Failure of amalgam


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why does amalgam restoration fail and a brief look at amalgam

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Failure of amalgam

  1. 1. by Dr.Anoop.V.Nair, PG, Dept of Cons & Endodontics KVG Dental College, Sullia
  2. 2. Contents • History • Overview • Alloy production • Generations • Alloy manipulation • Phases • Classification • What is an amalgam failure? • What types of failure? • Why failure? - Alloy - Dentist - Patient • References
  3. 3. • 618-907 AD- Tang dynasty in China, according to Geir Bjørklund, an active proponent of mercury free dentistry • In Germany by Dr. Strockerus in about 1528 • In 1603, German Tobias Kreilius boiled a concoction of copper, acids and mercury which was poured as a hot liquid onto diseased teeth • In 1819, first dental amalgam was probably introduced in England, ‘Bell’s putty’, by Thomas Bell, by mixing metals with mercury at room temperature
  4. 4. • In 1826, Taveau, from France described a silver paste filling material • 1833 the Crawcour brothers, two Frenchmen, brought amalgam to the United States • 1844 it was reported that fifty percent of all dental restorations placed in upstate New York consisted of amalgam. At that point the use of dental amalgam was declared to be malpractice, and the American Society of Dental Surgeons (ASDS), the only US dental association at the time, forced all of its members to sign a pledge to abstain from using the mercury fillings. This was the beginning of what are known as the first dental amalgam war. • The war ended in 1856 with the rescission of the old association.
  5. 5. • The American Dental Association was founded in its place in 1859, which has since then strongly defended dental amalgam from allegations of being too risky from the health standpoint. • Taft's text was published in 1859, Harris' in 1863. They stated that beginning in the early 19th century, eleven types of metallic fillings were used in teeth damaged by dental caries. The simple process of rolling metal into pellets to be placed into cavities was common. These pellets were made of some of the aforementioned materials like gold, lead, platinum, silver and amalgam as well as aluminum. • Sir Louis Regnart-"Father of Amalgam". He improved on a boiled mineral cement by adding mercury, which greatly reduced the high temperature originally needed to pour the cement onto a tooth.
  6. 6. • 1895-G V Black, a Chicago dentist standardized cavity preparation and amalgam manufacture. • The ratio of the mercury to the remaining metallic mixture in dental amalgam has not been always 50:50. It was as high as 66:33 in 1930. • 1930: ADA spec no 1 • In 1959, Eames introduced minimal mercury technique, with reduced mercury alloy ratio • Two texts used by American dentists of this time were, "A Practical Treatise on Operative Dentistry" written by J Taft, and "The Principles and Practice of Dental Surgery", written by Chapin A Harris.
  7. 7. BEFORE REACTIONBEFORE REACTION AFTER REACTIONAFTER REACTION AlloyAlloy MercuryMercury ReactionReaction ProductsProducts AlloyAlloy AMALGAM = an alloy containing Hg as the major ingredient. DENTALAMALGAM = an alloy of Hg with Ag-Sn. DENTALAMALGAM ALLOY = a Ag-Sn alloy (to be mixed with Hg).
