08.amalgam

amalgam

1. AMALGAM 1

2. (1) DEFINITION OF DENTAL AMALGAM It is the combination of dental amalgam alloy composed of silver, tin and copper with mercury (sometimes it contains zinc). DEFINITION OF AMALGAMATION PROCESS It is the process of alloying of mercury being in liquid state to Ag- Sn metal alloy being in the solid state. 2

3. (II) TYPES OF AMALGAM 1) According to copper content: 1- Conventional amalgam (Cu is less than 6%) 2- High copper amalgam (Non-∂ 2 amalgam) (Cu is more than 6%). 2) According to Zinc content: 1- Zinc containing amalgam. 2- Zinc- free amalgam. When zinc comes in contact with moisture (saliva) delayed 2 ndry expansion will occur. 3

4. CLINICAL EFFECT OF MOISTURE 1- Secondary delayed expansion. 2- Delayed pain. 3- Overhanging margins. 4- Recurrence of decay. 5- Weak & corrodible amalgam . 4

5. ACCORDING TO PARTICLES SHAPE 1- Lathe – cut alloy particles [Irregular shape needles]. 2- Spherical alloy particles. [Particles are rounded or spherical in shape] 3- Admixed alloy particles. 5

6. Lathe-cut 6

7. Spherical alloy 7

8. Admixed alloy 8

9. (4) ACCORDING TO PARTICLE SIZE: 1- Micro-cut alloy particle. 2- Fine-cut alloy particle. 3- Coarse-cut alloy particle. The best form is the Fine-cut . 9

10. SPHERICAL AMALGAM ALLOY PARTICLES CHARACTARISTICS: 1- Zinc content not required. 2- Less amount of Hg is needed. 3- Amalgamates more easily. 4- Less technique sensitive (adv.). 5- Increased early compressive strength. 6- Easier to condense, carve & polish. 10

11. MICRO-CUT AMALGAM ALLOY PARTICLES less than 10 microns * CHARACTARISTICS : - Greater amount of Hg required - Less plastic mass. - Decreased compressive strength. 11

12. Fine-cut amalgam alloy particles [10-30 microns] * CHARACTARISTICS : - Improved adaptation. - Smoother surface texture. - Easier carving & polishing. - Increased compressive strength. 12

13. COARSE-CUT AMALGAM ALLOY PARTICLES [Greater than 30 microns]. * CHARACTARISTICS : - Less amount of Hg required (adv but as particles are rough & large less adaptation) - Rough surface texture. - Decreased adaptation to cavity walls. - Increased compressive strength. 13

14. COMPOSITION OF AMALGAM ALLOY 1- Low-Cu alloy alloy (6%). 2- High-Cu alloy (6-30%) 14

15. COMPOSITION OF CONVENTIONAL SILVER/ TIN AMALGAM ALLOY: * Silver : not less than 65% by wt. * Tin : not less than 25% by wt. * Copper : not more than 6% by wt. * Zinc : not more than 0-2 % by wt. 15

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17. * Silver : It is the main ingredient of amalgam used to: - strength & hardness of amalgam. - flow. - Some expansion. 17

18. * Tin : tin is introduced to give plasticity of mass as tin has a great affinity to Hg so. It is attracted to Hg & so it gives plasticity to mass allows amalgamation process to take place easily * Strength * Flow * Cause contraction 18

19. *Copper: (like Ag) * strength * flow * produces expansion * Improves setting characteristics . 19

20. * Zinc: Acts as a scavenger or deoxidizer during manufacturing. It prevents the formation of oxides on Cu, Ag & Sn . Disadv .: if amalgam is applied below free gum margin , moisture contamination will cause excessive delayed secondary expansion ( 3-5 days after placement of restoration). 20

21. COMPOSITION OF HIGH COPPER AMALGAM ALLOY: * Silver : not less than 40 % * Tin : not less than 25% * Copper : 10 – 30% * Zinc : 0-2% - We cannot remove tin from the ingredients otherwise amalgam will be granular. - The increase in the % of copper is on the expense of Ag. 21

