introduction to ceramics1

7/29/2019 Introduction to Ceramics1

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Presented by

Dr Rinu Sharma

1st year PG resident

Department of Prosthodontics & Maxillofacial Prosthetics


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CONTENTS

Introduction to ceramic History of Dental ceramic

Basic constituents of ceramic

Molecular structure & Composition ofDental ceramic

Classification of Dental ceramic

Properties of Dental Ceramic

Conclusion

Reference

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Ceramic

An inorganic compound with nonmetallic

properties typically composed of metallic(semi metallic) and nonmetallic elements.

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The word ceramic is derived from the Greek word

keramos that translates to mean, burnt earth. or

fired material.

Since they are made by shaping and firing a non-

metallic mineral at a high temperature.

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It came from the ancient art of fabricating

Pottery where mostly clay was fired to

form a hard, brittle object .

Pottery is the foremost ceramic.

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History of Ceramics

Chinese are credited with

development of porcelains as early

as 1000 AD.

Germans were able to produce material akin to

chinese stone ware which was an improvement

over porous & crude earthenware.

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Around 1717, dEntrecolles ,a jesuit priest integratedhimself with chinese potters to learn the porcelainmanufacturing process.

Other materials during 18th

century were(1) human teeth, (2) animal teeth carved to the size andshape of human teeth, (3) ivory

Animal teeth were unstable toward the corrosive agents in

saliva, and elephant ivory and bone contained pores thateasily stained. Hippopotamus ivory appears to have beenmore desirable than other esthetic dental substitutes.

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John Greenwood carved teeth fromhippopotamus ivory for at least one of

the four sets of complete dentures he

fabricated for George Washington.

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In 1808, individually formed porcelain teeththat contained embedded platinum pins

were introduced in Paris by Giuseppangelo

Fonzi.

Fonzi called these teeth terrametallic

incorruptibles and their esthetic and

mechanical versatility provided a majoradvance in prosthetic dentistry.

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Although probably not involving feldspathicporcelains,

In 1723, Pierre Fauchard was credited withrecognizing the potential of porcelain enamels andinitiating research with porcelains to imitate color of

teeth and gingival tissues.

Approximately 1774, (Parisian apothecary AlexisDuchateau, with assistance of a Parisian dentist

Nicholas Dubois de Chemant ) ,made the first successful porcelain dentures.

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These were replacement of the stained and malodorous

ivory prostheses of Duchateau himself.

They referred the material as

mineral paste.

Chemant, then continued to

improvise porcelain formulations

& was awarded bothFrench & British patents.

He then fabricated porcelain dentures as part of his

practice.

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Porcelains were realized through developments thatranged from the formulations of Elias Wildman in 1838 to

vacuum firing in 1949.

In 1885 ,Logan resolved the retention problemencountered between porcelain crowns and posts that

were commonly made of wood by fusing the porcelain to

a platinum post (termed a Richmond crown).

These platinum post crowns represented the first

innovative use of a metal-ceramic system since platinum

pin denture teeth fabricated by Fonzi 79 years earlier.

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By combining burnished platinum foil as a substructurewith the high, controlled heat of a gas furnace, Dr.

Charles Land was capable of introducing the first fused

feldspathic porcelain inlays and crowns in 1886.

These crowns exhibited excellent aesthetics, but the low

flexural strength of porcelain resulted in a high incidence

of failures.

The all-porcelain crown system, despite its estheticadvantages, failed to gain widespread popularity until the

introduction of alumina as a reinforcing phase in dental

porcelain.

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In 1950s with the addition of leucite to porcelainformulations ,elevated the coefficient of thermalexpansion to allow their fusion to certain goldalloys to form complete crowns and fixed partialdentures.

Refinements in metal-ceramic systems

dominated dental ceramics research during thepast 35 years that resulted in improved alloys,porcelain-metal bonding, and porcelains.

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In 1980, the introduction of a shrink-freeall-ceramic crown system and a castableglass-ceramic crown system has providedadditional flexibility for achieving estheticsresults.

