Presentation on theme: "Dental Amalgam Prepared by : Dr.Dalia A. Abu-Alena in MDS,BDS."— Presentation transcript:
Dental Amalgam Prepared by : Dr.Dalia A. Abu-Alena in MDS,BDS
I.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.
II.Composition of Dental Amalgam: Silver Tin Copper Zinc Indium and Palladium Mercury
III.Classification of Dental Amalgam Alloys 1.Conventional (Low Copper )Alloy: a. Lathe-cut Particles. b. Spherical Particles (a) (b)
Classification of Dental Amalgam Alloys 2.High copper alloy: a. Admix Alloy. b. Unicompositional alloy. (a) (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% 11-13% 27-35% Hg 11 22 1+ 22
Setting Reactions of Dental Amalgams: 2)High copper alloy a)Admixed alloy 1.Ag 3 Sn + AgCu + Hg Ag 2 Hg 3 + Sn 8 Hg + Ag 3 Sn + AgCu ( ) ( 1 ) ( 2 ) ( ) 2.Sn 8 Hg + AgCu Cu 6 Sn 5 + Ag 2 Hg 3 + Ag 3 Sn ( 2 ) ( ) ( 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 )
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 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( %) 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 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 : Increase porosity. Reduced marginal integrity. Loss of strength. Release of metallic products.
VII.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: 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: 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.