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Dental Amalgam
Prof. Wedad Etman,
Professor of Operative Dentistry
Introduction
• Amalgam has been an accepted part of dental
therapeutics for more than �� years and is
still used for the majority of direct posterior
restorations.restorations.
• The reasons for its popularity lie in its ease of
manipulation, relatively low cost. an long life.
Some concern has been raised about mercury
toxicity from both biologic and an toxicity from both biologic and an
environmental point of view; however, it is
believed that amalgam presents an acceptable
risk-to-benefit ratio when properly used.
• Alloy: Alloy is a union of two or more metals
• Amalgam: Amalgam is an alloy in which mercury
occurs as a main constituent.
• Dental amalgam: The dental amalgam is an alloy • Dental amalgam: The dental amalgam is an alloy
of mercury with silver, tin, and varying amounts
of copper, zinc and other minor constituents.
Composition
• Mercury (Hg) in dentistry
– Have a bright , mirror-like surface
– Amalgamates i.e. Dissolves other metals (silver,
zinc) to produce a plastic mass at room zinc) to produce a plastic mass at room
temperature
Constituents in Amalgam
• Basic– Silver
– Tin
– Copper
– Mercury
• Other– Zinc
– Indium
– Palladium
• Silver 34-4 % about 6/8 of alloy
• Contributes to strength
• Flow (i.e. deformation under load)
• Regulates setting time to some extent• Regulates setting time to some extent
• It contributes to the setting expansion of amalgam
• Tarnish & corrosion resistance
• Tin 6�-6=% (¼ of amalgam alloy)
• Helps in amalgamation (has great affinity to mercury) but:
• During amalgamation Tin-mercury ɩ6 (gamma two
phases)phases)
• weakest phase reduces strength of amalgam
• Setting expansion of amalgam
• Flow
• Increases setting time
• Reduces strength, hardness, and setting expansion.
• Copper 6-3%:
• Contributes hardness & strength
• Flow
• Setting expansion• Setting expansion
Zinc -6%
• . � % or more (zinc containing alloy)
• . � % → non zinc alloy• . � % → non zinc alloy
• Act as a scavenger for foreign substances such
as oxides during manufacturing
• The most serious problem related to zinc is
delayed expansion
In Brief
• Mercury (@8% to �@%)
• Alloy powder (�4% to @3%)
• Silver …………………..…gives strength
• Tin…………………………….workability• Tin…………………………….workability
• Copper..strength & corrosion resistance
• Zinc………………….prevents oxidation
Indications
�- Restoration of posterior teeth (Class I & II)
(Moderate to large preparations)
6- In some cases restoration distal surface of the
caninecanine
8- Class V preparations (some cases)
@- Class VI preparation
�- Core build up for badly broken down teeth in
the posterior teeth
Contraindications
�. When esthetics is important (e.g. anterior teeth
)
6. Patients have a history of allergy to mercury or
other amalgam componentsother amalgam components
8. Remaining tooth structure requires support.
@. Treatment of incipient or early, primary fissure
caries.
Advantages
�) High compressive strength
6) Good adaptability to cavity walls
8) Low coefficient of thermal expansion
@) Indestructibility in oral fluids@) Indestructibility in oral fluids
�) Convenience of manipulation
3) Capable of taking & maintaining high
Polish
4) Fairly low cost.
Disadvantages
�. Objectionable esthetics (silver color)
6. low edge strength (must not be in thin sections)
8. Thermal conductivity (Pulp protection)
@. Galvanic current with other metallic restorations @. Galvanic current with other metallic restorations
or even non-uniform condensation
�. Do not support weakened tooth structure
�. Low tensile and shear strength. It is a brittle restoration that is greatly vulnerable to fracture under high tensile or shear stresses, such as the isthmus and the margins. isthmus and the margins.
6. Poor esthetics due to its objectionable metallic color, which may be further complicated by excessive discoloration due tarnish and corrosion.
