amalgam mod

AMALGAM

An amalgam is an alloy containing mercury.

DENTAL AMALGAM

An alloy of mercury with silver, tin, copper, & some times Zinc.

AMALGAMATION (Trituration)

Mixing of mercury with other metals.

Dental Caries

1 2

3 4

5 6

7 88

Uses• Direct, permanent, posterior restorations

• Large restorations

• Core build up material

• Die Materials

Classification

Based on Copper content

Low copper

or

Conventional alloys

contains less than 6%

of Copper.

High copper or

Copper enriched alloyscontains greater than 6%

of Copper.

Classification of High Copper alloys

High Copper Alloys

Admixed alloys

(Low copper+Spherical alloys)

Uni/Single Composition alloys

Lathe-cut v.s. Spherical

Irregular or Lathe-cutIrregular or Lathe-cut SphericalSpherical

Composition of low copper alloys

Ingredient Wt %

Silver 67 – 74

Tin 25 – 27

Copper 0 – 6

Zinc 0 - 2

Composition of Admixed high copper alloys

Ingredient Wt %

Silver 69

Tin 17

Copper 13

Zinc 1

Composition of Unicompositional High Copper alloys

Ingredient Wt %

Silver 40 – 60

Copper 13 – 30

Tin 17

Functions of each ingredient

Ingredient

Increase Decrease

Silver Strength, setting expansion, reactivity with mercury

creep

Tin Creep, Contraction, Rate of Amalgamation

Strength, Hardness & speed of Setting

Copper Hardness, strength, setting expansion, and tarnish.

Zinc Delayed expansion, & corrosion. Acts as an Oxide scavenger

Symbols of Phases

Phases in Amalgam Alloys and Set Dental Amalgams

Formula

Ag3Sn

1 Ag2Hg3

Sn7-8Hg

Ag4Sn (silver-rich)

Cu3Sn

Cu6Sn5

Silver-copper eutectic Ag-Cu

Setting reaction of low Cu alloys

Ag3Sn () + Hg

Ag2Hg31) + Sn7-8Hg(2)+ unreacted particles

Setting reaction of low Cu alloys

• When a powder (Ag3Sn, ) is triturated, the Ag and Sn in the outer portion of the particles dissolve into Hg (mercury).

• Hg also diffuses into the alloy particles.– Solubility for Ag = 0.035 wt%, for Sn = 0.6 wt%

Setting reaction of low Cu alloys• When the solubility is exceeded, crystals of

two binary metallic compounds precipitate into the mercury.– Ag2Hg3 compound (1) precipitates first.

– Sn7-8Hg compound (2) precipitates later.

As the remaining mercury dissolves the alloy particles, 1 and 2 crystals grow.

Setting reaction of low Cu alloys• As the mercury disappears, the amalgam hardens.

Particles become covered with newly formed crystals, mostly 1.

• Unconsumed particles (smaller after being partly dissolved) are surrounded and bound together by solid 1 and 2 phases

trituration condensable, carvable harden, no longer workable

Microstructure of low Cu alloys

• A typical low-copper amalgam is a composite in which the unconsumed particles are embedded in 1 and 2 phases.

P = and Ag-SnE = (Cu3Sn)

G1 = (Ag2Hg3) G2 = (Sn7-8Hg)

Low-copper Alloys

• Physical properties. -phase strongest,

. 2 phase weakest

3. Hardness: > 1 >>> 2

4. 2 poor corrosion resistance.

This phase has to be eliminated to increase strength and corrosion resistance.

High copper Alloys

• Introduced in 1977.

• Importance:

– Elimination of 2 phase

High-Cu: Admixed Alloys (1)• Spherical silver-copper (Ag-

Cu) eutectic alloy particles are added to lathe-cut low-copper amalgam alloy particles.

• The final powder is composed of two kinds of particles. “admixed”

• Ag-Cu particles act as strong fillers, strengthening the amalgam matrix.

