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  1. 1. 3/5/2012 ALLOY Versus AMALGAM • Alloy is a mixture of 2 or more metals Amalgam • AMALGAMMATION / TRITURATION – reaction when a silver based alloy is mixed with mercury, a liquid metal. • Dental Amalgam - Is an alloy that contains mercury as one of its component Why Amalgam?• Inexpensive ADVANTAGES DISADVANTAGES• Ease of use • Less technique sensitive • Esthetics, metallic color• Proven track record • More durable • No bonding to tooth surface – >100 years • Less costly • Extensive tooth preparation • Excellent abrasion and wear• Familiarity resistance• Life expectancy – 15 yrs • Tends to seal itself against• Resin-free leakage • Bacteria do not adhere to it – less allergies than composite as strongly as n composite Composition of Dental AmalgamIndications ( I,II,III, V,VI) Contraindications • Basic• Moderate to large • Esthetically prominent areas – Silver restoration of teeth – Tin• Restorations that are not in – Copper highly esthetic areas of mouth. – Mercury• Restorations that have • Other heavy occlusal contacts. – Zinc• Restorations that can’t be – Indium well isolated – Palladium• Pin retained 1
  2. 2. 3/5/2012 Basic Constituents Basic Constituents • Silver (Ag) – increases strength • Copper (Cu) – increases expansion – increases strength – Decrease setting time – reduces tarnish and corrosion • Tin (Sn) – decreased strength – reduces creep – decreases expansion • reduces marginal deterioration – increases setting time – Improves physical properties when compounded with Ag Phillip’s Science of Dental Materials 2003 Phillip’s Science of Dental Materials 2003 Dental Materials - Saunders Tarnish Corrosion• Oxidation that attacks the surface of the Am and • Oxidation from interaction of 2 dissimilar extends slightly below the surface. metals in the presence of a solution• Contact with oxygen, chlorides, and sulfides in containing electrolytes the mouth. • Galvanism• Dark dull appearance but not destructive to Am • Oxidation of one of the metals• Palladium and Polishing may help reduce tarnish• The rougher the surface, the more it tends to tarnish Creep Basic Constituents • Mercury (Hg)• Refers to the gradual change in shape of the – activates reaction restoration from compression by the opposing – only pure metal that is liquid at room temperature dentition. – spherical alloys • require less mercury – smaller surface area easier to wet » 40 to 45% Hg – admixed alloys • require more mercury – lathe-cut particles more difficult to wet » 45 to 50% Hg Phillip’s Science of Dental Materials 2003 2
  3. 3. 3/5/2012 Other Constituents • Zinc (Zn) • Indium (In) • decreases oxidation of other elements – decreases surface tension – provides better clinical performance • reduces amount of mercury necessary • less marginal breakdown • reduces emitted mercury vapor – reduces creep and marginal breakdown – causes delayed expansion • if contaminated with moisture during condensation – increases strength Powell J Dent Res 1989 Phillip’s Science of Dental Materials 2003 Other Constituents Component High copper Alloy % Low copper alloy %• Palladium (Pd) Silver 40 -70 68 – 72 – reduced corrosion Tin 12 – 30 28 – 36 – greater luster Copper 10 – 30 4–6 Zinc 0-1 0-2 Mahler J Dent Res 1990 Classifications Copper Content• Based on copper content • Low-copper alloys• Based on particle shape – 4 to 6% Cu • High-copper alloys – thought that 6% Cu was maximum amount • due to fear of excessive corrosion and expansion – Now contain 10 to 30% Cu • at expense of Ag Phillip’s Science of Dental Materials 2003 3
  4. 4. 3/5/2012 Setting Reaction of Low Copper Low Copper Amalgam Amalgam• “traditional” “conventional” (β+γ ) + Hg γ1 + γ2 + unconsumed alloy particles (β+γ )• COMPOSITION: ( Black’s) γ – greek letter gamma• 65% SILVER - used to designate the AgSn alloy or gamma phase• 25% Tin γ1 – AgHg• < 6% copper γ2 – SnHg• 1% zinc Low Copper Amalgam High Copper Am • Compared with low copper alloys, this have become a material of choice. • Improved mechanical properties • Corrosion resistance • Better marginal integrity • Imroved performance in clinical trials High Copper Am Admixed• 2 types • “Blended” , “admix”, or “dispersion” • These are called admixed alloys• Admixed as they contain atleast 2 kinds• Single composition of particles • Am made from these powders is stronger than am made from lathe cut low copper powder, bec• Both types contain more than 6 wt % copper of inc in residual alloy particles and resultant dec in matrix • Silver-copper particles as well as the AgSn paricles probably act as strong fillers in Am. 4