  8. 8. ALLOY PRODUCTION Melting / Casting / Comminution  IRREGULAR Particles Melting / Spray Atomization  SPHERICAL PARTICLES “Cast ingots --> filed into powder on a lathe- Comminution Irregular particles = lathe cut = filings Particles are polycrystalline Homogenization heat treatment to remove coring Annealing heat treatment of filings to relieve cold work Hot alloy sprayed into cold air Particles spherodize and solidify Spheres are acid-washed Generally spheres are Heat Treated
  9. 9. Mercury/Alloy Ratios: Decreased with time and advent of spherical alloy powders
  10. 10. * Eutectic alloy- is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition made up of the same ingredients. This is called eutectic composition and the temperature at which it solidifies is known as eutectic temperature. • Peritectic alloy similar to eutectic alloy, here, a liquid and solid phase of fixed proportions react at a fixed temperature to yield a single phase. The solid product forms at the interface between the two reactants, and forms a diffusion barrier and causes reactions to proceed much more slowly than eutectic. • Ternary- a complex formed by interaction of three molecules
  11. 11. Addition of Noble metals- GENERATIONS (Marzouk) First generation- GV Black 3 part silver + 1 part tin, peritectic alloy Alloy product of reaction between the beta-phase of solid solution of tin in silver with liquid phase of silver & tin. This is defined as gamma phase. Second generation- Addition of- Cu (admixture)- upto 4%, decrease plasticity and increase hardness & strength of alloy Zn- traces- deoxidizer or scavenger for alloy, decrease brittleness. Third generation- Ag3-Cu eutectic alloy (admixture/blending)
  12. 12. Fourth generation- Alloying of Cu to silver & tin- upto 29% ternary alloy, most of tin firmly bonded to Cu. Fifth generation- Alloying of silver, copper, tin & indium true quaternary alloy, none of tin is available to react with mercury. Sixth generation- Alloying of palladium (10%), silver (62%) and copper (28%), to form a eutectic alloy lathe-cut and blended into 1st, 2nd or 3rd gen amalgam- ratio 1:2 set amalgam, exhibits highest nobility
  13. 13. ALLOY MANIPULATION Manual Trituration Procedures: Alloy + Hg  mortar + pestle  manual mixing Mechanical Trituration Procedures: Powdered alloy + Hg  capsule + pestle  amalgamator Pelleted alloy + Hg  capsule + pestle  amalgamator Powdered alloy + Hg  pre-capsulated  amalgamator
  14. 14.  THE ORGINAL GAMMA PHASE (i.e., Ag3Sn or the alloy powder) which has not been completely dissolved in mercury. Mechanically strongest phase, for this reason it should occupy the maximum available space in the volume of the restoration.  GAMMA-1 Phase (Ag2Hg3) is one of the amalgamation products that form the matrix. It is the noblest phase i.e., Most resistant to tarnish & corrosion. Effort, made to make this phase occupy maximum space in bonding matrix of final product.  GAMMA-2 Phase (Sn7 Hg8) It is the phase which is the least resistant to tarnish & corrosion & every effort is made minimize its volume percentage in the matrix. Most of amalgam failures, due to this phase. Phases
  15. 15. MERCURY Phase - Unreacted residual mercury, present in isolated areas within the amalgam mass. - Mechanically weakest phase & when a certain volume limit exceeds, there will be drastic drop in the strength & hardness in addition to increase in creep & flow of restoration. VOIDS (porous) PHASE - Due to entrapment of air bubbles, in the process of building the amalgam restoration, despite any meticulous procedures. - Such voids act as a nidus not only for internal corrosion, but also leads to stress concentration & propagation which ultimately leads to early failure of structure of restoration. The trace element phase  In which copper & zinc might be found either as separate phases or combined with Ag, Sn & Hg. Cu- increase strength, brittleness, hardness and proportional limits of amalgam Zn- increase deformability, ultimate strengths, resistance to oxidation of final product.
  16. 16. The INTERPHASES In terms of the serviceability of final restoration, the most important components of the mass.  This especially to the interphases between the 3 components namely gamma, gamma-1 & gamma-2.  In the final restoration, the more continuous they are better is the bonding between the primary phases. Consequently, the more coherent & the more resistant to environmental variable the restoration will be. EPSILON Phase (Cu3Sn) AgSn alloys are quite brittle & difficult to comminute uniformly unless a small amount of copper is substituted for silver. This atomic replacement is limited to about 4-5 wt%, above which Cu3Sn is formed within the limited range of copper solubility, increased copper content hardens & strengthen the AgSn alloy.
  17. 17. ETA Phase (Cu6Sn5) • The crystals are found as meshes of rod crystals at the surfaces of the alloy particles as well as dispersed in the matrix. • Meshed ETA crystals on unconsumed alloy particles may strengthen bonding between the alloy particles & 1 grains. Crystals dispersed between 1 grains may interlock 1 grains. This interlocking is believed to improve the amalgam’s resistance to deformation in high copper alloys.
  18. 18. I. According to the number of alloyed metals  Binary alloys Only 2 alloys namely silver & tin  Ternary alloys Along with silver & tin copper was added to increase the strength of the alloy.  Quaternary alloys Indium was added to the above which act as a grain refiner.
  19. 19. II. According to the shape of powdered particles  spherical: alloy shape which has smooth surfaced spheres.  Lathe cut: irregular shapes ranging from spindles to shavings.  spheroidal: spherical with irregular spheres III. According to the powder particle size  micro cut  fine cut  coarse cut
  20. 20. IV. According to the copper content  Low copper alloys, which contain less than 4% of copper  High copper alloys, which contain more than 10% of copper & has improved physical properties & corrosion resistant. V. According to whether the powder consists of unmixed or admixed alloys. Certain amalgam made of only one alloy, others have one or more alloys or more alloys (blended) to the basic alloy e.g.; adding copper to the basic binary silver –tin alloys.