22. ** CHARACTARISTICS OF HIGH COPPER AMALGAM: (1) Higher early compressive strength. (2) Increased corrosion resistance. (3) Improved marginal integrity (4) Lower creep value 22

23. ** TYPES OF HIGH COPPER AMALGAM: ( 1) Admixed ( Lathe cut + Spherical) ( 2) Single composition (Spherical or Lathe –cut) 23

24. (1) Admixed high copper amalgam: * Composition: 10-20% copper - it is called Admixed type because some particles are spherical & some are lathe-cut . - 2/3 lathe-cut. - 1/3 spherical Ag-Cu (eutectic phase). 24

25. (2) Single COMPOSITION high copper amalgam : * COMPOSITION : 13-30% copper. - Ternary Ag- Sn -Cu. - Indium or palladium upto10 % ( to creep & corrosion resistance) - it is made of one type only of alloy lathe cut or spherical, not a mixture. - Each alloy particle contains Ag- Sn -Cu whether it. spherical or lathe – cut this is called ternary alloy. - Indium corrosion resistance. 25

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27. (IV) PROPERTIES OF AMALGAM RESTORATION: Advantages : (1) Adequate compressive strength. (2) High abrasion resistance. (3) Insolubility in oral fluids. (4) Adaptability to cavity walls. (5) Convenience of manipulation. (6) Biocompatibility with oral & dental tissues. 27

28. Disadvantages: [1] Dimensional changes. [2] Creep or flow tendency. [3] Inadequate tensile strength. [4] Low edge strength. [5] Thermal conductivity . [6] Galvanism. [7] Tarnish & corrosion. [8] Inharmonious color. If it is properly manipulated we can overcome some if not all of these dis -adv . 28

29. [1] Dimensional changes: - Regarding the dimensional changes amalgam undergoes .3 stages: a) First stages: When Hg is added to the alloy powder & after trituration by 10 min. Amalgam undergoes slight contraction due to the penetration of Hg into the alloy particles. 29

30. b) Second stage: After 10 min. of triturition & till the first 8 hours, there will be sever expansion due to the formation of σ 1 phase or silver – mercury phase. c) Third stage: After 24 hours there will be very slight contraction as a result of the setting of amalgam mass, all the phases of amalgam approach each other. 30

31. [2] Creep or flow tendency: Deformation of amalgam under load. * Creep : Deformation of amalgam restoration under load after it has completely set. * Flow : Deformation of amalgam restoration under load before it has set. 31

32. Disadvantages : 1- Flattening of contact area. 2- Over hanging. 3- Protrusion of restoration. 32

33. [3] Inadequate tensile strength: - Amalgam can fracture at the isthmus (junction b/w Occlusal & proximal parts) due to its low tensile strength under tension load. 33

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35. [4] Low edge strength: - The low edge strength is responsible for the fracture at the margins. (1) Amalgam ditch can occur I.e. v-shaped groove that occurs as a result of fracture of the margins of amalgam between amalgam & cavity walls at the cavosurface margin. To prevent this, the cavosurface angle must be 90 o to increase the bulk of amalgam at this area 35

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37. [5] Thermal conductivity: Amalgam can transmit thermal impulses to the pulp & this can be overcome by putting cement. - In deep cavities we put a liner to protect pulp from Thermal conductivity. - In shallow cavities there is enough dentin to protect pulp. 37

38. [6] Galvanism - If we have two dissimilar metals on the same side ex: amalgam & the other is gold, saliva acts as the electrolyte, amalgam acts as anode & gold acts as cathode so, when they come in contact ions are transmitted from amalgam to gold & this causes pain. As an electric current will pass. - This is associated with corrosion & it is called galvanic corrosion . 38

39. [7] Tarnish & corrosion Tarnish *It is an oxide film that causes discoloration (blackening ). corrosion * It is the disintegration of the outer surface. 39

40. * Indications: - Class I - Class II - Class v - and distal cavities of canine in class III. * Contra Indication: - Anterior cavities . - In the presence of other metallic restoration. To avoid galvanism. 40

