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Metals in DentistryDent 301

Dr Layla Abu-Naba’aPhD, MFD Irl

Assistant Professor of Prosthodontics

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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.

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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– others

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Shaping alloysAmalgamation with mercury

Amalgam fillingCasting at high temperatures

Crowns Inalys Onlays Denture bases

Cold working (wrought alloys) Orthodontic wires Gold foil fillings

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PropertiesTerms related to metal technology

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Bio-compatibility

Susceptibility

patient,

Dentist

lab technician (casting, grinding, polishing)

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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) skinBeryllium cause contact allergyberylliosis (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 boundaries

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Forces cause sliding of grains but not boundaries

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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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UsesInlaysOnlayspartial coverage crown( 3/4 & 7/8)complete coverage crownfixed partial dentures (bridges)Removable partial dentures

RemovableDie withWaxed Inlay

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Cast alloys- Classification

High noble

(Precious metals)60% (Au, Pd, Pt)40% AuNoble

(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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2. 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)

CLASSIFICATION OF ALLOYSCLASSIFICATION OF ALLOYS

CO

RR

OS

ION

CO

RR

OS

ION

TIMETIME

Act

ive

Immune

Passive

Au–Pt–Pd Ni-Cr …Au-Pd-Ag Pd-Ag Pd-X

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Gold alloysCarats (karats)24- 100% gold12- 50% goldOther preciousPd , Pt

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CLASSIFICATION OF ALLOYSCLASSIFICATION 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) (2) Copper (Cu) (3) Silver (Ag) (4) Palladium (Pd) (5) Platinum (Pt) (6) Zinc (Zn)

corrosion resistanceincreased hardnesscounteracts orange color of copperincreased MP and hardnessincreased MPoxygen scavenger

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Non-precious alloys

very stiff, cheap, hardUses:Partial dentures framePorcelain bonding alloysAttachments:bars, overdenture att, precision att, non-precision att, implant att

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Non-precious alloys

Partial dentures frame: Cr-Co Ni-Cr Gold IV

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Non-precious alloys

Porcelain bonding alloys

stand high temp Added indium &

tin to produce oxides in high temp

No Ag Cu- green stain

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CLASSIFICATION OF PFM ALLOYSCLASSIFICATION OF PFM ALLOYS2. Other Crown and Bridge Casting Alloys (cont):

b. Effects of Alloying Components in Gold Alloys:(1) Au, Ag, Pd, Pt (2) Pt (3) Pd (4) Ag (5) Fe, In, Sn (6) Zn

c. Effects of Alloying Components in Other Alloys:(1) Cr, Ti (2) Ni, Co, Fe

corrosion resistanceincreased MPincreased MP and hardnesscheaperoxide formers for gold alloysoxygen scavenger

oxide formers in other alloysincreased modulus

metal oxide

opaque 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 alloyssilver based alloys with tin(lower temp and stronger joint)

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Solders - Flux

a material applied o the surfaces to be joined by solderingincrease flow of solder, increase wettingContains borax for gold solders

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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 filestwisted to produce flutes or cutting edgesBrackets and bands cut and shaped

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Forms

Wires: various resistance to bending is created by annealingremovable partial dentures (clasps)arch wires, retainersligature wires in ortho and surgery

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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 alloyspainted 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, ceramiccustom, preformed

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Endodontic posts-Types By insertion:

active (threaded)passive ( friction and cement

retention)parallel or tapered

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Endodontic posts-Types By composition:

Metalfibre reinforced resinCeramic

By formCustompreformed

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Thank You