  21. 21. • A failing amalgam filling can be defined as a filling that has been a contributory cause of secondary injury in the organ of the tooth i.e, the tooth itself and its surrounding connective tissue. ( Knud Dreyer Jorgensen, Amalgams in dentistry, Dental Materials Research: Proceedings of the 50th Anniversary Symposium, Oct 6-8. 1969 Issue 354, By United States. National Bureau of Standards, American Dental Association)
  22. 22. • FRACTURE Marginal fracture Isthmus fracture Bulk fracture Tooth fracture • SECONDARY CARIES
  26. 26. • Manufacturing defects • Physical properties of amalgam Dimensional stability Strength Creep
  27. 27. • Contraction/expansion TIME D I M E N S I O C N H A A L N G E S STAGE 1- Initial contraction- absorption of Hg into alloy powder STAGE 2- Expansion, due to formation & growth of matrix crystals, reaches a plateau with cessation of matrix formation STAGE 3- Limited, delayed contraction of mass, absorption of unreacted Hg
  28. 28. • Factors affecting: • Constituents- More gamma phase- greater possibility of expansion - Greater traces of tin, less expansion • Mercury- More Hg, more prolonged second stage of amalgamation (expansion) - Greater amount of matrix crystals (gamma, gamma 1 or gamma 2), produces more expansion • Particle size- smaller size more surface area per unit volume first stage, dissolution occurs rapidly marked contraction second stage also rapid expansion plateau achieved too quickly (before cavity filled)- apparent expansion may not be noticed stage 3 contraction maybe more noticed.
  29. 29. Trituration- more energy used, smaller particles will be made more mechanical force will be present pushing mercury in between particles discourage expansion • More trituration energy, greater distribution of forming matrix crystals all over mix, preventing outward growth, which creates expansion of second stage. • More trituration energy, faster amalgamation proceeds, plateau of expansion curve occur before completely filling cavity preparation no apparent expansion, possibly limited contraction Condensation- more energy used, into condensing amalgam into cavity preparation, closer original particles of powder are brought together at expense of expanding matrix crystals. • Increased condensation energy, also squeezes more Hg out of the mix less formation of matrix crystals, inducing more contraction.
  30. 30. Particle shape- • More regular the particle shape is and smoother its surfaces are, faster and more effectively the mercury can wet the powder particles. • Makes faster amalgamation process in all stages, maximum expansion occurs before filling cavity, with no apparent expansion. Contamination- • Moisture- esp affects Zn containing amalgam. • Water from any source(saliva, blood, respiration etc) + Zn (in amalgam) ZnO + Hydrogen gases • Takes place- 24-72 hours after amalgam insertion. • Hydrogen gases, accumulate, exert pressure- upto 2000 PSI. • Protrusion of entire restoration outside cavity, increased microleakage space around restoration, restoration perforation, blister formation on restoration surface, increased flow & creep, pulpal pressure pain, delayed expansion- 400 µ/cm3
  31. 31. • Clinical significance
  32. 32. • Zn containing alloys • Moisture contamination • 3-5 days till months: 400µ/cm3
  33. 33. • Early hour strength (C.S.) • Strength after setting (C.S.) • Tensile strength Amalgam 1 hr 7 days T.S. Low Cu 145 343 60 Admix 137 431 48 Single comp 262 510 64
  34. 34. • Temperature • Trituration • Mercury content • Condensation • Porosity • Particle shape & size • Inteparticle distance • Dispersion • Gamma-2 phase • Corrosion
  35. 35. Temperature- • Amalgam loses 15% strength when temp elevated from room to mouth • Loses 50% strength when temperature elevated to 60% (hot coffee, soups) Trituration- • More energy used, more continuous interphases between matrix crystals & original particles, more evenly distributed matrix crystals over mix more coherent mass greater strength • If trituration, continued after complete matrix crystals formation, excess energy will crack crystals & interphases drop in strength of amalgam Mercury- weakest phase, liquid room temp., cannot resist any slip or dislocation within amalgam caused by external loading • Residual mercury- increase in Hg content from 53%- 55%, causes drop in compressive strength, more than 50%
  36. 36. Condensation- • More energy used, less residual mercury, higher relative percentage of strong original particles in restoration. • More continuous interphase between original particles & forming matrix • More even distribution of gamma1 or gamma 1-gamma 2 matrix crystals more consistent strength throughout restoration mass *condensation of an amalgam mass after formation of matrix crystals does not diminish strength as trituration does, because there is more resistance to crystal displacement during condensation than trituration.
