Amalgam Fillings

Pros and Cons of Amalgam fillings.

1. Amalgam fillings Turgut novruzlu Vinnitsa medical university, ukraine 2019

2. Introduction to amalgam Amalgam is metallic filling composed of mercury and powdered alloy made of mostly of silver, tin, zinc and copper. Amalgam is still extensively used in world due to its cost-effectiveness, strength and longevity. It has it’s down sides as well such as toxicity due to mercury and lo aesthetic look.

3. Mercury Mercury is non-metal at room temperature, it reacts with other metals 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. Mixing of materials The alloy ( containing silver and tin) and mercury held together in a capsule, they are separated by a plastic diaphragm ( schematic demonstration on next slide). When the diaphragm is broken and the capsule is placed into the mixing machine ( amalgamator) 2 components are mixed together (triturated) to form a silver coloured paste This paste is then condensed into the cavity This is very important stage well condensed amalgams are stronger than poorly condensed ones. The final set material should contain 45-50% mercury- because if amount of mercury is low, it will be harder to work (manipulate) with material.

5. Types of amalgam Amalgam is classified acc. to Particles that make up the powder or the consitutent metals of particles.

6. Further about particles -Spherical particles are formed by spraying molten alloy into and inert atmosphere. It falls as spheres and solidifies. -Lathe-cut - as the name indicates, we grind the particles form a solid block of alloy to create powder. It gives more resistance when packing into cavities -Dispersed(Admixed) Consists of spherical silver/copper particles and lathe cut silver/tin particles. It is more favorable bc it is more easily condensed and contains less mercury and has better physical properties.

7. Setting reactions Reaction which takes place when Alloy Powder+Mercury happens, is complex. Mercury diffuses into the alloy particles, particles become totally dissolved in mercury. The alloy structure of the surface layers is broken down and constituent metals undergo amalgamation with mercury. The reaction products cyrstalise to give new phases in the set amalgam. A considerable quantitiy of the initial alloy remains unreacted at the completion of setting.

8. Amalgam trituration classification A) According to copper content 1.Low copper alloy < 6% copper (conventional alloy) II. High copper 6-30% copper B) According to zinc content Zinc containing alloy >0.01% zinc II) Zinc free alloy <0.01 Zinc

9. Gamma phases The set materials contain unchanged particle cores –hat consist of Gamma phase, surrounded by a matrix of Gamma1 and Gamma II. The γ2 phase  is associated with increases corrosion, creep( plastic change over time) and lower strength. Modern amalgams have low Gamma II content due to higher amounts of Copper Copper helps to convert Gamma II into Gamma I phase. It is achieved by formation of silver-copper alloy ( Cu6Sn5) Ag+ Cu+y2>>y1 + Cu6Sn5

10. Indications Permanent restoration material for Class I, Class II, Class IV and class VI caries acc to Black Cuspal restorations Pin retained restorations Retrograde root canal material Teeth with questionable prognosis Economic status

11. Contraindications Extensive loss of tooth structure Small class I and class II cavities acc to Black Esthetics

12. advantages Ease of use High compressive strength Excellent wear resistence Favorable long term clinical results Economic Can be bonded to tooth structure Self sealing ability

13. Disadvantages Bas aesthetics Less conservative Non-insulating Corrosion and galvanism Lack of reinforcement of weakened tooth structure Difficulty in restoring proper tooth anatomy

14. Functions of constituents silver Whitens the alloy Decreases creep Increases strength Increases expansion on setting Increases tarnish* to corrosion resistance *Tarnish is a thin layer of corrosion that forms over silver or copper.

15. Functions of constituents Tin Reduce tarnish and corrosion Reduce strength and hardness Decrease expansion Decrease setting tie Increase creep

16. Functions of constituents Copper Increases hardness and strength Increases setting expansion Decreases creep Tarnish to corrosion resistance

17. Functions of constituents Zinc Acts as deoxidizer and scavenger Causes delayed expansion in amalgam It improves plasticity and makes amalgam easy to manipulate

18. Functions of constituents Palladium Added to enhance mechanical properties Increase tarnish to corrosion resistance

19. Functions of constituents Mercury Increases setting time Decreases strength Increases setting expansion Increase creep Decrease tarnish and corrosion resistance

20. Properties of amalgam Dimensional changes- The setting reaction for amalgam involves a dimensional change. Strenght - The strength of dental amalgam is developed slowly. It may take up to 24 hours to reach a reasonably high value and continues to increase slightly for some time after that. At the time when the patient is dismissed from the surgery, typically some 15–20 minutes after placing the filling, the amalgam is relatively weak. It is necessary, therefore, to instruct patients not to apply undue stress to their freshly placed amalgam fillings.

21. Properties of amalgam Plastic deformation (Creep)- is is an indication about viscoelastic behaviour of amalgam.It undergoes a certain amount of plastic deformatior or creep when subjected to dynamic intra-oral stress. Creep value of amalgam is 36MPa. The least creep percent is in uncompositional high copper alloy it is 0.05- 0.09. ( in ordinary lather cut low copper alloy it is 6.3% and in spherical lo copper alloys 1.3-1.5%) Corrosion : . The integrity of the alloy is not affected and no change in mechanical properties would be expected. Amalgam readily tarnishes due to the formation of a sulphide layer on the surface. Copper-enriched amalgams contain little or no γ2 phase. The copper–tin phase, which replaces γ2 in these materials, is still the most corrosion-prone phase in the amalgam. The corrosion currents produced, however, are lower than those for conventional amalgams.

22. Biological property of amalgam Certain mercury compounds are known to have a harmful effect on the central nervous system. The patient is briefly subjected to relatively high doses of mercury during placement, contouring and removal of amalgam fillings.  A lower, but continuing, dose results from ingestion of corrosion products. Another potential problem concerns allergic reactions to mercury in dental amalgam. Such allergic reactions, usually manifested as a contact dermatitis or lichenoid reaction, are well documented and can normally be explained by previous sensitization of the patient with mercury-containing medicaments.

23. Properties of amalgam