Dental Amalgam.pdf

Science of Dental Materials Direct Restorative Materials DENTAL AMALGAM  Amalgam Terminology Amalgam: An alloy containing mercury (Hg) as the major ingredient Dental Amalgam: An alloy of Mercury with Silver, Tin, Copper (may also contain Zinc, Palladium, Indium...

Science of Dental Materials Direct Restorative Materials DENTAL AMALGAM  Amalgam Terminology Amalgam: An alloy containing mercury (Hg) as the major ingredient Dental Amalgam: An alloy of Mercury with Silver, Tin, Copper (may also contain Zinc, Palladium, Indium, Selenium to improve handling and clinical performance)  Amalgam Terminology Dental Amalgam Alloy: An alloy of silver, copper, tin and other elements, formulated in form of powder particles or compressed pellet, before mixing with mercury Amalgamation: The process of mixing liquid mercury with one or more metals or alloys to form amalgam  Amalgam Alloys Main Ingredients Silver Tin Copper Other Ingredients Zinc Indium Palladium Platinum Concept of Amalgam  WHY AMALGAM? 1. Restoration of high stress bearing areas 2. Long clinical survivability 3. Adequate resistance to fracture 4. Maintenance of anatomical form 5. Easy to insert & not overly technique sensitive 6. Microleakage prevention after a period of time  Limitations of Dental Amalgam Silver coloured fillings limited to posterior teeth Subject to corrosion Creep causes marginal breakdown Mercury toxicity Classification of Amalgam Alloys Based on 1. Shape of the Alloy Particles 2. Amount of Copper Present 3. Amount of Zinc Present Classification based on Particle Shape 1. Lathe cut or Irregular Alloys 2. Spherical Alloys Classification Based on Copper Amount 1. Low Copper Lathe cut or Spherical 2. High Copper Admixed Single Composition Composition of Low & High Copper Amalgam Alloys Low Copper Alloys High Copper Alloys Silver (Ag) 69.4 % Silver 60 % Tin (Sn) 26.2 % Tin 27 % Copper (Cu) 2-5 % Copper 13-30 % Zn 0.8 % Zinc Less than 2 % Indium 0% Indium Less than 5 % Classification Based on Zinc Amount Zinc Containing Alloys Alloys containing zinc in excess of 0.01% Non-Zinc alloys Containing 0.01% or less zinc  Concept of Alloys & Phases Formed Alloys are combination of two or more elements, at least one of them is metal Metals are soluble in molten form. Based on the composition & temperature, solution of different metals results in; 1. Solid Solution 2. Eutectic Alloys & Intermetallic Alloys  Solid Solution If the two metals are completely soluble in solid state at atomic level, only one phase is formed (atoms of two metals located in the same crystal structure) Under microscope, grains resemble pure metal Most of the alloys used in dentistry are solid solution (gold alloys)  Eutectic & Intermetallic alloys When the two metals are not completely soluble, a complex alloy system results In solid state, a mixture of two or more phases forms At different compositions & temperatures, different phases exist In dental amalgam, silver-copper is a eutectic system Two phases, silver rich phase & copper rich phase Silver-tin is a intermetallic system  Melting Range of Alloys Due to the presence of different metals in alloys, there is a melting range Liquidus Above or at liquidus, all the mass is liquid Below liquidus, first solid forms Solidus Below or at solidus, all the mass is solid Above solidus, first liquid forms However, eutectic system have a melting point which is below the melting point of either of the component metals.  Phases in Dental Amalgam Phases in Amalgam Alloy Stiochiometric Formula & Set Amalgam γ Ag3Sn γ1 Ag2Hg3 γ2 Sn7-8Hg β Ag4Sn ε Cu3Sn η Cu6Sn5  Ag3Sn (γ) & Ag4Sn (β) in Amalgam Alloys Silver and tin make up the major portion of amalgam alloys present in both high copper and low copper amalgam alloys Alloy with 27% tin & 73% silver slowly cooled below 480°C, an intermetallic compound Ag3Sn (γ) formed When mixed with mercury, produce Ag 2 Hg 3 and Sn 7-8 Hg phases, forming dental amalgam of desired properties If conc. of tin is less than 26 %, Ag4Sn (β) phase formed which is a solid solution of silver and tin  Ag3Sn (γ) & Ag4Sn (β) in Amalgam Alloys In addition to phases formation after amalgamation, some silver-tin particles remain unreacted, acting as strong filler to strengthen amalgam  Influence of Ag-Sn on Amalgam Properties Larger or smaller quantities of tin in alloy effect final properties Tin concentration more than 26.8%, mixture of γ and tin-rich phase form Tin rich phase increases amount of tin-mercury (Sn7-8Hg), γ2 phase (weakest phase causes corrosion) High creep However amalgam shows less expansion on setting Silver Decreases creep Increases strength Increases the expansion on setting Increases tarnish resistance Decreases setting time Tin Controls the reaction between silver and mercury Without tin, reaction too fast and more setting expansion Reduces strength & hardness Reduce resistance to tarnish and corrosion  Silver-Copper Eutectic Added in high copper admixed amalgam alloy 71.9 wt% Ag & 29.1 wt % Cu Contains a copper rich phase and a silver rich phase, with crystal structure of pure copper and pure silver  Influence of Silver-Copper Eutectic on Dental Amalgam When mixed with mercury, react preferentially with silver- tin to produce Cu6Sn5 (η) phase Higher copper amount replaces Sn7-8 Hg (γ2 ) phase, giving high mechanical strength, creep & corrosion resistance  Zinc Acts as