80 MPa.
Undertrituration results in a grainy, crumbly mix.
Zinc acts as a deoxidizer and O2 scavenger, minimizing the formation of oxides during melting. Without zinc, amalgam becomes more brittle and less plastic during condensation.
Metal ingredients are heated, poured into a mold to form an ingot, which is then homogenized and cut into specific dimensions.
Spherical amalgam is more plastic, requires less mercury, and has better properties due to lower mercury content.
Elimination of the y2 phase is essential for improving the properties of the amalgam.
Ag & Sn dissolve in Hg, forming phases β (Ag-Sn), y (Ag3Sn), and ε (Cu3Sn)
η crystals are found as meshes of rod crystals at surfaces of alloy particles and dispersed in the matrix, reducing creep and preventing gamma 2 formation.
To prevent bending or pulling in tension that could compromise the restoration.
Sufficient pressure is needed to prevent voids and adapt the material to the walls of the cavity.
Voids and porosity may reduce compressive strength.
Microleakage can occur when contraction exceeds 50 microns.
The surface should be shiny after each increment.
Low-Cu amalgam restorations should be left undisturbed for at least 24 hours.
Liquid mercury is consumed in the formation of new solid phases.
Direct, permanent posterior restorations, large foundation restorations, and cores for crown or fixed partial denture restorations.
Made by melting desired elements together, then liquid metal is atomized into fine spherical droplets sprayed under high pressure of an inert gas, followed by heat treatment and acid washing.
The matrix band should be removed during the final carve.
High-Cu single composition alloys have each particle with the same chemical composition, unlike admixed alloys which contain different phases.
Easy to insert, not overly technique sensitive, maintains anatomical form, adequate resistance to fracture, prevents marginal leakage, can be used in stress-bearing areas, and has a relatively long life.
The y-phase is the strongest, while the y2-phase is the weakest and least stable in a corrosive environment.
Finishing decreases tarnish and corrosion.
Lathe-cut and atomized (spherical) powder.
High-Cu admixed alloys consist of two phases admixed together, containing more than 6% copper by weight, with spherical silver copper (Ag-Cu) eutectic alloy particles added to lathe-cut low-copper amalgam alloy particles.
Ag-Cu particles act as strong fillers that strengthen the amalgam matrix.
Tarnish is the result of silver sulfide forming on the surface and does not affect the mechanical properties of amalgam.
Moisture contamination leads to excessive absorption.
It is important to ensure sufficient mercury at the surface to diffuse into the next increment.
Finer particles result in a smoother surface, while lathe-cut particles require nearly 50% or more mercury compared to spherical alloys.
Crystals of mercury-containing compounds precipitate within the mercury.
As the content of liquid mercury decreases, the mixture hardens.
The main types are conventional low-copper amalgam and high copper amalgam.
'Dispersalloy' consists of 69% silver, 18% tin, 12% copper, and 1% zinc, with mixing proportions of 50% alloy and 50% mercury.
The most corrodible phase is Sn 7-8 Hg (y2).
Carving too deep makes it susceptible to fracture under direct occlusal loading.
Heat treatment of the alloy, size, shape & method of production of the alloy particles, surface treatment of the particles, and supplied form.
Lathe-cut alloys require small condensers and high force during condensation.
Spherical alloys use large condensers, are less sensitive to the amount of force, and involve vertical/lateral motion with vibratory action.
Larger particles may be pulled out during carving, producing a rough surface that is more susceptible to corrosion.
Epsilon develops crystals on the surface of gamma particles in the form of η (Cu6Sn5), which reduces creep and prevents gamma 2 formation.
The most common corrosion products are oxides and chlorides of tin.
It leads to greater marginal deterioration.
Overtrituration results in a hot mix that sticks to the capsule, decreases working/setting time, and causes a slight increase in setting contraction.
Alloy selection, mercury:alloy ratio, trituration procedures, condensation technique, marginal integrity, anatomy, final finish
Acid washed amalgam powders tend to be more reactive, and stress-relief processes like annealing can enhance the properties of the amalgam.
Brittle, subject to corrosion and galvanic action, may demonstrate marginal breakdown, does not help retain weakened tooth structure, and has regulatory concerns regarding disposal.
A eutectic is an alloy in which elements are completely soluble in liquid solution but separate into distinct areas upon solidification.
Spherical amalgam uses a large tip condenser, while mechanical condensers with high condensing force are more useful for lathe-cut alloys.
