Dental amalgam

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Dental amalgam

  1. 1. DENTAL AMALGAM
  2. 2. DEFINITION“Amalgam is a special type of alloy in which mercury is one of the component”
  3. 3.  Mercury is liquid at room temperature , it reacts with other metals that are in solid state, to form a plastic mass, which can be conveniently packed into a prepared tooth preparation. This plastic mass hardens by the formation of solid reaction product phases.
  4. 4. INDICATIONS As a permanent restorative material in class I, class II, class V, class VI caries Cuspal restorations Pin retained restorations As a foundation Post-endodontic access filling and core Die preparation Retrograde root canal filling material Teeth with questionable prognosis (interim restoration) Economic status
  5. 5. CONTRAINDICATIONS Esthetics Extensive loss of tooth structure Small class I and class II cavities
  6. 6. ADVANTAGES Ease of use High compressive strength Excellent wear resistance Favorable long-term clinical results Economic Can be bonded to tooth structure Self-sealing ability
  7. 7. DISADVANTAGES Lack of esthetics Less conservative Non-insulating Corrosion and galvanism Lack of reinforcement of weakened tooth structure Difficulty in restoring proper tooth anatomy
  8. 8. COMPOSITION (I) LOW COPPER ALLOYS: Silver -- 63-70% Tin -- 26-28% Copper -- 2-5% Zinc-- 0 -2% Setting reaction : Ag3Sn + Hg = Ag2Hg3 + Sn8Hg+ Ag3Sn (unreacted)
  9. 9.  (II) HIGH COPPER ALLOYS : Silver -- 69% Tin -- 17% Copper -- 13% Zinc -- 1% Setting reaction : Ag3Sn + Ag-Cu + Hg = Ag2Hg + Sn8Hg +Ag3Sn (unreacted)
  10. 10. CLASSIFICATIONBased on copper content : Low copper alloy -- < 6% copper (conventional alloy) High copper -- 6-30% copper (1) admixed alloy (2) single composition alloyBased on zinc content : (1) zinc containing alloy -- > 0.01% zinc (2) zinc free alloy -- < 0.01 zinc
  11. 11. Based on shape of alloy particles :(1) lathe cut alloy(2) spherical alloy(3) admixed alloyBased on size of alloy particles :(1) microcut(2) fine-cut(3) coarse-cut
  12. 12. Based on number of alloy metals : (1) binary alloy (silver-tin) (2) ternary alloy (silver-tin-copper) (3) quaternary alloy (silver-tin-copper-indium) Based on presence of noble metals :(1) noble metal alloys (palladium, platinum, gold) (2) non-noble metal alloys
  13. 13.  Based on the generations : (1) Basic silver-tin alloy (2) Low copper alloys (silver, tin, copper and zinc, Cu<4%) (3) High copper alloys (admixed alloys) (4) High copper alloys (single composition alloys) (5) Gallium based alloys (6) Noble metal alloys
  14. 14. FUNCTION OF EACH CONSTITUENT SILVER Whitens the alloy Decreases creep Increases strength Increases the expantion on setting Increases resistance to tarnis
  15. 15. TINReduce tarnish and corrosionReduce strength and hardness COPPERIncreases hardness and strength Increases setting expansion
  16. 16. ZINC Acts as a deoxidizer and scavengerCauses delayed expansion in amalgam
  17. 17. PROPERTIES DIMENSIONAL CHANGES : Most modern amalgams exhibit a very minor degree of contraction or expansion on hardening if they are properly handled By ensuring proper mercury content, plasticity of the mix, good condensation, burnishing, the amalgam can be well adapted to the prepared cavity Excessive contraction can lead to microleakage and secondary caries Excessive expansion can produce pressure on the pulp and post-operative sensitivity,or protrusion of restoration
  18. 18. Excessive delayed expansion can occur if azinc-containing amalgam is contaminatedby saliva or moisture during triturationor condensationThis delayed expansion can start 3-5daysafter the restoration is placed andcontinue for several months(400micronm)Zn+H2O=ZnO+H2(gas)
  19. 19. MICROLEAKAGE :Dental amalgam has a tendency to minimize microleakageIf the restoration is properly inserted, leakage decreases as the restoration ages in the mouthThis is due to the formation of corrosion products which forms at the interface between the tooth and the restoration. (copper and tin corrosion products)This corrosion products seals the interface and prevent the microleakage
  20. 20. STRENGTHExhibits high compressive strength andpoor tensile and shear strengthCompressive strength – 380 to 550 MpaTensile strength – 48 to 64 MpaAmalgam is brittle when placed inn thinsections, because of its low edge strengthHence amalgam should have adequatebulkIncrease in mercury , decreases thestrength of amalgam
  21. 21. CREEP Creep is progressive permanent deformation of set amalgam under dynamic loading during function Low copper amalgam – 2.5% creep (>Y2) High copper amalgam – 0.2% creep (<Y2) Clinically creep lead to protrusion of restoration making the amalgam more prone to fracture, overhangs
  22. 22. THERMAL PROPERTIES LCTE of amalgam is 2.5 times more than the tooth and amalgam is a good thermal conductor Hence pulp should be protected with either varnish, liners or bases
  23. 23. RIGIDITY MOE of high copper amalgam is 55 GPa(close to enamel). This increases the longivity of amalgam restoration
  24. 24. BIOCOMPATIBILITY It is related to the mercury vapour released during manipulation, placement and removal of amalgam However the amount is minimal and the possibility of toxic reactions in patients is less Careful handling of mercury reduces the risk to dentist or dental assistant
  25. 25. METALLURGIC REACTIONS (AMALGAMATION REACTIONS)
  26. 26. LATHE CUT LOW COPPER AMALGAM Y(Ag3Sn)+Hg---- Y1(Ag2Hg3)+Y2(Sn7Hg8)+unconsumed alloy particles +unreacted mercury
  27. 27. ADMIXED HIGH COPPER AMALGAM Stage 1 Y(Ag3Sn)+Ag-Cu(eutectic)+Hg---- Y1(Ag2Hg3)+Y2(Sn7Hg8)+Ag- Cu(unreacted)+Y(Ag3Sn)excessStage 2Y2(Sn7Hg8)+Ag-Cu(eutectic)---- n(Cu6Sn5)+Y1(Ag2Hg3)+Ag-Cu excess
  28. 28. SINGLE COMPOSITION ALLOYS(Ag-Sn-Cu)alloy particles+Hg---- Y1(Ag2Hg3)+n(Cu6Sn5)+unconsumed alloy particles
  29. 29. MANIPULATION OF AMALGAM(1) Selection of alloy and mercury(2) Mercury alloy ratio (Proportioning)(3) Trituration (Mechanical and hand)(4) Mulling(5) Condensation (Hand and mechanical)(6) Pre-carve burnishing(7) Carving(8) Post-carve burnishing(9) Polishing
  30. 30. THANK YOU

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