scavenger or deoxidizer during melting of alloy Unites with oxygen preferentially in molten form Formation of slag that can be removed Minimizes formation of other oxides and prevent oxidation Aids in manufacturing of amalgam alloy producing clean, sound casting Without zinc, amalgam is more brittle & less plastic during condensation & carving  Disadvantage of Zinc Addition Also causes delayed expansion of amalgam Improved manufacturing in oxygen free environment (presence of inert gas) can eliminate presence of zinc  Indium Decreases the amount of Hg required Decreases the mercury vapor during & after setting (oxides of indium formed on surface or due to lesser amount of Hg) Increases the wetting Low creep, lower early strength, but higher final strength than amalgam without indium  Palladium, Platinum Increases corrosion resistance & mechanical properties of the finished amalgam mass  Mercury Mercury is the only metal that is liquid at room temperature & pressure Freezing point −38.83 °C Boiling Pont 356.73 °C  Mercury Amalgam alloy powder mixed with liquid mercury Produce plastic mass that can be condensed in a cavity & carved to give anatomical shaped of tooth On setting, makes strong hard mass However, mercury & its compounds are known toxic agents, & have to be handled with care  Pre-amalgamated Alloys Majority of alloys do not contain mercury Sometimes upto 3 % mercury added in the alloys React more rapidly when mixed with mercury  Mercury Contamination Need to be pure for use in amalgam A surface layer of contaminants forms, interfering with setting reaction (Dull Surface) Highly reflective surface shows no contamination Mercury is triple distilled  Gallium-BasedAlloys Can be a substitute for mercury Becomes liquid at slightly above room temperature and can be alloyed with indium and tin Can be triturated with alloys for high-copper amalgam  Manufacturing of Amalgam Alloy Powder Two types Irregular or Lathe Cut Powder Atomized or Spherical Powder  1. Lathe Cut or Irregular Particles Metal ingredients heated, until melted and poured into mold to form ingot Different phases (γ, β, ε & η) are formed  Homogenizing Heat Treatment Rapid cooling makes cored structure of silver-tin alloy with non-homogeneous grains To produce more homogeneous distribution of Ag3Sn Ingot placed in oven & heated at 400°C (for 4 to 6 hrs)  Processing of Ingot Cooling of Ingot Slow cooling More amount of γ phase Rapid quenching Max amount of β Phase Ingot cut by placing in milling machine or lathe cut to be fragmented by a cutting tool Needle like chips formed, passed through sieve and ball milled to form proper size  Lathe Cut or Irregular Particles Particle size 60 to 120 µm in length 10-70 µm in width 10-35 µm in thickness  Aging Heat Treatment Stresses induced during cutting & ball-milling must be relieved (performance of amalgam becomes inconsistent Improve the shelf life of amalgam alloy Subjected to controlled temperature of 60 to 100°C for 1 to 6 hours  Atomized or Spherical Powder Spherical particles of low or high copper alloys Produced when all desired elements are melted together In molten stage, metallic ingredients form desired alloy  Spherical Particle Formation Liquid metal sprayed under high pressure of an inert gas through a fine crack in a crucible into a large chamber Fine spherical droplets of metal formed Given heat treatments and acid washed like lathe cut alloys  Atomization Inert gas & molten metal Spherical particles Amalgamation and Resulting Microstructure 1. Low Copper Amalgam 2. High Copper Amalgam 1. Admixed Alloy 2. Single Composition Alloy  Conventional Low Copper Amalgam  Amalgam alloy intimately mixed with mercury to wet the surface of particles  Amalgamation starts when liquid mercury contacts surface of silver-tin (β & γ phases) alloy particles  Silver and tin dissolve into the mercury  Mercury also diffuses into γ phase of alloy particles  Conventional Low-Copper Alloys γ = Ag3Sn Hg Unreacted alloy Ag-Sn Alloy Hg Strongest phase and Hg Sn Ag Ag Ag Sn corrodes the least Ag-Sn Sn Ag-Sn Alloy Alloy Mercury Forms 30% of volume of set amalgam  Amalgamation Mercury has limited solubility for silver (0.035 %) and tin (0.6 %) After solubility in mercury is exceeded, crystals of two metallic compounds precipitate out  Precipitation of γ1 γ1 = Ag2Hg3 Ag-Sn Alloy Acts as Matrix for unreacted alloy 1 2nd strongest phase Ag-Sn Ag-Sn Alloy Alloy Dominant phase 54 to 56 % volume (on average 60% of volume)  Precipitation of γ2 γ2 = Sn8Hg Ag-Sn Alloy Weakest and softest phase Corrodes fast, voids form Ag-Sn Ag-Sn Corrosion yields Hg which Alloy Alloy 2 reacts with more gamma () 11 to 13 % (on average 10% of volume) Volume decreases with time due to corrosion  Resulting Microstructure While γ1 and γ2 crystals are being formed, amalgam is soft and condensable As crystals grow Remaining mercury dissolves Crystals interlock and amalgam is hardened No longer condensable  Working Time Lapse of time between the end of trituration and when the amalgam hardens & is no longer workable  Resulting Microstructure The final product A composite of low copper amalgam containing unconsumed particles embedded in γ1 and γ2 phases Alloy Particles (β + γ) + Hg γ1 (Ag2Hg3) + γ2 (Sn7- 8Hg) + unconsumed Alloy Particles (β+ γ) Setting of Low Copper Amalgam + Hg + +  1 2  Characteristics of Phases in Low Copper Amalgam Physical properties of Hardened amalgam depends on; Phases present More Unconsumed Ag-Sn, stronger is amalgam γ2 Is the weakest phase Hardness of γ2 is approx. 