DENTAL RESTORATIVE MATERIAL : AMALGAM.pptx

DENTAL RESTORATIVE MATERIAL : AMALGAM.pptx

1. Amalgam Part II

2. Contents Manipulation of amalgam Mercury toxicity and health hazards Recent advances of amalgam restoration Repair of amalgam restoration Conclusion

3. Manipulation of amalgam

4. Steps in manipulation of amalgam Choice of alloy Choice of mercury Proportioning of Hg to alloy Trituration & methods Mulling Insertion of amalgam- Condensation Pre-carve burnishing Carving Burnishing Finishing & Polishing

5. Selection of alloy Alloy composition Particle shape Particle size Speed of set Pre amalgamated or standard alloy Zinc containing or zinc free alloy.

6. ALLOY COMPOSITION Use of disperse alloy has the advantage of its greater tarnish & corrosion resistance, improved compressive and edge strength with consequent reduction in marginal failure. • Jerman (1970) found that by adding 1.5% SnF to the alloy ,there was an increased fluoride content of the enamel adjacent to the restoration with an associated reduction in the enamel solubility. But there is no evidence that there is continuous leaching of fluoride from the set amalgam.

7. PARTICLE SHAPE Alloy particles which are more regular and smooth are more wettable. Therefore, they will react and combine more efficiently. The resultant, less interrupted interphases create a more coherent and strong mass. Advantages of spherical particle: Easier to produce Less sensitive to manipulative variables Eg : Breaking up during trituration. Superior 1-hr and final compressive strengths & tensile strengths. Increased plasticity of the mix with mercury.

8. PARTICLE SIZE Smaller the particle size indicates more surface area of the particles per unit volume. So when they are mixed with mercury the dissolution of first stage will occur more rapidly and more efficiently Smaller the particle size: Higher the 1hr & 24hr strength lesser the expansion more easily adapted to the cavity walls much less pitted, when carved more easily polished.

9. SPEED OF SET Setting time of an alloy is accelerated by increasing the Ag content. Min. Content of Ag is 65% in ADA. SP. 1. Quick setting alloys (Ag— 66.7%-74.3%) 2. Slow setting alloys (Ag— 43-48%) Advantages of fast setting alloy: reduces chair side time allow to fill proximal cavities at one appointment. Disadvantage: Rapid crystallization limits removal of Hg from successive condensed portions of amalgam already in the cavity

10. CHOICE OF MERCURY The most recent British standard sp. for dental mercury is B.S.4227 Mercury complying with the requirements of British &USA Pharmacopoeia or ADA sp.no.6 should be used. Hg must contain <0.02% by mass, non-volatile residue & there must be no visible surface contamination. It should have a mirror like surface. Contaminated Hg can only be purified by “Distillation procedures”

11. PROPORTIONING MECURY TO ALLOY The mercury alloy ratio signifies the number of parts by weight of mercury divided by the number of parts of alloy to be used for the particular technique

12. HIGH MERCURY TECHNIQUE: In this, the initial amalgam mix contains more mercury than what it is needed for powder (52-53% Hg) is used, producing a plastic mix Squeeze the mercury out of the increments during condensation being used for buildup of the restoration

13. Philips and Swartz(1949) have shown that regardless of the amount of mercury squeezed away or removed by condensation, the more the Hg used in the original mix the greater is the amount that will remain in the restoration. Philips and Boyd(1947) have shown that as the Hg:alloy ratio is increased, the % of residual Hg also increases proportionally. For each additional 15% of Hg used in the original mix, there is an avg increase of 1-1.5% residual Hg. The residual Hg content of the final restoration should be between 50-55%.

14. Traditionally Hg:alloy ratio were 7:5 & 8:5 by weight or even higher. In 1959, W. Eames was the first to promote the low mercury:alloy ratio i.e Hg:Alloy ratio of 1:1,which can only be triturated in a mechanical amalgamator. This technique also known as “NO SQUEEZE CLOTH TECHNIQUE” or “MINIMAL MERCURY TECHNIQUE”

15. • The Various methods of proportioning alloy & Hg are: 1)By weight eg : Crescent and Ash balances 2)By volume eg : Baker proportioner Amalganom S.S.White proportioner 3) Predispensed eg : S.S.White sigrens Amalcap capsules with mercury in cap Aristalloy tablets.

