DENTAL DENTAL AMALGAMAMALGAM

CONTENTSCONTENTS1. HISTORICAL BACKGROUND2. DEFINITIONS3. INDICATIONS4. CONTRAINDICATIONS5. ADVANTAGES6. DISADVANTAGES7. COMPOSITION8. CLASSIFICATIONS9. ALLOY MANUFACTURING10. PHASES OF AMALGAM11. KINETICS OF AMALGAMATION12. MANIPULATION FACTORS13. PROPERTIES OF AMALGAM14. MECURY TOXICITY15. AMALGAM FAILURES16. RECENT ADVANCEMENTS IN AMALGAM17. ALTERNATIVES TO AMALGAM

ALLOY MANUFACTURINGALLOY MANUFACTURING

1. LATHE-CUT ALLOY POWDER

Main Constituent Metals (Ag, Sn, Cu & Zn) melted & subjected to

Homogenizing Heat Treatment

cooled slowly to form Ingot fed to

Milling Machine / lathe to produce filings & further broken down by

Ball milling

Acid treatment Stress – Relief protocols

(Annealing Cycle)

2. ATOMIZED POWDER (SPHERICAL ALLOY) :

Molten alloy is forced under inert gas through fine crack in the crucible in to the chamber. If the droplets solidify before hitting a surface,

the spherical shape is preserved.

Spherical alloy

Acid treatment Heat treatment

• Average Particle size of modern powder ranges from 15-35 micro meters.

PHASES OF AMALGAMPHASES OF AMALGAM

PHASES FORMULA HARDNESS (VHN)

1. r Ag3 Sn 250 – 270

2. r1 Ag2 Hg3 App. 120

3. r2 Sn7-8 Hg App. 15

4. e Cu3 Sn ------

5. n Cu6 Sn5 ---------

6. silver-copper Ag-Cu ------

eutectic

KINETICS OF AMALGAMATIONKINETICS OF AMALGAMATION

• LOW COPPER ALLOYS :

When Powder (Ag3 Sn) is triturated with mercury, 2 processes occur:

1.Ag & Sn in the outer portion of particles dissolve into Hg.

2. Hg diffuses into alloy particles.• Hg has a limited solubility of Ag (0.035wt%) & Sn (0.6wt%)• When the solubility in Hg is exceeded, 2 binary metallic

compounds precipitate in to Hg. They are:

1. Body centered cubic Ag2 Hg3 (r1) phase

2. Hexagonal Sn7-8 Hg (r2) phase.• Later r1 & r2 crystals grow as the remaining Hg dissolves the

alloy particles. As Hg disappears, amalgam hardens.• Alloy & Hg in about 1:1 ratio, there is insufficient Hg to completely

consume original alloy particles. As a result unconsumed particles

are present in the set amalgam (of about 27% of original r phase)

• Simplified as:

r( Ag3 Sn) +Hg r1(Ag2 Hg3) + r2 (Sn7-8 Hg) + r (Ag3 Sn)Unreacted

• HIGH COPPER ALLOYS:1. ADMIXED ALLOY:

In 1963,Innes & Youdelis added spherical Ag-Cu eutectic alloy (71.9 wt% Ag & 28.1 wt% Cu) particles to lathe-cut low copper amalgam alloy. This has resulted in increased residual alloy particles & decreased matrix.

• Total Cu content ranges from 9wt% - 20wt%.

• When Hg reacts with Admixed powder :

a) Ag from Ag-Cu particles dissolves Hg.

b) Ag & Sn from Ag3 Sn dissolves Hg.

c) Sn from Ag3 Sn diffuses Ag-Cu alloy particles and reacts with

copper n-phase(Cu6Sn5) around unconsumed Ag-Cu.

• Reaction is summarized as:

Ag3 Sn +Ag-Cu eutectic +Hg r1 + n (Cu6 Sn5) + unconsumed alloy

particles.

• Here r2 phase is eliminated.

2. SINGLE COMPOSITON ALLOY :

• First alloy of this type contained of 60 wt% Ag, 27 wt% Sn

& 13 wt% Cu

• Total Cu content ranges from 13- 30 wt%.