10 % of γ1 γ2 is least stable in corrosion environment HIGH COPPER AMALGAM  High Copper Amalgam  High Copper Amalgam is the material of choice  Improved Mechanical Properties  Corrosion Characteristics  Better Marginal Integrity Two types 1. Admixed 2. Single Composition  Amalgam containing Admixed Alloy Copper rich phase in admixed amalgam Eliminates γ2 phase which is weakest and susceptible to corrosion Increased residual alloy particles & decrease in matrix amount Residual particles act as strong filler increasing the strength  Resulting Microstructure  η phase (Cu6Sn5) surrounds unconsumed silver-copper alloy particles  γ 1 phase forms simultaneously with η phase and surrounds both η covered silver-copper alloy particles and silver-tin lathe cut alloy particles  Resulting Microstructure Alloy Particles (β + γ) + Ag-Cu eutectic + Hg γ1(Ag2Hg3) + η (Cu6Sn5) + Unreacted Ag-Cu eutectic and unreacted Ag3Sn  Setting of Admix High Copper Amalgam + Hg + +  + spheres  1   Amalgam with Single Composition Alloy Each particle of these alloys has same chemical composition Alloy contains; Spherical Particles β (Ag4Sn), γ (Ag3Sn), ε (Cu3Sn) Greater amount of ε phase (Cu3Sn), finely dispersed within Ag3Sn phase Copper content is 13 wt% to 30 wt%  Amalgam with Single Composition Alloy  1 (Ag2Hg3) crystals grow binding together partially- dissolved  alloy particles  Ag-Sn Alloy  (Cu 6 Sn 5 ) crystals found as meshes of rod like cr ysta l s Ag-Sn Alloy Ag-Sn Alloy developed on surface of gamma 1 particles (Ag3Sn) and dispersed in the matrix Reduces creep Prevents 2 formation  Resulting Microstructure Ag3Sn + Cu3Sn + Hg Þ (Ag3Sn + Cu3Sn) + Ag2Hg3 + Cu6Sn5   Unconsumed 1  particles Admixed Vs Single Composition Alloy Difference from admixed amalgam Much larger η crystals are formed PROPERTIES OF AMALGAM 1. Dimensional Stability 2. Strength 3. Creep 4. Corrosion Resistance  Dimensional Stability ANSI/ADA Specification No.1 Amalgam should neither contract nor expand (-15 to +20 µm/cm) Contraction Expansion Marginal gap and Protrusion of filling from Microleakage cavity Secondary Caries Pressure on Pulp Plaque Accumulation Postoperative Sensitivity  Dimensional Changes Initial contraction, then begin to expand Contraction due to dissolution of particles and growth of γ1 crystals Continues as long as growth of γ1 phase γ1 Crystals impinge on each other, outward pressure produced, leading to expansion  Effect of Mercury on Dimensional Stability Higher mercury volume Results in expansion Mercury provides plastic matrix Reaction forming γ1 crystals can impinge upon one another, so more expansion After rigid matrix formed, no more expansion Low mercury/alloy ratio Contraction results Manipulative Process Effecting Dimensional Stability Increase in mercury consumption lead to contraction 1. Higher condensation pressure 2. Longer trituration time and use of smaller particle size  High Condensation Pressure Squeeze the mercury out of amalgam More contraction Longer Trituration Time And Use Of Smaller Particle Size More contraction Small particles have more surface area per unit volume More particles dissolving, silver enters solution faster, grow faster, consumption of mercury accelerated Dimensional Stability of Modern Amalgams Modern amalgams reveal a net contraction as compared to older amalgams Two reasons 1. Older amalgam contained large alloy particles & were mixed at high mercur y/alloy ratio with h an d trituration, so high expansion 2. High speed mechanical amalgamators used now, consume more mercury, so show more contraction  Postoperative Sensitivity Dimensional changes associated with postoperative sensitivity Amalgam do not adhere with tooth structure, so any contraction leads to interfacial gap During cavity preparation , cutting of dentin causes the pulpal fluid to flow outward Due to contraction in amalgam, interfacial gap fills with fluid. Any change in pressure of this fluid causes postoperative sensitivity Spherical particles may leak out, making uneven texture of amalgam next to cavity walls, show more sensitivity than lathe cut How to Overcome Postoperative Sensitivity? 1. Use of dentin bonding agents To seal dentinal tubules before placement of amalgam restoration 2. Use of cavity varnish on cavity walls, against which amalgam is condensed also produce good marginal seal High Copper Admixed Single Composition Lathe Cut Low Copper  Delayed Expansion or Secondary Expansion Zinc containing low copper or high copper amalgam By contamination with moisture during trituration Hydrogen produced by action of zinc and water, collects within restoration leading to expansion and internal pressure Zn + H2O ZnO + H2 Expansion starts after 3 to 5 days and continues for months STRENGTH OF DENTAL AMALGAM  Strength  Highly resistant to compressive stresses  Amalgam is viscoelastic, high loading rate gives high strength  However also brittle, so rapid stress application does not produce plastic deformation  Weaker in tension and shear  Susceptible to marginal breakdown  Good resistance to abrasion  Strength of Amalgam Silver-mercury and tin-mercury act as matrix to hold unreacted particles If only smaller amount of γ1 & γ2 phases formed required to hold particles Higher is the strength