  37. 37. Porosity- • Important to minimize the number & size of pores • Keep them away from critical areas of the restoration • Pores facilitate stress concentration, propagation of cracks, corrosion and fatigue failures of amalgam structures • Porosity of 1% reduces amalgam strength as 10% excessive mercury • Results from the fact that different phases of amalgam do not completely wet each other simultaneously during amalgam fabrication • Under-trituration, under condensation, irregular shaped particles of alloy powder, miscalculated diameter varieties of powder particles to occupy available spaces, insertion of too large increments into cavity preparation, delayed insertion after trituration or a generally non-wetting, non-plastic mass of amalgam.
  38. 38. Particle size & shape- • Alloy particles, more regular & smooth- more wettable • Will react & combine more efficiently • Resultant, less interrupted interphases create a more coherent and strong mass • Smaller the diameter of the original particles, greater will be the strength of the set amalgam. Compressive strength- • 1 day specimen- substantial increase in strength, average particle diameter 12 or less microns • 1 week specimen- substantial increase when average particle diameter 16 or less microns Tensile strength- • 1 day specimen- marked increase in strength when average particle diameter 18 microns or less • 1 week specimen- same increase when average particle diameter 12 microns or less
  39. 39. Interparticle distance- • Closer original particles of alloy are- stronger end product will be • When average interparticle distance is 38 microns or less, noticeable increase in compressive strength in 24 hr sample • 1 week sample- 32 microns or less • Tensile strength- 28 microns or less, marked increase in 24 hr specimen • 39 microns or less, marked increase in one week specimen Dispersion- • A solid state dispersion within amalgam mass of another phase, with one which has a different shape & dimension than original phases, can distort original space lattices, precipitating interferences with slip increasing amalgam strength • Eg:- addition of Cu or addition of Ag-Cu eutectic or Ag-Cu- Palladium near-eutectic alloys • Net result- greatly enhanced strength
  40. 40. Gamma 2 phase • Mechanically, second Weakest phase • Corrosion ability • Reduction or prevention of its formation- increase strength of amalgam, especially age strength Corrosion • Decreasing corrosion activity within an amalgam restoration will protect the adhesive integrity between the multiple phases, thus preventing the strength from deteriorating.
  41. 41. Flow Creep Measured during setting of amalgam Measured after amalgam sets Reflects change in dimension of amalgam after load Reflects constant change in dimension under either static or dynamic loading Incremental deformation Markedly pronounced after EQUICOHESIVE temperature More energy used to condense, less the creep, mercury increase will increase creep Dispersion or elimination of gamma-2 can reduce creep Lesser the creep, better will be the marginal integrity & longevity of the restoration
  42. 42. • ‘It is mainly the operator who causes the amalgam restoration to be a success or failure’ • The choice between spherical, spheroidal or lathe-cut alloy particles can be related to the type of patient population the dentist is involved with. • Spherical particle alloy- quick strength attainment - Require fast operator - exhibit more flow - deformation with time • Choice between zinc containing & zinc free- Zinc containing- problems in presence of moisture Zinc free- less plastic, less workable, more susceptible to oxidation, so should be used in cases only where elimination of moisture is impossible, eg:- root apices, subgingival lesions Marzouk, 1st edition
  43. 43. Proportioning of alloy & mercury Choose between *consider manufacturer’s recommendation which is based on metallurgical condition, thermal treatment, powder particle specification High mercury technique (increasing dryness technique) Minimum mercury/ Eame’s technique/1:1 Initial amalgam mix contains a little more Hg than needed for the powder (52-53%), producing a very plastic mix Initial amalgam mix contains equal amounts of mercury and powder alloy Necessary to continue squeezing the mercury out of the mix increments being introduced to build up the restoration, so that each increment will be drier than the previous one Necessary to squeeze mercury out of the mix during the incremental build-up of the restoration. 50% or less mercury only will be in the final restoration, with obvious advantages
  44. 44. • Restorations to be retained with multiple auxillary means of retention (pins, internal boxes, grooves)- need wetting or plastic consistency of amalgam increasing dryness technique • A very large restoration which needs more than one mix increasing dryness technique • Proportioning is done by weight and not by volume- volume is misleading because of trapped air and voids in mass • Choice between pre-weighed, pre-proportioned alloy mercury capsules or weight proportioning oneself in the office
