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Dental Amalgam

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Dental Amalgam

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Dental Amalgam

  1. 1. Presentation by: Dr. Piyush Verma Dept of Pedodontics & Preventive Dentistry
  2. 2. Index  Introduction  History  Classification  Indications & contraindications  Advantages/disadvantages  Composition of amalgam & Amalgamation reactions  Manufacturing process  Properties of amalgam  Manipulation of amalgam
  3. 3. Index  Mercury toxicity & various health hazards  Recent advances  Repair of amalgam restorations  Clinical considerations  Amalgam wars  Conclusion
  4. 4. Introduction  Dental amalgam is an alloy made by mixing mercury with a silver tin alloy. Dental amalgam alloy is a silver tin alloy to which varying amount of copper and small amount of zinc has been added.  According to Skinner’s, amalgam is a special type of alloy in which one of its constituent is mercury. In dentistry, it is common to use the term amalgam to mean dental amalgam.
  5. 5. History  Amalgam -- First used by Chinese. There is a mention of silver mercury paste by Sukung (659AD) in the Chinese medic  1578-lshitichen used 100 parts if Hg, 45 parts of Ag and 100 parts of Sn  Liu Wen-Thai (1508) and Li Shih-Chen (1578) discussed its formulation; 100 parts of mercury to 45 parts of silver and 900 parts of tin, trituration of these ingredients produced a paste said to be as solid as silver. .
  6. 6.  Introduced in 1800’s in France alloy of bismuth, lead, tin and mercury plasticized at 100ºC poured directly into cavity  1819, Bell advocated the use of a room temperature mixed amalgam as a restorative material, in England  1826, M.Traveau is credited with advocating the first form of amalgam paste , in France.
  7. 7.  1833  Crawcour brothers introduced amalgam to US  powdered silver coins mixed with mercury  expanded on setting  1895  To overcome expansion problems  G.V. Black developed a formula for modern amalgam alloy  67% silver, 27% tin, 5% copper, 1% zinc
  8. 8.  Black’s formula was well accepted and not much changed for nearly sixty years.(1890-1963)  1946 - Skinner, added copper to the amalgam alloy composition in a small amount. This served to increase strength and decrease flow. 
  9. 9.  Traditional or conventional amalgam alloys predominated from 1900 to 1970.  1960’s - conventional low-copper lathe-cut alloy was introduced  1962 - A spherical particle dental alloy was introduced, by Demaree and Taylor
  10. 10.  The work of Innes and Youdeis (1963) has led to the development of high copper alloys.  Had longer working time, less dimensional change, easy to finish, set faster, low residual mercury, low creep & higher early strength  Added spherical silver copper eutectic alloy(71.9wt% Ag and 28.1wt%Cu)particles to lathe cut low copper amalgam alloy particles.  These alloys are called admixed alloys
  11. 11.  1971 – Johnson designed a spherical particle alloy having the composition 64% Ag, 26% Sn and 10% cu by weight, and exhibiting no Sn8Hg after amalgamation.  1973 - first single composition spherical alloy named Tytin (Kerr) a ternary system (silver/tin/copper) was discovered by Kamal Asgar of the University of Michigan  1980’s alloys similar to Dispersalloy and Tytin was introduced
  12. 12. Classification (Marzouk) I. According to number of alloy metals: 1. Binary alloys (Silver-Tin) 2. Ternary alloys (Silver-Tin-Copper) 3. Quaternary alloys (Silver-Tin-Copper-Indium).
  13. 13. II.According to whether the powder consist of unmixed or admixed alloys. Certain amalgam powders are only made of one alloy. Others have one or more alloys or metals physically added (blended) to the basic alloy. E.g. Adding copper to a basic binary silver tin alloy
  14. 14.  III. According to the shape of the powdered particles.  1. Spherical shape (smooth surfaced spheres).  2. Lathe cut (Irregular ranging from spindles to shavings).  3. Combination of spherical and lathe cut (admixed).  IV. According to Powder particle size.  1. Micro cut  2. Fine cut  3. Coarse cut
  15. 15.  V. According to copper content of powder  1. Low copper content alloy - Less than 4%  2. High copper content alloy - more than 10%  VI. According to addition of Nobel metals  Platinum  Gold  Pallidum
  16. 16.  VII. According to compositional changes of succeeding generations of amalgam.  First generation amalgam was that of G. V Black i.e. 3 parts silver one part tin (peritectic alloy).  Second generation amalgam alloys - 3 parts silver, 1 part tin, 4% copper to decrease the plasticity and to increase the hardness and strength. 1 % zinc, acts as a oxygen scavenger and to decrease the brittleness.  Third generation: First generation + Spherical amalgam – copper eutectic alloy.  Fourth generation: Adding copper upto 29% to original silver and tin powder to form ternary alloy. So that tin is bounded to copper.  Fifth generation. Quatemary alloy i.e. Silver, tin, copper and indium.  Sixth generation (consisting eutectic alloy).
  17. 17.  According to Presence of zinc.  Zinc containing (more than 0.01%).  Non zinc containing (less than 0.01%).
