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Metals in dentistry

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Metals properties

Usually are:

� Hard

� Luster

� High density is dependent on molar mass of molecule as well as structure type of crystalline which determines amount of atomes to be able to be packed in lattice.

� Good heat nad electricity conductors because of metalic bondspresence

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Metallic bond

� Elecetron configuration Na - 1s22s22p63s1

� Valence elctron 3s1 is surranded by Na+

sodiumelctron’s cloud

� Accumulation of more amount of atomsbeing in sodiumcrystal is causing thatvalence elctrons are moving within entirecrystal volume

� Electron gas which penetrates inter-ionsspace as a result of electrostatic interactionattracts positive charged ions making themdensely packed

Sodium atom

Na2 molecule

Sodium crystal

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Metallic bondPresence of metalic bond in structure determines its:

• Opaqueness• Metalic gloss• Good electrical conductivity• Good thermal conductivity• Ductililty

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Metals usedin dentistry

Noble metals:

� Gold, palladium, platinum� High resistivity to corrosion

Non-noble metals

� Titanium , nickel, copper, silver, zinc� Provide modulus of elasticity and abrasion resistance of

dental alloys.

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Main type of metals used in dentistryGold

� Gold belongs to copper „family”

� Density 19,3 g/cm 3

� Melting temperature 1062 oC

� Boiling temperature 2600 oC

� Very soft, melleable, and ductile

� Good elctrical and heat conductor

� With silver, platinum and palladium makes solid solution

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Main type of metals used in dentistryGold

Dissolves in:� Aqua regia (mixture of hydrochloric and nitrate acids in 3:1

proportion, has very oxidative properties and has ability to dissolve gold, platinum, palladium and other nobel metals)

Au + HNO 3 + 4 HCl HAuCl 4 + NO + 2H2

� Chlorine water (water saturated with chlorine)

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Main type of metals used in dentistry – Platinum

• Belongs to platinum „family”.

• Density - 21,45 g/cm 3

• Melting point - 1773 oC

• Boiling point - 4300 oC

• Average hardness

• Easy to forging and rolling

• High resistance to chemicals

• Dissolves only in aqua regia making chloroplatinousH2PtCl6 acid

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Main type of metals used in dentistryPlatinum

� To expensive to be used in dentistry.

� Used as an additive to gold in the amount of 5-10%

� Platinum changes gold properties:� Adds elasticity� Changes color� Increases melting point

� Gold-platinum alloys are used for making :� Arches� Wire dental aplliances

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Main type of metals used in dentistryIridium

� Density - 22,42 g/cm 3

� Melting point - 2440 oC

� Boiling temperature - 4400 oC

� Silver-white metal, very fragile but hard

� High chemical resistance:� reacts only with chlorine and fluorium� DOES NOT dissolve in aqua regia

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Main type of metals used in dentistry

Irydium

� Alloys of irydium (10%) with platinum are more hard, more resistant and have more chemical resistance than pureplatinum

� Used for „stifts” for porcelain crowns

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Main type of metals used in dentistry – Palladium

� Density - 11,97 g/cm 3

� Melting temperature - 1549 oC

� Boiling point - 2540 oC

� Not very hard

� Plastic

� Melleable

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Main type of metals used in dentistryPalladium

Chemical reactivity� Dissolves in:

� Nitric acid� Sulpuric acid, � Very easily in aqua regia

� Addition of 20% palladium to gold with platinum gives „whitegold”.

� Alloy of palladium with silver in 9:1 proportion is used fo r makingparts of porcelain crowns

� Palladium is a part of platinum soldier

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Other metals used in dentistry – Silver

Chemical and physical properties:

� Not very hard

� Resistant to loads

� Easy to undergo chemical and thermal changes, ductile

� The best heat and electricity conductor

� Dissolves in nitric and sulphuric acid

Makes alloys with many metals:� With palladium and gold mix in any ratio in solid and

liquid state

� Combines with H 2S and makes silver sulphide (Ag 2S)

� Combines with chloride and makes silver chloride(AgCl)