8. Creep tendency (time-dependent deformation of set
material in the mouth) may result in form instability
in term of marginal deterioration, flattening of
contacts, saucering of occlusal anatomy and
formation of gingival overhangs. However, creep formation of gingival overhangs. However, creep
values are markedly decreased in recent high
copper amalgam.
Slow deformation of amalgam placed under a constant load
@. High thermal conductivity which may cause pulp irritation
unless it is adequately protected by adequate thickness of
remaining dentin bridge or by an intermediary insulating
base material if the cavity preparation is deep.
�. Lack of adhesion to tooth structure which dictates the use of
mechanical means of retention like undercuts and grooves in
the cavity preparation.
3. Electrical irritation through Galvanism can occur if another
metallic restoration with different degree of electro-
negativity was placed in its close proximity, e.g. cast gold.
The resultant currents can cause patient's discomfort or
leave a metallic taste in the mouth, and can accelerate the leave a metallic taste in the mouth, and can accelerate the
corrosive breakdown of the electro-negative metal.
4. Potential health hazards due to presence of mercury in dental
amalgam have raised concerns over its safety along many
years.
Types of Amalgam
According to particle shape:
�. Lathe cut
6. Spherical
According to the copper content:
�. Traditional / conventional (6-3% copper)
6. High copper amalgam (> 3% copper & up to 8 %)
According to the zinc content:
�. Zinc containing > . �% alloy
6. Non-zinc alloy < . �%
According to the mercury content:
�. Conventional @�% Hg
6. Mercury free galloy
8. Cold-welded Amalgam (Silver fill)
• Lathe cut: ball milled irregular shaped powder
particles ranging from spindles to shavings.
Spherical: atomized (round) smooth surfaced spheres:
• Require less mercury as they have smaller surface area per volume area per volume
• Develop more early strength due to its faster set
• Require less condensation force -
However, spherical amalgams have certain
disadvantages as:
• More difficult to obtain good interproximal• More difficult to obtain good interproximal
contacts and contours in class II restorations .
• Have shorter working time.
• Dissolution and precipitation
• Hg dissolves Ag and Snfrom alloy
Ag-Sn Alloy
Conventional Low-Copper Alloys
Hg Hgfrom alloy
• Intermetallic compoundsformed
Ag-Sn
Alloy
Ag-Sn
AlloyMercury
(Hg)
Ag
AgAg
Sn
Sn
Sn
AgAg33Sn + HgSn + Hg⇒⇒ AgAg33Sn + AgSn + Ag22HgHg33 + Sn+ Sn88HgHg
Phillip’s Science of Dental Materials 2003
γ γ γ� γ6
• Gamma (γγγγ) = Ag8Sn
– unreacted alloy
– strongest phase and
Ag-Sn Alloy
Hg
Hg
– strongest phase and
corrodes the least
– forms 8 % of volume
of set amalgam
Ag-Sn
Alloy
Ag-Sn
AlloyMercury
Ag
AgAg
Sn
Sn
Sn
Hg
Hg
AgAg33Sn + HgSn + Hg⇒⇒ AgAg33Sn + AgSn + Ag22HgHg33 + Sn+ Sn88HgHg
Phillip’s Science of Dental Materials 2003
γ γ γ� γ6
• Gamma � (γγγγ1) = Ag6Hg8
– matrix for unreacted alloy
and 6nd strongest phase
Ag-Sn Alloy
and 6nd strongest phase
– � micron grains
binding gamma (γγγγ)
– 3 % of volume
γγγγ"
AgAg33Sn + HgSn + Hg⇒⇒ AgAg33Sn + AgSn + Ag22HgHg33 + Sn+ Sn88HgHg
Phillip’s Science of Dental Materials 2003
γ γ γ� γ6
Ag-Sn
Alloy
Ag-Sn
Alloy
• Gamma 6 (γγγγ2) = Sn=Hg
– weakest and softest phase
– corrodes fast, voids form
– corrosion yields Hg which
reacts with more gamma (γγγγ)
Ag-Sn Alloy
reacts with more gamma (γγγγ)
