1. Dental Ceramics

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    Dental Ceramicsdr . Kirti sharma

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    Introduction to porcelain Definition of ceramics Pottery Feldspar

    Fluxes

    Silica Aluminum Oxide

    Quartz Kaolinite Greenware Sintering Fusing

    Earthenware Stoneware Porcelain Dental feldspathic porcelain

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    The basics from pottery to

    porcelain

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    Porcelain

    Marco polo, 13thcentury

    porcelino (italian)-cowrie orvenus shell

    Meaning little pig

    Shells thinness, translucency,

    hardness.

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    To quote a tenth century European reflecting onthe porcelain he encountered on his journeythrough China:

    "A ceramic so white that it was comparable onlyto snow, so strong that vessels needed walls only2-3 mm thick and consequently light could shinethrough it. So continuous was the internal

    structure that a dish, if lightly struck would ring likea bell.

    This is porcelain!"

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    covers variousmaterials

    hard,

    brittle,

    non metallic,

    heat-resistantand

    corrosion-resistant.

    Derived from:

    the Greek word

    keramos meaning

    potters clay/ burntstuff.

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    Shaping and then firing a nonmetallicmineral, such as clay, at a high

    temperature.

    The non metallic minerals:

    aluminum oxide (alumina) andsilicone dioxide (silica).

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    Refractory

    non-meltable

    skeletal structuresintered (fused) particles of a metallicoxide (aluminum oxide).

    Glassinfiltrated between the sinteredrefractory particles.

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    Pottery was the first, and still is theforemost ceramic.

    Pottery is made from clay, andcontains both of these components.

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    HISTORICAL

    PERSPECTIVE

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    The first ceramics were createdsometime before 5500 BC in the form

    of earthenware pottery. CLAY (with water->too sticky to

    handle)

    SAND and GROUND SEASHELLS Kiln

    Firing/sintering

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    Gases-VOIDSin CLAYfracture

    during FIRING

    BEATING ( WEDGING ) and raising thetemperature very slowly.

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    Before firing, the "ceramic" body is in a very fragilegreen state, and at this stage is called greenware.

    In its green state, the body has not yet actuallybeen converted into a ceramic.

    A fragile pile of microscopic rocks.

    When totally dry, the greenware/unfired bodyplaced into a kiln for a low temperature firingknown as a biscuit bake. During this low fire process,little if any feldspathic glass is produced.

    Greenware

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    mass of individual particles loosely held togetherby a

    water binderCalledSintering

    coherent solid

    the points at which the individual particles arein contact fuse at sufficiently high temperatures

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    Sintering appears to happen not so much becauseof melting, but because of diffusion of the rapidlymoving atoms between the neighboring refractory

    particles.

    Diffusion is accelerated at elevated temperatures.

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    Once biscuit fired-> ceramic easily handled; notyet fully fired; most of the feldspar still in crystallinestate.

    Apply glaze coat over it ( highly fluxed silica) andfired to a higher temperature.

    Glaze and feldspar melt to form a glass.

    This second firing is called glaze firing or fusing

    firing.

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    UP-DRAUGHT KILN

    EARLY KILNS---900 C---pottery fired at thistemperature is known as EARTHENWARE.

    (low temperature firing, porous, opaque, unsuitablefor storing liquids)

    higher kiln temperatures---impervious pottery---STONEWARE.

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    Europeans produced->stoneware.could be made to lookwhite, but in a thickness that it wasinvariably opaque.

    Chinese produced-> porcelain.whiteand made in such thin sections that itappeared translucent.

    In1717, the secret was leaked from Chinaby a Jesuit missionary, FatherdEntercolles-kaolin, silica and feldspar.

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    Clay bodies :

    earthenware,

    stoneware and

    domestic

    porcelain.

    Glass

    Alumina

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    Dental porcelain is a further subdivisionof domestic porcelain. It is impossible

    to understand dental porcelains andtheir associated cores without firstunderstanding the art and science ofceramics, and this begins at thepotters wheel.

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    Clay is a specialized form of mud.

    Clay requires three specific constituents toqualify as a good ceramic medium

    feldspar,

    quartzand

    kaolinite.

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    Water

    - reduces the friction between the clay particles

    - lends the clay plasticity so that it can easily beformed into shape by hand

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    Plasticity Minerals eg.ball clay or bentonite

    Increase the surface area available toretain water

    (NOTE: Manufacturers of dental porcelain frits addsugar and starch to their porcelain powders for thesame reason.)

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    Porcelain is defined as a:

    fine kind of earthernware having a translucent body

    and a transparent glaze. Blending of clay with other common minerals such as

    feldspar, flint (silica) and firing them at hightemperatures produced translucency and strength.

    Ceramic materials containing these additionalimportant ingredients were given the namePorcelain.

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    Dental porcelain belongs to one class of ceramics

    Consists of a glass and a crystalline phase

    ( glass-crystal composite)

    Other ceramics are composed entirely ofcrystalline oxides that are sintered together,sometimes under high pressure.

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    Dental porcelain:

    Kaolin omitted; feldspar translucency.

    Hence considered as a feldspathic glass with crystalline

    inclusions of silica.

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    The dental application of porcelain dates from1774,when a French apothecary named Alexis

    Duchateau considered the possibility ofreplacing his ivory dentures with porcelain

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    The use of porcelain in dentistry was first mentionedby Pierre Fauchard

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    1789Fused porcelain was introduced formanufacture of teeth.

    By 1820Porcelain denture teeth wereintroduced, which replaced ivory/ natural

    denture teeth in U.S.A.. 1837John Murphy of London introduced the

    plantium foil technique which made possible thedevelopment of present day method ofporcelain inlay construction.

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    1838Elias Wildman for