Dr. Gehan eloleimy-Amalgam-Structure-and-Properties-PPT

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DENTAL AMALGAM Stephen C. Bayne Department of Operative Dentistry School of Dentistry University of North Carolina Chapel Hill, NC 27599-7450  2006, Bayne and Thompson

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DENTAL AMALGAM Where is it?

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AMALGAM TERMINOLOGY AMALGAM = an alloy containing Hg as the major ingredient. DENTAL AMALGAM = an alloy of Hg with Ag-Sn. DENTAL AMALGAM ALLOY = a Ag-Sn alloy (to be mixed with Hg).

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ALLOY PRODUCTION Melting / Casting / Comminution  IRREGULAR Particles “Cast ingots --> filed into powder” Irregular particles = lathe cut = filings Hot alloy sprayed into cold air Particles spherodize and solidify Polycrystalline particles Homogenized by HT to remove coring Annealing HT to relieve cold work in filings Spheres are acid-washed Generally spheres are HT

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Hg / Alloy RATIOS

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ALLOY MANIPULATION

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CLASSIFICATION Copper content = low copper, high copper Particle size (and shape) = irregular, spherical Number of particle types = 1 or 2 Zinc content = Zn-containing, Zn-free

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Rx and MICROSTRUCTURE Ag Primary reactant Sn Creates solubility, fluidity Cu Reacts with Sn Zn Alloy processing aid Hg Reactant with Ag (and Sn)

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SETTING REACTIONS Low-Copper Dental Amalgam: S-Alloy + Hg  Residual Alloy + Matrix-1 + Matrix-2 Ag3Sn/Cu+ Hg  Ag3Sn/Cu + Ag2Hg3 + CuSn + Cu3Sn g + Hg  g + g 1 + e + h I-Alloy + Hg  Residual Alloy + Matrix-1 + Matrix-2 g + Hg  g (Ag3Sn) + g 1 + (g 2) S-Alloy + Hg  Residual Alloy + Matrix-1 + Matrix-2 Alloy + Hg  Alloy (Ag-Cu) + g 1 + e + h I/S-Alloy + Hg  Residual Alloy + Matrix-1 + Matrix-2 Ag-Sn + Hg  Ag-Sn + Ag-Hg + Sn-Hg Ag3Sn + Hg  Ag3Sn + Ag2Hg3 + Sn7-8Hg g + Hg  g + g 1 + g 2

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Rx and MICROSTRUCTURE

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Rx and MICROSTRUCTURE

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PHASE DIAGRAMS Ag3Sn + Hg >>> Ag2Hg3 = g1 (26Ag-74Hg)

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Overview of Manipulation Selection / Proportioning / Amalgamation / Manipulation / Polishing

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Amalgamators ENERGY = Speed x Time

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Unset amalgam A

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DIMENSIONAL CHANGES Dimensional changes on setting: CONTRACTION during alloy dissolution EXPANSION during impingement of reaction product crystals (EXPANSION if side reactions due to H2O contamination) Dimensional changes on depend on reaction variables: Particle size, Hg/alloy ratio, trituration time, condensation, ...

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AMALGAM PROPERTIES 2. Clinical Performance a. Longevity = 20-25 yrs ideally, 8-12 yrs practically b. Modes of failure = caries, marginal fracture, bulk B. Properties: 1. Physical 2. Mechanical 3. Chemical 4. Biological A. Introduction: 1. Specifications for Amalgam Properties a. ADA / ANSI and ISO b. Determination of “safety and efficacy”

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Physical Properties 1. Thermal conductivity = 2. Electrical conductivity = 3. Coefficient of thermal expansion = 4. Radiopacity = 5. Color = [>2 mm Aluminum] [Lustrous, shiny, white] 25 ppm/ºC [High] [High]

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Mechanical Properties

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Mechanical Properties TYTIN (Kerr Dental Mfg) = “tie up the tin” High-Copper, Spherical, 1 Particle, Zn-free 42% Hg mixed with alloy Fast-setting High early strength

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Chemical Properties

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Biological Properties Mercury Toxicity: OSHA maximum TLV = 50 mg/m3 (vapor) per 40 hr work week. Transient intraoral release (<35 mg/m3). Mercury Hypersensitivity: Low level allergic reaction. Estimated to be < 1 / 100,000,000

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Clinical Performance Reasons for Failure: Low-copper amalgam – marginal fracture and secondary caries. High-copper amalgam – marginal fracture and bulk fracture.

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Clinical Evaluation

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THANK YOU