  18. 18. INDICATIONS OF AMALGAM  Class I and class II cavities.-moderate to large restorations.  As a core build up material.  Can be used for cuspal restorations (with pins usually)  In combination with composite resins for cavities in posterior teeth. Resin veneer over amalgam.  As a die a material.  Restorations that have heavy occlusal contacts.  Restorations that cannot be well isolated  In teeth that act as an abutment for removable appliances
  19. 19. INDICATIONS OF AMALGAM  Class 3 in unaesthetic areas eg.distal aspect of canine.especially if Preparation is extensive with minimal facial involvement  Class 5 lesions in nonesthetic areas especially when access is limited and moisture control is difficult and for areas that are significantly deep gingivally.
  20. 20. CONTRA INDICATIONS OF AMALGAM  Anterior teeth where esthetics is a prime concern  Esthetically prominent areas of posterior teeth.  Small –to-moderate classes I and II restorations that can be well isolated.  Small class VI restorations
  21. 21. Advantages  Ease of use, Easy to manipulate  Relatively inexpensive  Excellent wear resistance  Restoration is completed within one sitting without requiring much chair side time.  Well condensed and triturated amalgam has good compressive strength.
  22. 22. Advantages  Sealing ability improves with age by formation of corrosion products at tooth amalgam interface.  Relatively not technique sensitive.  Bonded amalgams have “bonding benefits”.  Less microleakage  Slightly increased strength of remaining tooth structure.  Minimal postoperative sensitivity.
  23. 23. Disadvantages  Unnatural appearance (non esthetic)  Tarnish and corrosion  Metallic taste and galvanic shock  Discoloration of tooth structure  Lack of chemical or mechanical adhesion to the tooth structure.  Mercury toxicity  Promotes plaque adhesion  Delayed expansion  Weakens tooth structure (unless bonded).
  24. 24. Composition of amalgam Conventional Amalgam Alloys: (G.V. Black’s: Silver- tin alloy or Low copper alloy).  Low copper alloys are available as comminuted particles (Lathe -cut and Pulverized) and spherical particles. Low copper composition:  Silver : 63-70%  Tin : 26-28%  Copper : 2- 5%  Zinc : 0-2%
  25. 25. Role of individual component Silver:  Constitutes approximately 2/3rd of conventional amalgam alloy.  Contributes to strength of finished amalgam restoration.  Decreases flow and creep of amalgam.  Increases expansion on setting and offers resistance to tarnish.  To some extent it regulates the setting time.
  26. 26. Tin:  Second largest component and contributes ¼th of amalgam alloy.  Readily combines with mercury to form gama-2 phase, which is the weakest phase and contributes to failure of amalgam restoration.  Reduce the expansion but at the same time decreases the strength of amalgam.  Increase the flow.  Controls the reaction between silver and mercury.  Tin reduces both the rate of the reaction and the expansion to optimal values.
  27. 27. Copper:  Contributes mainly hardness and strength.  Tends to decrease the flow and increases the setting expansion Zinc:  Acts as Scavenger of foreign substances such as oxides.  Helps in decreasing marginal failure.  The most serious problem with zinc is delayed expansion, because of which zinc free alloys are preferred now a days. Indium/Palladium: They help to increase the plasticity and the resistance to deformation.
  28. 28. HIGH COPPER AMALGAM ALLOY (COPPER ENRICHED ALLOYS)  To overcome the inferior properties of low copper amalgam alloy -- shorter working time, more dimensional change, difficult to finish, set late, high residual mercury, high creep & lower early strength, low fracture resistant  Youdelis and Innes in 1963 introduced high copper content amalgam alloys. They increased the copper content from earlier used 5% to 12%.  Copper enriched alloys are of two types: 1) Admixed alloy powder. 2) Single composition alloy powder.
  29. 29. I. Admixed alloy powder:  Also called as blended alloys.  Contain 2 parts by weight of conventional composition lathe cut particles plus one part by weight of spheres of a silver copper eutectic alloy.  Made by mixing particles of silver and tin with particles of silver and copper.  The silver tin particle is usually formed by the lathe cut method, whereas the silver copper particle is usually spherical in shape.
  30. 30. I. Admixed alloy powder: Composition:  Silver-69 %  Copper-13 %  Tin-17 %  Zinc-1 %
  31. 31. I. Admixed alloy powder:  Amalgam made from these powders are stronger than amalgam made from lathe cut low copper alloys because of strength of Ag-Cu eutectic alloy particles.  Ag-Cu particles probably act as strong fillers strengthening the amalgam matrix.  Total copper content ranges from 9-20%.
  32. 32. II. Single composition alloy (Unicomposition):  It is so called as it contains particles of same composition.  Usually spherical single composition alloys are used.  As lathe cut, high copper alloys contain more than 23% copper.
  33. 33. II. Single composition alloy (Unicomposition): 1. Ternary alloy in spherical form, silver 60%, tin 25%, copper 15%. 2.Quaternary alloy in spheroidal form containing Silver: 59%, copper 13%, tin: 24%, indium 4%.