High-Cu: Admixed Alloys (2)

• Silver-Copper eutectic alloy

• 71.9 wt% Ag, 28.1 wt% Cu

Setting Reaction of High-Cu: Admixed Alloys

First:

Ag3Sn () + Ag-Cu (eutectic) + Hg

1 + + unreacted alloy of both types of particles

Later:

Sn7 – 8Hg + Ag – Cu Cu6Sn5 + Ag2Hg3

Eu 1

Setting Reaction of High-Cu: Admixed Alloys • Ag dissolves into the Hg from

the Ag-Cu alloy particles.

• Both Ag and Sn dissolve into Hg form the G1 & G2 alloy particles. (same as in low-Cu alloy)

• Sn in solution diffuses to the surface of Ag-Cu alloy particles and reacts with the Cu to form the phase (Cu6Sn5) (therefore,

the Sn7-8Hg or 2 is eliminated)

Setting Reaction of High-Cu: Admixed Alloys

• A layer of forms around unconsumed Ag-Cu particles.

1 phase is the matrix.

Microstructure:• The final structure composes

of the phase, Ag-Cu particles, particles, 1 matrix, and reaction layers.

High-Cu: Admixed Alloys

2 has been eliminated in this reaction, being replaced by .

• The effectiveness in eliminating 2 depends on percent of copper-containing particles.

(net copper concentration of > 12% in alloy powder)

High-Cu: Single-composition Alloys

• Each particle has the same chemical composition.

• Major components: Ag-Cu-Sn

Setting Reaction of Unicomposition Alloys

Alloy particles (Ag-Sn-Cu) + Hg

1 + + unreacted alloy particles

High-Cu: Single-composition Alloys

• Phases found in each single-composition alloy particle are (Ag-Sn), (Ag3Sn), and (Cu3Sn).

crystals are found as meshes of rod crystals at the surfaces of alloy particles (P), as well as dispersed in the matrix.

1

P

Properties of Amalgam

Strength

It is a brittle material.

Strong in compression

Weaker in tension & Shear.

Creep• It is defined as time dependent plastic deformation

under static or dynamic loads.

• According to ADA specification number 1 the creep should be less than 3%.

• But low copper alloys have a creep value of 0.8 to 8%.

• High copper alloys have a creep value between 0.1 to 0.4%.

CreepDetermination of creep• A cylindrical sample of 4 mm diameter and 8 mm

height is prepared, preserved for 7 days at 370C and then subjected to a static load of 36 N.

• The percentage decrease in the height in 3 hrs, in between the ends of 1 hour and 4 hours is taken as creep.

• Conventional alloy > Admixed alloy > Uni composition alloy

Dimensional changes• Expansion or contraction.

• Expansion leads to amalgam fracture or dislodgement from cavity, hyper occlusion, and Pulpal pain.

• Contraction leads to marginal leakage and secondary caries.

Contraction Expansion

Dimensional changes

Expansion

• After amalgamation, initially the γ1 crystals formed will start to grow in due time which push each other and causes expansion and this continues until the mass becomes rigid.

Contraction• Due to inadequate mercury, which required for later

reaction i.e.; growth of crystals and condensation.

36

Delayed Expansion

• Delayed expansion is a 4% as more expansion taking place in zinc containing alloys after a period of 3-7 days.

• This is due to moisture contamination during manipulation.

Zn + H2O ZnO + H2

Tarnish & Corrosion

TarnishIt is a process by which metal surface is dulled in

brightness or discolored through the formation of chemical film such as Sulphide and an oxide.

CorrosionIt is a process in which deterioration of a metal is

caused by reaction with its environment.

Tarnish & Corrosion• It is mainly due to γ2 phase, which acts as

anode due to more active electro chemical nature and other phases act as cathode and saliva acts as a medium.

• Corrosion products (oxides and chlorides of Sn) will be released in to the interfacial space between restoration and tooth structure that prevents the microleakage, called as self-sealing ability of amalgam.

Corrosion products

Marginal leakage• The initial marginal leakage of Amalgam

restoration reduces with the time.

Reason:

Corrosion products seals the marginal gap between the restoration & the tooth.

Corrosion products

Toxicity

• Mercury is toxic.

• Mercury should not be exposed to the atmosphere.

• Can discolor the tooth.