  5. 5. 3/5/2012 Spherical High Copper Amalgams Particle Shape• Unlike admixed, each particle of these alloy • Lathe cut alloy powders have the same chemical composition  Formed by shaving particles from a block of the alloy by a• Thus , single composition alloys lathe• Single composition, high copper, spherical • Spherical  Formed by spraying molten dental amalgams alloy into an inert gas • Admixed  Mixture of the two .• Have only 1 shape  Alloy maybe made from• The particles are a combination of silver 60 wt different particle shapes to % , tin 27 wt %, copper 13 wt % and other increase packing efficiency and elements reduce amount of Hg needed to obtain a workable mix. Setting Transformation • Alloy + liquid Hg = chemical reaction • Mixture – putty like consistency • Gradually becomes firmer • Working time – the Am can be carved • Initial set – it can’t be carved any more • Once fully set , they are hard , strong and durable Properties of Amalgam Dimensional Change• Dimensional change • Severe contraction leaves marginal gap – initial leakage• Strength • post-operative sensitivity – reduced with corrosion over time• Corrosion  Expansion leads to post operative sensitivity due to pressure• Creep on pulp ADA specification No.1 requires amalgam neither contract or expand more than 20 um/cm Measured at 37 deg between 5 mins and 24 hours after beginning of trituration. Phillip’s Science of Dental Materials 2003 5
  6. 6. 3/5/2012 Dimensional Change Effect of Moisture contamination• Net contraction • If a zinc containing low copper, or high copper – type of alloy amalgam is contaminated by moisture during • spherical alloys have more trituration or condensation, a large expansion contraction can take place. – less mercury • after 3-5 days – condensation technique • greater condensation = higher contraction • may continue for months reaching values < 400 um. – trituration time • overtrituration causes higher contraction • DELAYED EXPANSION or SECONDARY EXPANSION Phillip’s Science of Dental Materials 2003 Strength Strength• Develops slowly • High compressive strength – 1 hr: 40 to 60% of maximum • Low tensile and shear strength – 24 hrs: 90% of maximum • Therefore• Spherical alloys strengthen faster • Am MUST be supported by tooth structure – require less mercury • Am needs sufficient bulk ( 1.5 or more)• Weak in thin sections – unsupported edges fracture Phillip’s Science of Dental Materials 2003 Corrosion Creep • Reduces strength • Slow deformation of amalgam placed under a constant load • Seals margins – load less than that necessary to produce fracture • Gamma 2 dramatically affects creep rate – slow strain rates produces plastic deformation • allows gamma-1 grains to slide • Correlates with marginal breakdown Sutow J Dent Res 1991 Phillip’s Science of Dental Materials 2003 6
  7. 7. 3/5/2012 Clinical performance of Am Creep Restoration• Slow change in shape • Small amt of leakage under amalgam is unique• caused by compression • Properly inserted – leakage decreases as restoration ages• High-copper amalgams have • Corrosion products form along the interface creep resistance between the tooth and the resto – prevention of gamma-2 phase Minimal Mercury Technique Mercury/alloy ratio Eames Technique• Historically, the only way to achieve smooth and • Most obvious method for reducing mercury plastic mixes was to use mercury considerably in content is to reduce the original mercury/ alloy excess of that desirable in final restoration. ratio.• For convenional mercury –added systems, 2 • Sufficient mercury must be present in the original techniques were employed to remove excess mix to provide a coherent and plastic mass after mercury trituration1. Removal of excess mercury was accomplished by • But low enough so that the mercury content is at squeezing or wringing themixed amalgam in a an acceptable level without the need to remove squeeze cloth an appreciable amt during condensation2. Additional excess mercury was worked to top • Mercury content of finished should be about 50% during condensation of each increment wt% with lesser amt for spherical alloy Proportioning Proportioning• Recommended mercury / alloy ratio for most • Mercury / alloy dispensers modern lathe cut alloy is approx 1:1 or 50% • Preweighed pellets or tablets mercury • Liquid mercury dispenser spherical alloys its closer to 42% mercury• Proper proportioning = proper mix 7