  34. 34. AMALGAMATION REACTION/ SETTING REACTION Low copper conventional amalgam alloy  Dissolution and precipitation  Hg dissolves Ag and Sn from alloy  Intermetallic compounds formed Ag3Sn + Hg  Ag3Sn + Ag2Hg3 + Sn8Hg Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy Mercury (Hg) Sn Sn Sn Ag Hg Hg Ag Ag  1 2
  35. 35. Low copper conventional amalgam alloy  Gamma () = Ag3Sn  unreacted alloy  strongest phase and corrodes the least  forms 30% of volume of set amalgam Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy Mercury Ag Sn Sn Sn Ag Hg Hg Ag Hg
  36. 36. Low copper conventional amalgam alloy  Gamma 1 (1) = Ag2Hg3  matrix for unreacted alloy and 2nd strongest phase  10 micron grains binding gamma ()  60% of volume Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy 1
  37. 37. Low copper conventional amalgam alloy  Gamma 2 (2) = Sn8Hg  weakest and softest phase  corrodes fast, voids form  corrosion yields Hg which reacts with more gamma ()  10% of volume  volume decreases with time due to corrosion 2 Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy
  38. 38. Admixed High-Copper Alloys Initial reaction Ag3Sn + Ag-Cu + Hg Ag3Sn + Ag2Hg3 + Sn8Hg + Ag-Cu Ag-Sn Alloy Ag-Sn Alloy Mercury Ag AgAg Sn Sn Ag-Cu Alloy Ag HgHg   1 2
  39. 39. Final reaction Ag-Cu Alloy 1 Ag-Sn Alloy Ag-Sn Alloy 2  Sn8Hg + Ag-Cu Cu6Sn5 + Ag2Hg3 + Ag-Cu 1
  40. 40. Single Composition High-Copper Alloys Ag-Sn Alloy Ag-Sn Alloy Ag-Sn Alloy 1       Ag3Sn + Cu3Sn + Hg  Ag2Hg3 + Cu6Sn5 + Ag3Sn + Cu3Sn 1
  41. 41. Manufacturing Process Lathe-cut alloys  Ag & Sn melted together  alloy cooled  phases solidify  heat treat  400 ºC for 8 hours  grind, then mill to 25 - 50 microns  heat treat to release stresses of grinding
  42. 42. Manufacturing Process Spherical alloys  Atomizing process produces these different shapes.  First liquefying the amalgam alloy, it is sprayed through a jet nozzle under high pressure in a cold atmosphere.  If particles are allowed to cool before they contact the surface of chamber, they are spherical in shape.  If they are allowed to cool on contact with the surface they are flake shaped.
  43. 43. PROPERTIES: ADA specification No.1 for amalgam lists following physical properties as a measure of quality of the amalgam.  Creep  Compressive strength  Dimensional changes  Modulus of elasticity
  44. 44. Strength Compressive strength  Amalgam is strongest in compression and weaker in tension and shear  The prepared cavity design and manipulation should allow for the restoration to receive compression forces and minimum tension and shear forces.  The compressive strength of a satisfactory amalgam restoration should be atleast 310 MPa.
  45. 45. Compressive Strengths of Low-Copper and High Copper Amalgam Amalgam Compressive Strength (MPa) 1 h 7 day Low copper 145 343 Admix 137 431 Single Composition 262 510
  46. 46. Tensile strength  Amalgam is much weaker in tension  Tensile strengths of amalgam are only a fraction of their compressive strengths  Cavity design should be constructed to reduce tensile stresses resulting from biting forces  High early tensile strengths are important – resist fracture by prematurely applied biting forces
  47. 47. Product Tensile strength (Mpa) 15min 7 days LOW COPPER ALLOYS a) Lathe cut b) spherical 3.2 51 4.7 55 HIGH COPPER ALLOYS a) Admixed b) Unicompositional 3.0 43 8.5 56 Tensile strengths of amalgam
  48. 48. The factors affecting strength of amalgam are: 1) Temperature:  Amalgam looses 15% of its strength when its temperature is elevated from room temperature to mouth temperature  looses 50% of room temperature strength when temperature is elevated to 60OC e.g. hot coffee or soup.
  49. 49. 2) Trituration:  Effect of trituration on strength depends on the type of amalgam alloy, the trituration time and the speed of the amalgamator.  Either, under trituration or over-trituration decreases the strength for both traditional and high copper amalgams.  More the trituration energy used, more evenly distributed are the matrix crystals over the amalgam mix and consequently more the strength pattern in the restoration.  Excess trituration after formation of matrix crystals will create cracks in the crystals, lead to drop in strength of set amalgam
  50. 50. 3) Mercury Content:  Low mercury alloy content, contain stronger alloy particles and less of the weaker matrix phase, therefore more strength  Mercury is too less -- dry, granular mix, results in a rough, pitted surface that invites corrosion.  If mercury content of amalgam mix is more than 53-55%, causes drop of compressive strength by 50%.
  51. 51. 4) Effect of condensation:  For lathe-cut alloys Greater the condensation pressure, the higher the compressive strength Higher condensation pressure is required to minimize porosity and to express mercury from lathe-cut amalgam.  For spherical alloys Amalgams condensed with lighter pressure produce adequate strength.
  52. 52. 5) Effect of Porosity:  Can be due to  Under trituration, Particle shape, Insertion of too large increments into the cavity, Delayed insertion after trituration,  Non-plastic mass of amalgam.  Facilitate stress concentration, propagation of cracks, corrosion, and fatigue failure of amalgam restoration.
  53. 53. 6) Effect of rate hardening  Patient may be dismissed from the dental chair within 20 min, rate of hardening of the amalgam is of considerable interset  At the end of 20 min, compressive strength – 6% of the 1 week strength  ADA specification stipulates minimum compressive strength of 80 Mpa at 1 hr  Clinical significance -- Patient should be cautioned not to subject the restoration for high biting force for 8 hrs after placement– 70% of its strength is gained
  54. 54. Modulus of elasticity  High copper alloys tend to be stiffer than low copper alloys  When rate of loading increased, values of approx 62 Gpa have been obtained
  55. 55. Knoop Hardness  110 kg/mm2
  56. 56. DIMENSIONAL CHANGES:  When mercury is combined with amalgam it undergoes three distinct dimensional changes.  Stage -1: Initial contraction, occurs for about 20 minutes after beginning of trituration. Contraction results as the alloy particles dissolve in mercury. Contraction, which occurs, is no greater than 4.5 µcm.  Stage -2: Expansion- this occurs due to formation and growth of the crystal matrix around the unconsumed alloy particles.  Stage -3: Limited delayed contraction.