Other symptoms• Fatigue, • Weakness, • Headache, • Dizziness, • Renal disorder.

Room Air: Human Respiration

0 µg/m ³

0 sec 32 µg/m ³

500 m L

Room Air: Human Respiration

32 µg/m ³

500 m L

32 µg/m ³2½ sec

Manipulation of Amalgam

1. Selection of Alloy

2. Proportioning

3. Trituration

4. Condensation

5. Trimming & Carving

6. Polishing

1. Selection of Alloy

• Composition

• Particle size

• Particle Shape

• Presence or absence of Zinc

1. Selection of AlloyComposition• When hardness is

needed – Cu containing alloys.

• When fast setting is required – Spherical alloy powders.

Effect of Particle sizeSmall Particle• Rapid hardening.• Greater strength.• Gives smoother surface.

Large Particle• Rough surface.• Tendency to corrosion.• Pulled out of the surface

during carving.

1. Selection of Alloy

Particle shape

Lathe cut/Irregular particles• Have more surface area

more mercury is needed (50%).

• Need high condensation pressure.

Spherical Particles• Requires less mercury

(42%).

• Need less condensation pressure.

1. Selection of Alloy

Presence or absence of Zn

• Presence of Zn Leads to delayed expansion (3 to 5 days).

2. Proportioning

• It is the ratio of the amount (by weight) of alloy to mercury used for a particular technique.

Ideal proportioning

• Lathe cut – 1:1 (50:50)

• Spherical alloy – 40:60

2. ProportioningSqueeze dried technique: • A gauge cloth is taken and the mix is placed on it

and squeezed to remove excess mercury.

Eame’s technique or minimum mercury technique:• In this technique the actual volume of mercury taken

is regulated i.e.; in the ratio of 1:1.

Condensation technique or increasing dryness tech: • The mix is condensed to remove excess mercury,

which comes to surface.

3. Trituration

• it is a process in which both mercury and alloy powders are mixed to get a plastic mix.

• Objective: The objective is to remove the oxide layer formed on the particles so that mercury can react with powder.

3. Trituration

• Trituration is done in either mortar & Pestle or in an amalgamator/triturator.

• 2 types.– Hand Trituration – Mechanical Trituration

3. TriturationHand trituration • It is done with mortar

and pestle.

• The inner surface of mortar is roughened to increase friction.

• A pestle is a glass/ceramic rod with a round end.

3. TriturationMechanical Trituration• Mechanical amalgamators are

used.

• The amalgamators are devices with an automatic controlled timer and speed control device and work by either vibratory or oscillatory movements.

Advantages of mechanical trituration• Shortens mixing time.• Most standardized and accurate procedure.

4. Condensation• Condensation is a process of packing a plastic mass of

amalgam in to a prepared cavity by force under pressure.

Aims• Good marginal adaptability.

• Good bonding between incremental layers of amalgam.

• Removal of excess mercury.

• To increase the density of mix hence optimum mechanical properties & also decrease porosities & voids.

4. Condensation

• After mixing, amalgam mix should be condensed as soon as possible to achieve,

1. Proper adaptation to the cavity walls.

2. Elimination of excess mercury.

3. Bonding between amalgam increments.

4. Optimum strength.

Carriers

4. Condensation

Condensation of plastic mass Condensed restoration

5. Carving

• Carving is done to reproduce tooth anatomy for occlusal benefits.

• Carving is done after hearing amalgam cry i.e.; scrapping or ringing sound, which indicates initial set.

• Over carving and under carving should be avoided.

Finishing and polishing

• Finishing and polishing is done after 24 hours by using wet abrasives such as pumice.

• Care should be taken to avoid high temperatures.

Copper Amalgam

• Used as filling material in deciduous teeth.

• Have antibacterial effect due to the presence of Cu.

• Supplied in the form of pellets.

Mercury – 60 to 70%

Copper – 30 to 40%

Copper Amalgam

Manipulation

• The pellets/tablets are heated until droplets of mercury are appeared.

• Later triturated & condensed into a cavity.

Disadvantages

• Poor Hg hygiene associated with its use.