• The alloy particle is composed of a very fine distribution of Ag3 Sn (r) and

Cu3 Sn (e).

• Simplified reaction with Hg:

Ag3 Sn (r) + Cu3 Sn (e) + Hg Cu6 Sn5(n) +Ag2 Hg3 (r1)

• Here also r2 phase is eliminated.

MANIPULATION FACTORSMANIPULATION FACTORS

• CHOICE OF ALLOY

• CHOICE OF MECURY

• PROPORTIONING OF Hg to Alloy

• TRITURATION & METHODS

• INSERTION OF AMALGAM

1. HAND CONDENSATION

2. MACHANICAL CONDENSATION

• PRE-CARVE BURNISHING

• CARVING

• BURNISHING

• FINISHING & POLISHING.

CHOICE OF ALLOYCHOICE OF ALLOY

• The factors to be considered are:

1. Alloy composition

2. Particle shape

3. Particle size

4. Speed of set

5. Pre amalgamated or standard alloy

6. Zinc containing or zinc free alloy.

ALLOYCOMPOSITIONALLOYCOMPOSITION

• The generally accepted specifications for amalgam alloy require the composition of the constituent metals to be :

65% min. Ag

29% max. Sn

6% max. Cu

2% max. Zn

• Use of disperse alloy has the advantage of its greater tarnish & corrosion

resistance, improved compressive and edge strength with consequent reduction in marginal failure leading to ditching.

• Jerman(1970) found that by adding 1.5% SnF to the alloy ,there was an increased fluoride content of the enamel adjacent to the restoration with an associated reduction in the enamel solubility. But there is no evidence that

there is continuous leaching of fluoride from the set amalgam.

PARTICLEPARTICLE SHAPE SHAPE

• The disadvantage of lathe-cut particles is that, although they are similar in size as a result of sieving, they are not necessarily similar in shape.

• Advantages of spherical particle:

1. Easier to produce

2. Less sensitive to manipulative variables Eg: Breaking up during trituration.

3. Superior 1-hr and final compressive strengths & tensile strengths.

4. Increased plasticity of the mix with mecury.

PARTICLE SIZEPARTICLE SIZE

• The original particle size alters the character of the finished , carved & polished surface.

• Smaller the particle size:

1) Higher the 1hr & 24hr strength

2) lesser the expansion

3) more easily adopted to the cavity walls

4) much less pitted, when carved

5) more easily polished.

• Use of fine cut amalgam alloy particle is advocated.

SPEED OF SETSPEED OF SET

• Setting time of an alloy is accelerated by increasing the Ag content.

• Min. Content of Ag is 65% in ADA. SP.

1. Quick setting alloys (Ag— 66.7%-74.3%)2. Slow setting alloys (Ag— 43-48%)

• Advantages of fast setting alloy:a) reduces chair side timeb) allow to fill approximal cavities at one appointment.

• Disadvantage: Rapid crystallization limits removal of Hg from successive condensed portions of amalgam already in the cavity.

CHOICE OF MERCURYCHOICE OF MERCURY• The most recent British standard sp. for dental mercury is B.S.4227• Mercury complying with the requirements of British &USA

Pharmacopoeia or ADA sp.no.6 should be used.• Hg must contain <0.02% by mass, non-volatile residue & there must

be no visible surface contamination.• It should have a mirror like surface.• Contaminated Hg by the metals amalgam alloy can only be purified

by “Distillation procedures”• Tarnished Hg which comes out from wet mixes after trituration with

amalgam alloy can be cleaned by :1) Passing through pin pricked hole in filter-paper held in

a glass filter funnel & allowed to drop in to a carefully cleaned glass dispenser.

or2)Through clean chamois skin to restore its previous

brightness.

PROPORTIONING MECURY TO PROPORTIONING MECURY TO ALLOYALLOY

• Philips and Swartz(1949) have shown that regardless of the amount squeezed away in the squeeze cloth or removed by condensation,the more the Hg used in the original mix the greater is the amount that will remain in the restoration.

• Philips and Boyd(1947) have shown that as the Hg:alloy ratio is increased, the % of residual Hg also increases proportionally. For each additional 15% of Hg used in the original mix, there is an avg increase of 1-1.5% residual Hg.