  45. 45. • Do not leave previous mixes remnants in the capsule, as this will get incorporated into a new mix without proper binding or plasticity, weakening the final product. • Scratches in the capsules may trap mercury or traces of old mixes, compromising quality of amalgam product. • Cracks in the capsules that leak mercury will pollute the office and reduce mercury in the mix, sometimes with undesirable effects
  46. 46. • Improper case selection • Improper selection of alloy and mercury • Improper Cavity preparation • Improper manipulation of alloy • Improper Pulp protection • Improper Matrix adaptation • Contamination
  47. 47. • Extensive loss of tooth structure and undermined enamel. • Poor retention and resistance form • Areas of high masticatory loads • Parafunctional habits • Extensive/open contacts
  48. 48. • Improper outline form • Cavity outline in stress bearing areas • Improper resistance form • Improper retention form • Improper convenience form
  49. 49. • Inadequate occlusal extension- include pits & fissures • Inadequate extension of the proximal box- if proximal box walls are not adequately extended into embrasures they are not amenable to cleaning secondary caries • Overextension of cavity preparation walls- 1/4th the intercuspal distance facio-lingual width • If cavity preparation extends to half the intercuspal distance, capping of cusps should be considered, if cavity preparation extends to 2/3rd, cusp capping becomes mandatory. • Minimum thickness in cusp capping should be 2mm over functional cusps and 1.5mm over non-functional cusps.
  50. 50. Minimum depth of 1.5mm to provide bulk Flat pulpal floor Butt joints in regions where occlusal stresses encountered Round off axio pulpal line angle
  51. 51. Failure to diverge mesial & distal walls of occlusal cavity preparation Retentive devices should be prepared entirely in dentin without undermining enamel Incomplete removal of carious tooth structure
  52. 52. correct Insufficient gingivally Insufficient occlusally correctexcessive • Matrix should be stable after it has been applied- if unstable, distorted restoration, gross marginal excesses • Cervical excess can irritate peridontium • Unstable matrix- proper condensation cannot be carried out soft amalgam filled with voids
  53. 53. shape surface size • If large cavity, demands working time exceeds 3-4 mins, use multiple mixes • Elimination of Hg by excessive squeezing, may reduce strength • Very small plugger holes- punch holes in amalgam • Very large plugger holes- may not condense amalgam in corners • Light tapping- to remove Hg to surface, adequate condensation pressure
  54. 54. Mechanical condensation Lathe cut alloys Spherical alloys
  55. 55. • Over- carving- • Will reduce thickness of amalgam & increase chances of fracture. • Under-carving
  56. 56. • Failure due to improper pulp protection • Failure due to contamination • Failure due to improper instructions
  57. 57. • Oral hygiene • Excessive stress • Malposed occlusion • Galvanism • Parafunctional habits • Failure to follow instructions
  58. 58. •Electrochemical •Chemical
  59. 59. • Mercury level • Surface texture • Galvanic action • Moisture contamination By-products are tin-oxide, copper-oxide, silver sulfides
  60. 60. • Improper cavity preparation and finishing • Excess mercury • Creep • Corrosion
  61. 61. If varnish not applied, continuous leakage around restoration occurs, may cause postoperative sensitivity and amalgam blues due to penetration of corrosion products into dentinal tubules.
  62. 62. Newer modifications
  63. 63. RESIN COATED AMALGAM • To overcome the limitation of microleakage with amalgams, a coating of unfilled resin over the restoration margins and the adjacent enamel, after etching the enamel, has been tried. Although the resin may eventually wear away, it delays microleakage until corrosion products begin to fill the tooth restoration interface. • Mertz-fairhurst and others evaluated bonded and sealed composite restorations placed directly over frank cavitated lesions extending into dentin versus sealed conservative amalgam restorations and conventional unsealed amalgam restorations. The results indicate that both types of sealed restorations exhibited superior clinical performance and longevity compared with unsealed amalgam restorations over a period of 10 years
  64. 64. FLUORIDATED AMALGAM • Fluoride, being cariostatic, has been included in amalgam to deal with the problem of recurrent caries associated with amalgam restorations. The problem with this method is that the fluoride is not delivered long enough to provide maximum benefit. • Several studies investigated fluoride levels released from amalgam. These studies concluded that a fluoride containing amalgam may release fluoride for several weeks after insertion of the material in mouth. • As an increase of up to 10–20-fold in the fluoride content of whole saliva could be measured, the fluoride release from this amalgam seems to be considerable during the first week. • An anticariogenic action of fluoride amalgam could be explained by its ability to deposit fluoride in the hard tissues around the fillings and to increase the fluoride content of plaque and saliva, subsequently affecting remineralization. In this way, fluoride from amalgam could have a favorable effect not only on caries around the filling but on any initial enamel demineralization. The fluoride amalgam thus serves as a “slow release device”.