16. Various methods of proportioning 1)PREWEIGHED TABLET : specific weight of powder with appropriate Hg is dispensed into mixing capsule proportion– by wt – not by volume %Hg can be adjusted from 48-55%. 2)DISPOSABLE CAPSULE 3)SELF ACTIVATING CAPSULE 4)PRE AMALGAMATED ALLOYS 5)REUSABLE CAPSULE

17. REUSABLE CAPSULE A typical reusable capsule is a hollow tube with rounded ends constructed as two pieces that could be friction fit or screwed together. Amalgam alloy was dispensed into the capsule as a pellet of pressed powder of standard weight. Mercury was dispensed into the capsule as a standard-sized droplet from an automatic dropper bottle.

18. A small metal or plastic pestle was added to the capsule, and it was closed. The capsule and its contents were automatically mixed using an amalgamator. The typical amalgamator has been designed to grasp the ends of the capsule in a claw that is oscillated in a figure-of-eight pattern.

19. SIZE OF MIX Capsules containing 400, 600 or 800mg of alloy and the appropriate Hg are available Color coded for easy identification of capsules. 400mg - single mix. 600mg – single mix. 800mg – double mix 1200mg – for amalgam core

20. Mechanical instruments have now been developed which dispense & triturate the alloy & Hg.

21. DISPENSING OF ALLOY AND MERCURY: The more common method of dispensing alloy & Hg is the Automatic release type of dispenser which proportions volumetrically. Ryge etal (1958) have analyzed the accuracy of 12 different methods of obtaining the desired proportions of alloy & Hg. Hg dispenser should be held vertically and not at 45◦. It should be half filled to ensure uniform spills.

22. On standard electrical amalgamators, the trituration speed and trituration time are manually set on the front of the equipment. Settings vary for different products. Electronic amalgamators have digital controls and permit programming of settings.

23. Modern amalgams are produced from precapsulated alloy and mercury. The components are separated in the capsule by a special diaphragm that is broken when the capsule is “activated” just before mixing. Precapsulated (pre-proportioned) amalgam provides convenience and some degree of assurance that the materials will not be contaminate before use or spilled before mixing.

24. TRITURATION The purpose of trituration is to mix the amalgam alloy intimately with mercury so as to wet the surface of the powder particles to allow the reaction between liquid mercury and silver alloy. Prior to 1940’s Amalgam was triturated by hand in a mortar & pestle.

25. Mortar pestle method It is the oldest method used. Suggested by Dr.Marcus.L.Ward . Here pestle is held in a pen grasp with 2-3 psi load and rapid convenient circular motion is used until a shiny, homogeneous mass is obtained. WORK = PESTLE SPEED X PESTLE LOAD X TIME Need 60-120s for trituration.

26. RUBBER THUMB-STALL METHOD In 1934, Mary Gayler advocated this method. This technique has the advantage not destroying the original particle size, but a higher Hg : alloy ratio is used to obtain amalgamation in 1 minute.

27. MECHANICAL AMALGAMATION Am algamators : there are three basic movements of mechanical triturat or The mixing arm carrying a capsule moves back and forth in a straight line such movements can occur at varying speeds the mi x ing arms travels back and forth in a figure of eight also at varying spee d the mixing arm travels in a centrifugal fashion

28. Advantages of Amalgamators Uniform and reproducible mix can be attained minimal trituration time is required a greater alloy : mercury ratio is used for preparing the mix as they are proportioned by the manufacturer atmospheric mercury contamination is reduced

29. Mechanical amalgamators are available in the following speeds: Low speed: upto 3400 cycles/minute. Medium speed: upto 3800 cpm . High speed: upto 4400 cpm . Spherical/irregular low-copper alloys – triturated at low speed High copper alloys – high speed Time of trituration on amalgamators ranges from 3-30 seconds.