This introduced advanced ceramics with

innovative processing methods, andstimulated a renewed interest in all-ceramicprostheses.

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Ceramic

Three essential constituents of Ceramic clay areFeldspar, quartz and kaolinite.

Feldspar

Feldspars are naturally occurring crystalline rocks whichhave an internal, crystalline structure.

When glass cools slowly, crystals form which is a process

known as devitrification.

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Feldspar cooled over a period of millions of

years.

There are twelve naturally-occurring feldspars.

Their formulas are similar and can be inferred

from the three formulas provided here.

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Feldspars melt into a glass-like consistency and flowlike a thick liquid at high temperatures.

Too much feldspar are unsuitable as potters clay since

objects made from it would simply melt into a puddleinstead of maintaining its shape.

Potters clays contain no more than 15% feldspar, and

porcelain clays may contain up to 25%

Where as some glazes contain 100% feldspar, since the

purpose of glaze is to melt and flow over the

surface

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Feldspars melt at 1150 C.

Feldspathic glass surrounds refractory clay particlesand fills the pores between them.

Due to fluxes, feldspathic glasses bind to refractoryparticle surfaces which help bind the ceramic bodytogether.

The more feldspathic glass a ceramic bodycontains, the denser the fired body will be.

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Quartz

Quartz is pure, crystalline silica.

Silica in crystalline quartz is not combined with fluxmolecules and does not melt.

The quartz particles remain separate, un-melted,and dispersed throughout the glassy phaseproduced by the melting feldspar.

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The alkaline metal ions (fluxes) from feldspar

encourages bonding of outer layers of refractory

quartz particles to the surrounding feldspathic

glass matrix

Quartz melts at 1713 C

Most dental ceramic work is done between 850C

and 1100 C.

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Kaolinite

It is known as kaolin (China Clay).

Kaolinite (Al2O3 2SiO2 2H2O)

is found in nature.

Kaolin is a hydrated aluminum

silicate.

Kaolinite has a crystalline structure.

It acts as binder to increase mouldability of unfired porcelain.

But because it is opaque,it is added in very small quantity if atall in dental ceramics.(Claus 1980, Phillips 1982)

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Thus, most important materials in potters clay

are feldspar, quartz, and kaolinite.

The proportions of these minerals determine

ceramic characteristics.

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Stoneware

Stoneware is a hard, strong and vitrified ware whichfires above 1200 C. It has low porosity.

- Contains clay & small amount

of hard stone called flint.

Eg. Modern dinnerware

-There is more feldspathic glass that binds alumina andsilica together.

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Domestic Porcelain

- Domestic porcelain is made from China Clay.- The large amount of glass in the mix reduces porosity to

nearly zero, and produces a very dense, hard, and

translucent glassy body .

BUT,

- Porcelain clay is prone to

slumping since there is less

refractory material for

support . The glass wants to flow at high temperature .

Thus, The firing temperature must be precisely controlled

in order to fully vitrify the glass.

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Dental Porcelain

In the early 1900's, when dental porcelain was firstformulated, it had the same general composition as

domestic porcelain.

Even small quantities of kaolin in the mixture cause

porcelain to lack translucency hence later, little or no

kaolin was left in porcelains chosen for dental use.

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Thus, The first ceramics used in dentistry in the late

eighteenth century were porcelains, which were made

from a highly refined & fired white clay.

The term porcelain however is said to have been coined

by Marco Polo in the 13th century from the termporcellana ,Italian name for the cowrie shell.

Polo referred it to describe Chinese

porcelain to fellow Europeansbecause of the shell's thinness,

translucency, hardness, and

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Thus,Porcelain :Refers to those ceramic materials initially derived from

combination of Quartz ,Kaolin & Feldspar sintered athigh temperature.

Dental porcelain :Are made up of an amorphous glass matrix & at least one

crystalline phase.

Dental ceramics :

Term that encompasses to all types of ceramic dentalproducts. Everything from denture teeth to all ceramicrestoratives to metal ceramic porcelains are labeled asdental ceramics.

