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 PROCESSIt is the process of alloying of mercury being in liquid state to Ag-Sn metal alloy being in the solid state.
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- Zink- free amalgam.When zinc comes in contact with moisture (saliva) delayed 2ndry expansion will occur.Zn + H2O ZnO + H2
4CLINICAL EFFECT OF MOISTURE 1- Secondary delayed expansion.2- Delayed pain.3- Overhanging margins.4- Recurrence of decay.5- Weak & corrodible amalgam.
5ACCORDING 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.
9(1) IN CASE OF THE LATHE-CUT TYPE: METHOD OF MANUFACTURING: All the alloy ingredients are melted forming an ingot (cast) then after cooling & solidification, we subject the ingot to a milling machine & so, we get fillings, needle shaped type.
10(2) IN CASE OF THE SPHERICAL ALLOY PARTICLES: METHOD OF MANUFACTURING: Pour the melted ingot into an inert gas chamber (N2 gas) [no O2 to prevent the oxidation] by spraying [Atomization] when they are sprayed by inert gas upon solidification, they will solidify in the form of spheres.
11(3) IN CASE OF THE ADMIXED TYPE: They manufacture lathe-cut alone & spherical alone & then they are mixed together.
12(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 .
13SHERICAL 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.
14MICRO-CUT AMALGAM ALLOY PARTICLES less than 10 microns* CHARACTARISTICS :- Greater amount of Hg required (Greater S.A: Surface appear granular) .- Less plastic mass.- Decreased compressive strength.
16COARSE-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.
20* Silver : It is the main ingredient of amalgam used to: - strength & hardness of amalgam.- flow.- Some expansion.
21* 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
23* Zinc:Acts as a scavenger or deoxidizer duringmanufacturing.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).
24* Reaction of conventional amalgam: It is a crystallization reaction: Ag3 + Hg Ag2Hg3 + Sn7Hg + Ag3Sn.σ + Hg σ σ unreacted σintermediate weakest strongeststrength phase phase
25- The strongest phase is σ , it gives very strong amalgam restoration followed by σ1then the weakest phase is σ2 which is susceptible to corrosion.- We have to eliminate Sn-Hg phase as much as possible to avoid weak amalgam restoration.
26(2) COMPOSITION OF HIGH COPPER AMALGAM ALLOY: * Silver : not less than %* Tin : not less than %* 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.
27** CHARACTARISTICS OF HIGH COPPER AMALGAM: (1) Higher early compressive strength.(2) Increased corrosion resistance.(3) Improved marginal integrity(4) Lower creep value
28** TYPES OF HIGH COPPER AMALGAM: (1) Admixed ( Lathe cut + Spherical)(2) Single composition (Spherical or Lathe –cut)
29(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).
30* Reaction : Mercury will penetrate bet. The particles * Ag3Sn (σ ) + Hg Ag2Hg3(σ1 ) Sn7Hg (σ2 ) + Ag3Sn (σ ).* Sn7Hg (σ2 ) + AgCu Ag2Hg3 (σ1 ) Cu6Sn5(E)* σ2 in the 1st reaction would be attacked by AgCu of the eutectic.* Cu has a very great affinity to Sn so, it forms a compound called Cu6Sn5.
31- The aim of this reaction is: How to get rid of Ag3Sn but at the same time presence of Sn is v.imp as it has more affinity to Cu than Hg so, it will react with Cu & form E form.* σ2 phase is eliminated & the net result is:σ σ σ EResultant is Cu6Sn5 phase.
32(2) Single COMPOSITION high copper amalgam : - Ternary Ag-Sn-Cu.- Indium or palladium 10% ( 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.
33* Reaction : Ag- Sn Cu + Hg Ag2Hg3(σ)+Cu6Sn5(E). - Sn has more affinity to Cu than Hg So, we have no σ2 phase no SnHg phase as it will not leave Cu& bond with Hg.
34(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.
35Disadvantages:  Dimensional changes.  Creep or flow tendency.  Inadequate tensile strength. Low edge strength. Thermal conductivity . Galvanism. Tarnish & corrosion. Inharmonious color.If it is properly manipulated we can overcome some if not all of these dis-adv.
36 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.
37b) Second stage:After 10 min. of triturition & till the first 8 hours, there will be sever expansion due to the formation of σ1 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.
38 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.
43 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 90o to increase the bulk of amalgam at this area
45 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.
46 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 a node & 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 .
47 Tarnish & corrosion Tarnish corrosion *It is an oxide film that causes discoloration (blackening).corrosion* It is the disintegration of the outer surface.
48* 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.
52Manipulation 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.1- Ratio 1:1 or 5:5 technique.2- Ratio 5:8 technique.* The ratio is by weight and not by volume.
534- Tarnish and corrosions. Excess mercury leads to :1- strength.2- Flow and creep.3- Expansion.4- Tarnish and corrosions.
54Less 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.
55Methods 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 be1) clean and dry.2) Vertical to obtain proper measurement.3) Half filled.
58Disadvantages: a) Some alloys can cling to the wall of the dispenser. b) Each dispenser is for one type of alloy l.e. can’t be used universally for all types of alloys
594- 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
625- Self-activated capsules: The process of amalgamation activates the capsuleAdvantages of proportioning capsule:1- More convenient.2- Proper Hg alloy ratio variables of dentists are eliminated.3- Prevent spill of Hg preventing Hg hazards.
63II- Trituration: * Definition: It is the process by which the alloy and mercury are amalgamated together into:- Coherent.- Homogeneous.- Smooth.- Plastic mass of amalgam.
64* 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.e.g: 2kg or 4 kg is 1 min. In 60 revolution.79
69Aims 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.37
70C. Climb along the side of the mortar and form a curl at its top. * Properly triturated amalgam will appear:A. Homogeneous.B. Smooth.C. Climb along the side of the mortar and form a curl at its top.21
71* 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.20
72Over 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.31
73B. 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.48
76II. 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.47
80* 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.56
815- 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 condensed must be either flat, smooth or serrated.6- Condensation should be completed under clean dry condition.60
82* 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.73
83e- 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.
842- 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.
85Carving 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.
87Excess Hg at the margins may cause: a- Marginal disintegration .b- Marginal leakage.c- Tarnish and corrosion.
885- In compound cavities, the occlusal portion is carved 1st 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.
89Double burnishing technique Means the amalgam is pre and post carving burnishedPre carving burnishingUsing large sized burnisher with heavy pressure
90Benefits of precarving burnishing A-Increase adaptation of amalgam to cavity walls and marginsB-Bring the mercury to the surfaceC- More cohesive amalgamD-Continue the process of condensation
91Post carving burnishing Small sized burnisher with gentle strokes just to smoothen the amalgam
92Finishing 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.mediumfinethey are used to correct surface discrepancies.
93b- Interproximal finishing instruments as: i- finishing strips in form of : coarse.mediumfineii- Abrasive discs.they are used to correct over hangs and give smooth interproximal surface.c- Finishing burs12 fluted.
942- 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 .
95* 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.
102ADVANTAGES: 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.
103DISADVANTAGES: 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.