Prepared by : Dr.Dalia A. Abu-Alena in MDS,BDS Dental Amalgam Prepared by : Dr.Dalia A. Abu-Alena in MDS,BDS
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 mass.
Amalgam Advantages Disadvantages
Composition of Dental Amalgam: Silver Tin Copper Zinc Indium and Palladium Mercury
Classification of Dental Amalgam Alloys Conventional (Low Copper )Alloy: Lathe-cut Particles. Spherical Particles (a) (b)
Classification of Dental Amalgam Alloys High copper alloy: Admix Alloy. Unicompositional alloy. (a) (b)
Silver -Tin Binary System
Setting Reactions of Dental Amalgams: Low Copper Alloy: Ag3Sn + Hg Ag2Hg3 + Sn8Hg + Ag3Sn ( ) (1) ( 2) () 54%-56% 11-13% 27-35% 1 Hg 2 Hg 1+ 2
Setting Reactions of Dental Amalgams: High copper alloy Admixed alloy Ag3Sn + AgCu + Hg Ag2Hg3 + Sn8Hg + Ag3Sn + AgCu ( ) (1 ) (2 ) ( ) Sn8Hg + AgCu Cu6Sn5 + Ag2Hg3 + Ag3Sn (2) ( ) (1 ) ( )
Setting Reactions of Dental Amalgams: High copper alloy Unicompositional Alloy: Ag3Sn + Cu3Sn + Hg Cu6Sn5 + Ag2Hg3 ( ) ( ) ( ) (1 )
Microstructure of Set Low Copper Amalgam. (Ag3Sn) 2(Sn8Hg) Voids 1(Ag2Hg3)
Microstructure of Set High-Copper Admixed Amalgam. 1(Ag2Hg3) Eutectic(Ag3Cu2) (Cu6Sn5) (Ag3Sn)
Properties of Dental Amalgam
Properties of Dental Amalgam Compressive strength Tensile Strength Elastic Modulus Creep Dimensional Changes Tarnish and Corrosion:
Properties of Dental Amalgam 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 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: Unreacted Ag3Sn () phase. (strongest) Ag2Hg3(1)phase. Sn8Hg (2)phase.(weakest)
Properties of Dental Amalgam Elastic Modulus: -High- copper alloys are stiffer than low-copper alloys. -Amalgam are viscoelastic.
Properties of Dental Amalgam 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 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).
Properties of Dental Amalgam Dimensional Changes: Delayed Excessive Expansion ? Zinc – containing alloy + Moisture.
Properties of Dental Amalgam Tarnish and Corrosion: -Corrosion of various phases: - Ag3Hg3 ( 1)…..Least corrodible. -Ag3Sn(). -Ag3Cu2(eutectic). -Cu3Sn( ). -Cu6Sn5( ). -Sn8Hg (2).…….Most corrodible
Properties of Dental Amalgam Tarnish and Corrosion: Excessive corrosion can lead to : Increase porosity. Reduced marginal integrity. Loss of strength. Release of metallic products .
Manipulation of Dental Amalgam: Selection of alloy. Proportioning and dispensing. Trituration. Condensation. Carving. Finishing and polishing.
Manipulation of Dental Amalgam: 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: Proportioning and dispensing: proportioned capsules containing alloy particles and mercury in compartments separated by a disk or membrane are available.
Manipulation of Dental Amalgam: 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: Trituration: - Hand Trituration -Mechanical Trituration
Manipulation of Dental Amalgam: 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.
Manipulation of Dental Amalgam: Condensation: -Hand Condensation. -Mechanical Condensation.
Manipulation of Dental Amalgam: Carving:
Manipulation of Dental Amalgam: 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.