Dental ceramics

Dental Ceramics
Dr. Deepak K. Gupta

Introduction
• Ceramic is defined as
product made from non-
metallic material by firing
at a high temperature.
• Application of ceramic in
dentistry is promising
– Highly esthetic
– stronger, wear resistant,
– impervious to oral fluids
and absolutely
biocompatible
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• Spring-retained maxillary and mandibular
dentures of U.S. President George Washington,
– made from hippopotamus ivory by dentist John Greenwood.
– Two of the first dentures made for the president using
extracted human teeth

Advantages & Disadvatages
• Advantages
– Biocompatible as it is chemically inert.
– Excellent esthetic.
– Thermal properties are similar to those of enamel
and dentine
• Disadvatages
– High hardness - abrasion to antagonist natural
dentitions and difficult to adjust and polish.
– Low tensile strength so it is brittle material

APPLICATIONS OF CERAMICS IN
PROSTHETIC DENTISTRY
• Inlays and onlays
• Esthetic laminates (veneers) over natural teeth
• Single (all ceramic) crowns
• Short span (all ceramic) bridges
• As veneer for cast metal crowns and bridges
(metal ceramics)
• Artificial denture teeth (for complete denture and
partial denture use)
• Ceramic orthodontic brackets

Classification: Craig
• Based on the Application
– Metal-ceramic: crowns, fixed partial prostheses
– All-ceramic: crowns, inlays, onlays, veneers,
and fixed partial prostheses.
– Additionally, ceramic orthodontic brackets, dental
implant abutments, and ceramic denture teeth
• Based on the Fabrication Method
– Sintered porcelain: Leucite, Alumina, Fluorapatite
– Cast porcelain: Alumina, Spinel
– Machined porcelain: Zirconia, Alumina, Spinel
• Based on the Crystalline Phase
– Glassy (or vitreous) phase
– Crystalline phases

Classification: Anusavice
• uses or indications
– Anterior and posterior crown,
veneer, post and core,
– fixed dental prosthesis, ceramic
stain, glaze
• composition;
• principal crystal phase or matrix
phase
• Processing method
– casting,
– sintering,
– partial sintering
– glass infiltration,
– slip casting and sintering,
– hot-isostatic pressing,
– CAD-CAM milling, and copy milling
• firing temperature
– ultralow fusing,
– low fusing,
– medium fusing,
– High fusing
• Microstructure
– amorphous glass,
– crystalline,
– crystalline particles in a glass matrix
• Translucency
– opaque,
– translucent,
– transparent
• Fracture resistance : low, medium, high
• Abrasiveness

Classification of Dental Ceramics by
Sintering Temperature

Basic Structure
• Basically porcelain is a
type of glass - three
dimensional network of
silica (silica tetrahedral)
• Since Pure glass melts at
too high a temperature –
Modifiers added to lower
the fusion temperature
– Sodium or potassium
• But this weakens the
strength and make it
brittle facebook.com/notesdental

Composition
• It mainly consist of silicate glasses, porcelains,
glass ceramics, or highly crystalline solids.
• Wide variety of porcelain products available in
the market
• So its virtually impossible to provide a single
composition for them all.
• So we will discuss about traditional porcelains
- feldspathic porcelains

Composition (Percentage by Weight)
of Selected Ceramics)

Basic Constituents: feldspathic
porcelain
1. Feldspars are mixtures of (K2o. Al2o3.6SiO2) and
(Na2o. Al2o3.6SiO2), fuses when melts forming a
glass matrix.
2. Quartz (SiO2), remains unchanged during firing,
present as a fine crystalline dispersion through
the glassy phase.
3. Fluxes used to decrease sintering temperature.
4. Kaolin act as a binder.
5. Metal oxides: provide wide variety of colors

METAL CERAMIC RESTORATIONS
• Also known as Porcelain
fused to metal (PFM)
• It has the advantage of
being esthetic as well as
adequate strength.
• Most commonly used

Parts of PFM
• Core: cast metallic framework. Also known as coping
• Opaque Porcelain: first layer consisting of porcelain
modified with opacifying oxides.
– Mask the darkness of the oxidized metal framework
– metal-ceramic bond
• Final buildup of dentin and enamel porcelain

METAL-CERAMIC BOND
• Most important requirement for good long-term
performance.
• The bond is a result of chemisorption by diffusion
between the surface oxide layer on the alloy and the
porcelain.
• Roughening of surface interface also increases the
bond strength
– increases surface area of wetting for porcelain.
– Micromechanical retention
• Noble metal alloys, which are resistant to oxidizing –
easily oxidising metal like indium (In) and tin (Sn):
form an oxide layer

FAILURE OF METAL-CERAMIC
BONDING
• Cohesive failure: Porcelain-porcelain, metal-
metal, oxide-oxide.
• Adhesive failure: Porcelain-oxide, metal-oxide,
metal-porcelain.
• Mixed failure: Any combination of the previous
failures.