30. Trituration energy Effective trituration depends upon combination of duration and speed of mixing The mixing time may vary upon speed and a parameter called coherence time( tc ) Coherence time( tc ) - It is defined as the minimum time required for mixing to form a single coherent pellet of amalgam.

31. Stages of trituration

32. Testing of amalgam mix A properly triturated and mulled amalgam mix should meet the following tests.

33. Effects of under and over trituration Working time decreases. Dimensional changes are seen. Creep increases. Compressive and tensile strength decreases.

34. Excess mercury is squeezed out of the muslin cloth A thick condensable plastic paste is obtained

35. MULLING It is a continuation of trituration. To improve the homogeneity of the mass, assure a consistent mix & handling ease. This is made more cohesive by hand mulling.

36. 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. Purpose of condensation is to get a continuous homogenous mass that is well adapted to all margins, walls and line angles.

37. Hand condensers It allows a operator to readily grasp it & exert a force of condensation Condensers are instruments with serrated tips of different shapes & sizes The shapes are oval, crescent, trapezoidal, triangular, circular or square Size of condenser tip & direction & magnitude of the force placed, depends on the type of amalgam alloy selected

38. Hand condensation Once the increment of amalgam is inserted into the cavity preparation it should be condensed with pressure to avoid voids and to adapt the material to the walls, the condenser point is forced into the amalgam mass under hand pressure.

39. Condensation is started at the center and then is stepped little by little towards the cavity wall.

40. After condensation of the first increment sufficient mercury should left over the first increment so that it can bond with the next increment. The procedure of adding an increment,condensing it,adding another increment and so forth is continued until the cavity is overfillled . In case the cavity is large well condensed amalgam restoration can be achieved when the mix has proper consistency.

41. Condensation pressure When a given force is applied,smaller the condenser greater the pressure exerted on the amalgam. For eg -when a thrust of 40N exerted 2mm diameter 13.8MPa condensation pressure 3.5mm diameter 4.6MPa condensation pressure. Serrated condenser is preferred than round condenser in case of the corner of the cavity. The shape of condenser points should conform to the area under condensation.

42. 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.

43. Ultrasonic Condensers Not recommended Disadvantage - Causes the release of considerable quantities of mercury vapor in the dental office

44. Burnishing (Pre-carve Burnishing) Carried out using a large burnisher for 15 seconds Use light force and move from the center of the restoration outwards to the margins. 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

45. Carving Carving is anatomical sculpturing of the Amalgam 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.

46. Objectives of carving to produce a restoration with Amalgam No underhangs The proper physiological contours. Minimal flash. Proper occlusal anatomy and occlusal contact points Adequate, compatible marginal ridges. Proper size, location, extent and tightness of contact areas. Adequate embrasures and maintains the health and integrity of Periodontium

47. 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 It is done to remove scratches and irregularities, facilitating easier and efficient finishing and polishing Heat generation should be avoided If burnishing raises temperature above 60C, causes release of mercury accelerates corrosion & fracture at margins

48. Finishing and polishing of amalgam It is necessary to complete the carving, to refine the anatomy, contours, and marginal integrity and enhance the surface finishing of the restoration. It reduces the surface roughness of the restoration and makes it less prone to tarnish and corrosion.

49. AFTER INITIAL SETTING Prophy cup with pumice It provides initial smoothness to restorations

50. FINAL POLISHING A well polished surface of Amalgam reduces fatigue failure of the restoration under cyclic loading of mastication Finishing and polishing removes surface irregularities this minimizes concentration cell corrosion and prevents plaque adherence Done only after amalgam sets, delayed at least 24 hrs following condensation High Cu single composition spherical alloy due to high strength can be polished at the same appointment, once material gains strength Always - low speed, low pressure Wet polishing is preferable where a wet abrasive powder is made into a paste for polishing

51. Mercury toxicity and hygiene

52. Mercury toxicity depends on Amount of exposure Length of exposure Length of mercury accumulation in body Amount of accumulated mercury - Overall health of the patient ( for detoxification)

53. Concentration of mercury The Occupational Safety & Health Administration (OSHA) has set a Threshold Limit Value of 50 microgram/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 microgram.