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Dental ceramic

An inorganic compound with nonmetallic

properties typically consisting of oxygen and oneor more metallic or semi metallic elements (e.g.,

aluminum, calcium, lithium, magnesium,

potassium, silicon, sodium, tin, titanium, and

zirconium) that is formulated to produce the wholeor part of a ceramic based dental prosthesis.

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Molecular structure of Ceramics

Most ceramics are made from compounds of a metal anda non-metal.

They contain a mixture of covalent and ionic bonding, the

proportions of which determine the mechanical properties

Ceramics are crystalline, but their crystal structures are

often more complex than metals.

Ceramics involve covalent bonding, but the molecularstructures are three-dimensional and complex compared

to polymers.

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As a result ceramics cannot undergo atomic likemetals or chain realignment like polymers.

They are not capable of changing shape without

fracturing, unless they are heated to considerably

higher temperatures.

This is why we can only form ceramic objects bymechanically grinding or by heating them until

they become plastic.

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Dental ceramics are actually fired twice.

The first time they are fired until all the ingredients

are fused together at so high a temperature thatthe material becomes liquid. This liquid is then

cooled rapidly, making it a solid glass.

The glass is crushed to a powder, technically

called a frit

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This powder becomes the basis for the additions

necessary to make the various special purposedental ceramics.

The powder is mixed with water to form a formable

paste for dental restoration.

This is then fired a second time, until the softeningtemperature of the glass is reached. At this point theglass powder particles start to soften on their outside

surfaces and bond together at the contact points.

This is a process called sintering. Thus dentalporcelains are nothing but, sintered glass.

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So, what is a glass?

Glass is defined as a material where the looselyarranged mixture of atoms found in the liquid

state has been kept down to a temperature low

enough that the substance has the mechanical

properties of a solid .

Glass is shortly defined as supercooled liquid

Theoretically any material can be made into aglass if it can be cooled quickly enough

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If this liquid is cooled normally, the atoms go

back to their positions in a regular crystal

structure and the metal crystals reform.

The atoms have no time to form a crystal

structure, and remain in their random liquid

positions

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The easiest glasses to form are made from theoxides of small multivalent atoms such as silicon,boron, germanium or phosphorus.

The most common glasses are based on Silica(SiO2) which is the most common mineral on thesurface of the earth.

The dental ceramic we use is also a glass mademainly from silica.

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The atom arrangement in its structure consists of

two covalently bonded atoms, two oxygen to one

of silicon.

Silicon has four electrons in its outer shell,

oxygen has six, so that the resulting structure has

each oxygen atom bonded to two silicon atoms,

and each silicon atom bonded to four oxygen are

double bonds.

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This is the basic geometric unit of the resulting

structure, a pyramidal shape called a

tetrahedron.


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If all the pyramids are joined at regular intervals

and spaces, there will be a crystal structure

lattice, and the resulting material is a crystalline

compound .

If the pyramids are joined at irregular intervals

and spaces, as would happen if molten silicawas rapidly cooled, the compound is a silica

glass.

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In the diagrams below a triangle representsone silica pyramid

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Regular bonded structure of tetrahedra

a crystalline material

Irregular bonded structure of tetrahedra

a glass


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Thus, Basic structure of

ceramics Its basic structure is similar to that of glass. It

therefore consists of a three dimensional networkofsilica(silica tetrahedra).

Pure glass melts at too high a temperature fordental use. Adding certain chemicals lowers the

melting temperature by disrupting the silica

network.

The glass obtains porcelain like qualities when

the silica network is broken by alkalieslikesodium and potassium.

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This also lowers the fusion temperature.Thesechemicals are therefore known as glassmodifiersorfluxes.

Other substances which act like glass modifiers arealumina (Al203) and boric oxide (B203)

Adding certain opacifiersreduces the transparencyand completes the transformation of glass to dentalceramic.

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Manufacturing process

(Feldspathic porcelain) In recent years are made mainly with potash feldspar

(K20.AL20.SiO2) and small additions of quartz

(SiO2).

The ground ingredients are carefully mixed together.

