Dental Ceramics

Dr. Deepak K. Gupta

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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 mandibulardentures 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

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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

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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

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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

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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

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Classification of Dental Ceramics by Sintering Temperature

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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

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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

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Composition (Percentage by Weight) of Selected Ceramics)

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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

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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

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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

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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

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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.

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CERAMICS FOR METAL-CERAMICRESTORATIONS

• 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

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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.

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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

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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

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Build-upThere are three types of porcelain useda. 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.

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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.

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SINTERING FURNACE

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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

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STRENGTHENING: DEFICIENCIES ARE IN DENTAL PORCELAIN

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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

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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

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VITA In-Ceram® SPINELL GLASS POWDER

VITA In-Ceram® ALUMINA GLASS POWDER

VITA In-Ceram® ZIRCONIA GLASS POWDER

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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.

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Heat-Pressed All-Ceramic Materials

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Heat-Pressed All-Ceramic Materials• Leucite-Based Ceramic

– First-generation heat-pressed ceramics containleucite (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

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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

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Slip-Cast All-Ceramic Materials

• 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

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Slip-Cast All-Ceramic Materials

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Slip-Cast All-Ceramic Materials

• Zirconia-Toughened Alumina Slip-CastCeramics– 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

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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

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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

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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

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CEREC AC, Sirona Dental System

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SUMMARY

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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

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