  65. 65. BONDED AMALGAM • Conventional amalgam is an obturating material as it merely fills the space of prepared cavity, and thus, does not restore the fracture resistance of the tooth, which was lost during cavity preparations. In addition, the provision for adequate resistance and retention form for amalgams may require removal of healthy tooth structure. Further, since amalgam does not bond to tooth structure, microleakage immediately after insertion is inevitable. So, to overcome these disadvantages of amalgam, adhesive systems that reliably bond to enamel and dentin have been introduced. • Amalgam bond is based on a dentinal bonding system developed in Japan by Nakabayashi and co-workers. The bond strengths recorded in studies have varied, approximately 12–15 MPa, and seem to be routinely achievable. Using a spherical amalgam in one study of bonded amalgam, Summitt and colleagues reported mean bond strength of 27 MPa. The authors believed that this higher bond strength was achieved because the bonding material was refrigerated until immediately before its use.
  66. 66. • Bond strengths achieved with admixed alloys tend to be slightly lower than those with spherical alloys. One study compared post- insertion sensitivity of teeth with bonded amalgams to that of teeth with pin-retained amalgams. After 6 months, teeth with bonded amalgams were less sensitive than teeth with pin-retained amalgams. This difference in sensitivity was not present 1 year after insertion. This is possibly because of corrosion products in nonbonded amalgam restorations filling the interface, and thus, decreasing microleakage and sensitivity. • If bonding proves successful over the long term, method of mechanical retention can be eliminated, thus reducing the potential for further damage to tooth structure that occurs with pin placement or use of amalgapins. If mechanical retention is not needed, cavity design can allow more sound tooth structure to be preserved.
  67. 67. CONSOLIDATED SILVER ALLOY SYSTEM • One amalgam substitute being tested is a consolidated silver alloy system developed at the National Institute of Standards and Technology. • It uses a fluoroboric acid solution to keep the surface of the silver alloy particles clean. • The alloy, in a spherical form, is condensed into a prepared cavity in a manner similar to that for placing compacted gold. One problem associated with the insertion of this material is that the alloy strain hardens, so it is difficult to compact it adequately to eliminate internal voids and to achieve good adaptation to the cavity without using excessive force.
  68. 68. FUTURE OF DENTAL AMALGAM • The prediction that amalgam would not last until the end of the 20th century was wrong. • Its unaesthetic appearance, its inability to bond tooth, concerns about the mercury and versatility of other materials have not not led to the elimination of this inexpensive and durable material. As other materials and techniques improve, the use of amalgam will likely continue to diminish, and it will eventually disappear from the scene. • Yet, amalgam continues to be the best bargain in the restorative armamentarium because of its durability and technique insensitivity. Amalgam will probably disappear eventually, but its disappearance will be brought about by a better and more aesthetic material, rather than by concerns over health hazards. When it does disappear, it will have served dentistry and patients well for more than 200 years.
  69. 69. References • Dental Materials Research: Proceedings of the 50th Anniversary Symposium, Oct 6-8. 1969 Issue 354, By United States. National Bureau of Standards, American Dental Association • Dental amalgam: An update Ramesh Bharti, Kulvinder Kaur Wadhwani, Aseem Prakash Tikku, and Anil Chandra J Conserv Dent. 2010 Oct-Dec; 13(4): 204–208 • Textbook of dental materials by Sharmila Hussain • Dental materials: Prep manual for under graduates by Patil • Sturdevant’s Art and Science of Operative Dentistry • Operative dentistry- modern theory and practice- Marzouk, Simonton, Gross- 1st edition • Essentials of Operative Dentistry- Anand Sherwood • Textbook of operative dentistry- Vimal K Sikri • Skinner’s Science of Dental Materials- 9th edition • Pictures- various sources from the internet
  70. 70. •Thank you