Alkali metal carbonates are added as fluxes

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Heated to 1200 deg C


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the feldspar decomposes to form a glassy phase with an

amorphous structure & crystalline phase consisting of

leucite

small shattered fragments are obtained, called a Frit.

Coloring pigments are added to obtain the delicate

shades necessary to mimic natural teeth.

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Rapidly quenched in water

Ball milled to obtain particular size


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Thus formed porcelain has 2 phases

- Glass phase - Crystalline phase leucite

- brittleness - high thermal expansion

- translucency - high strength- high surface tension

Most of the chemical reaction takes place duringthe manufacture.

During subsequent firing in the dental laboratory,the porcelain powder simply fuses together to formthe desired restoration.

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Constituents of ceramic

Feldspar Basic glass former

Kaolin Binder

Quartz Filler

Alumina Glass former and Flux

Alkalis Glass modifiers

Color pigments Modifies color

Opacifiers Reduces transparency

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A typical dental ceramic will contain about

50-70% silica;10-20% alumina;

4-10% sodium oxide,8-10% potassium oxide1 or 2 % calcium oxide.

There will also be smaller amounts ofmany other metal oxides.

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Aluminum oxide

Aluminum oxide (Al2O3) exists in two separateforms within clay and porcelain bodies.

When chemically combined with other feldsparconstituents, aluminum oxide acts as a stabilizer

. Aluminum atoms bond with silicon via a shared

oxygen atom and are an integral part of the

amorphous silicon matrix. In this form, it doesntaffect glass transparency

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But it is also added as a separate constituent in theform of kaolinite which because of large amounts offlux contained in feldspars, melts into a glass.

The by-product left over when the kaolinite melts isa precipitate of pure crystalline aluminum oxidecalled alumina. Alumina crystals remain un-meltedand are scattered throughout the glass melt.

In this form, aluminum oxide causes glass tobecome opaque

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Silica

Silicon dioxide(SiO2), like alumina, exists in two separateforms within clay and porcelain bodies.

When chemically combined with flux and aluminumoxide, silica exists as a molecular component in theamorphous melted glass gel.

In this form, it is called a glass former.

Silica also exists as un-melted crystalline, quartz particles

scattered throughout the glass melt. This is part of the refractory substructure which supports

clay and porcelain bodies.

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Glass Modifiers

Alkalies such as sodium, potassium and calciumare glass modifiers.

They interrupt the oxygen silicon bond forminglinear chains of silica.

This ease of movement is responsible for increased fluidity& lower softening temperature.

They also increase the Thermal expansion

However, too high a concentration of glass modifiers is notdesired because- It reduces the chemical durability of ceramic.

- It may cause the glass to devitrify during firing.

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Opacifiers

Since pure feldspathic porcelain is quitecolorless, opacifiers are added toincrease its opacity in order to simulatenatural teeth.

Oxides of zirconium, cerium, titaniumand tin are commonly used opacifiers.

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Color Modifiers

Color modifiers are required to adjust theshades of the dental ceramic.

Various metallic oxides provide a variety of color,e.g. titanium oxide (yellowish brown), nickeloxide (brown), copper oxide (green),manganese oxide (lavender), cobalt oxide(blue), etc.

These powders are blended together withun pigmented powdered frit to provide theproper hue & chroma.

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Other Specialized Porcelain

PowdersShoulder porcelain

A ceramic that is formulated to be sintered at the

cervical area of metal ceramic crown to produce an

esthetic and fracture resistant butt joint margin.

These powders are fired (sintered) at temperatures

higher than regular body porcelains.

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Opaquer Porcelains

It is a specialized type of porcelain which is madeopaque by additon of insoluble oxides (opacifiers).

These oxides have high refractive indices so theycan scatter the light.

It serves three major function :- wets metal surface to establish metal-ceramic bond.

- masks the color of metal substructure

- initiates development of the selected shade.

Some color modifiers can be added to achieveinternal shade modification.

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Body porcelain

They vary in the amount & type of metallic oxide pigments

Dentin porcelain

It is major determinant of shade of any porcelain restoration. Maycontain 5 10 % free alumina. Extends till Incisal / occlusal one

third.

