Metals in dentistry

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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 bonds
presence

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Metallic bond
Elecetron configuration Na - 1s22s22p63s1
Valence elctron 3s1 is surranded by Na+
sodium elctron’s cloud
Accumulation of more amount of atoms
being in sodium crystal is causing that
valence elctrons are moving within entire
crystal volume
Electron gas which penetrates inter-ions
space as a result of electrostatic interaction
attracts positive charged ions making them
densely packed
Sodium atom
Na2 molecule
Sodium crystal

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Metallic bond
Presence of metalic bond in structure determines its:
• Opaqueness
• Metalic gloss
• Good electrical conductivity
• Good thermal conductivity
• Ductililty

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Metals used in 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 dentistry
Gold
Gold belongs to copper „family”
Density 19,3 g/cm3
Melting temperature 1062oC
Boiling temperature 2600oC
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 dentistry
Gold
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 + HNO3 + 4 HCl HAuCl4 + 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/cm3
• Melting point - 1773oC
• Boiling point - 4300oC
• Average hardness
• Easy to forging and rolling
• High resistance to chemicals
• Dissolves only in aqua regia making chloroplatinous
H2PtCl6 acid

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Main type of metals used in dentistry
Platinum
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 dentistry
Iridium
Density - 22,42 g/cm3
Melting point - 2440oC
Boiling temperature - 4400oC
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 pure
platinum
Used for „stifts” for porcelain crowns

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Main type of metals used in dentistry – Palladium
Density - 11,97 g/cm3
Melting temperature - 1549oC
Boiling point - 2540oC
Not very hard
Plastic
Melleable

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Main type of metals used in dentistry
Palladium
Chemical reactivity
Dissolves in:
Nitric acid
Sulpuric acid,
Very easily in aqua regia
Addition of 20% palladium to gold with platinum gives „white
gold”.
Alloy of palladium with silver in 9:1 proportion is used for making
parts 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 H2S and makes silver sulphide (Ag2S)
Combines with chloride and makes silver chloride
(AgCl)
In oral
cavity

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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 dentistry
Mercury
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 used in dentistry
Titanium
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), in
military, 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 than
traditional 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 about
20 years are made from alloy of Titanium (43-47%) and
Nickel (53-57%)
• Other application of Ni-Ti alloys are implants plates and for
curing bite in chieldren
Other metals used in dentistry
Titanium

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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 cell
fluids with chemical reaction.
After implant is introduced directly to bone
contact osteogenesis starts - process which is building up of
bone directly on the implant surface.
That leads to the direct structural and functional
connection between living bone and the surface of
implant - 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 an
artificial tooth root (synthetic material) that is surgically
anchored into jaw to hold a replacement tooth or bridge in place

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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 can be divided in 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 yellow or silver color sometimes
are 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 formed
and become larger
Smaller grains gives better alloy properties.
In order to have the smallest possible grains other
components are added such as iridium or ruthenium.
In alloys with high quantities of non-nobel metals crystals
with large diameter are dominant.

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Alloy properties are usually not an average from
properties of metalic components
Addition of even small amount of any metal to alloy can
cause dramatic change in its properties
For example: small amount (5-10%) of platinum in gold
alloy increases hardness and elasticity of alloy.
Palladium and nickel increase hardness of alloy.
Alloy properties are determined by many factors:
composition, manufacturing condition, mechanical and
thermal 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 cavity
environment
• Biocompatibility : should not be toxic and cause
allergy

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Proper mechanical properties, especially:
• High plastic resistance, especially for alloys
exposed to high stress
• Proper ductility protecting against breaking
during the fixing
• Proper hardness which results in milling dificulties
and 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)
< 25any
With 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 become
liquid
solidus – temperature in which alloy during the cooling
became 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 than
shape change may occur

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Metal alloys – alloy density
Density of dental alloys are in the range from 4,5 g/cm3 (titanium alloys)
to 18,5 g/cm3 (some nobel alloys)
7,5
7,5
4,5
1275
1400 – 1500
1700
With excess of nobel
metals
Based on nickel
Based on cobalt
Based on titanium
12,4
10,6
10,6
865 – 925
1100 – 1190
1020 – 1100
Nobel
Silver- gold- copper
Palladium – copper
Silver -palladium
18,5
15,6
1045 – 1140
910 – 1065
Higly nobel
Gold - platinum
Gold- 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 at
which 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 liquid
mercury
Sillver alloy – it is the powder consisting of silver, tin and
copper
After mixing silver alloy with mercury chemical reaction
takes place which gives amalgam:
silver alloy + mercury -> amalgam
At the begining it is plastic and after it hardens it is harder
than 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 in
mercury
During dissolving process chemical reaction takes place which leads to mixture
cristalization which results in thickening and hardening of amalgam
Hardening of amalgam starts before all alloys molecules are totally dissolved
Fixed amalgam contains large amount of silver alloy surrounded by new
product 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