l06 metals
TRANSCRIPT
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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