Enamel porcelain

It is more translucent than dentin. Shades are usually in violet togray range. It is predominantly alumina free.

Translucent

It imparts depth & natural enamel like translucency withoutaltering body shade.

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Stains

They are porcelain powders containing a highconcentration of metallic oxides (color modifiers)which give them greater fluidity.

Stains are created by mixing metallic oxides withlow fusion point glasses below the maturingtemperature of enamel & dentin porcelains.

Stains are used to provide individual colorvariation in the finished restoration

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Glazes

They are generally colorless low fusingporcelains that posses considerable fluidityat high temperature.

They fill small porosities & irregularities &when fired help to create the external sheenor glassy appearance of natural tooth.

They contain a lot of glass modifiers whichalso makes them somewhat less chemicallydurable.

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Reinforced Core Porcelains

These are specialized porcelains containing a highconcentration of a reinforcing material which make themstronger than regular feldspathic porcelains.

They are used to create a strong inner core which

imparts strength to the ceramic.Variety of reinforcing materials are currently being used .They include:

- Alumina (alumina reinforced porcelain)- Magnesia based (spinell)

- Leucite (leucite reinforced porcelain).

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Classification of Ceramics

Ceramics can be classified as

According to firing temperature

According to its micro structure

According to processing methods

According to type of restoration

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According to respective fusing temperature

range.

High fusing 1300" C (2372" F)

Medium fusing 1100"-1300" C (201 3"-2072" F)

Low fusing 850"-1100" C (1562"-2012" F)

Ultra-low fusing


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The medium-fusing and high-fusing types

are used for the production of denture

teeth. The low-fusing and ultralow-fusing

porcelains are used for crown and bridgeconstruction.

Low firing temperatures reduces the risk for

growth of the metal oxide.

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Potential advantages of ultralow-fusing ceramics

are

the reduction in sintering times, decrease in sag deformation of FPD framework

less thermal degradation of ceramic firing ovens

and less wear of opposing enamel surfaces

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According to microstructure,

Predominantly Glass

Particle filled Glass Polycrystalline

J. Robert Kelly, Dental ceramics What is this stuff anyway?.

JADA, Vol. 139,Sept. 2008

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Predominantly glass

Dental ceramics that best mimic the opticalproperties of enamel & dentin have a high glasscontent.

Manufacturers use small amounts of filler particlesto control optical effects such as color and opacity.

eg. Alumino-silicates found in nature, also known as

feldspars.Feldspars are modified in various ways to create theglass used in dentistry

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Particle filled glass

Manufacturers add filler particles to the base glass

composition to improve mechanical properties, such as

strength, thermal expansion and contraction behavior.

These fillers usually are crystalline, but they can also

be particles of high-melting glasses that are stable at

the firing temperatures of the ceramic.

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Eg. ceramics containing high concentrations of

lithium disilicate crystals is an example of a particlefilled glass-ceramic

The filler can be :

-Alumina ( In-ceram Alumina)

- Magnesium aluminate (In-ceram Spinell)

- Mixture of 70 % alumina & 30 percent zirconia

( In-ceram Zirconia)

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Polycrystalline

Polycrystalline ceramics contain no glass.All of the atoms are packed into regularcrystalline arrays through which it is muchmore difficult to drive a crack than it is in

atoms of less dense and irregular networkfound in glasses.

Hence, polycrystalline ceramics generallyare much tougher and stronger than glass-based ceramics

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Well-fitting prostheses made from polycrystallineceramics were not practical before the availabilityof computer-aided manufacturing because of highfiring temperature & resulting shrinkage.

However 15-20 % shrinkage can becompensated by constructing an over sizedceramic pattern which will shrink during sintering,resulting into desired size to accurately fit theprepared tooth.

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Predominantly glass-based ceramics are lightly filled with colorants and

opacifiers to mimic natural esthetics and are the weakest ceramics.Glasses containing 35 to 70 percent filler particles for strength . It can be

Moderately esthetic as full-thickness restorations, but generally are veneered.