CERAMICS FOR METAL-CERAMIC
RESTORATIONS
• Must fulfill five requirements:
– simulate the appearance of natural teeth,
– fuse at relatively low temperatures,
– have thermal expansion coefficients compatible with alloys
used for metal frameworks,
– Compatible in the oral environment,
– have low abrasiveness.
• Composition: silica (SiO2), alumina (Al2O3), sodium oxide
(Na2O), and potassium oxide (K2O)
• Opacifiers (TiO2, ZrO2, SnO2),
• Various heat-stable coloring oxides
• Small amounts of fluorescing oxides (CeO2) - appearance of the
dentin/enamel complex structure

METAL FOR COPING OF METAL
CERAMIC RESTORATION
• The alloy must have a high
melting temperature to
withstand high firing temp of
porcelain.
• Adequate stiffness and
strength of the metal
framework.
• High resistance to
deformation at high
temperature is essential.
• Adequate thickness of metal.

FABRICATION OF METAL-CERAMIC
PROSTHESES
• Casting of Metal Core
– Wax framework is fabricated on the die.
– The framework is cast by lost wax technique.
– Sandblasting of the cast metal copy.
– Degassing is done to form oxide layer to improve
bonding to ceramic.
• Processing of Porcelain over metal core
– Condensation and Build-up
– Firing or sintering
– Glazing
– Cooling

Condensation
• The plastic mass of powder and water is applied
to the metal coping.
Function of condensation
– Adapt the porcelain to the required shape.
– Remove as much water from the material as possible
to decrease firing shrinkage.
Methods of condensation
– Vibration
– Spatulation
– Brush

Build-up
There are three types of porcelain used
a. Opaque porcelain: Mask the color of the
cement used for adhesion of the restoration.
b. Body or dentin porcelain: Makes up the bulk
of the restoration by providing most of the
color or shade.
c. Enamel porcelain: It provides the translucent
layer of porcelain in the incisal portion of the
tooth.

FIRING OR SINTERING
• It is to fuse the particles of porcelain powder producing
hard mass.
Stages of firing:
a. Low bisque stage: Particles lack complete adhesion,
low amount of shrinkage occur, and very porous.
b. Medium bisque stage: water evaporates with better
cohesion to the powder particles and some porosity.
Most of the firing shrinkage occurs in this stage.
c. High bisque stage: fusion of particles to form a
continuous mass, complete cohesion and no more
shrinkage.

SINTERING FURNACE

GLAZING
• The glazing is to obtain a
smooth surface that simulates a
natural tooth surface.
• It is done either by:
– Auto glazing: rapid heating up to
the fusion temperature for 1-2
minutes to melt the surface
particles.
– Add on glazing: applying a glaze
to the surface and re-firing.
• Auto glazing is preferred to an
applied glaze
AUTOGLAZED VENEER
CERAMIC

STRENGTHENING: DEFICIENCIES ARE
IN DENTAL PORCELAIN

ALL-CERAMIC RESTORATION
• All-ceramic restorations use a
wide variety of crystalline
phases.
• Several processing techniques
are available for fabricating all-
ceramic restorations:
– Sintering: Alumina and leucite
– Heat-pressing: Inceram and IPS
impress
– Casting: Dicor
– Slip-casting: Inceram Alumina,
Iceram spinell, in-ceram zirconica
– CAD/CAM: VitaBlock, Dicor MGC
Lava DVS Cross-Section

Sintered All-Ceramic Materials
• Two main types of all-ceramic materials
• Alumina-Based Ceramic
– developed by McLean in 1965
– aluminous core ceramic used in the aluminous porcelain
crown
– high modulus of elasticity and relatively high fracture
toughness, compared to feldspathic porcelains
• Leucite-Reinforced Ceramic
– 45% by volume tetragonal leucite
– higher flexural strength (104 MPa) and compressive
strength
– increased resistance to crack propagation