Effect of Mercury on the Strength High mercury content left in mass Favors formation of matrix phases rather than unconsumed particles More γ2 and γ1 phase than γ phase Weaker is the amalgam  Effect of Mercury Content For either high copper admixed or low copper amalgam Increase in mercury content more than 54 %, strength is reduced Optimum properties produced for amalgams having 44-48 % mercury Those proportioned at more than 50% mercury, necessary to reduce the level at manipulation Use of Lesser Amount of Mercury However mercury should wet particles, otherwise dry, granular mix results, resulting pitted surface causing corrosion  Effect of Particle size on Strength Smaller sized particles increase surface area per unit volume of powder Require more mercury to form acceptable amalgam Favored technique Small average particle size (modern powder size 15 to 35 µm) To produce more rapid hardening of the amalgam Great early strength Lathe Cut Particles Spherical Alloy Particles When packed have more Give good packing leaving voids or spaces in between less space & wet easier with & higher surface area mercury and have less Require more mercury to surface area fill the spaces Require lesser amount of Amalgam containing lathe mercury cut or mixture of lathe cut More plastic and spherical tend to resist condensation Tensile and Transverse Strength Tensile strength value of amalgam lower than compressive strength Week in thin sections and unsupported edges readily fracture As brittle in nature, need adequate support from surrounding tissue Strength Of Different Phases In Low Copper Amalgam Strongest to weakest Ag3Sn (γ) Ag2Hg3 (γ1) Sn8Hg (γ2) Voids Strength of Different Types of Amalgam Spherical particles and copper-enriched alloys develop more strength more rapidly than conventional lathe cut martials  Effect of Amalgam Hardening Rate 1 hour strength of amalgam is only 6% of the compressive strength Minimum requirement is 80 MPa Patient may bite leading to fracture Always instruct the patient not to bite for 8 hours after placement (amalgam gains 70% strength by that time)  One Hour Strength of Dental Amalgam Single composition alloy have highest 1 hour strength More than 250 Mpa So reduce the possibility of premature fracture by application of high occlusal load by the patient Lowest 1 hour strength of low copper alloys 45 MPa Comparison Of Mechanical Properties Of Lathe-cut Amalgam With Tooth  Effect of Trituration on Strength Depends upon type of amalgam alloy, the trituration time, speed of amalgamator Undertrituration decreases the strength  Effect of Condensation on Strength Greater the condensation pressure especially in lathe cut alloys Expresses mercury out, so high strength In spherical alloys, there is lesser amount of mercury So even with lighter pressure, produce high strength  Effect of Porosity Voids and porosity effect compressive strength of set amalgam Decreased plasticity due to delayed condensation or undertrituration Greater porosity and less strength Increased condensation pressure Adaptation at margins Low number of voids CREEP IN DENTAL AMALGAM  Creep Static Creep Time dependent deformation subjected to a constant stress Dynamic Creep Plastic deformation in a material when the applied stress is fluctuating such as fatigue type stress (Masticatory forces) Creep Time dependent plastic deformation of materials that are used at temperature close to their melting point Melting point of major phase in amalgam i.e γ1 has a melting point of 400 K Used at mouth temperature of 310 K So amalgam shows creep  Static Creep in Amalgam C a u s e s t h e a m a l ga m to f l o w, s o unsupported amalgam protrudes from cavity margin Weak Edges Marginal deterioration Possible ingress of caries Prone to corrosion  Marginal Breakdown Failure at edges where material breaks off called Ditching Creep in Amalgam  Influence of Microstructure on Creep γ2 phase increases creep rate More than 1.0 % creep shows the presence of γ 2 phase γ 2 phase allows the sliding of γ 1 phase, so more creep in low copper amalgam Creep in High Copper Amalgam Lower creep rate less than 1.0 % in high copper amalgam Especially in single composition, as Ƞ rods act as barrier to deformation of γ1 phase Small quantities of other metal i.e palladium in high copper alloys show less creep  Effect Of Manipulative Measures On Creep Low mercury/alloy ratio and high condensation pressure for lathe cut or admixed alloy Decreased creep Creep in Amalgam  Amalgam Compressive Compressive Creep % Tensile Strength MPa Strength MPa Strength (1 hr) (7 days) MPa Low Copper 145 343 2.0 60 Admix 137 431 0.4 48 Single 262 510 0.13 64 Composition TARNISH & CORROSION IN DENTAL AMALGAM  Corrosion Progressive destruction of metal by chemical or electrochemical reaction with its environment Effects the structure and mechanical properties Damage Caused by Amalgam Corrosion Poor appearance of restoration Increased porosity Reduced marginal integrity leading to ditching initially Loss of strength Release of metallic products into oral environment Corrosion in Different Phases Different phases with different corrosion potential Ag2Hg3 (γ1) (Highest corrosion resistance) Ag3Sn (γ) Ag3Cu2 Cu3Sn (ε) Cu6Sn5 (η) Sn7-8Hg (γ2)  Effect of Phases on Corrosion Sn7-8Hg (γ2 ) Phase is most electrochemically reactive and readily forms anode in an electrolytic cell Breaks down