Dental Amalgam

Dental AmalgamDental Amalgam

I.I. Dental AmalgamDental Amalgam

Amalgam: is an alloy of mercury with one or more other metals.

Dental amalgam alloy: is an alloy that contains solid metals of silver, tin, copper and some times zinc.

Dental amalgam: is the alloy that results when mercury is combined with the previously mentioned alloys to form a plastic mass.

II.II. Composition of Dental Composition of Dental AmalgamAmalgam::

SilverTin CopperZincIndium and PalladiumMercury

III.III. Classification of Dental Classification of Dental Amalgam AlloysAmalgam Alloys

1. Conventional (Low Copper )Alloy:

a. Lathe-cut Particles.

b. Spherical Particles

(a)

(b)

Classification of Dental Classification of Dental Amalgam AlloysAmalgam Alloys

2. High copper alloy:

a. Admix Alloy.

b. Unicompositional

alloy.

(a)

(b)

IV.IV. Silver -Tin Binary SystemSilver -Tin Binary System

V.V. Setting Reactions of Setting Reactions of Dental Amalgams:Dental Amalgams:

1) Low Copper Alloy:

Ag3Sn + Hg Ag2Hg3 + Sn8Hg + Ag3Sn ( ) (1) ( 2) () 54%-56% 11-13% 27-35%

Hg 12

Hg

1+ 2

Setting Reactions of Dental Setting Reactions of Dental Amalgams:Amalgams:

2) High copper alloya) Admixed alloy

1. Ag3Sn + AgCu + Hg Ag2Hg3 + Sn8Hg + Ag3Sn + AgCu ( ) (1 ) (2 ) ( )

2. Sn8Hg + AgCu Cu6Sn5 + Ag2Hg3 + Ag3Sn (2) ( ) (1 ) ( )

Setting Reactions of Dental Setting Reactions of Dental Amalgams:Amalgams:

2) High copper alloyb) Unicompositional Alloy:

Ag3Sn + Cu3Sn + Hg Cu6Sn5 + Ag2Hg3

( ) ( ) ( ) (1 )

Microstructure of Set Low Microstructure of Set Low Copper Amalgam.Copper Amalgam.

(Ag3Sn)

2(Sn8Hg)

Voids

1(Ag2Hg3)

Microstructure of Set High-Microstructure of Set High-Copper Admixed Amalgam.Copper Admixed Amalgam.

1(Ag2Hg3)

(Ag3Sn)

Eutectic(Ag3Cu2)(Cu6Sn5)

VI.VI. Properties of Dental Properties of Dental AmalgamAmalgam

VI.VI. Properties of Dental Properties of Dental AmalgamAmalgam

1. Compressive strength2. Tensile Strength3. Elastic Modulus4. Creep5. Dimensional Changes6. Tarnish and Corrosion:

VI.VI. Properties of Dental AmalgamProperties of Dental Amalgam

1. Compressive strength-Amalgam is strongest in compression

and much weaker in tension and shear.

-HCU materials have the highest compressive strength.

Properties of Dental AmalgamProperties of Dental Amalgam

2. Tensile Strength:-Amalgam is strongest in compression

and much weaker in tension and shear.

-HCU materials have the highest early tensile strength.


Strength of various phases:1. Unreacted Ag3Sn () phase.

(strongest)

2. Ag2Hg3(1)phase.

3. Sn8Hg (2)phase.(weakest)


3. Elastic Modulus:-High- copper alloys are stiffer than

low-copper alloys.

-Amalgam are viscoelastic.


4. Creep-Low-copper lathe cut alloy has the highest value

of creep (6.3%).-The low creep values of high- copper alloys(0.05-

0.09%) increase the brittleness of amalgam and decrease the relief of stresses at contact areas under load.


5. Dimensional Changes:-Low-copper alloy have the greatest

dimensional change(-19.7m/cm).-High-copper unicompositional alloy

have the least dimensional change (-1.9 m/cm).

-Other alloys are ranging from (-8.8 to –14.8 m/cm).


5. Dimensional Changes:

Delayed Excessive Expansion ?

Zinc – containing alloy + Moisture.


6. Tarnish and Corrosion:-Corrosion of various phases:

- Ag3Hg3 ( 1)…..Least corrodible.

-Ag3Sn().

-Ag3Cu2(eutectic).

-Cu3Sn( ).

-Cu6Sn5( ).

-Sn8Hg (2).…….Most corrodible


6. Tarnish and Corrosion:

Excessive corrosion can lead to : Increase porosity. Reduced marginal integrity. Loss of strength. Release of metallic products .

VII.VII. Manipulation of Dental Manipulation of Dental Amalgam:Amalgam:

1) Selection of alloy.

2) Proportioning and dispensing.

3) Trituration.

4) Condensation.

5) Carving.

6) Finishing and polishing.

Manipulation of Dental Amalgam:Manipulation of Dental Amalgam:

1) Selection of alloy:

It is estimated that the majority of the dental amalgams currently placed are high – copper alloys , spherical- unicopositional or admixed types .


2) Proportioning and dispensing:

proportioned capsules containing alloy particles and mercury in compartments separated by a disk or membrane are available.


3) Trituration:

Trituration is the process by which mercury is allowed to react with the alloy powder . This procedure allows the rubbing of the surface oxide on amalgam particles , exposing an active surface to react with mercury .


3) Trituration:

- Hand Trituration

-Mechanical Trituration


Effect f over-trituration and under-trituration:– Working time decreases with over- trituration.– Setting contraction increases with over- trituration.– Compressive and tensile strengths increase with

over-trituration of lath cut alloys;however they decrease with over- and under-trituration of spherical alloys.

– Creep increases with over- trituration.


4) Condensation:

-Hand Condensation.

-Mechanical Condensation.


5) Carving:


6) Finishing and polishing:

Mercury ToxicityMercury Toxicity

Properties of mercury.

Sources of mercury exposure.

Mercury hygiene.

Recent Modifications of Dental Recent Modifications of Dental Amalgam AlloysAmalgam Alloys

Indium containing amalgam.Palladium containing amalgam.Copper amalgam.Mercury free gallium based alloy.

Dental Amalgam

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