide
(alumina) or zirconium-oxide (zirconia) creating a high-strength,
highly aesthetic, metal-free crown or bridge.
In other traditional restorations, this porcelain is layered onto a
metal substructure and often display color brightness, an opaque
"headlight", and dark oxide lines (a "black line" in the vicinity of the
gum line).
As these dark metal substructures are not conducive to a natural
appearance, metal-free restorations are typically more aesthetically
pleasing to the patient
But as the PFM restorations having a different core porcelain
material than the outer layer has a disadvantage of the chipping of
the outer porcelain layer because the bond between the 2 layers is
not as strong as wanted
24. All-ceramic restorations
monolithic restoration :it is fabricated in full from a single block of
material.
The material used for this type of restorations has to be strong enough,
especially for posterior teeth
Very strong porcelains are mostly opaque with no fluorescence
using a monolithic restoration means using one color from the cervical
area to the occlusal and depending only on outer stains this whole
process is considered less esthetic
Plus it can be abrasive of the opposing tooth
Monolithic anterior crowns, with less occlusal stress can be fabricated
entirely from an esthetic porcelain material
27. Glass ceramics with crystalline fillers
Glass ceramics with Leucite filler :
E.x. IPS empress® :
Can be press-ceramic or
CAD/CAM machinable ceramic
Provided as ingots or blocks
Indications: Single-tooth restorations (Inlays, onlays,
veneers, anterior and posterior crowns)
Not suitable for bridges or more than one unit restoration
,because its toughness and strength range from medium to
high
28. Glass ceramics with crystalline fillers
Glass ceramics with Lithium disilicate (LS2) fillers
E.x. IPS empress 2® or IPS e.max®
Supported with zirconium oxide for added strength , it may
also be used for bridges in the posterior area.
either the press or the CAD/CAM technology
Indications
Thin veneers (0.3 mm)
Minimally invasive inlays and onlays
Partial crowns and crowns
Implant superstructures
3-unit anterior/premolar bridges (only IPS e.max Press)
3-unit bridges (zirconium-oxide supported only IPS e.max
CAD)
29. Oxide Ceramics with glass infiltration
Example : Vident® all-ceramic In-ceram® products
1-( VITA In-ceram Alumina)®
Alumina based ceramic 75% Al2O3 with 25% glass infiltrations
single unit anterior or posterior crowns and three-unit anterior bridges.
2-(VITA In-ceram Spinell)®
spinell based caramics78% MgAl2O4 with 22%Glass infiltration
for single unit anterior crowns only
3-(VITA In-ceram Zirconia) ®
56% Al2O3 ,24% ZrO2 with 20 % glass infiltration
high level of translucency & flexural strength
indicated for single unit posterior and three-unit posterior bridges.
All available in machinable block form for cerec inLaband other milling
systems
30. Polycrystalline ceramics
Doesn’t contain a glass phase at all, usually made from alumina or zirconia
oxides
Considered a very hard dental material so its used as a core layered with
more esthetic other dental ceramics like fieldspathic ceramics, or can be used
as monolithic crowns, Monolithic ceramic crowns tend to be dense in
appearance with a high value and they lack translucency and fluorescence
Alumina cores without glass are produced by milling pre-sintered blocks of
the material utilizing a CAD/CAM dentistry technique.
The zirconia substructure (core) is usually designed using CAD/CAM
techniques of an impression, model or patient mouth, then its milled from a
block of zirconia in a soft pre-sintered state, then sintered again in a furnace
where it shrinks by 20% and reaches its full strength of approximately
850MPa.
31. Zirconia
Zirconia is the hardest known ceramic in industry and the
strongest material used in dentistry
The zirconia used in dentistry is zirconium oxide which has
been stabilized with the addition of yttrium oxide. its full
name is yttria-stabilized zirconia or YSZ.
Advantage of zirconia cores :
1- allow light to pass as a normal tooth would and that gives a
natural look, unlike other metal cores that block the light.