to give tin containing corrosion products and mercury Excess mercury will decrease strength Less corrosion in copper rich γ2 free amalgam In high copper, Copper-tin phase may act as anode  Corrosion Products in Low Copper Amalgam Most common corrosion products in traditional amalgam Oxides and chlorides of tin (SnO, SnO2, Sn4(OH)6Cl2) Found at tooth-amalgam interface or within the bulk of older amalgam restorations Less commonly found in high copper amalgam Phase is most anodic of the phases present  Corrosion Products in High Copper Amalgam Copper containing corrosion products also found in high copper Cu2O, CuCl2, 3Cu(OH)2, CuCl, CuSCN However, corrosion process is limited as Ƞ phase in high copper amalgam is less susceptible to corrosion than γ2 phase of low copper amalgam  Benefit of Corrosion in Amalgam Corrosion products may seal the marginal gap Inhibit the ingress of oral fluids and bacteria  Tarnish Discoloration of a metal surface when a sulfide, oxide, chloride or other chemicals cause a thin film to form Integrity of alloy is not effected No change in mechanical properties Dental amalgam tarnishes due to the formation of a layer of sulphide on surface  How to Stop Tarnish & Corrosion in Amalgam Restoration? Tarnish can be removed by polishing the surface of amalgam restoration If polishing fails to restore, means that corrosion has occurred Only clinical solution is to replace the restoration  Galvanism Presence of metallic restorations in the mouth may cause a phenomenon, called galvanism Combination of dissimilar metal in physical contact (two adjacent restorations e.g. amalgam and gold inlay) Difference in potential These restorations in combination with saliva (acts as electrolyte) make up electric current When brought up in contact, the cell is short-circuited Patient feels pain and anodic restorations may corrode & release of free mercury The Galvanic Cell Manipulation of Amalgam  Factors Affecting The Success Of Amalgam Restorations 1. Cavity Preparation 2. Selection of Alloy Based on composition and the form in which alloy is available 3. Dental mercury (free of any impurity) Arsenic as contaminant, lead to pulpal damage  Factors Affecting The Success Of Amalgam Restorations Manipulative variables (a good modern dental alloy can be manipulated so that restoration lasts for, on Avg. 12 to 15 years) 1. Mercury / Alloy ratio 2. Trituration Method 3. Consistency of the Mix 4. Condensation 5. Carving and Finishing  Mercury/Alloy Ratio Low copper lathe cut alloys 1:1 or 50 % mercury Spherical Alloys 42 % Mercury (requires less mercury)  Mercury % varies from 43 to 54 %  Mercury/Alloy Ratio Excessive mercury has deleterious effects on physical and mechanical properties of amalgam Too low mercury content Mix will be dry and grainy Insufficient matrix to cohesively bond the mass Impair the strength of high copper amalgam Less corrosion resistance  Manipulative Procedures Employed to Reduce Mercury Left In Restoration 1. Squeezing or wringing mixed amalgam in cloth before insertion into cavity 2. Mercury worked to top during condensation and excess removed as mercury restoration build up  In both the above methods, no control on the amount of mercury removed  Eames Technique Best way to reduce mercury in the restoration is to reduce the original mercury/alloy ratio A l l oys d e s i g n e d fo r m a n i p u l at i o n w i t h re d u c e d mercury/alloy ratios; Minimal mercury technique or Eames technique  Proportioning Parts by weight of mercury and alloy e.g. 1:1 Or Percentage by weight of mercury & alloy e.g 1:1 means 50% mercury and 50% alloy Should be exact as minimum mercury used in Eames technique  Proportioning 1. Volumetric dispensers 2. Disposable capsules containing pre-proportioned mercury and alloy  Mercury And Alloy Dispensers Pre-weighed pellets or tablets Individual tablet uniform in weight Accurate mercury dispenser is required Mercury in liquid form measured by volume  Use of Mercury Dispenser Dispenser held vertical (45 tilt may change m/a ratio) Dispenser should be half filled (otherwise weight of mercury dispensed may be erratic) Free of contaminants (if present block the orifice of device)  Advantages of Volumetric Dispensers Less expensive than capsules Only fine grained alloy can be used More freedom in the alloy to mercury ratio Attractive for those who want more wet mix initially Sufficient plastic mix allow proper amalgamation and handling Good condensation technique to get rid of excess mercury  Pre-proportioned Capsules Containing pre-proportioned mercury and alloy Alloy in pellet form or pre-weighed portion of powder Appropriate quantity of mercury physically separated from powder using a membrane  Advantages Of Pre-proportioned Material 1. Eliminates chances of mercury spills during proportioning 2. Reliable mercury/alloy ratio 3. Clean mercury free of dust (dirty mercury does not react as well with silver alloy) However, More expensive & minor adjustment can not be made in mercury/alloy ratio  Types of Amalgam Capsules Reusable Capsules Disposable Capsules  Structure of Reusable Capsule Reusable Capsule Available with friction fit or screw cap lids Lid should be properly fit, otherwise fine mist of mercury is sprayed out of capsule  May be inhaled, or change mercury/alloy ratio Should be free of previous mix when used again  Capsule-Pestle Combination Pestle may