Dental Amalgam Prepared by Dr Dalia A AbuAlena

Dental Amalgam Prepared by : Dr. Dalia A. Abu-Alena in MDS, BDS

I. Ø Amalgam: is Dental Amalgam an alloy of mercury with one or more other metals. Ø Dental amalgam alloy: is an alloy that contains solid metals of silver, tin, copper and some times zinc. Ø Dental amalgam: is the alloy that results when mercury is combined with the previously mentioned alloys to form a plastic mass.

II. Composition of Dental Amalgam: Ø Silver Ø Tin Ø Copper Ø Zinc Ø Indium and Palladium Ø Mercury

III. Classification of Dental Amalgam Alloys 1. Conventional (Low Copper )Alloy: (a) a. Lathe-cut Particles. b. Spherical Particles (b)

Classification of Dental Amalgam Alloys (a) 2. High copper alloy: a. Admix Alloy. b. Unicompositio nal alloy. (b)

IV. Silver -Tin Binary System

V. Setting Reactions of Dental Amalgams: 1) Low Copper Alloy: Ag 3 Sn + Hg ( ) Ag 2 Hg 3 + Sn 8 Hg + Ag 3 Sn ( 1) ( 2) ( ) 54%-56% Hg 1 Hg 2 11 -13% 27 -35% 1+ 2

Setting Reactions of Dental Amalgams: 2) High copper alloy a) Admixed alloy 1. Ag 3 Sn + Ag. Cu + Hg 2. ( ) 2. Sn 8 Hg + Ag. Cu 3. ( 2) Ag 2 Hg 3 + Sn 8 Hg + Ag 3 Sn + Ag. Cu ( 1 ) ( 2 ) ( ) Cu 6 Sn 5 + Ag 2 Hg 3 + Ag 3 Sn ( ) ( 1 ) ( )

Setting Reactions of Dental Amalgams: 2) High copper alloy b) Unicompositional Alloy: Ag 3 Sn + Cu 3 Sn + Hg ( ) Cu 6 Sn 5 + Ag 2 Hg 3 ( ) ( 1 )

Microstructure of Set Low Copper Amalgam. (Ag 3 Sn) 2(Sn 8 Hg) Voids 1(Ag 2 Hg 3)

Microstructure of Set High. Copper Admixed Amalgam. 1(Ag 2 Hg 3) Eutectic(Ag 3 Cu 2) (Cu 6 Sn 5) (Ag 3 Sn)

VI. Properties of Dental Amalgam

VI. Properties of Dental Amalgam 1. 2. 3. 4. 5. 6. Compressive strength Tensile Strength Elastic Modulus Creep Dimensional Changes Tarnish and Corrosion:

VI. Properties 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 Amalgam 2. Tensile Strength: -Amalgam is strongest in compression and much weaker in tension and shear. -HCU materials have the highest early tensile strength.

Properties of Dental Amalgam l Strength of various phases: 1. Unreacted Ag 3 Sn ( ) phase. (strongest) 2. Ag 2 Hg 3( 1)phase. 3. Sn 8 Hg ( 2)phase. (weakest)

Properties of Dental Amalgam 3. Elastic Modulus: -High- copper alloys are stiffer than low-copper alloys. -Amalgam are viscoelastic.

Properties of Dental Amalgam 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.

Properties of Dental Amalgam 5. Dimensional Changes: -Low-copper alloy have the greatest dimensional change(-19. 7 m/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).

Properties of Dental Amalgam 5. Dimensional Changes: Delayed Excessive Expansion ? Zinc – containing alloy + Moisture.

Properties of Dental Amalgam 6. Tarnish and Corrosion: -Corrosion of various phases: - Ag 3 Hg 3 ( 1)…. . Least corrodible. -Ag 3 Sn( ). -Ag 3 Cu 2(eutectic). -Cu 3 Sn( ). -Cu 6 Sn 5( ). -Sn 8 Hg ( 2). ……. Most corrodible

Properties of Dental Amalgam 6. Tarnish and Corrosion: Excessive corrosion can lead to : Ø Increase porosity. Ø Reduced marginal integrity. Ø Loss of strength. Ø Release of metallic products.

VII. Manipulation of Dental Amalgam: 1) 2) 3) 4) 5) 6) Selection of alloy. Proportioning and dispensing. Trituration. Condensation. Carving. Finishing and polishing.

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.

Manipulation of Dental Amalgam: 2) Proportioning and dispensing: proportioned capsules containing alloy particles and mercury in compartments separated by a disk or membrane are available.

Manipulation of Dental Amalgam: 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.

Manipulation of Dental Amalgam: 3) Trituration: - Hand Trituration -Mechanical Trituration

Manipulation of Dental Amalgam: l Effect f over-trituration and undertrituration: – 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.

Manipulation of Dental Amalgam: 4) Condensation: -Hand Condensation. -Mechanical Condensation.

Manipulation of Dental Amalgam: 5) Carving:

Manipulation of Dental Amalgam: 6) Finishing and polishing:

Mercury Toxicity ü Properties ü Sources of mercury exposure. ü Mercury hygiene.

Recent Modifications of Dental Amalgam Alloys Indium containing amalgam. Palladium containing amalgam. Copper amalgam. Mercury free gallium based alloy.