  57. 57. Factors that affect the dimensional changes: 1) Particle size and shape:  More regular the particle shape, more smoother the surface area.  Faster and more effectively the mercury can wet the powder particles and faster amalgamation occurs in all stages with no apparent expansion. 2) Mercury:  More mercury , more will be the expansion, as more crystals will grow.  Low mercury: alloy ratio favors contraction
  58. 58. 3) Manipulation:  During trituration, if more energy is used for manipulation, the smaller the particles will become , mercury will be pushed between the particles, discouraging expansion.  More the condensation pressure used during condensation, closer the particles are brought together; more mercury is expressed out of mix inducing more contraction.
  59. 59. Moisture contamination (Delayed Expansion):  Certain zinc containing low copper or high copper amalgam alloys which get contaminated by moisture during manipulation results in delayed expansion or secondary expansion  Occur 3-5 days after insertion and continues for months.  Zinc reacts with water, forming zinc oxide and hydrogen gases.
  60. 60. Complications that may result due to delayed expansion are:  Protrusion of the entire restoration out of the cavity.  Increased micro leakage space around the restoration.  Restoration perforations.  Increased flow and creep.  Pulpal pressure pain. Such pain may be experienced 10-12 days after the insertion of the restoration
  61. 61. Flow and Creep:  Time dependent plastic deformation  When a metal is placed under stress, it will undergo plastic deformation.  The high copper alloys, as compared with conventional silver tin alloys, usually tend to have lower creep values.
  62. 62. Factors influencing creep: A) Phases of amalgam restorations  Creep rates increases with larger 1 volume fraction and decreases with larger 1 grain sizes.  2 is associated with high creep rates.  In absence of 2, low creep rates in single composition alloy may be due to  phase which act as barrier to deformation of 1 phase.
  63. 63. B) Manipulations:  Greater compressive strength will minimize creep rates.  Low mercury: alloy ratio, greater the condensation pressure and time of trituration, will decrease the creep rate.
  64. 64. Corrosion Excessive corrosion can lead to:  Increased porosity.  Reduced marginal integrity.  Loss of strength.  Release of metallic products in to the oral environment.
  65. 65. Phases in decreasing order of corrosion resistance  Ag2Hg3  Ag3Sn,  Ag-Cu  Cu3Sn  Cu6Sn5  Sn7-8Hg.
  66. 66. Low copper amalgam system:-  Most corrodible phase is tin-mercury or 2 phase.  Neither the  nor the 1 phase is corroded as easily.  The corrosion results in the formation of tin oxychloride, from the tin in 2 and also liberates Hg. Sn7-8Hg + 1/202 + H2O + Cl- Sn4 (OH) 6 Cl2 + Hg Tin oxychloride
  67. 67.  Reaction of the liberated mercury with unreacted  can produce additional l and 2 (Mercuroscopic Expansion).  Results in porosity and lower strength.
  68. 68. The high copper admixed and unicomposition alloy :-  Do not have any 2 phase in the final set mass  The η phase formed has better corrosion resistance.  However,  is the least corrosion resistant phase in high copper amalgam  Corrosion product CuCl2.3Cu (OH)2 has been associated with storage of amalgams in synthetic saliva. Cu6Sn5 + 1/202 +H2O + Cl- CuCl2.3Cu (OH)2 + SnO.
  69. 69. Types of Corrosion: 1) Galvanic corrosion: Dental amalgam is in direct contact with an adjacent metallic restoration such as gold crown 2) Crevice Corrosion:  Local electrochemical cells may arise whenever a portion of amalgam is covered by plaque on soft tissue.  The covered area has a lower oxygen and higher hydrogen ion concentration making it behave anodically and corrode.
  70. 70. Stress Corrosion:  Regions within the dental amalgam that are under stress display a greater probability for corrosion, thus resulting in stress corrosion.  For occlusal dental amalgam greatest combination of stress and corrosion occurs along the margins.
  71. 71. MANIPULATION OF DENTAL AMALGAM
  72. 72. PROPORTIONS OF ALLOY TO MERCURY  Correct proportioning of alloy and mercury- essential for forming a suitable mass of amalgam  Some alloys require mercury – alloy ratios in excess of 1:1 (Eames technique)  whereas others use ratios of less than 1:1 with the percentage of mercury varying from 43% to 54%.
  73. 73.  Automatic mechanical dispensers for alloy & mercury have been used in the past  Capsules with pre proportioned amounts of alloy & mercury have been substituted
  74. 74. Cross section sketch of a disposable capsule containing amalgam alloy & mercury
  75. 75. SIZE OF MIX  Manufacturers commonly supply capsules containing 400, 600, or 800 mg of alloy and the appropriate amount of mercury.  For large size cavities - capsules containing 1200 mg of all0y are also available.
  76. 76. TRITURATION  Process of mixing the amalgam alloy particles with mercury  Originally, the alloy and mercury were mixed, and was triturated by hand with a mortar and pestle  Mechanical amalgamation saves time and standardizes the procedure.