  8. 8. 3/5/2012 Proportioning Trituration• Disposable amalgam capsules• Preportioned mercury Trituration• OBJECTIVEs : • Sphrerical or irregular low copper alloy – low speed• To provide a proper amalgamation of mercury and • High copper – high speed alloy• Achieve a workable mass at a minimum time • AMALGAMATOR Speed:• Reduce particle size leading to faster and more • Low – 3200-3400 cycles/min complete amalgamation • Medium – 3700-3800 cycles/min • High – 4000-4400 cycles/min• Capsules serves as mortar • INCREASED TRITURATION TIME = DECREASED• a cylindrical metal or plastic piston serves as the pestle WORKING AND SETTING TIME Dentist-Controlled Variables • Manipulation – trituration – condensation – burnishing – polishing 8
  9. 9. 3/5/2012 Trituration Mercury content • Mixing time • Sufficient mercury should be mixed with the – refer to manufacturer alloy to coat the alloy particles and to allow a recommendations thorough amalgamation. • Overtrituration – “hot” mix • Each particle of the alloy must be wet by the • sticks to capsule mercury; otherwise a dry , granular mix results – decreases working / setting time – slight increase in setting contraction • Any excess of mercury left in the restoration • Undertrituration can produce a marked reduction in strength – grainy, crumbly mix  Properly triturated – warm, smoth- max strength , smooth Phillip’s Science of Dental Materials 2003 Condensation Hand Condensation • GOAL: • Never touch with bare hands • To compact the alloy into the prepared cavity • Gloves so that greatest possibitlity of density is attained • Immediatley condensed once inserted in the cavity • Mercury rich layer is brought to the surface of the restoration, so that successiv elayers bond • With sufficient pressure to each other • Ave force applied: 13.3-17.8 N or (3-4 lb) • A fresh amalgam mix should be condensed within 3-4 mins Condensation Carving and Finishing• All amalgams except spherical alloys are • Reproduce proper tooth anatomy condensed by small condensers to reduce voids • Immediately after condensation • After carving = SMOOTHED by.. BURNISHING• Spherical alloys: large increments and condensers to fill entire cavity. • Burnish the surface and margins • After , it will still be rough at a microscopic level • FINAL POLISHING – after 24 hours 9
  10. 10. 3/5/2012 Side Effects of mercury Allergy• Am restoration is possible bec of mercury. • Antibody – antigen reaction • Itching,• The use of mercury has raised concerns as • Rashes well as alleged side effects that may be • Sneezing sustained by patients who received amalgam • Difficulty in breathing restorations • Swelling • Contact Dermatitis or Coombs’Type IV hypersensitivity • But these are experienced by less tha 1% of treated population. Toxicity Toxicity• It is still thought that mercury toxocity from • The most significant contribution to mercury dental restoration is cause of certain undiagnosed assimilation from dental amalgamis illnesses • VAPOR PHASE • Encounter is brief• And a real hazard may exist for dentists and • Mercury vapor amt – NO EFFECT level dental assistants when mercury vapor is inhaled • The threshold value for mercury industry workers- during mixing and placement of amalgam. • 350 -500 ug per dya ( 40 hr /wk)• Improvements in encapsulation technology, scrap • Patients get far below the values by US federal got storage, elimination of carpets and other mercury • Max level occupational exposure (safe) 50 um per retention sites cubic meter of air per day Potential hazards form mercury can be reduced by:• Mercury in blood • Well ventilated Operatory• Patients w/ Am – 0.7 ng/ml• Patients w/o Am- 0.3 ng/ml • Well sealed containers ( Am scraps, capsules)• 1 saltwater meal per wk raised mercury level in blood : • Proper disposals• From 2.3 to 5.1 ng/ml • Spilled mercury- cleaned up as soon as posiible• Daily normal intake of Hg:• 15 um – food • Mercury suppressant powders• 1 ug – air • If comes in contact with skin – wash with soap• 0.4 ug - water and H2O 10