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42. [VI] Clinical application of amalgam restoration [1] Cavity preparation & pulp protection. [2] Matrix & wedge application. [3] Alloy selection & proportioning . [4] Triturition & condensation. [5] carving & burnishing. [6] Wedge & matrix removal. [7] Finishing & polishing. 42

43. Manipulation The ratio (or the alloy / mercury ratio): The amount of mercury needed is to coat all the particles to produce homogeneous coherent mass of amalgam. Ratio 5:8 to 10:08 technique . * The ratio is by weight and not by volume . 43

44. Excess mercury leads to : 1- strength. 2- Flow and creep. 3- Expansion. 4- Tarnish and corrosions. 44

45. Less mercury leads to : 1- non-coherent. 2- Weak. 3- Less resistance to tarnish and corrosion. N.B : Each in Hg by 15% results in 1.5% excess in the final restoration. 45

46. Methods of proportioning: 1- Simple weighing balance . 2- Tablets or pellets where amount of Hg is measured according to the manufacture by a mechanical dispenser. 3- Automatic mechanical dispenser . Dispenser should be 1) clean and dry. 2) Vertical to obtain proper measurement. 3) Half filled. 46

47. Disadvantages: a) Some alloys can cling to the wall of the dispenser. b ) Each dispenser is for one type of alloy i.e . can’t be used universally for all types of alloys 47

48. 4- Preproportioning capsules (the best method) proper alloy and Hg ratio is done by manufacturing and are put in a capsule. A disc or membrane separates Hg and alloy to prevent premature amalgamation. Activation is done before trituration . This is done by removal of the membrane, and provide contact between alloy and Hg. This could be done by - Pressure. - Twisting cover of capsule 48

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51. 5- Self-activated capsules: The process of amalgamation activates the capsule Advantages of proportioning capsule: 1- More convenient. 2- Proper Hg alloy ratio variables of dentists are eliminated. 3- Prevent spill of Hg preventing Hg hazards. 51

52. II- Trituration : * Definition: It is the process by which the alloy and mercury are amalgamated together into: - Coherent. - Homogeneous. - Smooth. - Plastic mass of amalgam. 52

53. * Methods of trituration : a. Manual trituration using Mortar and Pestle. b. Mechanically using electric amalgamator. A. Hand trituration : i - Glass mortar and pestle are used. ii- Should be cleaned to prevent contamination. iii- The face of the Pestle must have the same shape as the surface of the mortar for effective trituration . iv- Both Mortar and Pestle should present an even rough working surface for effective trituration . v- The trituration process must be standardized by rate, time and pressure . 53

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56. Aims of trituration . a. To rub off the oxide layer on the alloy particles. b . For further reduction of the size of the alloy particles. c. To bring the mercury into contact with the alloy particles to start the reaction. 56

57. * Properly triturated amalgam will appear: A. Homogeneous. B. Smooth. C. Climb along the side of the mortar and form a curl at its top. 57

58. * Under triturated leads to: A. Weak. B. Non-homogeneous. C. Excess mercury. D. Appear dull. E. Non-coherent. F. Undergo more expansion. G. More tarnish and corrosion. 58

59. Over triturated leads to: A. Sets faster. B. Greater one hour strength. C. Smooth surface. D. Less flow. E. More tarnish and corrosion resistance. F. The only disadvantages is that it may undergo contraction farther than expansion. 59

60. B. Mechanical Trituration : . This method: 1- Saves time. 2- Gives better standardization, for the triturated amalgam. * Mulling of amalgam: It is a process of mulling the properly triturated amalgam for few sec. In a piece of rubber to acquire a max. degree of plasticity. 60

61. II. Condensation: * Definition: It is the process of packing of the properly triturated amalgam in the prepared cavity. *Aims: 1. The adaptation of amalgam to cavity walls and margins. 2. The adaptation between successive layer of amalgam . 3. Express excess mercury and density of the alloy. 4. The compressive strength of amalgam. 61