– � % of volume
– volume decreases with time
due to corrosion
AgAg33Sn + HgSn + Hg⇒⇒ AgAg33Sn + AgSn + Ag22HgHg33 + Sn+ Sn88HgHg
Phillip’s Science of Dental Materials 2003
γ γ γ� γ6
γγγγ#
Ag-Sn
Alloy
Ag-Sn
Alloy
Admixed High-Copper Alloys
• Ag enters Hg from Ag-Cu spherical eutectic particles– eutectic
• an alloy in which the elements are completely soluble in liquid solution but separate into distinct areas upon solidification
• Both Ag and Sn enter Hg from Ag8Sn particles AgAg
Ag-Cu Alloy
AgHgHg
particles
Phillip’s Science of Dental Materials 2003
AgAg33Sn +Sn + AgAg--Cu + HgCu + Hg⇒⇒ AgAg33Sn +Sn + AgAg--Cu + AgCu + Ag22HgHg33 + Cu+ Cu66SnSn55γ γ γ� η
Ag-Sn
Alloy
Ag-Sn
AlloyMercury
Ag
Ag
SnSn
• Sn diffuses to surface of
Ag-Cu particles
– reacts with Cu to form
ηηηη
Ag-Cu Alloyηηηη
(eta) Cu3Sn� (ηηηη)
• around unconsumed
Ag-Cu particles
Ag-Sn
AlloyAg-Sn
Alloy
Phillip’s Science of Dental Materials 2003
AgAg33Sn +Sn + AgAg--Cu + HgCu + Hg⇒⇒ AgAg33Sn +Sn + AgAg--Cu + AgCu + Ag22HgHg33 + Cu+ Cu66SnSn55γ γ γ� η
• Gamma � (γγγγ1) (Ag6Hg8)
surrounds (ηηηη) eta phase
(Cu3Sn�) and gamma (γγγγ)
Ag-Cu Alloyηηηη
(Cu3Sn�) and gamma (γγγγ)
alloy particles (Ag8Sn)Ag-Sn
Alloy
γγγγ"
Ag-Sn
Alloy
Phillip’s Science of Dental Materials 2003
AgAg33Sn +Sn + AgAg--Cu + HgCu + Hg⇒⇒ AgAg33Sn +Sn + AgAg--Cu + AgCu + Ag22HgHg33 + Cu+ Cu66SnSn55γ γ γ� η
Single Composition
High-Copper Alloys
• Gamma sphere (γγγγ) (Ag8Sn)
with epsilon coating (εεεε)(Cu Sn)
Ag-Sn Alloyεεεε
Ag(Cu8Sn)
• Ag and Sn dissolve in HgAg-Sn Alloy
Ag-Sn Alloy
Mercury (Hg)
Ag
Sn
Ag
Sn
AgAg33Sn + CuSn + Cu33Sn + HgSn + Hg⇒⇒ AgAg33Sn + CuSn + Cu33Sn + AgSn + Ag22HgHg33 + Cu+ Cu66SnSn55
Phillip’s Science of Dental Materials 2003
γ γ γ� ηε ε
• Gamma � (γγγγ1) (Ag6Hg8) crystalsgrow binding together partially-
dissolved gamma (γγγγ) alloyparticles (Ag8Sn)
εεεε
Ag-Sn Alloy
ηηηη
• Epsilon (εεεε) (Cu8Sn) develops
crystals on surface of gamma particle (Ag8Sn)
in the form of eta (ηηηη) (Cu3Sn�)
– reduces creep
– prevents gamma-6 formation
Ag-Sn Alloy
Ag-Sn Alloy
γγγγ"
AgAg33Sn + CuSn + Cu33Sn + HgSn + Hg⇒⇒ AgAg33Sn + CuSn + Cu33Sn + AgSn + Ag22HgHg33 + Cu+ Cu66SnSn55
Phillip’s Science of Dental Materials 2003
γ γ γ� ηε ε
High copper amalgam alloys
• more than 3% & up to 8 % copper
• Two types are available
�- Admixed or dispersion alloy
6- Single composition6- Single composition
�- Admixed or dispersion alloy
6/8 Lathe cut particles (conventional) & �/8 Spherical
6- Single composition amalgam silver-tin-copper
High copper content ranging from �6 to 8 %
Manipulation of Amalgam
�. Trituration
6. Condensation
8. Carving8. Carving
@. Burnishing
�. Polishing
�. Trituration
• It is the process by which the alloy and
mercury are amalgamated together into a
coherent, homogenous smooth plastic mass
of amalgamof amalgam
• Its either Hand or Mechanical
Amalgamator (Triturator)
• Speeds vary upward
from 8 rpm
• Times vary from �–6
secondsseconds
• Mix powder and liquid
components to achieve
a pliable mass
• Reaction begins after
components are mixed
• Mixing time– refer to manufacturer
recommendations• Click here for details
• Overtrituration• Overtrituration– “hot” mix
• sticks to capsule
– decreases working / setting time
– slight increase in setting contraction
• Undertrituration– grainy, crumbly mix
Phillip’s Science of Dental Materials 2003
Proportioning
(Alloy / Mercury ratio)
• recommended ratio that gives optimum
performance & best physical properties
