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CERAMICS

Ceramics (2)

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Page 1: Ceramics (2)

CERAMICS

Page 2: Ceramics (2)

INTRODUCTIONGreek term "keramos" which means pottery. an article having a glazed or unglazed body

of crystalline or partly crystalline structure, or of glass, which body is produced from essentially inorganic, non-metallic substances and either is formed from a molten mass which solidifies on cooling, or is formed and simultaneously or subsequently matured by the action of the heat.

BIOCERAMICS.

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I GENERATION BIOCERAMICSIn 1960’sBIO-INERTNESSInteraction with the living tissue as low as

possible.Alumina & Zirconia

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II GEN BIOCERAMICS1980’sBIOACTIVE or BIO-RESORBABLEFavorable interaction with bodyAble to form strong interaction with living tissuecrystalline calcium phosphates, bioactive

glasses and glass-ceramicsbone tissue augmentation, bone cements or the

coating of metallic implants

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III GEN BIOCERAMICSStart of 21st centuryconcept replacement of tissues is been

substituted with regeneration of tissues.Able to induce regeneration and repair of

living tissues based on genesporous second generation bioceramicsOrganic & inorganic hybrids, mesoporous of

silica, stargels, templated glasses.

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CERAMICS IN ARTHROPLASTYoxide ceramics formed by closely packed crystals of Very small

and very pure crystals oxides of aluminum or zirconium metals

Sliding ceramics1930 Rock, 1st person to consider the possibility

of ceramics in A’plasty.1970 French surgeon Boutin implanted the first

ceramic-on-ceramic cemented total hip joint in France

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MANUFACTURING PROCESSParticulates of C. + H20 + organic binderMouldingHot isostatic pressure.Evaporation of water, burning the binder by

thermal treatmentSintering with Cao / MgoFinal ceramic structure.

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MATERIAL PROPERTIESHardnessWettabilityBiocompatiblityExcellent tribological propertiesChemical & corrosion resistantGood surface finish

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HARDNESS: very resistant to scratches from the tiny

particles harder the surfaces coupled together, the less

wear the coupling system produces WETTABILITY: Self lubricating, because of ionic structure

which produces hydrophilic surface.Synovial fluids gets attracted & spreads out

which minimizes adhesive wear.

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BIO-COMPATABILITY Exist in highly oxidative stateChemically inert, resistant to oxidative

degradation. Insoluble in water, hydrative degradation not

possible. Results in less wear, smaller wear particle

size, decreased cytotoxity & osteolysis.

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TRIBOLOGICAL PROPERTY wear rate of alumina-alumina bearing

coupling is extremely low (0.001 mm/year). If compared with metal-polyethylene (0.2 mm/ yr)

4000 times lessfluid film lubrification - reduces the

coefficient of clutch.

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Evaluation I GENERATION: 1974-1988 Grain size – 4.5 micrometers burst strength of 46 KN Impurities high rate of #

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II GENERATION: 1990-1993 Grain size – 3.2 micro burst strength – 58 III GENERATION: From 1994 grain size – 1.8 micro burst strength – 65 KN Improved mech, HIP, Laser etching.

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ALUMINAOld A. ceramic materials the crystals of

aluminum oxides were large, not assembled closely; there were many impurities and voids between them [5%].

impurities - weak points for propagation of fracture cracks.

The coarse structure and impurities were the cause of the frequent fractures

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Modern alumina [0.5% impurity]: HIPing process extrudes impurities out off the material and packs the crystals very close together.

very tough structure, tougher than the metallic stem on which it is seated, and even more tough then the natural thighbone.

disadvantage of the modern alumina ceramic is lower toughness

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high alumina ceramics : materials that have the minimal content of 97% of alumina.

high purity alumina ceramics: percentage of minimal alumina is of 99%.

HPA: commonly used for arthroplasty.Biolax forte.

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Zirconia Toughened Alumina (ZTA) ceramic

Mixed-oxide ceramics.75% of alumina and the rest are zirconium,

Yttrium and chrome oxides. superior strength and resistance to wear. Biolax deltabending strength around 1000 MPa, more than

the double of the alumina standard (400 MPa). Burst strength - 100 KN

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Zirconia ceramic one of the stronger ceramics introduced to reduce the risk of fracture.Pure zirconia is an unstablematerial showing three different crystalline

phasesStabilisation of zirconia by adding oxides to

maintain the tetragonal phaseSmaller Femoral heads [22 mm]

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More smoother finishZirconia femoral heads should articulate

only against polyethylene socketsIt ages in the body’s temperature and the

surface of the zirconia ball roughens

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Advantages as bearing materialSmoother surface & less co-efficient of

friction & wear.Superior lubrication property.Harder & less susceptible to third body

wearInert with no ion release.best used in young and active patients who

have a high risk of loosening and osteolysis in the mid to long term.

