Treatment of dental caries: AMALGAM.

1. Treatment of dental caries:AMALGAM. Properties, indications, inserting, carving, polishing. 3.Year - DM

2. AMALGAM • Amalgam is the most widly used permanent filling in dentistry. It is prepared by mixing the alloy with mercury. • The reaction between mercury and alloy is termed an amalgamation reaction. • It results in the formation of a hard restorative material of silvery – grey appearance

3. Amalgam Use and Benefits • Dental amalgam, in widespread use for over 150 years, is one of the oldest materials used in oral health care. • Its use extends beyond that of most drugs, and is predated in dentistry only by the use of gold. • Dental amalgam is the end result of mixing approximately equal parts of elemental liquid mercury (43 to 54%) and an alloy powder (57 to 46%) composed of silver, tin, copper, and sometimes smaller amounts of zinc, palladium, or indium.

4. Amalgam • MERCURY (Hg)– is a liquid at room temperature and it is able to form a workable mass when mixed with the alloy. • The reaction between mercury and alloy is termed anamalgamation reaction. • Dental amalgam has been used for many years with a large measure of success. • It is the most widely used of all available filling materials.

5. Composition • The composition of the alloy powder particles varies from one product to another. • Composition of CONVENTIONAL AMALGAM ALLOY: Metal: Weight: Silver (Ag) .......................... 65% min. Tin (Sn) ..............................29% max. Copper (Cu) ..............................6% max. Zinc (Zn) ...............................2% max. Mercury (Hg) ............................ 3% max.

6. Composition • 1. Silver- Increases strength, expansion and reactivity. Decreases creep. Corrosion products are AgCl and AgS. • 2. Tin- Increases reactivity and corrosion. Decreases strength and hardness. Corrosion products are SnO, SnCl, and SnS. • 3. Copper - Increases strength, expansion and hardness. Decreases creep. Corrosion products are CuO and CuS.

7. Composition • 4. Zinc - Increases plasticity, strength and the Hg:alloy ratio. Decreases creep. Causes secondary expansion. Corrosion products are ZnCl and ZnO. • 5. Mercury - Wets the alloy particles. Decreases strength if in excess amounts. Implicated in toxic and allergic reactions.

8. Effects on properties of an amalgam restoration imparted by ingredients.

9. Amalgam • The role of zinc (Zn) : is as a SCAVENGER during the production of the alloy. The alloy is formed by melting all the constituent metals together. • There are tendency for oxidation to occur. • OXIDATION of tin (Sn), copper (Cu) or silver would seriously affect the properties of the alloy and amalgam. • Zinc reacts rapidly and preferentially with the available oxygen, forming a slag of zinc oxide (ZnO) which is easily removed. • Many alloys contain no zinc. They are described as ZINC- FREE ALLOYS.

10. Amalgam: properties • 1. DIMENSIONAL CHANGES • 2. STRENGTH • 3. PLASTIC DEFORMATION (CREEP) • 4. CORROSION • 5. THERMAL PROPERTIES • 6. BIOLOGICAL PROPERTIES

11. 1. DIMENSIONAL CHANGES • A large contraction would result in a marginal gap down which fluids could penetrate. • A large expansion would result in the protrusion of the filling from the cavity. • Zinc reacts readily with water producing hydrogen: Zn + H2O –––––––––––– ZnO + H2 The liberation of hydrogen (H2) causes a considerable expansion.

12. 2. STRENGTH • 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. • 15 – 20 minutes after placing the filling , the AM is relatively weak. I tis necessary, to instruct patients not to apply undue stress to their freshly placed AM fillings. • There is good correlation between strength and mercury content. • Optimum properties are produced for amalgams containing 44-48% mercury.

13. 3. PLASTIC DEFORMATION (CREEP) • Amalgam undergoes a certain amount of plastic deformation or creep when subjected to dynamic intra-oral stresses. • The gamma 2 phase of AM is responsible for the relatively high values of creep. • The copper- enriched amalgams, which contain little or no gamma 2 in the set material, have significantly lower creep values • Gamma 2 phase is responsible for high creep.

14. 4. CORROSION • Corrosion is a matter which may significantly affect the structure and machanical properties. The heterogeneous, multiphase structure of AM makes it prone to corrosion. • The gamma 2 phase of a conventional AM is the most electrochemically reactive and readily forms the anode in an electrolytic cell. • The rate of corrosion is accelerated if the AM filling contacts a gold restoration. • Smooth surfaces are less prone to concentration cell corrosion.