54. Toxic reaction 3 -7µg/kg body weight LOWEST DOSE TO ELLICIT TOXIC REACTIONS 500µg/kg body weight Paresthesia 1000µg/kg body weight Ataxia 2000µg/kg body weight Joint pain 4000µg/kg body weight Hearing loss

55. Amount of mercury released during manipulation of amalgam

56. Pathway through which mercury enters human body

57. Concentration 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.

58. Maximum allowable level of mercury in blood is 3 µg/L 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 µg/L ) than patients without amalgams (0.8 µg/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

59. 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.

60. Long- term response -- oral lichen planus or lichenoid reactions with erosive areas on the tongue or buccal mucosa adjacent to an amalgam restoration.

61. 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.

62. Sources of mercury exposure

63. DENTAL MERCURY HYGIENE Educate all personnel involved in the handling of mercury or dental amalgam on the potential hazard of mercury vapor and the necessity for observing good mercury hygiene practices. Make personnel aware of the potential sources of mercury vapor in the dental operatory . Personnel should be knowledgeable about the proper handling of amalgam waste and be aware of the environmental issues

64. Work in well-ventilated spaces with fresh air exchanges and outside exhaust. If the spaces are air-conditioned, air conditioning filters should be replaced periodically. Regularly check the dental operatory atmosphere for mercury vapor. Monitoring should be considered in case of a mercury spill or suspected spill Dosimeters may be used for monitoring. Mercury vapor analyzers which provide rapid readouts, also are appropriate.

65. Use proper work area design to facilitate spill contamination and cleanup. Floor coverings should be nonabsorbent, seamless, and easy to clean. Use only precapsulated alloys ; discontinue the use of bulk mercury and bulk alloy. Use an amalgamator with a completely enclosed arm. Use care in handling amalgam. Avoid skin contact with mercury or freshly mixed amalgam.

66. Use high-volume evacuation when finishing or removing amalgam. Evacuation systems should have traps or filters. Check and clean or replace traps and filters periodically to remove waste amalgam (including contact amalgam) from the waste stream. Salvage and store all scrap amalgam (i.e., noncontact amalgam remaining after a procedure) in a tightly closed container, either dry or under radiographic fixer solution.

67. Amalgam scrap should not be stored in water. If the scrap is stored dry, mercury vapor can escape into room air when the container is opened.

68. Dispose of mercury-contaminated items in sealed bags according to applicable regulations. Do not dispose of mercury contaminated items in regulated (medical) waste containers or bags or along with waste that will be incinerated. Clean up spilled mercury properly using trap bottles, tape or freshly mixed amalgam to pick up droplets, and commercial cleanup kits. Do not use a household vacuum cleaner. Remove professional clothing before leaving the workplace.

69. Recent advances of amalgam

70. Gallium based alloys HISTORY Metallic element Gallium was 1st predicted by Mendeleef in 1871, was 1st isolated by ‘de Boisbandran ’ in 1875. 1920s, Gallium (Ga) was one of the substitutes suggested for Hg (Putt Kammer , 1928)

71. This is direct filling material contains no mercury and can be mixed and condensed similar to Silver Amalgam Gallium is liquid at room temperature Its use is based on remarkable ability of liquid gallium to wet surfaces of many solid Melting temperature of Ga can be suppressed below room temperature with addition of appropriate amounts of In and Sn.

72. Composition Alloy : Silver- 50% Tin - 25% Copper- 13% Palladium- 20% Liquid: Gallium – 62% Indium – 25% Tin – 25% The reaction between Silver-tin particles and Gallium involves formation of Gallium silver phase and a pure tin phase

73. G-Amalgamation CuGa2 and PdGa5 surrounding the unreacted alloy particles which are held together by matrix of Ag9In4 Properties 1 hr. Comp. Strength - 343 MPa 1 day Comp strength - 533 MPa Tensile strength - 57 MPa Creep - 0.17%

74. ADVANTAGES Rapid solidification. Good marginal seal by expanding on solidification. Heat resistant. Compressive & tensile strength increases with time comparable with silver amalgam Creep value are as low as 0.09% DISADVANTAGES low resistance to corrosion moisture contamination leads to expansion. Mix is mushy & sticks to everything except tooth

75. Mean hardness, the compressive strength, 24h tensile Strength and 24h flexural strength of Pd free Ga-alloy, were significantly lower than tin. Ga-alloy were consistently rougher than Hg based amalgam after polishing.