  77. 77. Amalgamator
  78. 78. Mechanical amalgamators are available in the following speeds:  Low speed: 32-3400 cpm.  Medium speed: 37-3800 cpm.  High speed: 40-4400 cpm.  Spherical/irregular low-copper alloys – triturated at low speed  High copper alloys – high speed  Time of trituration on amalgamation ranges from 3-30 seconds. Variations in 2-3 seconds can also produce a under or over mixed mass.
  79. 79.  Over-trituration: Alloy will be hot, hard to remove from the capsule, shiny wet and soft.  Under-trituration: Alloy will be dry, dull and crumbly; will crumble if dropped from approx 30 cm.  Normal Mix: Shiny appearance separates in a single mass from the capsule. Under-trituration Normal Mix
  80. 80. Objectives of Trituration are:  To achieve a workable mass of amalgam within a minimum time  To remove the oxide layer  To pulverize pellets into particles, that can be easily attacked by the mercury.  To reduce particle size  To keep the amount of 1 or 2 matrix crystal as minimal as possible, yet evenly distributed
  81. 81. Mixing variables 1) Working time & dimensional change All types of amalgam, spherical or irregular – decreases with overtrituration Overtrituration – slightly higher contraction for all types of alloys
  82. 82. 2) Compressive & tensile strength  Irregular shaped alloys – increase by overtrituration  Spherical alloys -- greatest at normal trituration time
  83. 83. 3) Creep  Overtrituration increases creep  Undertrituration lowers it
  84. 84. Condensation  Refers to the incremental placement of the amalgam into the prepared cavity and compression of each increment into the others  Amalgam should be condensed into the cavity within 3 min after trituration.
  85. 85. Aims of condensation  Adapt amalgam to the margins, walls and line angles of the cavity.  Minimize voids and layering between increments within the amalgam.  Develop maximum physical properties.  Remove excess mercury to leave an optimal alloy: mercury ratio.
  86. 86. Purpose of Condensation  To get a continuous homogenous mass that is well adapted to all margins, walls and line angles.  Best carried out using hand instruments.
  87. 87. Hand condenser :  Should allows a operator to readily grasp it & exert a force of condensation  Size of condenser tip & direction & magnitude of the force placed, depends on the type of amalgam alloy selected
  88. 88.  Irregular shaped alloys – Condensers with relatively small tip, 1 to 2 mm High condensation forces in vertical direction As much mercury-rich mass as possible should be removed  Spherical amalgam alloys Condensers with large tips are used Condensed in lateral direction High copper spherical amalgams – vertical & lateral direction condensation with vibration  Condensation pressure – load of 15 lb is recommended to be applied to each increment
  89. 89. Mechanical Condensers:  Useful for condensing irregular shaped alloys when high condensation forces are required  Need was eliminated with the advent of spherical alloys  Tend to lead to unreliable condensation as well as generation of heat and mercury vapor, both of which are undesirable.
  90. 90. Ultrasonic Condensers:  Not recommended  Causes the release of considerable quantities of mercury vapor in the dental office
  91. 91. SPEED OF PLACEMENT  Once amalgam is triturated, phase formation commences and the setting reaction is underway.  Amalgam must be placed in a plastic state  No amalgam should be placed more than 3 minutes after the start of mixing.  Attempting to condense a partly set amalgam into a cavity will result in Poor adaptation, Reduced marginal seal and A weak restoration.
  92. 92. Burnishing First Burnish (Pre-carve Burnish)  Carried out using a large burnisher for 15 seconds  Use light force and move from the center of the restoration outwards to the margins.
  93. 93. Objectives of precarve burnishing :  Continuation of condensation, further reduce the size and number of voids on the critical surface and marginal area of the amalgam.  Brings any excess mercury to the surface, to be discarded during carving.  Adapt the amalgam further to cavosurface anatomy.
  94. 94. Carving  Using remaining enamel as a guide, carve gently from enamel towards the center and recreate the lost anatomy of the tooth.  Amalgam should be hard enough to offer resistance to carving instrument  A scarping or "ringing" (amalgam crying) should he heard.  If carving is started too soon, amalgam will pull away from margins.
  95. 95. Objectives of carving : To produce :  A restoration with no underhangs  A restoration with the proper physiological contours.  A restoration with minimal flash.  A restoration with adequate, compatible marginal ridges.  A restoration with proper size, location, extend and interrelationship of contact areas.
  96. 96. Final Burnish (Post carve burnishing)  Following carving, check the occlusion and carry out a brief final burnish.  Use a large burnisher at a low load and burnish outwards towards the margins  Improves smoothness  Heat generation should be avoided If temp raises above 60C, causes release of mercury accelerates corrosion & fracture at margins
  97. 97. Finishing & Polishing  Finishing can be defined as the process, which continues the carving objectives, removes flash and overhangs and corrects minimal enamel underhangs.  Polishing is the process which creates a corrosion resistant layer by removing scratches and irregularities from the surface.  Can be done using descending grade abrasive, eg. rubber mounted stone or rubber cups.  A metallic lusture, is always done with a polishing agent (precipitated chalk, tin or zinc oxide).
  98. 98. Objective of finishing and polishing :  Removal of superficial scratches and irregularities Advantages:  Minimizes fatigue failure of the amalgam under the cyclic loading of mastication  Minimizes concentration cell corrosion which could begin in the surface irregularities  Prevents the adherence of plaque
  99. 99.  Usually, 24 hours should pass after amalgam insertion before any finishing and polishing commences.  However, some new alloys can be polished after 8-12 hours still others require only a 30-minute wait after insertion.