• The residual Hg content of the final restoration should be between50-55%.

• Traditionally Hg:alloy ratio were 7:5 & 8:5 by weight or even higher.• Eames (1959) has fathered the change from using increased

Hg:Alloy ratio to using Hg:Alloy ratio of 1:1,which can only be triturated in a mechanical amalgamator. This technique also known as “NO SQUEEZE CLOTH TECHNIQUE” or “MINIMAL MERCURY TECHNIQUE”

• Eames etal (1961) recognized the advantage of a more plastic mix and advise when using a 1:1 ratio of Hg & alloy to over triturate

slightly.• The problem then arises which is the best method of dispensing the

correct proportions of Hg to alloy.• The Various methods of proportioning alloy & Hg are:

1)By weight

eg: Crescent and Ash balances

2)By volume

eg: Baker proportioner

Amalganom

S.S.White proportioner

3)Predispensed

eg: S.S.White sigrens

Amalcap capsules with mercury in cap

Aristalloy tablets.

Mechanical instruments have now been developed which will, in one appliance, dispense & triturate the alloy & Hg.

• The more common method of dispensing alloy & Hg is the Automatic release type of dispenser which proportions volumetrically.

• Ryge etal (1958) have analyzed the accuracy of 12 different methods of obtaining the desired proportions of alloy & Hg.

According to them, the best method of obtaining an accurate Hg:alloy ratio was to use pre-dispensed alloy produced by manufacturer together with a good Hg volume dispenser.

• Hg dispenser should be held vertically and not at 45o. It should

be half filled.

TRITURATIONTRITURATION• The purpose of trituration is to bring the particles of alloy into contact with

the mercury.• Prior to 1940’s Amalgam was triturated by hand in a mortar & pestle.

• Its objectives are :

1) to get workable mass in minimum time

2) to remove oxide layer from powder

3) to reduce particle size, increase surface area & thus increasing the rate of

amalgamation

4) to keep the r1 & r2 crystals as minimum as possible yet bind the particles.

• Methods of trituration are:

1)Mortar & pestle

2) Rubber thumb-stall

3) Mechanical amalgamation / Amalgamator.

Mortar pestle method

• Is the oldest method used.• Suggested by Dr.Marcus.L.Ward.

• Here pestle is held in a pen grasp with 2-3 pounds load and rapid convenient circular motion is used until a shiny, homogeneous mass is obtained.

• WORK = PESTLE SPEED X PESTLE LOAD X TIME• Need 60-120s for trituration.

RUBBER THUMB-STALL METHOD:

• In 1934, Mary Gayler advocated this method.• This technique has the advantage not destroying the original particle size,

but a higher Hg : alloy ratio is used to obtain amalgamation in 1minute.

MECHANICAL AMALGAMATION:

• Types of motion:

1) Off-centre-centrifugal action

2) Reciprocating figure of “8”.

• Advantages:

1) Trituration is achieved rapidly (20-25sec)

2) More standard mix can be obtained.

Stages of triturationStages of trituration

OVER TRITURATEDOVER TRITURATED

TESTING OF MIXTESTING OF MIX

OVER TRITURATEDOVER TRITURATED

UNDER TRITURATEDUNDER TRITURATED

OVER TRITURATED

MULLINGMULLING

• Is a continuation of trituration.• Enhances uniformity, coherence & handling ease.• In the mortar & pestle method due to continuous folding off the mass

from the side of the mortar to the centre, a layered mass is developed. This is made more cohesive by hand mulling.

Mix is kneeded in a piece of rubber dam or between finger & palm For 2-5sec.

PRE-CARVE BURNISHINGPRE-CARVE BURNISHING

• Large egg shaped burnisher is used.

• Advantages:

1) Less Hg

2) Porosity

3) r2 phase

CARVINGCARVING

• To produce restoration with proper physiological & anatomical contour.

• Use sharp instrument.• Don’t attempt to produce deep anatomical

fissure (Mahler’ 58).• Marginal ridge – wide, round & carved to

the level of adjacent marginal ridge• Use large spoon excavator - Gross

occlusal carving.