be plastic or metal Size, shape and weight of pestle is important Generally, diameter and length of pestle should be less than the dimensions of capsule Using too large pestle will give non-homogenous mix If pellet form of alloy used, pellet or piece of pellet may remain wedged between capsule wall and pestle Capsule with Pestle Reusable Capsules Dispensing of Mercury & Alloy into Reusable Capsule  Disposable Capsules No need of dispensing the mercury and alloy Less chances of mercury loss  Activation of Disposable Amalgam Capsules Older types of capsules required activation during trituration Newer types are self activating capsules Automatically release mercury into the alloy chamber during 1st few oscillations of amalgamator Premeasured Capsules Requiring Activation Mercury & Pestle Alloy Activation Pressing the Plunger force mercury and pestle into the lower chamber  Size of Mix Manufacturers supply capsules containing 400, 600, or 800 mg of alloy with appropriate amount of Hg Amount is sufficient for most restorations 1200 mg also available if larger amount required for severely broken tooth  Trituration Objectives 1. Provide proper amalgamation of mercury and alloy 2. Alloys are covered with a layer of oxide  Oxide layer removed by abrasion during trituration for mercury to penetrate 3. Attain correct consistency of mix  Manual Trituration Procedures Alloy + Hg mortar + pestle manual mixing  Mechanical Trituration Procedures Powdered alloy + Hg capsule + pestle amalgamator Pelleted alloy + Hg capsule + pestle amalgamator  Mechanical Trituration Preproportioned alloy and mercury dispensed in capsule secured in arms of machine Arms oscillate at high speed moving the capsule back & forth to accomplish trituration in usually less than 20 sec. Amalgamators Holder or arms to hold capsule Capsule Housing placed over capsule area to confine lost mercury from capsule Controls for s p e e d and duration of mixing alloy and mercury Advantages of Mechanical Trituration A uniform and reproducible mix produced Shorter trituration time Greater alloy/mercury ratio can be used  Speed of Mechanical Trituration No exact mixing time recommended Wide variety of amalgamators, difference in speed & oscillation pattern & capsule design Spherical or irregular low copper triturated at slow speed (low energy) High copper require high speed (high energy) 1. Low speed amalgamators 3200 to 3400 cpm 2. Medium speed amalgamators 3700 to 3800 cpm 3. High speed amalgamators 4000 to 4400 cpm  Coherence Time (tc) Minimum mixing time required for amalgam to form a single coherent pallet To avoid undertrituration or overtrituration To achieve good compressive strength, low creep and dimensional stability A voltage regulator controls the speed of mixing Manufacturers recommend the time and speed for different alloys or preproportioned capsules and amalgamators  Time of Mechanical Trituration Spherical alloys require less amalgamation time than do lathe cut alloys Increased trituration time or speed Shorten the setting or working time Normally 5-20 sec  Consistency of Mix Three mixes different in physical appearance resulting from variations in conditions of trituration of alloy and mercury 1. Under-triturated mix 2. Normal Mix 3. Over-triturated Mix  Under-Triturated Mix Appears dull and crumbly Mix will be weak Rough surface after carving Reduced strength & Susceptible to tarnish  Normal Mix Appears shiny and separates in a single mass from capsule Properly triturated High strength, high dimensional stability and smooth carved surface  Over-triturated Mix Appears soupy Tends to stick to the inside of capsule Low strength  Overtrituration Increase in reaction rate Working time of all types of amalgam decreases High contraction Strength of spherical alloys decreases with overtrituration due to over formation of γ1 & η products High copper admixed amalgam also show decreased strength High creep  Undertrituration Mercury does not completely wet the outer surface of amalgam particles No reaction between mercury and alloy over the entire surface of particle Mass remains soft, so increases the working time Reduced compressive and tensile strength due to voids & insufficient formation of γ1 & η products to hold particles Lowers the creep Poor corrosion resistance Effect of Trituration on Dimensional Stability Prior to the introduction of capsules and amalgamators Traditional amalgam contained large particles and were hand triturated Slight expansion when set Effect of Trituration on Dimensional Stability High speed mechanical amalgamators, low mercury/alloy ratio and high condensation pressure Reduce the amount of mercury in the mix Favor contraction CONDENSATION  Condensation Goal of Condensation 1. Compact the alloy into prepared cavity until proper density is achieved 2. Removal of excess mercury from the mix (in case of low copper alloys) 3. Fewer voids  Re s u l t s i n i n c re a s e i n st re n gt h o f a m a l ga m , l o w dimensional changes and reduction in creep  Condensation Methods 1. Hand Condensation 2. Mechanical condensation 3. Ultrasonic Condensers  Hand Condensation More common method Different sizes and shapes of hand condensers  Size & Shape of Condensers Smaller condensers (2 to 3 mm diameter) are more effective (exert more pressure) used for low copper amalgam to remove excess mercury Larger condensers exert lower force