• i.e. reduce the amount of mercury left in • i.e. reduce the amount of mercury left in
the restoration to an acceptable level
• Dispensing of alloy & Hg
Alloy:
• dispensed either by: weight or by volume
• Pre-weighed pellet or tablets• Pre-weighed pellet or tablets
• Hg:
• Can be measured by weight or volume
Methods of proportioning:
• Simple weighing balance for both alloy &
mercury
• Mechanical dispensers for both alloy & • Mechanical dispensers for both alloy &
mercury (by weight)
Dispensers can achieve quit accurate ratios of
Hg to alloy
But: Risk of office Hg contamination
Hg ratio
• Either excess or little mercury in the final
amalgam has a marked effect on its properties
• Excess mercury gives large amount of weak
reaction products and causes lowering of C.S.reaction products and causes lowering of C.S.
• Little mercury non coherent dry grainy mix
Pre-proportioned capsules
• contains 6 compartments
• �st ……… alloy powder or pellet
• 6nd ……………………….. Hg
• Separated by a membrane which is ruptured • Separated by a membrane which is ruptured
either manually
• Before mixing or by itself during mechanical
mixing
• Some capsules require
• activation before trituration,
• others are activated when machine starts vibrating (self-activating capsules)
color coding of capsules indicates:
• number of spills
• type of amalgam
Some Capsules contain plastic or metal pestle to help in trituration
Capsules are expensive BUT
• They are more convenient
• More time saving
• Correct proportioning & less • Correct proportioning & less
waste
• Better mercury hygiene
Amalgam Capsules
• Contain (in separate
compartments):
– powdered amalgam
alloyalloy
– liquid mercury
• Some are manually
activated, others self-
activated
• Pestle usually included
Mechanical trituration:
• By the use of amalgamators
Amalgamator (Triturator)
• Speeds vary upward
from 8 rpm
• Times vary from �–6
secondsseconds
• Mix powder and liquid
components to achieve
a pliable mass
• Reaction begins after
components are mixed
Factors that control the quality of trituration
• Speed (medium- high or low speed in rpm)
The more speed less time
• Time of mixing (8-6 seconds or more)
e.g. spherical less than conventionale.g. spherical less than conventional
• size of mix………… large more time
• Force exerted by capsule (size) & pestle (weight)
• Distance traveled by the arms holding the capsule
Quality of trituration
Properly triturated amalgam is convenient to handle
• shiny • warm • homogenous
Poorly triturated amalgam is
• dull, gray appearance
• dry & crumbly & non cohesive• dry & crumbly & non cohesive
• inconvenient to manipulate
Over triturated amalgam is
• more plastic (or soupy)
• more difficult to remove from capsule
• faster setting • low strength
Mulling
• It is the process by which the mix is given a
cohesive form done by rubbing (mulling) of
amalgam a few seconds in a piece of rubber
dam between thumb & fingers dam between thumb & fingers
• Never done in bare hands to avoid
Contamination
• Conventional types requires more Hg � -3 %
by weight range from:
4: � to =: �
• For good wetting of alloy with hg • For good wetting of alloy with hg
• The excess hg will be removed later by
squeezing before condensation
6- Condensation
• It is the process of packing and adaptation of
the triturated amalgam in the prepared cavity
• It should start immediately after trituration• It should start immediately after trituration
Methods of condensation