Completely polycrystalline ceramics (no glass), which are used to create strong

substructures and frameworks via computer-aided design/ computer-aided

manufacturing processes, always are veneered.


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According to processing methods

Powder / Liquid glass based systems

Machinable or pressable blocks of glassbased systems

CAD/CAM or Slurry/Die processed

mostly crystalline( alumina or Zirconia )

systems

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Powder/liquid with or without


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Powder/liquid, with or without

crystalline fillers

These are the porcelains that are made forveneering cores made from either metal, aluminaor zirconia, but can be used for porcelainveneers on either a refractory die or platinum foil

technique.

They are ideally suited for anterior teeth,especially when bonding to enamel.They are not

the ideal material for inlays and onlays becausethey are much weaker than denselymanufactured blocks of glass based ceramics.

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Manufactured blocks with or without


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Manufactured blocks, with or withoutcrystalline fillers

These materials are ideally suited for inlay

and onlay restorations, anterior crowns and

veneers, and possibly bicuspid crowns.

They have to be bonded and can be used full

contour as there are polychromatic

machinable versions available.

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CAD/CAM or slurry/die-


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CAD/CAM or slurry/die-

generated mostly or all-

crystallineAlumina materials in this classification are

(Procera),which is solid sintered alumina, and

In-Ceram,which is glass infiltrated.

These materials work well for cores for single

crowns that are veneered with a powder/liquid

glass-based material.

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According to type of restoration


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g y

Restorations

All ceramic

FELDSPAR

HIGH LEUCITE

(OPTEC)

LOW LEUCITE

CAST GLASSCERAMIC

LEUCITE

(EMPRESS)

MICA(DICOR)

CORE

ALUMINA

ALUMINA

(PJC)

SLIP CAST

(INCERAM)

MAGNESIA

MAGNESIAMOLDED

(CERESTORE)

Porcelain fusedto metal

(Metal Ceramic)

FELDSPAR

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Properties of dental ceramic

Depends on Their composition

Microstructure

Flaw population- fabrication defect

- surface cracks

Nature and amount of reinforcing material

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General properties of feldspathic porcelain

StrengthPorcelain is brittle and tends to fracture.

The strength of porcelain is usuallymeasured in terms of flexure strength (or

modulus of rupture).

Flexure strength

It is a combination of compressive, tensileas well as shear strength.

( 75.8 MPa - 141.1 MPa).

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Compressive strength (350 - 550 MPa)

Porcelain has good compressive strength .

Tensile strength (20 - 60 MPa)

Tensile strength is low. When porcelain is placed undertension, it can result in brittle fractures.

Shear strength (110 MPa)

It is low and is due to the lack of ductility causedby the complex structure of porcelain.

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Why low tensile strength ?

The presence of the covalent bonds in porcelainshould have produced much greater strength but it

fails to have so.

This was explained by,

Irwin (1957) Griffith (1921) and Orowan (1944, 1949, 1955).

- when a brittle material is subjected to tensilestresses, specific crack formed in certain location

were associated with greatly increased stress

levels.

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Ceramics tend to have no mechanism for plasticallydeforming without fracture as do metals, cracks may

propagate through a ceramic material at low average

stress levels.

As the crack propagates through the material, the stress

concentration is maintained at the crack tip unless the

crack moves completely through the material or meets

another crack, a pore, or a crystalline particle

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Thus,Reducing the depth of surface flaws in the surface

of a ceramic is one of the reasons that polishing

and glazing of dental porcelain is so important.

If porcelain is glazed there will be no microcracks orporosity in the surface region. The tensile stresses

caused by bending are greatest in surface region &

a crack is also most likely to start from same region.

Hence, preventing crack on surfaces minimizesoverall crack mechanism & improves strength.

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TYPE FIRINGENVIRONMENT

SURFACECONDITION

FLEXURALSTRENGTH


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ENVIRONMENT CONDITION STRENGTH(Mpa)

AIR GROUND 75.8

FELDSPATHICPORCELAIN

AIR GLAZED 141.0

VACUUM GROUND 79.6

VACUUM GLAZED 132.0

ALUMINOUSPORCELAIN

AIR GROUND 136.0

AIR GLAZED 139.0

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After being Glazed, the component will have more thandoubled its flexural strength. Also depends on type of material


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Modulus of Elasticity

Porcelain has high stiffness (69 GPa) and doesnot undergo plastic deformation.