In oralcavity

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� Silver in pure form is not used in dentistry� Silver salts are poisones !� Can be applied unless there will be no contact

with oral cavity fluids. (e.g.: in stifts)

� Application :• as a stift for crowns• for temporary dental work• as a component of dental gold

Other metals used in dentistry – Silver

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Permanent protetic suplement - porcelain crowns on the base made from metal or steel

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Permanent protetic suplement Porcelain crowns fused to steel or gold base

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Crown and bridge on metal alloy base

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Removeable denture

http://www.wikidoc.org/index.php/Removable_partial_dentures

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Other metals used in dentistryMercury

� In room temperature it is thick fluid metal

� Belongs to zinc”family”

� Density 13,54 g/cm3

� Freezing temperature -38,89oC

� Boiling temperature 356,90oC

� Dissolves all metals except ferrum and platinum„families”

� Reacts with nitric acid only

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Other metals usedin dentistryTitanium

� atomic number 22

� posseses high mechanical strength,

� corosion resistant (including sea water and chlorine)

� gray color

� can be added as an addition to iron, aluminum, vanadium, molibdenium and other alloys.

� Titanium alloys are used in airspace industry ( engines), inmilitary, metalurgic processes, moto, medical ( dentures, orthopedic braclets), in sports (bicycle frames and components,

tennis rackets, baseball bats, hiking equipment, golf clubs)

http://images-of-elements.com/titanium.php

http://www.gtagaming.com/downloads/gta-san-andreas/weapon-mods/10718

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• Used in dentistry

• Posesses much more lower thermal conductivity thantraditional prosthetic materials

• High hardness, mechanical strength and longevity

• Hypoalergenic and corrosion resistant

• For bones treatments alloys of titanium and Al, Nb (niobum). For example Blount braces with longevity about20 years are made from alloy of Titanium (43-47%) andNickel (53-57%)

• Other application of Ni-Ti alloys are implants plates and for curing bite in chieldren

Other metals used in dentistryTitanium

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Titanium is a metal very often used in implants and

more often in protetic

Main adventure is to create oxidation layer on the surface

which protects against corrosion and interaction of cellfluids with chemical reaction.

After implant is introduced directly to bonecontact osteogenesis starts - process which is building up ofbone directly on the implant surface.That leads to the direct structural and functionalconnection between living bone and the surface ofimplant - osteointegration

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Osteointegration on the surface of implant

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Dental implants

A dental implant, sometimes called a tooth implant, is anartificial tooth root (synthetic material) that is surgicallyanchored into jaw to hold a replacement tooth or bridge inplace

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Parts of implant

http://www.dentalorg.com/dental-implant-overview-part-1.html

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Metal alloys – classification criteria

Alloys canbe dividedin respect to: 1. Amount of noble or non-noble components. For

example: 60% Au, 10% Pl, 5% Pt i 25% Cu –combined „nobility” of alloys is 75%. (Copper is not noble and does not count)

2. Dominant metal. For example: alloys based on gold.

3. Color – alloys in yellowor silver color sometimesare called „white” .

4. Application – alloys for making fillings or solders

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Metal alloys

� Metal alloys have crystal structure.

� During solidification of melted alloys crystals are formedand become larger

� Smaller grains gives better alloy properties.

� In order to have the smallest possible grains othercomponents are added such as iridiumor ruthenium .

� In alloys with high quantities of non-nobel metals crystalswith large diameter are dominant.

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Alloy properties are usually not an average fromproperties of metalic components

� Addition of even small amount of any metal to alloy cancause dramatic change in its propertiesFor example: small amount (5-10%) of platinum in goldalloy increases hardness and elasticity of alloy. Palladium and nickel increase hardness of alloy.

� Alloy properties are determined by many factors: composition, manufacturing condition, mechanical andthermal treatment, crystal structure etc.