2- The normal too hot/cold sensations that can be felt with
other crowns does not normally occur because of reduced
thermal conductivity
disadvantage of core zirconia :bond strength of layered
porcelain fused to zirconia core is not strong enough
32. Zirconia
1- tetragonal polycrystalline zirconia, partially stabilized with yttrium oxide
there is pre-sintered zirconia and HIP (hot isostatic pressing) zirconia then
used with cad/cam technology
has very high strength & toughness , suitable for posterior long span bridges
Its usually opaque
Example : Lava™Zirconia from 3M™ESPE™ , (VITA In-Ceram) YZ™
Suggested indications
Monolithic full-contour crowns..
3,4 5- and 6-unit bridges.
Curved and long-span bridges.
Cantilever bridges.
Inlay and onlay bridges.
Anterior adhesive bridges.
Primary crowns/Telescopes and Implant abutments.
33. Alumina
2- alumina oxide polycrystalline
Example :
(Vita In-ceram AL) ™= 100 %Al2O3
IPS e.max ZirCAD™
Indicated for posterior crowns and bridges
High strength and toughness
Opaque
Fabricated by sintering and CAD/CAM technology
Note : alumina cores can be glass infiltered which has
significantly higher porcelain bond strength over CAD/CAM
produced zirconia and alumina cores without glass
34. Fabrication of dental ceramics
The traditional ceramic process generally follows this sequence:
Milling → Batching → Mixing → Forming → Drying → Firing →
Assembly.
Milling is the process by which materials are reduced from a
large size to a smaller size
Forming is making the mixed material into shapes. Forming can
involve: (1) Extrusion, such as extruding "slugs" to make bricks,
(2) Pressing to make shaped parts, (3) Slip casting
Sintering is the process of forming a solid mass of material by
heat and/or pressure, without melting it to the point of
liquefaction
35. CAD/CAM (computer-aided design and computer-aided
manufacturing):
CAD/CAM dentistry uses subtractive processes (such as
CNC milling) and additive processes (such as 3D
printing) to produce physical instances from 3D models.
Two basic techniques can be used for CAD/CAM
restorations:
- Chairside single-visit technique
-Integrated chairside–laboratory CAD/CAM procedure
36.
37. CAD/CAM
Increasing the speed of design and creation
Increasing the convenience or simplicity of the design,
creation, and insertion processes
making possible restorations and appliances that otherwise
would have been infeasible.
Utilizing in-office CAD/CAM restorations can be done in a
single patient visit.
Reducing unit cost and making affordable restorations and
appliances that otherwise would have been prohibitively
expensive.
However, to date, chairside CAD/CAM often involves extra
time on the part of the dentist, and the fee is often at least two
times higher than for conventional restorative treatments
using lab services.
38.
39. CAD/CAM
CAD/CAM use special partially sintered ceramic, which
are fired again after machining.
CAD/CAM restorations created with glass-ceramic
CEREC technology appear to last well, demonstrated
excellent fit, strength and longevity
As adjunctive techniques, software, and materials
improved, the chairside use of CAD/CAM (use within
dental offices/surgeries) increased.
For example, the commercialization of Cerec by Siemens
made CAD/CAM available to dentists who formerly
would not have had avenues for using it.
40. CAD/CAM systems include a digital impression system, 3D dental
design software and a chairside mill that function as a single
system.
an image (scan) is taken of the prepared tooth and the surrounding
teeth.
This image, called a digital impression, draws the data into a
computer.
Proprietary software then creates a replacement part for the
missing areas of the tooth, creating a virtual restoration.
This is called reverse engineering.
The software sends this virtual data to a milling machine where the
replacement part is carved out of a solid block of ceramic or
composite resin.
Stains and glazes are fired to the surfaces of the milled ceramic
crown or bridge to correct the otherwise monochromatic
appearance of the restoration.
41. aesthetic drawbacks:
They rely mostly on superficial staining to achieve a more
natural appearance, unlike hand-layered porcelain
restorations, which possess a deep-set coloration due to
the multi-layering.