Surface HardnessPorcelain is much harder (460 KHN) than

natural teeth.If a roughened surface contacts tooth enamel

or dentin under high occlusal forces( whichmay occur because of bruxing/ premature

occlusal contacts, and/or inadequate occlusaladjustments), It can cause wear of opposingnatural teeth.

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W R i t


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Wear Resistance

They are more resistant to wear than natural teeth. Theceramics should exhibit uniform surface so that asperitiessuch as large crystalline inclusions do not project out from thesurface.

Enamel wear or abrasion can be minimized by different ways,like

Use of ultra low fusing ceramics.

Polishing functional ceramic surfaces periodically.

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Th l P ti


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Thermal PropertiesThermal conductivity

Porcelain has low thermal conductivity.Metal atoms transfer their outermost electrons to the non metallicatoms & thereby stabilize their highly mobile electrons. Thus, theydo not readily conduct electricity or heat.

Coefficient of thermal expansion & contractionIt depends on the type of material & firing temperature .eg. Leucite can be incorporated modify thermal expansion &contraction behavior. Mismatch in this coefficient of adjacentmaterials ,results in compressive & tensile stresses.

Dimensional StabilityFired porcelain is dimensionally stable.

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Ch i l t bilit


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Chemical stability

It is insoluble and impermeable to oral fluids.Also it is resistant to most solvents.

However, hydrofluoric acid causes etching of

the porcelain surface typically by selectiveleeching of sodium ions thereby disrupting thesilica network.

A source of this is APF (acidulated phosphatefluoride 1.23%) and stannous fluoride 8% whichare used as topical fluorides.

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When glazed feldspathic porcelain is contacted by

these fluorides, a surface roughness is produced in 4mins.

If contacts for about 300 mins a generalized severe

degradation of porcelain surface has occurred whichleads to staining, plaque accumulation & further

breakdown of structure.

So, we should avoid the use of APF gels whenceramic restoration is present or the surface of

restoration should be protected with petroleum jelly.

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Hydrofluoric acidis however used toetch the porcelain surface to improve

the bonding with resin cement.

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Esthetic Properties

The esthetic qualities of porcelain are excellent.

It is able to match adjacent tooth structure in

translucence, color and intensity.

The color stability is also excellent.

It can retain its color and gloss for years. 93


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Biocompatibility


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Biocompatibility

Excellent compatibility with oral tissues.

The dental ceramics in use today have relatively low firing

temperatures, but usually greater than 900C and are

resistant to dissolution in the mouth.

Formulations have been developed with firing temperatures

as low as 640C, however, these materials tend to show

considerable surface degradation in the oral environment

and hence are not so much useful.

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Conclusion


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Conclusion

Thus,

A closer understanding of the dynamics of the

material with respect to design of the restoration and

the intended use is required to enable these

restorations to perform productively.

The new generation of ceramic materials present

interesting options, both in terms of material selectionand in terms of fabrication techniques.

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R f


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References Kenneth J. Anusavice, Phillips Science of Dental Materials . Dental

Ceramics,11th edition

Robert G. Craig, Restorative Dental Materials. Ceramics,11th edition.

John F. Mc Cabe, Applied Dental Materials. Ceramics and PorcelainFused to Metal, 9th edition.

W. Patrick Naylor, Introduction to Metal Ceramic Technology. J. Robert Kelly, Dental ceramics What is this stuff anyway?. JADA,

Vol. 139,Sept. 2008

Edward A. Mc laren, Ceramics in dentistry Part I

Arvind Shenoy & Nina Shenoy, Dental ceramics: An update,

J Conserv Dent. 2010 Oct-Dec; 13(4): 195203.

J. Robert Kelly, Ceramics in dentistry : historical roots & current

perspectives, Journal or prosthetic dentistry, Vol 75, 1

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THANK YOU

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