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66. * Requirements for proper condensation: 1. Only fresh mixes should be used. (Mixes more than 3.5min. Should be discarded, this is to avoid layering of amalgam. 2. We must use successive increments for effective condensation. 3. Great condensation pressure is required, directed , towards cavity wall, and margins. 4. Each condensed layer must be properly stable other wise weak amalgam will result. 66

67. 5- A proper sized and designed condenser must be used: i . It should be small enough to exert great pressure, but not too small to cause holes in the amalgam. ii . It should be properly angulated to reach all areas of the cavity. iii. The face of the condenser must be either flat , smooth or serrated. 6- Condensation should be completed under clean dry condition. 67

68. * Condensation technique: 1- By hand condensation and it should be as follows. a . The restoration is built from small successive increment. b . In case of compound cavities, the box should be filled first to the level of pulpal floor, then the occlusal . c . Small piece of amalgam is carried by amalgam carrier and forced into the cavity. d . The first layer is condensed with great force using small condenser from the center of the cavity to cavity margins . 68

69. e- The mercury rich amalgam on the surface is removed with spoon excavator. f- The process is repeated until the cavity is completely filled. g- A final dry piece is condensed to over fill the cavity and over come the excess mercury of the last layer and then this layer is removed leaving the surface of amalgam with no excess mercury. 69

70. 2- Mechanical condensation: by ultrasonic device * Advantages of mechanical condensation: 1- It is more standardized . 2- Less fatigue to the operator. 3- It produces homogenous amalgam. 4- More strength property for the final amalgam. 5- Less flow. 6- More stability. 7- Less expansion. 70

71. Carving of Amalgam : 1- We use suitable amalgam carver. 2- Amalgam must not be carved unless it becomes hard enough to resist carving instrument ( for about 3.5 min). 3- Sharp instrument must be used for carving, to not disturb the matrix. 4- Avoid carving towards cavity margins to avoid under filling and expression of excess mercury towards the margin. 71

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73. Excess Hg at the margins may cause: a- Marginal disintegration . b- Marginal leakage. c- Tarnish and corrosion. 73

74. 5 - In compound cavities, the occlusal portion is carved 1 st before removal of matrix. 6- After carving of the occlusal portion , the matrix holder is unscrewed and band is removed either buccally or lingually . Avoid its removal occlusally to avoid fracture of the margins. 7- The proximal contour is carved and then contact is checked by using dental floss, silk . 74

75. Double burnishing technique Means the amalgam is pre and post carving burnished Pre carving burnishing Using large sized burnisher with heavy pressure 75

76. Benefits of precarving burnishing A-Increase adaptation of amalgam to cavity walls and margins B-Bring the mercury to the surface C- More cohesive amalgam D-Continue the process of condensation 76

77. Post carving burnishing Small sized burnisher with gentle strokes just to smoothen the amalgam 77

78. Finishing and polishing of Amalgam: It should be done to give a luster-like smooth surface after at least 24 hrs. * Finishing and polishing is achieved by using: 1- Rotating finishing instruments which include: a- Finishing stones as carburundum green stones in form of : coarse. medium fine they are used to correct surface discrepancies. 78

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80. b- Interproximal finishing instruments as: i - finishing strips in form of : coarse. medium fine ii- Abrasive discs. they are used to correct over hangs and give smooth interproximal surface. c- Finishing burs12 fluted. 80

81. 2- Rotating polishing instruments include: a- Rubber cups in form of coarse, medium or fine applied with polishing paste at low speed. b- Rotating soft brush applied with polishing paste . 81

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85. * If amalgam restoration is not finished and polished, then the surface remains rough leads to : a- Surface porosities. b- Food and plaque accumulation. c- Tarnish and corrosion. d- Concentration of stresses. 85

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92. ADVANTAGES: 1- High compressive strength properties (45000PSI). 2- Low coefficient of thermal expansion. 3- Indestructibility in oral fluid. 4- Easy of manipulation. 5- It is capable to take and maintain a good polish. 92

93. DISADVANTAGES : 1- Low tensile strength. 2- Bad esthetics due to unnatural color and the tendency for corrosion . 3- High thermal conductivity. 4- Slight changes in dimension during setting. 93

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