  100. 100. RESISTANCE & RETENTION FORMS
  101. 101. Primary retention form Attained by:  Mechanical locking of inserted amalgam into surface irregularities to allow good adaptation  Preparation of vertical walls that converge occlusally
  102. 102. Primary resistance form  For tooth : Maintaining as much unprepared tooth structure as possible Having pulpal & gingival walls perpendicular to occlusal forces Having rounded internal prepartaion angles Removing unsupported & weakened tooth structure  Placing pins into the tooth as a part of final stage of tooth preparation
  103. 103. Primary resistance form  For amalgam :  Adequate thickness – 1.5 -2 mm in areas of occlusal contact, 0.75 mm in axial areas Marginal amalgam of 90 degrees or greater Box like preparation form  Rounded axiopulpal line angles in class II preparations
  104. 104. Secondary resistance & retention form  When insufficient resistance/retention forms are present in tooth, additional preparation is indicated  Such features include :  Placement of grooves, locks, coves, pins, slots or amalgam pins  Larger the tooth preparation, greater the need of secondary resistance & retention forms
  105. 105. BIO-COMPATIBILITY –MERCURY TOXICITY
  106. 106.  Amalgams have been used for 150 years  About 200 million amalgams are inserted each year in the United States and Europe  Concern -- mercury in dental amalgam may pose threats to the health of patients, to the health of dental care providers and to the environment.
  107. 107. Mercury is available in 3 forms:  Elemental mercury (liquid or vapor).  Inorganic compounds.  Organic compounds.
  108. 108.  ELEMENTAL MERCURY Liquid mercury:  Absorbed relatively poorly across skin or mucosa. Most mercury becomes charged (ionized) before it reaches the blood. Ionized mercury is excreted well through kidneys and urine. There is no known risk to patients from liquid mercury.
  109. 109.  ELEMENTAL MERCURY Mercury vapor: Less benign -- rapidly absorbed into the blood via the lungs , remains uncharged and therefore highly lipid soluble, for several minutes. Can cross the blood-brain barrier where it becomes charged and exists in extra cellular fluid of the brain and returns into the blood much more slowly.
  110. 110.  High tissue levels- can lead to impaired brain function, insanity and death may occur at 4000 g/kg.  Low tissue levels- can lead to restlessness, tremors, and loss of concentration.
  111. 111. Inorganic compounds of mercury  S0urce – Drinking water, food  Amalgam contains several different inorganic mercury compounds,  They are of low or very low toxicity and are apparently harmless when swallowed.  Poorly absorbed, do not accumulate in body tissues and are well excreted.
  112. 112. Organic compounds of mercury  Source -- Drinking water, food (sea food)  Some organic compounds of mercury are highly toxic at low concentrations  But none are known to form in the oral environment through dental amalgam use.
  113. 113. Source g Hg vapour g inorganic Hg g methyl Hg Atmosphere 0.12 0.038 0.034 Drinking Water --- 0.05 --- Food & Fish 0.94 --- 3.76 Food & Non-Fish --- 20.00 --- ESTIMATED DAILY INTAKE OF MERCURY
  114. 114. CONCENTRATIONS OF MERCURY  The Occupational Safety & Health Administration (OSHA) has set a TLV of 0.05 mg/m3 as the maximum amount of mercury vapor allowed in the work place.  Average Daily dose of mercury from dental amalgam for patients with more than 12 restored surfaces has been estimated at up to 3 g.
  115. 115. CONCENTRATIONS OF MERCURY Clarkson TW (1997) --  Lowest dose of mercury that elicits a toxic reaction – 3to7 g/kg body weight  Paresthesia -- 500 g/kg body weight  Ataxia -- 1000 g/kg body weight  Joint pain -- 2000 g/kg body weight  Hearing loss & death -- 4000 g/kg body weight
  116. 116. CONCENTRATIONS OF MERCURY Mercury release has been quantified for a number of procedures:  Trituration: 1-2g  Placement of amalgam restoration: 6-8 g.  Dry polishing: 44 g.  Wet polishing: 2-4 g.  Amalgam removal under water spray & high velocity suction: 15-20 g
  117. 117. CONCENTRATIONS OF MERCURY The release of mercury is:  Greater for low-copper amalgams, because of corrosion related loss of tin and increased porosity.  Greater from Unpolished surfaces  Increased by tooth brushing, which removes a passivating surface oxide film-although this re-forms rapidly.
  118. 118. Mercury in urine  Body cannot retain metallic mercury, but passes it through urine  Skare I et al (1990) – urine mercury level peak at 2.54 g/L 4 days after placing amalgam restorations, return to zero after 7 days On removal of amalgam, urine mercury levels reach a maximum value of 4g/L, return to zero after 7 days
  119. 119. Mercury in blood  Maximum allowable level of mercury in blood is 3 g/L  Chang SB et al(1992) showed that freshly placed amalgam restorations elevated blood mercury levels to 1 to 2 g/L  As with urine mercury levels, there is first an increase of around 1.5 g/L, which decreases in about 3 days
  120. 120.  Ott KH et al (1996) monitored blood mercury levels for 1 year, showed that patients with amalgams had lower than average blood mercury level (0.6 g/L ) than patients without amalgams (0.8 g/L )  Mackert JR et al(1997) indicated higher blood mercury levels in dentists, stated that -  elevated blood mercury levels may relate to mercury spills in the office Both blood & serum mercury levels seem to correlate best with occupational exposure, not with number of amalgam & length of time with amalgam in place
  121. 121. BIO-COMPATIBILITY –MERCURY TOXICITY Sensitivity to amalgam restorations  Skin lesions being more common than oral lesions.  An urticarial rash may appear on the face and limbs and this may be followed by dermatitis.  Long- term response -- oral lichen planus or lichenoid reactions with erosive areas on the tongue or buccal mucosa adjacent to an amalgam restoration.