Required for spherical amalgam as these contain less mercury & is more plastic  Hand Condensation Should not touch with bare hands to avoid contact with free mercury Condensed in small increments, mercury brought to top of each increment and is removed After condensation of each increment, surface should be shiny If large cavity, prepare new mix because original one loses its plasticity Mechanical & Ultrasonic Condensation Mechanical condensers use tapping or vibrating motion Exert high load with high magnitude of movement May damage the tooth (cuspal fracture) Ultrasonic condensers discouraged Increase the local heat of amalgam Gently increase mercury evaporation from setting amalgam  Condensation Pressure Smaller is the condenser, greater the pressure is exerted & vice versa Increasing pressure from 3 to 7 MPa increases compressive strength 66.7 N force is recommended To ensure maximum density and adaptation to cavity walls  Results of Delayed Condensation Should be performed immediately after mixing & before amalgam sets Any delay (especially in zinc containing alloys) results in; 1. Amalgam may have attained some set 2. Condensation of partially set material fractures and breaks up the matrix 3. Delayed expansion of 100 to 200 µm/cm 4. Weaker mass due to increase in mercury content and creep  Overpacking Cavity overpacked with amalgam & carved Gives a chance to control the final shape and occlusion more closely Surface layers contain more mercury & so can give inferior properties Carving Objectives To remove the mercury rich layer from surface To rebuild the anatomy of the tooth Re-establishing contact with the opposing dentition  Carving and Finishing Started when amalgam is hard enough to resist carving instrument Start at 2 to 3 min after mixing & cease as the amalgam hardens (5 to 10 min)  Carving If started too early, plastic amalgam may be pulled from margins Too deep carving or when the amalgam is set Bulk of amalgam at marginal area reduced May fracture at margins under masticatory stress  Occlusal Contacts If the patient taps his teeth together or moves from side to side in contact Any areas of contacts show up as bright burnished spots Spherical amalgam easier to carve than lathe cut Fine grained products easier to carve than coarse-grain.  Burnishing After carving, surface and margins are smoothened by burnishing to remove scratches and pits Occlusal anatomy burnished using ball burnisher Burnishers  Finishing & Polishing A well finished and polished restoration Retain its surface appearance Easier to keep clean Rough surface contains microscopic pits in which acids and food particles accumulate Pits encourage galvanic action on the surface leading to tarnish or corrosion  Finishing & Polishing For low copper and high copper admixed amalgam Performed after 24 hours during 2nd appointment due to low early strength Patient is cautioned not to bite on restoration Single composition high copper have about twice as high strength as that of low copper and high copper admixed Finishing may be done at the first appointment  Final Finishing Rubber polishing cup and extremely fine polishing or prophylaxis paste Temperature above 60°C cause release of mercury rich layer on surface which is weak and leads to failure  Overview of Manipulation Placement and Carving Burnishing Polishing TIME Condensation Onset of Onset of Onset of End of 24 hours MIXING WORKING SETTING SETTING Selection / Proportioning / Amalgamation / Manipulation / Polishing  Advantages of Amalgam High Mechanical Strength Adequate resistance to fracture Maintain anatomical form Long term clinical survival Decreased marginal leakage as restoration ages Formation of corrosion products at interface  Disadvantages of Amalgam Aesthetics. Does not match tooth colour Does not bond to tooth structure Corrosion Mercury toxicity  Comparison with Resin Composite Composites are More Aesthetic More technique sensitive Placed with less removal of tooth structure Thermal Insulation No corrosion MERCURY TOXICITY WITH DENTAL AMALGAM  Biocompatibility of Mercury Concerns on use of Mercury in oral environment for more than 170 years 200 million amalgams inserted in USA & Europe every year Biocompatibility issues for patients having amalgam restorations Allergy Toxicity Allergy Antigen antibody reaction Itching, rashes, sneezing, difficulty in breathing, swelling With Dental Amalgam Coombs’ Type IV Hypersensitivity reaction Toxicity Ability of a material to cause; Injury to Biological tissues Improper biochemical function Organ Damage Cell Destruction to Death  Sources of Mercury Exposure to mercury can occur from different sources Diet (Sea food) Water Air (Coal burning, volcanoes) Occupational Exposure (making batteries, thermometer, fluorescent lamps) Amalgam Restorations  Sources of Mercury WHO estimate that Eating sea food once a week Urine mercury level raises 5 to 20 µg/L 2 to 8 times level of exposure from amalgam (1 µg/L)  Sources and Forms of Mercury 1. Organic compounds Most toxic form (Methyl and ethyl mercury) Methy l me rc u r y a bs o r b e d i n wate r f ro m a i r converted to methyl mercury by bacteria and is ingested by fish) 2. Mercury Vapor 3. Inorganic form (Least toxic) Inorganic silver mercury compound  Mercury Vapor Mercury is volatile at room temperature High vapor pressure (20 mg per cubic meter of air) 400 times the maximum