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Requirements for metal alloys

Alloys should posses:

• Ease of melt

• Ease to make a cast (melted alloys with high density and good flow are easier to be cast)

• Ease of processing

• Corrosion resistance and dullness in oral cavityenvironment

• Biocompatibility : should not be toxic and causeallergy

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Proper mechanical properties, especially:

• High plastic resistance, especially for alloysexposed to high stress

• Proper ductility protecting against breakingduring the fixing

• Proper hardness which results in milling dificultiesand its resistance to grinding

• Should not be expensive. Ideal alloy shoud not be expensive in terms of material and processing

Requirements for metal alloys

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Metal alloys – classification criteria according to ANSI/ADA(American National Standards Institute /American Dental Association)

< 25anyWith advantage of

noble metals

> 25anyNoble

> 60> 40Very noble

Nobel metal content

Gold content

[weight %]

Alloy type

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Metal alloys - the most important parameters

� Melting temperature range

� Density

� Strength and hardnes

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Metal alloys – melting temperature range

� Metal alloys are melting in specific temperature range.

� During the heating melting temperature range: 950o -1000oC

950oC first symptoms of melting

975oC part of the alloy is liquid but some of the components are still solid

1000oC entire alloys become liquid

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Metal alloys – melting temperature range

� liquidus - temperature in which alloy entirely becomeliquid

� solidus – temperature in which alloy during the coolingbecame solid

� Alloy may be used for casting when its temperature is higher than liquidus.

� Solidus is important during soldering.

� If soldering will make alloy warmer above solidus thanshape change may occur

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Metal alloys – alloy density

Density of dental alloys are in the range from4,5 g/cm3 (titanium alloys) to 18,5 g/cm3 (some nobel alloys)

7,5

7,54,5

1275

1400 – 1500 1700

With excess of nobel metalsBased on nickel

Based on cobaltBased on titanium

12,410,6

10,6

865 – 9251100 – 1190

1020 – 1100

NobelSilver- gold- copper

Palladium – copper

Silver -palladium

18,5

15,6

1045 – 1140

910 – 1065

Higly nobelGold - platinumGold- copper- silver

Density [g/cm3] Melting range [oC]Alloy type

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Metal alloys – alloys strength

� Yield point – indicates force applied to the surface unit atwhich permanent deformation will appear

� Yield point unit is Mega pascal (MPa)

Yield point for alloys is in th erange of: 260-1150 MPa

� Alloy deformation – magnitude express in percentage (%)

� Yield point 750 MPa and deformation 0,2% -it means that force of 750 MPa is causing deformation of alloy by 0,2%

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Metal alloys – hardness

� Influences polish of alloy� Hardness is related to yield point. � Hardness is express in kg/mm2.

-it means amount of mass [kg] needed to be apply to make notch of 1 mm2 area

� hardness of dental alloys is in the range:125 – 425 kg/mm2

� Enamel hardness is 343 kg/mm2

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Amalgam

� Amalgam – it is the mixture of silver alloy with liquidmercury

� Sillver alloy – it is the powder consisting of silver, tin andcopper

� After mixing silver alloy with mercury chemical reactiontakes place which gives amalgam:

silver alloy + mercury -> amalgam

� At the begining it is plastic and after it hardens it is harderthan other dental filling

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Amalgam

� Currently alloys with high quantity of copper are used (13 – 30%)

� Amalgams made of silver alloy with high content of copper (in comparison to small amount of Cu 2 – 4%)are:

� More resistant to crushing and elongation� Less resistant to corrosion� More susceptible to edge ckracking

� Example of composition of silver alloy with high content of copper:Silver 40 – 60%Tin 27 – 30%Copper 13 – 30%

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Amalgamation

� Combining silver alloy with mercury starts process of dissolving alloy inmercury

� During dissolving process chemical reaction takes place which leads to mixturecristalization which results in thickening and hardeningof amalgam

Hardening of amalgam starts before all alloys molecules are totally dissolved

� Fixed amalgam contains large amount of silver alloy surrounded by newproduct of chemical reaction which took place in amalgam

� Simplified reaction schematic:Silver alloy (tin - silver - copper) + mercury

Silver alloy (unreacted) + copper-tin + silver-mercury

After amalgamation process ends there is no „free” mercury in amalgam

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THE END