Trituration is the mixing of amalgam alloy particles with mercury in a triturator.
Oxides and chlorides of Sn.
At least 65% by weight Ag, 29% Sn, and <6% Cu, available in lathe-cut or spherical particles.
The strength of an amalgam is a function of the volume fractions of unconsumed alloy particles and mercury-containing phases.
The measures of amalgam quality include dimensional change, compressive strength, and creep.
Ag-Cu-Sn
Smaller particles increase surface area per unit volume, requiring less mercury to form acceptable amalgam, and contribute to more rapid hardening and greater early strength.
Burnishing is done to enhance the finish and integrity of the restoration.
The final structure consists of the y phase, Ag-Cu particles, ε particles, y1 matrix, and η reaction layers.
Polishing increases smoothness, decreases plaque retention, and reduces corrosion.
The presence of y2 increases the creep rate.
Each phase is given a Greek symbol based on the amount of Tin (Sn) they contain, and amalgam alloys have a narrow range of compositions.
Silver and Tin, with Copper added to harden and strengthen the silver-tin alloy.
Amalgam is an alloy containing mercury, formed by mixing liquid mercury with one or more metals/alloys.
Zinc-containing alloys can have problems with moisture contamination.
Resistance to compression forces.
Either undertrituration or overtrituration decreases strength.
They can be finished at the first appointment.
B phase (Ag-Sn), Y phase (Ag3Sn), e phase (Cu3Sn)
Alloy composition, Gamma sphere (y) – Ag3Sn with epsilon coating (ε) – Cu3Sn
Burnishing removes excess mercury, improves margin adaptation, and can enhance smoothness.
Sufficient mercury must be present to provide a coherent and plastic mass after trituration, while also being low enough to maintain an acceptable mercury content.
Delaying condensation permits the amalgam to set partially, making it impossible to remove mercury effectively and reducing plasticity, leading to poor adaptation to cavity walls.
During amalgamation, mercury dissolves the surface of alloy particles, forming a composite plastic mass.
Amalgam capsules contain powdered amalgam alloy and liquid mercury in separate compartments.
It can cause abnormal expansion.
The silver-copper eutectic alloy is composed of 71.9% by weight silver and 28.1% by weight copper.
Amalgam must be predominantly silver and tin, with zinc content specified as Zn >0.01% for zinc-containing and Zn < 0.01% for non-zinc.
The outer portion of the metal particles dissolves into mercury while mercury diffuses into the metal particles.
Amalgam should neither contract nor expand more than 20 microns/cm.
Overmixed amalgam becomes soupy and sticky, decreases working time, and slightly increases contraction.
An amalgamator mixes powdered and liquid components to achieve a pliable mass, with speeds varying upward of 3000rpm.
Lathe-cut alloys.
The main reaction occurs between Ag3Sn and mercury, resulting in a stronger amalgam with a greater number of unconsumed Ag-Sn particles in the final structure.
The elimination of y2 depends on the percentage of copper-containing particles, and it is replaced by the η phase.
Excessive expansion can occur, leading to intense pain and potential wedging against cavity walls.
Free mercury can contaminate and weaken the gold restoration, leading to galvanic corrosion.
Time-dependent strain or deformation produced by stress.
It is caused by hydrogen produced from contamination by moisture during trituration or condensation.
The main reactions produce alloy phases Ag2Hg3 (y1) and Sn7Hg (y2), with Ag and Sn dissolving into mercury during trituration.
When Sn diffuses to the surface of Ag-Cu particles, it reacts with Cu to form Cu6Sn5 (η) around the unconsumed Ag-Cu particles.
Gamma 1 (y1) – Ag2Hg3 crystals grow binding together partially dissolved gamma alloy particles Ag3Sn.
High-copper amalgam contains 6-60% by weight Cu, making mechanical cutting harder, and is mostly provided in spherical form produced by atomization.
Early finishing involves using a prophy cup with pumice after the initial set to provide initial smoothness, especially recommended for spherical amalgams.
It results in a dry granular mix, rough pitted surface, and corrosion.
They have η rods that limit the deformation of the y1 phase and no y2, resulting in decreased creep rate.
'Tytin' consists of 59% silver, 28% copper, and 13% tin, with mixing proportions of 57.7% alloy and 42.5% mercury.
Contraction results as particles dissolve and the y1 phase grows, with lower Hg:alloy ratios and higher condensation pressure contributing.
