amalgam1

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Amalgam

ALLOY Versus AMALGAM

• Alloy is a mixture of 2 or more metals

• AMALGAMMATION / TRITURATION – reaction when a silver based alloy is mixed with mercury, a liquid metal.

• Dental Amalgam - Is an alloy that contains mercury as one of its component

Why Amalgam?

• Inexpensive

• Ease of use

• Proven track record – >100 years

• Familiarity

• Life expectancy – 15 yrs

• Resin-free – less allergies than composite

ADVANTAGES

• Less technique sensitive

• More durable

• Less costly

• Excellent abrasion and wear resistance

• Tends to seal itself against leakage

• Bacteria do not adhere to it as strongly as n composite

DISADVANTAGES

• Esthetics, metallic color

• No bonding to tooth surface

• Extensive tooth preparation

Indications ( I,II,III, V,VI)

• Moderate to large restoration

• Restorations that are not in highly esthetic areas of mouth.

• Restorations that have heavy occlusal contacts.

• Restorations that can’t be well isolated

• Pin retained

Contraindications

• Esthetically prominent areas of teeth

Composition of Dental Amalgam

• Basic – Silver – Tin – Copper – Mercury

• Other – Zinc – Indium – Palladium

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Basic Constituents

• Silver (Ag) – increases strength – increases expansion – Decrease setting time

• Tin (Sn) – decreased strength – decreases expansion – increases setting time – Improves physical properties when compounded with Ag

Phillip’s Science of Dental Materials 2003

Dental Materials - Saunders

Basic Constituents

• Copper (Cu)

– increases strength

– reduces tarnish and corrosion

– reduces creep

• reduces marginal deterioration


Tarnish

• Oxidation that attacks the surface of the Am and extends slightly below the surface.

• Contact with oxygen, chlorides, and sulfides in the mouth.

• Dark dull appearance but not destructive to Am

• Palladium and Polishing may help reduce tarnish

• The rougher the surface, the more it tends to tarnish

Corrosion

• Oxidation from interaction of 2 dissimilar metals in the presence of a solution containing electrolytes

• Galvanism

• Oxidation of one of the metals

Creep

• Refers to the gradual change in shape of the restoration from compression by the opposing dentition.

Basic Constituents • Mercury (Hg)

– activates reaction – only pure metal that is liquid

at room temperature – spherical alloys

• require less mercury – smaller surface area easier to wet

» 40 to 45% Hg

– admixed alloys • require more mercury

– lathe-cut particles more difficult to wet » 45 to 50% Hg


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• Zinc (Zn) • decreases oxidation of other elements

– provides better clinical performance • less marginal breakdown

– causes delayed expansion • if contaminated with moisture during condensation


Other Constituents

• Indium (In) – decreases surface tension

• reduces amount of mercury necessary

• reduces emitted mercury vapor

– reduces creep and marginal breakdown

– increases strength

Powell J Dent Res 1989

Other Constituents

• Palladium (Pd)

– reduced corrosion

– greater luster

Mahler J Dent Res 1990

Component High copper Alloy % Low copper alloy %

Silver 40 -70 68 – 72

Tin 12 – 30 28 – 36

Copper 10 – 30 4 – 6

Zinc 0-1 0 - 2

Classifications

• Based on copper content

• Based on particle shape

Copper Content

• Low-copper alloys

– 4 to 6% Cu

• High-copper alloys

– thought that 6% Cu was maximum amount

• due to fear of excessive corrosion and expansion

– Now contain 10 to 30% Cu

• at expense of Ag


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Low Copper Amalgam

• “traditional” “conventional”

• COMPOSITION: ( Black’s)

• 65% SILVER

• 25% Tin

• < 6% copper

• 1% zinc

Setting Reaction of Low Copper Amalgam

(β+γ ) + Hg γ1 + γ2 + unconsumed alloy particles (β+γ )

γ – greek letter gamma

- used to designate the AgSn alloy or gamma phase

γ1 – AgHg

γ2 – SnHg

Low Copper Amalgam High Copper Am

• Compared with low copper alloys, this have become a material of choice.