level that is considered acceptable Has no colour, odor, or taste so cannot be readily detected More dense than water, so a small spill is significant  Mercury Vapor Released from amalgam during; Trituration Condensation Setting Polishing Removing Mastication and drinking of hot beverages  Mercury Vapor Under normal conditions, vapor pressure is reduced because Mercury covered with saliva Covered with sealant resin for several days Addition of indium (8% to 14% ) Fresh amalgams release more mercury as compared to 2 years old amalgam restoration  Amount of Vapor Inhalation Patient with amalgam restorations monitored for mercury vapor inhaled over 24 hr period 1.7 µg per day Patient with 8 to 10 amalgam restorations 1.1 to 4.4 µg per day Too low when compared to exposure value for workers in mercury industry i.e. 350 to 500 µg per day Maximum mercury concentration is at marginal area in amalgam restoration  Recommendations by OSHA Maximum safe occupational exposure: 50 µg of mercury per cubic meter of air per day Threshold Limit Value (TLV) given by OSHA 0.05 mg/m3 maximum amount of mercury vapor allowed at workplace All dental offices have to comply with this standard ADA estimated that 1 out of 10 dental offices exceeded safe level Routes of Mercury Entry into Biological System Metallic mercury absorbed through; Skin by direct contact Ingestion Inhalation Most common risk to dental personnel  Mercury in Blood & Urine Blood and serum mercury levels correlate to occupational exposure and diet Urine mercury level relates to amalgam Body cannot retain metallic mercury, passes it through urine Using radioactive mercury, amount of mercury in urine through dental amalgam can be estimated  Mercury in Urine Peak urine mercury level after 4 days of placing amalgam 2.54 µg/L After 7 days return to zero On removal of mercury Max. 4 µg/L Return to zero after a week Peak mercury urine levels are about twice as great when amalgam is removed than inserted  Mercury in Urine WHO estimate that urine level on eating sea food once a week raise mercury level to 5 to 20 µg/L 2 to 8 times that level of exposure from amalgam Neurological changes detected as urine mercury level exceed 500 µg/L  Mercury in Blood According to one study, Average mercury level in patients with amalgam 0.7 ng/mL compared with 0.3 ng/mL (nanogram permillilitre) in people with no amalgam Seafood raises raised average blood mercury level from 2.3 to 5.1 ng/mL  Exposure of Mercury To Dental Staff Dentists and assistants (nurses) are most effected Inhalation of mercury vapor during mixing, placement and removal, or due to mercury spills in dental office Exposure of Mercury To Dental Staff Very few cases of mercury toxicity reported in past few years Improvement in encapsulation technology Capsule design Scrap storage methods Elimination of carpets and other mercury storage sites SYSTEMIC EFFECTS OF MERCURY TOXICITY  Systemic Effects Neurological, Gastrointestinal & renal systems are commonly effected Mercury Vapor: Primary Neurologic Toxicity Organic Mercury: Most devastating to CNS Inorganic Mercury: Acute; Severe corrosive gastroenteritis, acute tubular necrosis Chronic: GIT, Nerologic & renal dysfunction  Effect on Developing Fetus Exposed to methyl mercury in uterus suffer various adverse effects Mental Retardation, Cerebral palsy, Deafness, Blindness Dysarthria (Speech disorder due to weakness or lack of coordination of speech muscles In adults, sensory & motor impairment is documented  Concentration of Mercury Leading to Toxic Systemic Effects Lowest dose of mercury that elicits toxic reaction is 3 to 7 µ g/Kg body weight 500µg /Kg body weight: Paresthesia (tingling of extremities) 1000µg/Kg body weight: Ataxia (Incoordination of muscle movement) 2000µg/Kg body weight: Joint pain 4000µg/Kg body weight: Hearing loss and death  Allergic Reactions Most likely physiologic side effect of dental amalgam C o n ta c t D e r m a t i t i s o r C o o m b s Ty p e I V hypersensitivity reactions Hyperemia, edema, vesicle formation, Itching Remote coetaneous reactions  Effect of Mercury on Teeth & Associated Structures Gingivitis Stomatitis Mercury penetration from restoration into tooth structure Can reach underlying Dentin or even pulp Reports of inflammatory reactions of dentin and pulp Mercury found in lysosomes of macrophages and fibroblats in some patients PRECAUTIONS TO AVOID MERCURY HAZARDS Precautions to Avoid Mercury Hazards 1. Well ventilated operatory 2. Excess mercury, waste, disposable capsules and amalgam removed during condensation Should be collected and stored in well-sealed containers 3. Proper disposal to prevent environmental pollution 4. No carpeting in dental office (Difficult to remove mercury) Precaution to Avoid Mercury Hazards 5. Amalgam scrap and materials contaminated with mercury should not be incinerated (heat treatment of waste) or subject to heat sterilization 6. If mercury spilled, should be cleaned as soon as possible Vacuum cleaners merely disperse mercury 7. Mercury suppressant powders are also helpful as temporary measure  Precaution to Avoid Mercury Hazards 9. Reusable capsule should have tightly fitting cap to avoid mercury leakage 10. If mercury comes in contact with skin, wash with soap and water 11. While grinding amalgam, water spray and suction should be used 12. Eye protection, disposable mask and glove should be used