CARVING TECHNIQUECARVING TECHNIQUE

REMOVAL OF MATRIX BANDREMOVAL OF MATRIX BAND

FINISHING & POLISHINGFINISHING & POLISHING

• Finishing: process which continues the carving objectives, removes flash & overhang.

• Polishing: process which creates a corrosion resistant layer by removing scratches & irregularites from the surface.

• Advantages.

FINISHINGFINISHING

• # 12-15 bladed steel burs (worn)

• Rhein trimmers (gingival area)

• # 12 BP bald or Blacks knives (interproximal areas)

• Fused Alumina white stone (marginal adoptation)

• Water resistant strip (cervical areas)

• Done usually after 24 hrs

POLISHINGPOLISHING

• Polish all surfaces of restoration

• Amalgam line (Mosteller” 57)

• Fine sand paper discs (Buccal & lingual embrasures of proximal surfaces)

• Linen strips (Proximal surface below the contact area)

• Gingival excess of amalgam:1) E.V.A prophylaxis system with safe sided

& safe edged diamond tip2) Ultra sonic scaler points

• Smooth, highly polished matrix band (contact area)

• Final polishing :SnO or Whitening made into paste with alcohol, applied with bristle or goat hair brush.

• Temperature should not be raised >65o

PROPERTIES OF AMALGAMPROPERTIES OF AMALGAM

1)Dimensional changes

Effect of moisture contamination

Mercuroscopic expansion

2)Strength

3)Creep

4)Tarnish &corrosion

5)Thermal property

6)Elastic modulus

1) DIMENSIONAL CHANGES1) DIMENSIONAL CHANGES• Amalgam undergoes dimensional changes in 3 stages:

Initial contraction

Expansion

Delayed contraction

• According to ADAsp.1, Amalgam should neither contractnor expand more than 20micro.m/cm at 37o between 5mnts & 24hrs after beginning of trituration

• Measured by Interferometer

• Factors affecting dimensional changes:1) Constituents

2) Hg

3) Particle size

4) Trituration

5) Condensation• Moisture contamination:

Delayed expansion: Occurs due to contamination of Zn

containing alloys with water during trituration or condensation.

Zn+H2O ZnO + H2

Reaches about >400micro.m

• Its clinical consideration:1) Protrusion of restoration out of

cavity

Unsupported margins

# of restoration2) Increased flow & creep3) causes pulpalgia (2000psi)4) decreases compressive strength (24%)

• Management : Use Zn free alloys Isolation

MECUROSCOPIC EXPANSIONMECUROSCOPIC EXPANSION

• By Jorgensen• Results from when Hg released from corrosion

of r2 phase reacts with remaining alloy particles.

• Mechanism:

Sn8Hg + 1/2 O2+ H2O + Cl- Sn4(OH)6Cl2 + Hg

• Causes further weakening of the restoration

2) STRENGTH2) STRENGTH• Amalgam has high compressive strength & low

tensile strength

• The compressive strength of a satisfactory amalgam should be atleast 310MPa.

• ADA SP. Stipulates a minimum compressive strength of 80MPa at 1hr.

• Factors affecting strength:1)temperature2)Trituration3)Hg4)Condensation5)Particle shape &size6)Porosity7)r2 phase8)Interparticular distance9)Corrosion.

CREEPCREEP

• Is a time dependent plastic deformation of crystalline material under the influence of a static or dynamic stress.

• Can be correlated with marginal breakdown.• Creep rate: 1)Low Cu---0.8-8%

2)High Cu--- <0.1% • Factors affecting creep:

1)Higher condensation forces Creep

& Elimination of r2 phase

2) Excess Hg Creep

TARNISH & CORROSIONTARNISH & CORROSION

• Amalgam often tarnish &corrode in oral environment• Tendency towards tarnish is unaesthetic due to

formation of black AgS• Corrosion occurs in the interface between tooth &

restoration.• Corrosion products Oxides & chlorides of Sn• Galvanism (differences in EMF) • Higher Hg:Alloy ratio corrosion• Smooth& homogeneous surface minimizes tarnish

& corrosion

• THERMAL PROPERTY:-- GOOD CONDUCTOR OF HEAT

-- Cf. Of thermal exp, is 3 times greater than dentin.