VITA In-Ceram® SPINELL
GLASS POWDER
VITA In-Ceram® ALUMINA
GLASS POWDER
VITA In-Ceram® ZIRCONIA
GLASS POWDER

Heat-Pressed All-Ceramic Materials
• Application of external
pressure at high temperature
to sinter and shape the
ceramic
• Produce all-ceramic crowns,
inlays, onlays, veneers, and
more recently, fixed partial
prostheses.
• Ceramic ingots are brought to
high temperature in a
phosphate-bonded
investment mold produced by
the lost wax technique.

• Leucite-Based Ceramic
– First-generation heat-pressed ceramics contain
leucite (KAlSi2O6 or K2O • Al2O3 • 4SiO2) as reinforcer
– Heat-pressing temperatures: 1150° and 1180° C for 20 minutes.
– ceramic ingots: variety of shades
– amount of porosity in the heatpressed ceramic is 9 vol %
• Lithium Disilicate–Based Materials
– second generation of heat-pressed ceramics
contain lithium disilicate (Li2Si2O5)
– major crystalline phase: 890° to 920° C temperature range
– 65% by volume of highly interlocking prismatic lithium disilicate
crystals
– amount of porosity after heat-pressing is about 1 vol %
– Higher resistance to crack propagation

Slip-Cast All-Ceramic Materials
• Introduced in dentistry in the 1990s
• Condensation of a porcelain slip on a refractory die -
aqueous slurry containing fine ceramic particles.
• Porosity of the refractory die helps condensation by
absorbing the water from the slip by capillary action.
• Restoration is incrementally built up, shaped
• Finally sintered at high temperature on the refractory die
• Usually the refractory die shrinks more than the
condensed slip
• Restoration can be separated easily after sintering
• Sintered porous core is later glass-infiltrated

• Alumina and Spinel-Based Slip-Cast Ceramics
– alumina content of the slip: more than 90%, with a
particle size between 0.5 and 3.5 μm
– 1st stage: drying at 120° C for 6 hrs
– 2nd stage: sintering for 2 hours at 1120° C and 2 hours
at 1180° C
– 3rd stage: porous alumina coping is infiltrated with a
lanthanum-containing glass during a third firing at
1140° C for 2 hours
– 68 vol% alumina, 27 vol% glass, and 5 vol% porosity
– Indication: short-span anterior fixed partial prostheses

• Zirconia-Toughened Alumina Slip-Cast
Ceramics
– Zirconia-toughened alumina slip-cast
– 34 vol% alumina, 33 vol% zirconia stabilized with 12
mol% ceria, 23 vol% glassy phase, and 8 vol% residual
porosity.
– alumina grains appear in darker contrast whereas
zirconia grains are brighter
• Main advantage of slip-cast ceramics: high
strength;
• Disadvantages: high opacity

Machinable All-Ceramic Materials
• Machining can be done by either
2 ways
• Soft Machining Followed by
Sintering
– Some all-ceramic materials can also
be machined in a partially sintered
state and later fully sintered
– Requires milling of an enlarged
restoration to compensate for
sintering shrinkage
– ceramics that are difficult to
machine in the fully sintered state,
such as alumina and zirconia

Machinable All-Ceramic Materials:
Hard Machining
• Milled to form inlays,
onlays, veneers, and crowns
using CAD/CAM technology
• produce restorations in one
office visit
• 3M ESPE Lava Chairside
Oral Scanner C.O.S., 3M
ESPE; CEREC AC, Sirona
Dental Systems, LLC; E4D
Dentist, D4D Technologies;
iTero, Cadent, Inc

Computer Aided Designing/Computer
Aided Milling (CAD/CAM)
• After the tooth is prepared
• The preparation is optically scanned and the
image is computerized
• Restoration is designed with the aid of a
computer
• Restoration is then machined from ceramic
blocks by a computer-controlled milling
machine

CEREC AC, Sirona Dental System

SUMMARY

References
• Phillips' Science of Dental Materials- Phillip
Anusavice_12th
• Basic Dental Materials -2nd.ed Mannapalli
• Clinical Aspects of Dental Materials Theory,
Practice, and Cases, 4th Edition
• Craig's Restorative Dental Material 13th
edition

THANKS……
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