• Improved mechanical properties

• Corrosion resistance

• Better marginal integrity

• Imroved performance in clinical trials

High Copper Am

• 2 types

• Admixed

• Single composition

• Both types contain more than 6 wt % copper

Admixed

• “Blended” , “admix”, or “dispersion” • These are called admixed alloys as they contain atleast 2 kinds of particles • Am made from these powders is stronger than

am made from lathe cut low copper powder, bec of inc in residual alloy particles and resultant dec in matrix

• Silver-copper particles as well as the AgSn paricles probably act as strong fillers in Am.

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Spherical High Copper Amalgams

• Unlike admixed, each particle of these alloy powders have the same chemical composition

• Thus , single composition alloys

• Single composition, high copper, spherical dental amalgams

• Have only 1 shape

• The particles are a combination of silver 60 wt % , tin 27 wt %, copper 13 wt % and other elements

Particle Shape

• Lathe cut alloy

• Spherical

• Admixed

Formed by shaving particles from a block of the alloy by a lathe

Formed by spraying molten alloy into an inert gas

Mixture of the two .

Alloy maybe made from different particle shapes to increase packing efficiency and reduce amount of Hg needed to obtain a workable mix.

Setting Transformation

• Alloy + liquid Hg = chemical reaction

• Mixture – putty like consistency

• Gradually becomes firmer

• Working time – the Am can be carved

• Initial set – it can’t be carved any more

• Once fully set , they are hard , strong

and durable

Properties of Amalgam

• Dimensional change

• Strength

• Corrosion

• Creep

Dimensional Change

• Severe contraction leaves marginal gap – initial leakage

• post-operative sensitivity

– reduced with corrosion over time Expansion leads to post operative sensitivity due to pressure

on pulp ADA specification No.1 requires amalgam neither contract or expand more than 20 um/cm Measured at 37 deg between 5 mins and 24 hours after beginning of trituration.


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Dimensional Change

• Net contraction – type of alloy

• spherical alloys have more contraction

– less mercury

– condensation technique • greater condensation = higher contraction

– trituration time • overtrituration causes higher contraction


Effect of Moisture contamination

• If a zinc containing low copper, or high copper amalgam is contaminated by moisture during trituration or condensation, a large expansion can take place.

• after 3-5 days

• may continue for months reaching values < 400 um.

• DELAYED EXPANSION or SECONDARY EXPANSION

Strength

• Develops slowly – 1 hr: 40 to 60% of maximum

– 24 hrs: 90% of maximum

• Spherical alloys strengthen faster – require less mercury

• Weak in thin sections – unsupported edges fracture


Strength

• High compressive strength

• Low tensile and shear strength

• Therefore

• Am MUST be supported by tooth structure

• Am needs sufficient bulk ( 1.5 or more)

Corrosion

• Reduces strength

• Seals margins

Sutow J Dent Res 1991

Creep

• Slow deformation of amalgam placed under a constant load – load less than that necessary to produce fracture

• Gamma 2 dramatically affects creep rate – slow strain rates produces plastic deformation

• allows gamma-1 grains to slide

• Correlates with marginal breakdown


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Creep

• Slow change in shape

• caused by compression

• High-copper amalgams have

creep resistance – prevention of gamma-2 phase

Clinical performance of Am Restoration

• Small amt of leakage under amalgam is unique

• Properly inserted – leakage decreases as restoration ages

• Corrosion products form along the interface between the tooth and the resto

Mercury/alloy ratio

• Historically, the only way to achieve smooth and plastic mixes was to use mercury considerably in excess of that desirable in final restoration.

• For convenional mercury –added systems, 2 techniques were employed to remove excess mercury

1. Removal of excess mercury was accomplished by squeezing or wringing themixed amalgam in a squeeze cloth

2. Additional excess mercury was worked to top during condensation of each increment

Minimal Mercury Technique Eames Technique

• Most obvious method for reducing mercury content is to reduce the original mercury/ alloy ratio.