76. Consolidated silver alloy system Developed at the National Institute of Standards and Technology • Silver particles are suspended in a dilute fluoroboric acid solution to keep the alloy surfaces clean The alloy, in a spherical form, is condensed into a prepared cavity in a manner similar to that for placing compacted direct filling gold DISADVANTAGE - 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

77. Indium containing alloy powder Powell et al 1989, added pure indium powder into dispersed phase high Cu alloy & triturated with mercury They found significant decrease in mercury evaporation from amalgam. Youdelis also found that less mercury is required for mixing amalgam when it contains indium in concentrations up to 10%. Indium-containing admixed high-copper amalgam exhibited a reduction in creep and an increase in strength.

78. Fluoride containing amalgam Addition of fluorides to conventional amalgam was proposed by Innes and Youdelis 1966, Serman 1970. Addition of calcium fluoride Stannous fluoride Sodium fluoride

79. “ slow release device”

80. 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.

81. 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 amount

82. 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

83. AMALGAM BONDING SYSTEM Bonding interface may include tag formation. Diffusion impregnation of resin into pretreated dentin & subsequent polymerization resulting in hybrid layer formation. The bond is micromechanical . Good bonding occurs with tooth but bond to amalgam is still poor. Failure of bonded amalgam can take place as adhesive between tooth and amalgam cohesive within amalgam

84. AMALGAM BONDING SYSTEM AVAILABLE ARE- Panavia EX Prisma universal bond 2 All bond 2, Scotch bond multipurpose

85. Advantages 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. Disadvantages 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 .

86. Amalgam bonding technique

87. RESIN COATED AMALGAM 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 and others evaluated- bonded and sealed composite restorations placed directly over cavitated lesions extending into dentin V/S 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.

88. Packable powders An alternative to cohesive gold, which utilizes similar cold-welding to achieve condensation was described by Daniel et al. It consists of surface-treated, silvercoated , intermetallic, silver-tin particles. These are condensed (ideally as a wet slurry) in the presence of Fluoroboric acid, which removes oxide from the silver particles and enables cold-welding to take place. The result is a solid with properties somewhere between those of amalgam and cohesive gold.

89. 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 amalgam

90. 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.

91. AMALGAM REPAIR Amalgam restoration sometimes fracture due to faults made during cavity preparations and restorations procedures or where recurrent caries are present. An important factor related to the quality of amalgam repair is the strength of the joined amalgam surfaces. Variables that may affect the degree of bond strength of a repaired amalgam restoration include Type of amalgam alloy used Surface treatment of the aged amalgam alloy used Age differences between old and new amalgam

92. When a freshly triturated Amalgam is directly condensed onto the roughened surface of existing Amalgam, the flexural strength of the repaired structure can reach 50% of that of unrepaired Amalgam. A bond of upto 50% of unrepaired strength can be obtained when a repair is carried out subsequent to the first appointment. Basic requirement is to condition the surface with 10% polyacrylic acid for 10 sec before placement. Various studies results reported that use of resin bonding materials increased bonding ability of amalgam to another amalgam part (without using any bonding material, amalgam did not join to the original amalgam block)

93. 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 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.

94. CONCLUSION Amalgam restorations have served the profession well and will continue to do so in the years to come. In terms of longevity, they are probably superior to composite resins, especially when used for large restorations and cusp capping. The new high copper single composition alloys offer superior properties but may not offer as good seal as older amalgams. The use of amalgam can be continued as a material of choice if esthetics is not a concern.

95. 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”10th Edition M.A. Marzouk D.D.S. M.S.D. et al, “Operative Dentistry Modern theory and Practice” S. Mahalaxmi, “Materials used in Dentistry”.2 nd Edition Vimal. K. Sikri, “Silver Amalgam”, Text book of Operative Dentistry” 1st Edition

96. Thank you