15. 5. THERMAL PROPERTIES • AM has a relatively high value of thermal diffusivity Dentine is replaced by a good thermal conductor. • The coefficient of thermal expansion value for AM is about three times greater than that for dentine. • This results in considerably more expansion and contraction in the restoration than in the surrounding tooth when a patient takes hot or cold food or drink. • Thermal expansion may cause microleakage around the fillings since is no adhesion between AM and tooth substance. • Microleakage plays an important part in initiating such lessions.

16. 6. BIOLOGICAL PROPERTIES • Certain mercury compounds are known to have a harmfull effect on the central nervous system. • Some studies have shown a higher concentration of mercury in the blood and urine of patients with AM fillings than those without. • Another potential problem concerns allergic reactions, usually manifested as a contact dermatitis. • Mercury or freshly mixed AM should never be touched by hand. • Mercury is readily absorbed by the skin.

17. Usage and preparation of amalgam • The dental specialist has the direct responsibility for the correct preparation and use of amalgam. • Incorrect use may produce a faulty restoration that can cause or contribute to the loss of a tooth. • Therefore, the dental specialist must use extreme care in preparing a good mix of amalgam that will provide the best qualities obtainable from the alloy.

18. MANIPULATIVE VARIABLES The manipulating of AM involves the following sequence of events: • 1. Proportioning and dispensing • 2. Trituration • 3 Condensation • 4.Carving • 5. Polishing

19. 1. PROPORTIONING AND DISPENSING • Alloy/mercury ratios vary between 5:8 and 10:8. • Those mixes containing greater quantities of mercury are „wetter“ and are generally used with hand mixing. • Those mixes containing smaller quantities of mercury are „drier“ and are generally used with mechanical mixing. • Spherical particle alloys,for example , require less mercury to produce a workable mix.

20. 1. PROPORTIONING AND DISPENSING • For optimum properties, the final set amalgam should contain less than 50% mercury. • The optimal final mercury content ranges from an average of 45% for lathe-cut materials to an average of 40% for spherical materials.

21. 2. TRITURATION • The mixing or trituration of AM may be carried out by hand or in an electrically powdered machine which vibrates a capsule containing the mercury and alloy. • Trituration by hand is not extensively practised in developed countries nowadays. Mechanical mixing is far more widely used - amalgamator. • Trituration times 5 - 20 seconds are normal.

22. 2. TRITURATION The advantages of mechanical trituration are as follows: • 1. A uniform and reproducible mix is produced. • 2. A shorter trituration time can be used. • 3. A greater alloy/mercury ratio can be used. Amalgamator

23. 3. CONDENSATION • Material is condensed into the prepared cavity using a flat-ended, steel hand instrument called an amalgam condenser. The technique chosen for condensation must ensure the following. • 1. Adequate adaptation of the material to all parts of the cavity base and walls. • 2. Good bonding between the incremental layers of amalgam • 3. Optimal mechanical properties in the set amalgam by minimizing porosity and achieving a final mercury content of 44-48%.

24. 3. CONDENSATION • There should be a minimal time delay between trituration and condensation. • If condensation is commended too late, the amalgam will have achieved a certain degree of set and adaptation, and final mechanical properties are all affected. • There is a good correlation between the quality of an AM restoration and the energy expended by the operator who condenses it. • It needs to use a high condensating force. • Lower forces are required to condense spherical particle amalgams than lathe-cut materials.

25. Condensing instruments • Amalgam   carriers   and condensers are used for this purpose.

26. 4. CARVING • Soon after condensing the AM, the surface layer , which is rich in mercury, is carved away with a sharp instrument. • If carving is delayed too long the material may become too hard to carve and there is a danger of chipping at the margins.

27. 4. CARVING • Amalgam carvers

28. 5. POLISHING • Polishing is carried out in order to achieve a lustrous surface having a more acceptable appearance and better corrosion resistance. • The fillings should not be polished untill the material has achieved a certain level of mechanical strength, otherwisw there is a danger of fracture , particularly at the margins. • Many products require a delay of 24 hours between placing and polishing.

29. 5. POLISHING • AM polishing kits

30. AM polishers Black Dark purple Green

31. Amalgam indications • In primary and permanent dentition • In stress bearing areas of the mouth • Small to moderate - sized cavities in the posterior teeth • As a foundation to crowns • When oral hygiene is bad • When moisture control is a problem • When cost is a concern

32. Amalgam contraindications • When esthetics is important • When pation has a history of allergic reactions to the alloy • When cost is not a concern

33. Amalgam filling

34. Amalgam filling

35. Thank you for attention!