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Treatment of dental caries: AMALGAM. Properties, indications, inserting, carving, polishing. 3.Year - DM. AMALGAM. Amalgam is the most widly used permanent filling in dentistry. It is prepared by mixing the alloy with mercury.

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treatment of dental caries amalgam

Treatment of dental caries:AMALGAM.

Properties, indications, inserting, carving, polishing.

3.Year - DM

amalgam
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
amalgam use and benefits
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.

amalgam1
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.
composition
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.

composition1
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.
composition2
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.
amalgam2
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.
amalgam properties
Amalgam: properties
  • 1. DIMENSIONAL CHANGES
  • 2. STRENGTH
  • 3. PLASTIC DEFORMATION (CREEP)
  • 4. CORROSION
  • 5. THERMAL PROPERTIES
  • 6. BIOLOGICAL PROPERTIES
1 dimensional changes
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.

2 strength
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.
3 plastic deformation creep
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.
4 corrosion
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.
5 thermal properties
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.
6 biological properties
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.
usage and preparation of amalgam
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.
manipulative variables
MANIPULATIVE VARIABLES

The manipulating of AM involves the following sequence of events:

  • 1. Proportioning and dispensing
  • 2. Trituration
  • 3 Condensation
  • 4.Carving
  • 5. Polishing
1 proportioning and dispensing
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.
1 proportioning and dispensing1
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.
2 trituration
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.
2 trituration1
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

3 condensation
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%.
3 condensation1
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.
condensing instruments
Condensing instruments
  • Amalgam   carriers   and condensers are used for this purpose.
4 carving
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.
4 carving1
4. CARVING
  • Amalgam carvers
5 polishing
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.

5 polishing1
5. POLISHING
  • AM polishing kits
slide30
AM polishers

Black

Dark purple

Green

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