Presentation on theme: "Prepared by : Dr.Dalia A. Abu-Alena in MDS,BDS"— Presentation transcript:
1Prepared by : Dr.Dalia A. Abu-Alena in MDS,BDS Dental AmalgamPrepared by :Dr.Dalia A. Abu-Alena inMDS,BDS
2Dental AmalgamAmalgam: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.
14Properties of Dental Amalgam Compressive strengthTensile StrengthElastic ModulusCreepDimensional ChangesTarnish and Corrosion:
15Properties of Dental Amalgam Compressive strength-Amalgam is strongest in compression and much weaker in tension and shear.-HCU materials have the highest compressive strength.
16Properties 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.
17Properties of Dental Amalgam Strength of various phases:Unreacted Ag3Sn () phase. (strongest)Ag2Hg3(1)phase.Sn8Hg (2)phase.(weakest)
18Properties of Dental Amalgam Elastic Modulus:-High- copper alloys are stiffer than low-copper alloys.-Amalgam are viscoelastic.
19Properties 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( %) increase the brittleness of amalgam and decrease the relief of stresses at contact areas under load.
20Properties 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).
22Properties of Dental Amalgam Tarnish and Corrosion:-Corrosion of various phases:- Ag3Hg3 ( 1)…..Least corrodible.-Ag3Sn().-Ag3Cu2(eutectic).-Cu3Sn( ).-Cu6Sn5( ).-Sn8Hg (2).…….Most corrodible
23Properties of Dental Amalgam Tarnish and Corrosion:Excessive corrosion can lead to :Increase porosity.Reduced marginal integrity.Loss of strength.Release of metallic products .
24Manipulation of Dental Amalgam: Selection of alloy.Proportioning and dispensing.Trituration.Condensation.Carving.Finishing and polishing.
25Manipulation 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 .
26Manipulation of Dental Amalgam: Proportioning and dispensing:proportioned capsules containing alloy particles and mercury in compartments separated by a disk or membrane are available.
27Manipulation 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 .
28Manipulation of Dental Amalgam: Trituration:- Hand Trituration-Mechanical Trituration
29Manipulation 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.
30Manipulation of Dental Amalgam: Condensation:-Hand Condensation.-Mechanical Condensation.