-- If RDT is <2mm, protection of pulp is necessary

• ELASTIC MODULUS:--High Cu alloys are more stiffer than low

Cu

alloys.

-- 62 GPa

MECURY TOXICITYMECURY TOXICITY• FORMS OF Hg:

Organic & Inorganic Most toxic organic forms are Methyl

Hg & Ethyl Hg Least toxic form of Hg – Inorganic.

• Concentration of Hg: OSHA has set a threshold limit value of

0.05 mg/m3.• Max allowable Hg level in blood 3 micro

Gms/L.

• Chronic exposure – assessed by urinary Hg concentration.

Hg thermometer: Hg level

1000 Pronounced symptoms

500 Mild to Moderate

100 Subtle changes

25 No known Health effects

4 Upper limit of urinary Hg

• Sources of Hg exposure – Dental office:

Amalgam raw materials being stored in use

During trituration, insertion & intraoral hardening

Amalgam scrap

During finishing & polishing

During Amalgam removal

Dental Hg hygiene recommendationsDental Hg hygiene recommendations

• Train all personals regarding potential hazard of Hg vapor & make them aware of its potential sources

• Working in well ventilated spaces• Periodically monitor dental operatory

atmosphere for Hg vapor (DOSIMETERS & Hg Vapor Analyzers)

• Facilitate Hg spill contamination cleanup• USE only Pre-capsulated alloys• USE Amalgamator with enclosed arm

• AVOID skin contact with Hg / freshly mixed amalgam

• USE high volume evacuation• Store all scrap amalgam in tightly closed

container• Recycle amalgam scrap when feasible• Dispose Hg contaminated items in sealed bags• USE trap bottles / tape / freshly mixed amalgam

to pick up spilled Hg

AMALGAM FAILURESAMALGAM FAILURES

• INCLUDE:

Bulk restoration fracture

Corrosion & excessive marginal #

Sensitivity or pain

Secondary caries(70%)

# of tooth structure forming restorative – tooth preparation walls

CAUSED OF FAILURECAUSED OF FAILURE

• Grouped under 3 headings:

Faults in cavity design

- weakened tooth structure

- sharp internal line angles

- non-retentive proximal boxes

- incorrect cavo-surface design

- shallow preparation

Poor clinical techniques:

- residual caries

- poor matrix techniques

- contamination

- poor condensation

- over & under filling and

over carving

Limitations of the material

RECENT ADVANCEMENT RECENT ADVANCEMENT IN DENTAL AMALGAMIN DENTAL AMALGAM

AMALGAM BONDING SYSTEMAMALGAM BONDING SYSTEM

• Used to seal underlying tooth structure & bond the amalgam to enamel & dentin

• 4-META based bonding systems are used frequently.

• It is important to develop micro-mechanical bonding since no chemical bonding occurs.

• Hence bonding system is applied in much thicker layers(10-50mMts).

Bonding systems used:

• ALLBOND-2(Bisco)

• Amalgam bond plus (parkell)

• Panavia (Kuraray)

• Scotch bond multi-purpose plus(3M-ESPE)

• Potential advantages:

Improved retention

Decreased micro leakage

Improved resistance form

Decreased post-operative sensitivity

• Primary indication:

when weakened tooth structure remains & bonding may improve the overall resistance form of the restored tooth.

GALLIUM BASED ALLOYSGALLIUM BASED ALLOYS• Gallium has similar atomic structure and characteristics

to Hg • They consist of Gallium(65%), Indium, Tin, copper,

Palladium.

DISADVANTAGE: • 16 Times more experience • Very sticky• High level of corrosion • High level of expansion (1% or 60 mMts/ cm) • Toxicology unknown• Two types of Gallium alloys :• Palladium – Ga – Sn Ag-cu powder mixed with

liquid of Ga-In-Sn

REFERENCESREFERENCES• SKINNER”S- Science of dental materials• Sturdevant”s Art & science of operative dentistry

(4th edition)• Operative dentistry- Modern theory &practice

-- M.A.Marzouk• Pickard”s manual of operative dentistry• Operative dentistry-Gillmore & Lund• Clinical restorative materials & techniques

-- Karl. F. Leinfelder• Bonding of amalgam restoration, oper dent, 2000, 25 ,121-129.