L06 Metals

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Metals in DentistryDent 301Dr Layla Abu-Nabaa PhD, MFD Irl Assistant Professor of Prosthodontics1

Definitions & Concepts

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Metals

Are opaque hard (except mercury) and lustrous structures at ambient temperatures They form in crystalline structures in which the atoms are closely packed The resulting assembly is both heat and electricity conductive.3

Alloys

A mixture of two or more metals Each metal adds or modifies the resulting properties Dental applications are famous

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Alloys

Famous alloys are named after the predominant components: Steel alloys Gold alloys Chrome cobalt alloys Amalgam Titanium alloys others5

Shaping alloys

Amalgamation with mercury

Amalgam filling Crowns Inalys Onlays Denture bases Orthodontic wires Gold foil fillings

Casting at high temperatures

Cold working (wrought alloys) 6

PropertiesTerms related to metal technology

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Bio-compatibilitySusceptibility patient, Dentist lab technician (casting, grinding, polishing)8

Bio-compatibilityHigh Noble > Noble> non-noble? Less corrosion less exposure to metalic products Allergic responses

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Nickel female > male 9-12% ask about jewellery allergy

bridges > Cr-Co partial denture (more contact)

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(contact allergy ) gingival margin, cheek mucosa, (distant allergy) skin Beryllium cause contact allergy berylliosis (lung disease from inhalation of vapour)

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Crystal structure

When cooling or amalgamation , Crystals form around impurities that act as nuclei Dendrites extend and become in contact Each crystal is now a grain separated by boundaries12

Forces cause sliding of grains but not boundaries13

More grains Rapid cooling more nuclei

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Crystal arrangements

Equiaxed: Crystal arranged having same dimensions around the nucleus

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Elongated: in a fibrous form produced by forces applied after re-crystallization temperature

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Types of Metals

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Cast Alloys

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Cast alloysLocationIntra-coronal Extra- coronal

Fabrication byLost wax technique formed outside the mouth

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Uses

Removable Die with Waxed Inlay

Inlays Onlays partial coverage crown( 3/4 & 7/8) complete coverage crown fixed partial dentures (bridges) Removable partial dentures20

Cast alloys- ClassificationHigh noble (Precious metals) 60% (Au, Pd, Pt) 40% Au Noble (semiprecious metals) 25% (Au, Pd, Pt)

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Base metal< 25% noble metals (Cu,Ni,Ag,Zn,Sn,Ti, Al,Cr, Co, Br, Fe, C, molybdenum, gallium, vanadium)22

CLASSIFICATION OF ALLOYS1. Other Crown and Bridge Casting Alloys: a. ADA Classification System (see phase diagrams) (1) High-gold alloys (IMMUNE) (a) Au-Pt-Pd (b) Au-Pd-Ag (2) Low-gold alloys (SEMI-IMMUNE) (3) Gold-substitute alloys (PASSIVE) (a) Ag-Pd (85% of all PFM alloys) (b) Pd-X (4) Base-metal alloys (PASSIVE) (a) Ni-Cr (with or without Be) (b) Co-Cr (c) Fe-Cr (5) Titanium alloys (PASSIVE) (6) Other alloys Al Bronzes, Brasses (ACTIVE)CORROSION

Ac ti

ve

Passive Immune

TIME

AuPtPd Au-Pd-Ag Pd-Ag Pd-X Ni-Cr 23

Gold alloysCarats (karats) 24- 100% gold 12- 50% gold Other precious Pd , Pt24

CLASSIFICATION OF ALLOYS1. Full Gold Crown and Bridge Alloys (REVIEW of precious alloys) ADA Classification System (see phase diagrams) (1) Type I 83% Au+ (Non-heat hardenable) -- inlay (2) Type II 78% Au+ (Non-heat hardenable) -- inlay, onlay, (3) Type III 78% Au+ (Heat hardenable) -- onlay, crown (4) Type IV 75% Au+ (Heat hardenable) -- crown, bridge partial denture frame b. Effects of Alloys Components: (1) Gold (Au) corrosion resistance (2) Copper (Cu) increased hardness (3) Silver (Ag) counteracts orange color of copper (4) Palladium (Pd) increased MP and hardness (5) Platinum (Pt) increased MP (6) Zinc (Zn) oxygen scavenger25

a.

Non-precious alloysvery stiff, cheap, hard Uses: Partial dentures frame Porcelain bonding alloys Attachments: bars, overdenture att, precision att, non-precision att, implant att26

Non-precious alloys

Partial dentures frame:

Cr-Co Ni-Cr Gold IV

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Non-precious alloysPorcelain bonding alloys

stand high temp Added indium & tin to produce oxides in high temp No Ag Cu- green stain28

CLASSIFICATION OF PFM ALLOYS1. Other Crown and Bridge Casting Alloys (cont): b. Effects of Alloying Components in Gold Alloys: (1) Au, Ag, Pd, Pt corrosion resistance (2) Pt increased MP (3) Pd increased MP and hardness (4) Ag cheaper (5) Fe, In, Sn oxide formers for gold alloys (6) Zn oxygen scavenger Effects of Alloying Components in Other Alloys: (1) Cr, Ti oxide formers in other alloys (2) Ni, Co, Fe increased modulusopaque body

c.

metal

oxide

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Solders Uses:join metals together (units of bridge, contacts, space maintainer) repair cast restorations (close holes, marginal deficiencies)30

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SoldersTypes: gold based alloys silver based alloys with tin (lower temp and stronger joint)32

Solders - Flux a material applied o the surfaces to be joined by soldering increase flow of solder, increase wetting Contains borax for gold solders33

Cast denture framework with a new high-strength Ti-6Al-7Nb alloy.

Orthodontic cast retainer made of super-elastic Ti-Ni alloy.

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Wrought Alloys

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Definition Shaped after casting by mechanical force compression (malleability) or tension (ductility) annealed: strengthen by heat36

Types

SS(Fe, C, Ni, Cr, Mg) high noble (Pg, P) NiTi (highly flexible)37

Forms Endodontic reamers and files twisted to produce flutes or cutting edges Brackets and bands cut and shaped

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FormsWires: various resistance to bending is created by annealing removable partial dentures (clasps) arch wires, retainers ligature wires in ortho and surgery41

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Implant materialsUses: To anchor prosthesis (crown, bridge, removable denture, extra-oral prosthesis) Types:Sub-periosteal trans-osteal endo-osteal

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Sheet/Plate Titanium

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Implant materials - compositionTi alloys painted by:calcium phosphates plasma proteins

other materials -not commonly usedCeramics Composites Polymers46

Endodontic postsPosts are placed in the pulp canals of a sealed tooth. Supports build up of a core47

Endodontic posts-Types

metal, fibre reinforced resin, ceramic custom, preformed48

Endodontic posts-Types

By insertion:active (threaded) passive ( friction and cement retention) parallel or tapered49

Endodontic posts-TypesBy composition:Metal fibre reinforced resin Ceramic

By formCustom preformed50

Thank You

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