L06 Metals

Metals in Dentistry Dent 301 Dr Layla Abu-Naba’a PhD, MFD Irl Assistant Professor of Prosthodontics 1

Definitions & Concepts

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Metals 

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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  

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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 others 5

Shaping alloys Amalgamation with mercury

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Amalgam filling

Casting at high temperatures

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Crowns Inalys Onlays Denture bases

Cold working (wrought alloys)

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Orthodontic wires Gold foil fillings

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Properties Terms related to metal technology

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

Bio-compatibility High 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 

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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 boundaries 12

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Forces cause sliding of grains but not boundaries 13

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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 alloys Location Intra-coronal ✂ Extra- coronal ✂

Fabrication by Lost 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 dentures ✂

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Cast alloys- Classification High 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) ✂

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CLASSIFICATION OF ALLOYS

Ac ti

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

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1. Other Crown and Bridge Casting Alloys:

Passive Immune

TIME

Au–Pt–Pd → Au-Pd-Ag → Pd-Ag → Pd-X → Ni-Cr23 …

Gold alloys Carats (karats) 24- 100% gold 12- 50% gold Other precious ✂Pd , Pt 24

CLASSIFICATION OF ALLOYS 1. Full Gold Crown and Bridge Alloys (REVIEW of precious alloys) a.

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 scavenger 25

Non-precious alloys very stiff, cheap, hard Uses: ✂Partial dentures frame ✂Porcelain bonding alloys ✂Attachments: bars, overdenture att, precision att, non-precision att, implant att 26

Non-precious alloys Partial dentures frame:

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Cr-Co Ni-Cr Gold IV

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Non-precious alloys Porcelain bonding alloys ✂

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stand high temp Added indium & tin to produce oxides in high temp No Ag Cu- green stain 28

CLASSIFICATION OF PFM ALLOYS 1. 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

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Effects of Alloying Components in Other Alloys: (1) Cr, Ti → oxide (2) formers in other alloys Ni, Co, Fe → increased modulus opaque

metal

oxide

body

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

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Solders Types: ✂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 solders 33

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 heat ✂

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Types

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

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

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Forms Wires: various resistance to bending is created by annealing ✂removable partial dentures (clasps) ✂arch wires, retainers ✂ligature wires in ortho and surgery 41

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Implant materials Uses: ✂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 - composition Ti alloys ✂painted by: calcium phosphates ✂ plasma proteins ✂

other materials -not commonly used Ceramics ✂ Composites ✂ Polymers ✂

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Endodontic posts Posts are placed in the pulp canals of a sealed tooth. ✂Supports build up of a core ✂

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Endodontic posts-Types

metal, fibre reinforced resin, ceramic ✂custom, preformed ✂

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Endodontic posts-Types By insertion:

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active (threaded) ✂ passive ( friction and cement retention) ✂ parallel or tapered ✂

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Endodontic posts-Types By composition: Metal fibre reinforced resin Ceramic

By form Custom preformed 50

Thank You

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