Dental Amalgam [Lecture by Dr.Wedad Etman @AmCoFam]

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