• Sufficient mercury must be present in the original mix to provide a coherent and plastic mass after trituration

• But low enough so that the mercury content is at an acceptable level without the need to remove an appreciable amt during condensation

• Mercury content of finished should be about 50% wt% with lesser amt for spherical alloy

Proportioning

• Recommended mercury / alloy ratio for most modern lathe cut alloy is approx 1:1 or 50% mercury

spherical alloys its closer to 42% mercury

• Proper proportioning = proper mix

Proportioning

• Mercury / alloy dispensers

• Preweighed pellets or tablets

• Liquid mercury dispenser

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Proportioning

• Disposable amalgam capsules

• Preportioned mercury

Trituration

Trituration

• OBJECTIVEs :

• To provide a proper amalgamation of mercury and alloy

• Achieve a workable mass at a minimum time

• Reduce particle size leading to faster and more complete amalgamation

• Capsules serves as mortar

• a cylindrical metal or plastic piston serves as the pestle

• Sphrerical or irregular low copper alloy – low speed

• High copper – high speed

• AMALGAMATOR Speed:

• Low – 3200-3400 cycles/min

• Medium – 3700-3800 cycles/min

• High – 4000-4400 cycles/min

• INCREASED TRITURATION TIME = DECREASED WORKING AND SETTING TIME

Dentist-Controlled Variables

• Manipulation

– trituration

– condensation

– burnishing

– polishing

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Trituration

• Mixing time – refer to manufacturer

recommendations

• Overtrituration – “hot” mix

• sticks to capsule

– decreases working / setting time

– slight increase in setting contraction

• Undertrituration – grainy, crumbly mix

Properly triturated – warm, smoth- max strength , smooth


Mercury content

• Sufficient mercury should be mixed with the alloy to coat the alloy particles and to allow a thorough amalgamation.

• Each particle of the alloy must be wet by the mercury; otherwise a dry , granular mix results

• Any excess of mercury left in the restoration can produce a marked reduction in strength

Condensation

• GOAL:

• To compact the alloy into the prepared cavity so that greatest possibitlity of density is attained

• Mercury rich layer is brought to the surface of the restoration, so that successiv elayers bond to each other

• A fresh amalgam mix should be condensed within 3-4 mins

Hand Condensation

• Never touch with bare hands

• Gloves

• Immediatley condensed once inserted in the cavity

• With sufficient pressure

• Ave force applied: 13.3-17.8 N or (3-4 lb)

Condensation

• All amalgams except spherical alloys are condensed by small condensers to reduce voids

• Spherical alloys: large increments and condensers to fill entire cavity.

Carving and Finishing

• Reproduce proper tooth anatomy

• Immediately after condensation

• After carving = SMOOTHED by.. BURNISHING

• Burnish the surface and margins

• After , it will still be rough at a microscopic level

• FINAL POLISHING – after 24 hours

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Side Effects of mercury

• Am restoration is possible bec of mercury.

• The use of mercury has raised concerns as well as alleged side effects that may be sustained by patients who received amalgam restorations

Allergy

• Antibody – antigen reaction • Itching, • Rashes • Sneezing • Difficulty in breathing • Swelling • Contact Dermatitis or Coombs’Type IV

hypersensitivity • But these are experienced by less tha 1% of

treated population.

Toxicity

• It is still thought that mercury toxocity from dental restoration is cause of certain undiagnosed illnesses

• And a real hazard may exist for dentists and dental assistants when mercury vapor is inhaled during mixing and placement of amalgam.

• Improvements in encapsulation technology, scrap storage, elimination of carpets and other mercury retention sites

Toxicity

• The most significant contribution to mercury assimilation from dental amalgamis

• VAPOR PHASE

• Encounter is brief

• Mercury vapor amt – NO EFFECT level

• The threshold value for mercury industry workers-

• 350 -500 ug per dya ( 40 hr /wk)

• Patients get far below the values by US federal got

• Max level occupational exposure (safe) 50 um per cubic meter of air per day

• Mercury in blood • Patients w/ Am – 0.7 ng/ml • Patients w/o Am- 0.3 ng/ml

• 1 saltwater meal per wk raised mercury level in blood : • From 2.3 to 5.1 ng/ml

• Daily normal intake of Hg: • 15 um – food • 1 ug – air • 0.4 ug - water

Potential hazards form mercury can be reduced by:

• Well ventilated Operatory

• Well sealed containers ( Am scraps, capsules)

• Proper disposals

• Spilled mercury- cleaned up as soon as posiible

• Mercury suppressant powders

• If comes in contact with skin – wash with soap and H2O

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