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Oxinium materials Zirconium is a strong and biocompatible

metal similar to titanium Thin layer of zirconium oxide is coated on

the surface of the solid zirconium metal femoral head made out of Oxinium that

articulates with a polyethylene cup

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combines the benefits of metals and ceramics. It offers superior wear resistance on its surfacezirconium metal itself, with characteristics close

to titanium, is a material without the risk of brittle fracture.

oxidized zirconium is black

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Ceramics for total knees The total knee joints doesn’t have congruent

joint surfaces. Thus, in a total knee joint with both joint

surfaces made from ceramic materials, there would appear large localized stresses that would destroy components made from the contemporary ceramics

difficult to fabricate such a large yet thin ceramic component as is the form of the femoral component

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Oxinium total knee prosthesis

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Bioactive ceramics

Osteoconductive propertyacting as a scaffold to enhance bone formation

on their surface used either as a coating on various substrates

or to fill bone defects.Calcium phosphate ceramics.hydroxyapatite (HA) and tricalcium phosphate

(TCP). In solid form, neither of these materials exhibits

adequate fatigue resistance for use as a load-bearing implant

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Hydroxyapatite (Ca10(PO4)6(OH)2)

Synthetic apatiteMost similar material from structural & chemical

point of view to the mineral component of bone.bone-graft substitute, HA coating to prosthesis.bonding mechanism - attachment at the surface

of the HA of osteogenically-competent cells which differentiate into osteoblasts

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A cellular bone matrix is then formed at the surface of the HA.

An amorphous area is present between the surface and the bone tissue containing thin apatite crystals.

As maturation occurs, this bonding zone shrinks HA becomes attached to bone through a thin epitaxial layer, resulting in a strong interface with no layer of fibrous tissue interposed between the bone and HA.

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Such integration rarely, if ever, occurs with porous or smooth metal implants

hot plasma spray technique.optimal thickness of the coating- 50 micronsThinner coatings may not supply sufficient Ca

and P long enough to be effective,Thicker layers can experience sufficient stress

under implant cyclic bending and shear and tensile loads to be subject to fatigue failure

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Tricalcium phosphate (Ca3(PO4)2)

exists in either alpha or beta crystalline forms. The beta form is the most stable. The rate of biodegradation is higher when

compared with HA.Degradation occurs by combined dissolution

and osteoclastic resorption.to stimulate early bone in-growth into porous

surfaces.

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Bone graft substitutesPorous coraline ceramicsChiroff et al, first recognised that, corals made

from marine invertebrates have a structure similar to both cortical & cancellous bone.

Exoskeleton of genus porite [ICF- 190mm], structure similar to cortical bone.

Genus gonipora – similar to cancellous bone

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Hydrothermal exchange process converts delicate coral carbonate in to hydroxyapatite without altering the internal structure.

Invaded & converted to mature lamellar B.Only surface resorption & no remodeling.Reconstruct metaphyseal defects.

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Bioactive glasses.

Bioglass 45S5bonding mechanism to bone - series of surface

reactions ultimately leading to the formation of a hydroxycarbonate apatite layer at the glass surface.

Greater production of bone, compared with HA.poor mechanical properties

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wollastonite (CaOSiO2)

glass ceramic developed by Kokubo et alosteoconductive properties similar to

Bioglass 45S5increased mechanical strength. It has been used as a spacer at the iliac

crest, for vertebral prostheses and as a shelf in procedures about the shoulder

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Bioactive bone cementExplored in order to avoid complications related

to PMMA debris and to enhance fixation of the prosthesis.

calcium-phosphate based bone cement and glass-ceramic bone cement.

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Calcium phosphate cementsBiocompatible & resorbable cementInjectable cements Replaced by creeping substitution with host

bone.As bone void fillers with uniform &

predictable drug eluding property.Deliver the antibiotics.N-SRS, ETEX alpha - BSM

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Norian SRSN. skeletal repair system.Augmentation of fracture repair.[DHS,

pedicle screw]Combination of monocalcium phosphate,

tricalcium phosphate, calcium carbonate & a sodium phosphate solution in to inj. Paste

Hardens with in minutes into dahllite [carbonated HA] in a nonexothermic reaction.

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ETEX alpha BSMCalcium orthophosphate cementDicalciumphosphate dihydrate, octocalcium

P & many precipitating apatites.Poorly crystalline apatite which will mimic

bone, aiming superior resorption & osteointegration.

Easy intraop handling characteristics..

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OSTEOSETMedical grade calcium sulphateHigh tech processing [retains all biological adv

& consistent mech / resorption profile]Provide structural support & is bioabsorbable

and biocompatible.Resorption profile matches with the rate at

which host environment can lay down bone around the compound.

Available as pelletsAntibiotic delivery – aminoglycosides/ ideal.

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FUTUREScaffold fabricated with a synthetic

bioceramic which after being supplemented with moieties of biological activity is implanted in a living organism to induce tissue regeneration,