�- Hand condensation
6- mechanical condensation
8- ultrasonic condensation8- ultrasonic condensation
Objectives of condensation
�- Properly adapt amalgam to cavity walls
6- Elimination of excess mercury
8- Pushing together alloy particles
@- Elimination of voids holes@- Elimination of voids holes
Condensation
• Forces– lathe-cut alloys
• small condensers
• high force
– spherical alloys– spherical alloys• large condensers
• less sensitive to amount of force
• vertical / lateral with vibratory motion
– admixture alloys• intermediate handling between lathe-cut and spherical
During hand condensation two
techniques could be used:
• A -Increasing dryness technique:
• �st increment of amalgam condensed into the cavity
not squeezed dry while the following layers were
dryer until the surface of the cavity
• So the dryer layers act as a blotter to absorb excess
mercury
• B- Minimal mercury technique: (Eames technique)
• Decreasing the mercury alloy ratio before mixing as
to �:� So mercury in the mix will be � %
8- Carving
• Carving is carried out to produce/simulate
functional anatomy of the restoration
• Objectives:
– Is to remove mercury rich layer on the surface– Is to remove mercury rich layer on the surface
– Re-establish contour & contact
• Carving should be done with sharp instruments as
dull instrument disturb crystallization & draw excess
mercury to the surface
• Alloy mass should be properly hardened before
starting carving to prevent amalgam from pulling
from the margins
• Carving could be done in any direction except
towards the cavity margins to avoid creation towards the cavity margins to avoid creation
submerged margins & prevent excess mercury from
being drawn to this critical area
@- Burnishing
• Pre-carve
– removes excess mercury
– improves margin adaptationimproves margin adaptation
• Post-carve
– improves smoothness
• Combined
– less leakage
Ben-Amar Dent Mater 1987
Pre-carve Burnishing
• This step is performed before carving
• A large ball or egg-shaped brusher is rubbed upon the surface
of the over-filled cavity
• It smoothens margins and improves the adaptation• It smoothens margins and improves the adaptation
• It draws the excess mercury out to be removed by carving
• It Increases the corrosion resistance
• It decreases porosity
Post-carve burnishing
• A small burnisher is used to apply force to the
carved amalgam surface
• This will produce a shiny surface
• Improves smoothness & marginal integrity• Improves smoothness & marginal integrity
�- Early Finishing
• After initial set
– prophy cup with pumice
– provides initial smoothness to restorations
– recommended for spherical amalgams
Polishing
• Increased smoothness
• Decreased plaque retention
• Decreased corrosion• Decreased corrosion
• Clinically effective?
– no improvement in marginal integrity
• Mayhew Oper Dent �Q=3
• Collins J Dent �QQ6
– Click here for abstract
Classifications
• Based on copper content
• Based on particle shape
• Based on method of adding •
copper
Phases of amalgam
• Hardened amalgam is a multiphase structure:
• The strongest phase is gamma phase Y
• The weakest phase is Y6 (tin mercurySn= Hg) • The weakest phase is Y6 (tin mercurySn= Hg)
most susceptible to corrosion
Cu-Sn phase has:
• High strength
• Good corrosion resistance
So high copper alloys show:So high copper alloys show:
• Reduced tarnish & corrosion
• Less marginal breakdown
• Higher compressive strength particularly Early strength