Dental Amalgam
1.Dental 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
1.Composition of Dental Amalgam:
●Silver ●Tin ●Copper ●Zinc ●Indium and Palladium ●Mercury
1.Classification of Dental Amalgam Alloys
1. Conventional (Low Copper )Alloy:
(a )
2. Lathe-cut Particles. 3. Spherical Particles
(b )
Classification of Dental Amalgam Alloys
1. High copper
(a )
alloy:
2. Admix Alloy. 3. Unicompositional alloy.
(b )
1.Silver -Tin Binary System
1.Setting Reactions of Dental Amalgams:
1.Low Copper Alloy:
Ag3Sn + Hg Ag2Hg3 + Sn8Hg + Ag3Sn ( ) ( 1) ( 2) ( )
54%-56% 11-13% 27-35%
H g H g
2
1
Setting Reactions of Dentalalloy Amalgams: 1. High copper
1. Admixed alloy
1. Ag3Sn + AgCu + Hg Ag2Hg3 + Sn8Hg + Ag3Sn + AgCu ( )( 1)( 2)( ) 1. Sn8Hg + AgCu Cu6Sn5 + Ag2Hg3 + Ag3Sn ( 2) ( ) ( 1 ) ( )
1. High copper alloy
Setting Reactions of Dental Amalgams:
1. Unicompositional Alloy:
Ag3Sn + Cu3Sn + Hg Cu6Sn5 + Ag2Hg3 ( ) ( ) ( ) ( 1)
Microstructure of Set Low Copper Amalgam.
(Ag3Sn) 2 (Sn8Hg) Void s
1
(Ag2Hg3)
Microstructure of Set HighCopper Admixed Amalgam.
1
(Ag2Hg Eutectic3) (Ag3Cu2) (Cu6Sn5)
(Ag3Sn)
1.Properties of Dental Amalgam
1.Properties of Dental Amalgam 1.Compressive strength
2.Tensile Strength 3.Elastic Modulus 4.Creep 5.Dimensional Changes 6.Tarnish and Corrosion:
1.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
1.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
●Strength of various phases:
1. Unreacted Ag3Sn ( ) phase. (strongest) 2. Ag2Hg3( 1)phase. 3. Sn8Hg ( 2)phase.(weakest)
Properties of Dental Amalgam
1.Elastic Modulus:
-High- copper alloys are stiffer than low-copper alloys. -Amalgam are viscoelastic.
Properties of Dental Amalgam
1. 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
1. 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
1. Dimensional Changes:
Delayed Excessive Expansion ?
Zinc – containing alloy + Moisture.
Properties of Dental Amalgam
1. Tarnish and Corrosion:
-Corrosion of various phases: - Ag3Hg3 ( 1)…..Least corrodible. -Ag3Sn( ). -Ag3Cu2(eutectic). -Cu3Sn( ). -Cu6Sn5( ). -Sn8Hg ( 2).…….Most corrodible
Properties of Dental Amalgam
1. Tarnish and Corrosion:
Excessive corrosion can lead to :
●Increase porosity. ●Reduced marginal integrity. ●Loss of strength. ●Release of metallic products .
1.Manipulation of Dental Amalgam:
1. Selection of alloy. 2. Proportioning and dispensing. 3. Trituration. 4. Condensation. 5. Carving. 6. 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:
1. Proportioning and dispensing: proportioned capsules containing alloy particles and mercury in compartments separated by a disk or membrane are available.
Manipulation of Dental Amalgam:
1. 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:
1. Trituration: - Hand Trituration -Mechanical Trituration
Manipulation of Dental Amalgam:
●Effect f over-trituration and undertrituration:
○ Working time decreases with over- trituration. ○ Setting contraction increases with overtrituration. ○ 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:
1. Condensation: -Hand Condensation. -Mechanical Condensation.
Manipulation of Dental Amalgam:
1. Carving:
Manipulation of Dental Amalgam:
1. Finishing and polishing:
Mercury Toxicity
●Properties of mercury. ●Sources of mercury exposure. ●Mercury hygiene.
Recent Modifications of Dental Amalgam Alloys
●Indium containing amalgam. ●Palladium containing amalgam. ●Copper amalgam. ●Mercury free gallium based alloy. 