  122. 122. BIO-COMPATIBILITY –MERCURY TOXICITY AMALGAM TATTOO
  123. 123. AMALGAM TATTOO Possible causes are:  Scraps of amalgam may fall into open surgical or extraction wounds.  Excess amalgam may be left in the tissues following sealing the apex of a root canal with a retrograde amalgam.  Pieces of amalgam may be forced into the mucosa.
  124. 124. Sources of Mercury Exposure in Dental Office:  Dental amalgam raw materials being stored for use.  Mixed but unhardened dental amalgam during triturations, insertion and intraoral setting.  Dental amalgam scrap that has insufficient alloy to completely consume the mercury present.  Dental amalgam undergoing finishing and polishing procedure.  Dental amalgam restoration being removed.
  125. 125. DENTAL MERCURY HYGIENE Recommendations from the ADA include the following:  The work place should be well ventilated, with fresh air exchange and outside exhaust  Use only precapsulated alloy, discontinue use of Bulk mercury & bulk alloy  Avoid the need to remove excess mercury before or during packing by selecting an appropriate alloy: mercury ratio  Use an amalgamator with a completely enclosed arm.
  126. 126.  Mercury and unset amalgam should not be touched by the bare hands.  Floor coverings should be non absorbent & easy to clean  Spilled mercury should be cleaned up using trap bottles, tape or freshly mixed amalgam to pick up droplets  Do not use a house hold vaccum cleaner to clean spilled mercury.  Skin accidentally contaminated by mercury should be washed thoroughly with soap and water.
  127. 127.  If a mercury hygiene problem is suspected, personnel should undergo urine analysis to detect mercury levels  Remove professional clothing before leaving the work place
  128. 128. Scrap amalgam disposal  In a tightly closed container  Under radiographic fixer solution  Dispose mercury contaminated items in sealed bags  Donot dispose mercury contaminated items in medical waste containers or bags or along with the waste that will be incenerated
  129. 129. CLINICAL TECHIQUES TO ENHANCE MARGINAL SEAL 1) Copal resin varnish:  Apply two thick coats to the cavity walls and margins before placing the amalgam and it will gradually dissolve, beginning at the cavosurface, over 2-3 months.  As the varnish dissolves out, the gap will be filled with corrosion products from the amalgam and dissolution of the varnish will cease.
  130. 130. CLINICAL TECHIQUES TO ENHANCE MARGINAL SEAL 2) Glass-ionomer linings  Placed under an amalgam will seal the dentinal tubules and release small quantities of fluoride  Will not affect enamel margins or enhance the seal at the margin.
  131. 131. CLINICAL TECHIQUES TO ENHANCE MARGINAL SEAL 3) Oxalate solutions :  Such as potassium oxalate, can be applied to the cavity surface to reduce the permeability of the tubules and possibly seal the dentine.  The crystals this deposited will not wash out but will allow deposition of corrosion products.
  132. 132. RECENT ADVANCES 1) BONDED AMALGAMS  During the 1990’s some clinicians began to routinely bond amalgam restorations to enamel and dentine  After preparation of the cavity, enamel and dentine etched using a conventional etchant, a chemically cured resin-bonding agent applied to the walls of the cavity.  Amalgam is immediately condensed into the cavity before the resin bond has cured
  133. 133. Advantages of Bonded-Amalgam :  Conservation of tooth structure.  Fracture strength was as high as for composites  Decreased marginal leakage in class 5 restorations compared with unbonded amalgams  Some operators claim elimination of post-insertion sensitivity.  Reduces incidence of marginal fracture and recurrent caries.  Can be done in single sitting.  Allows for amalgam repairs.
  134. 134. Disadvantages of Bonded-Amalgam :  Clinical difficulty of application of more viscous bonding agents  Lightly filled resin bonding agents tend to pool at the gingival margin resulting in a higher potential for micro leakage.  Carving is difficult.  Requires practitioner to adapt to new technique.  Increases cost of amalgam restorations.
  135. 135. 2) Gallium alloys  Mercury free metallic restorative materials proposed as substitute for mercury containing amalgam are gallium containing materials and pure silver and/or silver based alloys  Puttkammer (1928), suggested the use of gallium in dental restoration  Attempts to develop satisfactory gallium restorative materials were unsuccessful until Smith et al in 1956, showed that improved Pd-Ga and Ag-Ga materials has physical and mechanical properties that were similar to or even better than those of silver amalgam.
  136. 136. ADVANTAGES OF GALLIUM BASED ALLOYS:  Rapid solidification.  Good marginal seal by expanding on solidification.  Heat resistant.  The compressive and tensile strength increases with time comparable with silver amalgam  Creep value are as low as 0.09%  It sets early so polishing can be carried out the same day  They expand after setting therefore provides better marginal seal
  137. 137. REACTION : Ag3Sn + Ga  Ag3Ga + Sn.
  138. 138. REACTION :  After mixing, the alloy tends to adhere to the walls of capsule, thus difficult to handle.  Moreover, by adding few drops of alcohol, the problem of sticking can be minimized.
  139. 139. Biologic considerations of Gallium based alloys :  Surface roughness, marginal discoloration and fracture were reported. With improvement in composition, these defects were reduced but not eliminated  Could not be used in larger restorations as the considerable setting amount of expansion leads to fracture of cusps and post operative sensitivity.  Cleaning of instruments tips is also difficult  Less popular because it is costlier than amalgam.
  140. 140. 3) Fluoride releasing amalgam  Have been shown to have anticaries properties sufficient to inhibit the development of caries in cavity walls.  Concentration of fluoride is sufficient to enhance remineralization  Tviet and Lindh (1980) -- greatest concentration of fluoride i.e. about 4000µg/mL in enamel surfaces exposed to fluoride-containing amalgams were found in the outer 0.05µm of the tissue.
  141. 141.  In dentin, the greatest concentrations, i.e. about 9000µg/ml were found at a depth of 11.5µm.  However, this release of fluoride decreases to minor amounts after 1 week.  Forsten L (1976) -- fluoride released from amalgams loaded with soluble fluoride salts was detectable within the first month and thereafter fluoride was not released in measurable amounts.  Garcia Godoy et al( 1990) – fluoride release can continue as long as 2 years (but at a much lower rate than that for GIC).
  142. 142. Marginal fracture of amalgam  Referred to as “Marginal breakdown”, “ditching”, and “crevice formation”.  Regardless of the type of amalgam, marginal fracture increases with time  The rate of increase is greater for low-copper amalgams.
  143. 143. CLINICAL TECHNIQUES TO PREVENT MARGINAL FRACTURE  Excess amalgam, left lying over the occlusal or proximal surface should be carved correctly  The angle of the carvo-surface margin should be greater than 70º and the cavity should be designed to allow for this.  On completion of packing, burnish the margins both before and after carving to improve marginal adaptation.
  144. 144. Repair Of Amalgam Restorations  When an amalgam restoration fails, as from marginal fracture, it is repaired  A new mix of amalgam is condensed against the remaining part of the existing restoration  The strength of the bond between the new and the old amalgam is important
  145. 145. Factors contributing to strength of repair  Presence of porosity and  phase at the junction.  Inadequate condensation.  Contamination of the surface of the existing amalgam.  Corrosion & contamination from saliva.
  146. 146. CLINICAL CONSIDERATIONS Marginal Adaptation And Seal :  Lack of marginal adaptation in first few weeks  May be associated with marginal deterioration, accumulation of debris, recurrent caries, post- restoration sensitivity or pulpal reactions.
  147. 147. CLINICAL CONSIDERATIONS Self-Sealing :  After 48 hours, “self sealing” occurs  Low-copper amalgam -- seal within 2-3 months  High-copper amalgams -- corrode less and therefore take 10-12 months to provide a comparable seal.
  148. 148. Amalgam wars  In 1845, American Society of Dental Surgeons condemned the use of all filling material other than gold as toxic, thereby igniting "first amalgam war'. The society went further and requested members to sign a pledge refusing to use amalgam.  In mid 1920's a German dentist, Professor A. Stock started the so called "second amalgam war". He claimed to have evidence showing that mercury could be absorbed from dental amalgam, which leads to serious health problems. He also expressed concerns over health of dentists, stating that nearly all dentists had excess mercury in their urine.
  149. 149. Amalgam wars  "Third Amalgam War' began in 1980 primarily through the seminars and writings of Dr.Huggins, a practicing dentist in Colorado.  He was convinced that mercury released from dental amalgam was responsible for human diseases affecting the cardiovascular system and nervous system  Also stated that patients claimed recoveries from multiple sclerosis, Alzheimer’s disease and other diseases as a result of removing their dental amalgam fillings.
  150. 150. CONCLUSION There are certain advantages inherent with amalgam such as technique insensitive, excellent wear resistance, less time consuming, less expensive which are not present in the newer materials, these factors will continue to make amalgam the material of choice for many more years to come.
  151. 151. References  Stephen. C. Boyne, Duane. F. Taylor, “Dental materials”, The Art and Science of operative Dentistry, Mosby 3rd Edition 1997:219-235.  Kenneth J Anusavice, D.M.D., PhD., “Philip’s Science of Dental materials”, W.B. Saunders Company, 10th Edition 1996: 361-410.  M.A. Marzouk D.D.S. M.S.D. et al, “Operative Dentistry Modern theory and Practice”, IEA inc 1997:105-120.  Craig, “Science of Dental Materials”.  Jagannathan, K, “Cruise for Gamma 2 Free Mercury”, “Materials in Restorative Dentistry”, MADC & H, 1998 66-69.  John F. McCabe, Angus W.G. Walls, “Dental Amalgam”, Applied Dental Materials, Blackwell Science, 8th Edition, 1998:157-168  Satish Chandra, Shaleen Chandra, “Dental Amalgam”, A Text Book of Dental materials with Multiple Choice Questions”, Jaypee Brothers; 1st Edition 2000.  Vimal. K. Sikri, “Silver Amalgam”, Text book of Operative Dentistry” CBS publishers, 1st Edition 2002, 204-242.
  152. 152. Thank you…

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