Lecture 1 & 2- Dental Amalgam (Slides)

8/4/2019 Lecture 1 & 2- Dental Amalgam (Slides)

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DENTAL AMALGAMDENTAL AMALGAM


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OverviewOverview

Basic compositionBasic composition

ClassificationsClassifications

Basic setting reactionsBasic setting reactions

PropertiesProperties

Clinical handling notesClinical handling notes

ManipulationManipulation


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Why Amalgam?Why Amalgam?

InexpensiveInexpensive

Ease of useEase of use

Proven track recordProven track record

>100 years>100 years

FamiliarityFamiliarity

Drawbacks:Drawbacks: EstheticsEsthetics

Mercury contentMercury content


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Dental Caries

1 2

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65

7 8


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Constituents in AmalgamConstituents in Amalgam

BasicBasic

SilverSilver

TinTin

CopperCopper MercuryMercury

OtherOther

ZincZinc

IndiumIndium

PalladiumPalladium


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ClassificationClassification

According to the shape of particles inAccording to the shape of particles in

the powder:the powder: Irregular: Formed by shaving particlesIrregular: Formed by shaving particles

from a block of the alloy by a lathefrom a block of the alloy by a lathe

(lathe(lathe--cut alloy)cut alloy)

Spherical: Formed by spraying moltenSpherical: Formed by spraying molten

alloy into an inert gas (spherical alloy)alloy into an inert gas (spherical alloy) Admixed: Mixture of the two (admixedAdmixed: Mixture of the two (admixed

alloy).alloy).


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Setting reaction continue,Setting reaction continue,

AgAg--Sn + Hg AgSn + Hg Ag--Hg + SnHg + Sn--Hg +unreacted AgHg +unreacted Ag--SnSn

What does actually occur during the settingWhat does actually occur during the setting

reaction:reaction:

Silver and Tin dissolve into mercury and saturateSilver and Tin dissolve into mercury and saturatethe solution and also absorb mercury.the solution and also absorb mercury.

Newly formed particles start to precipitate untilNewly formed particles start to precipitate untilthere is no more Hg to react (takes 24 hrs).there is no more Hg to react (takes 24 hrs).

1

2


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Setting transformationSetting transformation

After mixing: amalgam is packed in cavity.After mixing: amalgam is packed in cavity.

When amalgam reaches initial set, itWhen amalgam reaches initial set, itcannot be carved, but still not fullycannot be carved, but still not fully

reacted (brittle). Needs 24 hours to attainreacted (brittle). Needs 24 hours to attain

full strength.full strength.


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Setting reactionSetting reaction

When the alloy is mixed withWhen the alloy is mixed with

mercury, three phases occur:mercury, three phases occur: Gamma phase (Gamma phase () silver) silver--tin alloy phase,tin alloy phase,

strongest with least corrosionstrongest with least corrosion

Gamma 1 phase (Gamma 1 phase (11) consists of) consists of

mercury reacting with silver, not asmercury reacting with silver, not as

strong asstrong as .. Gamma 2 phase (Gamma 2 phase (22) consists of) consists of

mercury reacting with Tin. Weak phasemercury reacting with Tin. Weak phase

and corrodes easily.and corrodes easily.


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Physical propertiesPhysical properties

Tarnish: oxidation that attacksTarnish: oxidation that attacks

amalgam surface and extendsamalgam surface and extendsslightly below the surface.slightly below the surface.

Cause: contact withCause: contact with OxygenOxygen

ChloridesChlorides

SulfidesSulfides


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Continue,Continue,

Clinical picture: dark and dullClinical picture: dark and dull

appearanceappearance Tarnish is more likely to occur withTarnish is more likely to occur with

rough surfacesrough surfaces How to avoid and minimize itHow to avoid and minimize it::

PalladiumPalladium Polishing after 24 hrsPolishing after 24 hrs

Excessive heat from polishing?Excessive heat from polishing?


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Corrosion: what causes it,Corrosion: what causes it,

Chemical reaction between amalgamChemical reaction between amalgamandand

saliva/food leading to oxidation ofsaliva/food leading to oxidation of

amalgam.amalgam.

Contact between to dissimilar metalsContact between to dissimilar metals(galvanism) oxidation of amalgam(galvanism) oxidation of amalgam

Interaction of amalgam componentsInteraction of amalgam components


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Continue,Continue,

The outcome ofThe outcome of

corrosion:corrosion: WeakensWeakens

restorationrestoration

Deterioration of itsDeterioration of itsmarginsmargins

Stain surroundingStain surrounding

tooth structure astooth structure ascorrosion productscorrosion products

penetrates dentinalpenetrates dentinal

tubulestubules


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Dimensional change: expansion andDimensional change: expansion and

contraction.contraction.

This property is affected by:This property is affected by: Moisture contaminationMoisture contamination

Composition of the alloyComposition of the alloy

Ratio of Hg : alloy powderRatio of Hg : alloy powder


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Strength:Strength: High compressive strengthHigh compressive strength

400400--450 MPa, but low tensile strength450 MPa, but low tensile strength(12% of C.S) and low shear strength,(12% of C.S) and low shear strength,

therefore enough bulk of amalgam istherefore enough bulk of amalgam is

needed to provide enough strengthneeded to provide enough strength.. High copper amalgam have higherHigh copper amalgam have higher

strength values after the first hour ofstrength values after the first hour ofplacement than low copperplacement than low copper

amalgams.amalgams.


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Fracture


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Handling characteristicsHandling characteristics

Available amalgam is mostly high copper,Available amalgam is mostly high copper,

spherical or admixed amalgamspherical or admixed amalgam

Spherical amalgam has a higher surfaceSpherical amalgam has a higher surfacearea therefore requires less mercury forarea therefore requires less mercury for

the reactionthe reaction

Softer when condensedSofter when condensed

Higher 1 and 24 hrs strength compared toHigher 1 and 24 hrs strength compared to

admixedadmixed Newly placed spherical amalgam shrinkNewly placed spherical amalgam shrink

more compared to admixed.more compared to admixed.


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ManipulationManipulation

Dispensing of alloyDispensing of alloy

and mercury:and mercury: CapsulatedCapsulatedavailable withavailable with

different quantitiesdifferent quantities

depending on thedepending on the

size of restorationsize of restoration

Single mix or spillSingle mix or spill

DoubleDouble

MoreMore


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TriturationTrituration

Mixing timeMixing time

refer to manufacturerrefer to manufacturerrecommendationsrecommendations

OvertriturationOvertrituration hothotmixmix

sticks to capsulesticks to capsule

decreases working / setting timedecreases working / setting time

slight increase in setting contractionslight increase in setting contraction

UndertriturationUndertrituration grainy, crumbly mixgrainy, crumbly mix
http://images.google.com/imgres?imgurl=http://www.brooks.af.mil/dis/promix.jpg&imgrefurl=http://www.brooks.af.mil/dis/promix.htm&h=516&w=708&sz=36&tbnid=SgsZQi0AQTwJ:&tbnh=100&tbnw=137&start=3&prev=/images%3Fq%3Dtriturator%26hl%3Den%26lr%3D%26ie%3DUTF-8%2


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Placement and condensation:Placement and condensation:

Dappen dishDappen dish

Amalgam carrierAmalgam carrier

Condenser is used to fill the cavity layerCondenser is used to fill the cavity layer

by layer using vertical and lateralby layer using vertical and lateralcondensationcondensation

Cavity overfilled so that when carved,Cavity overfilled so that when carved,

excess mercury is removedexcess mercury is removed


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Burnishing and carving:Burnishing and carving:

Burnishing maybe done before carvingBurnishing maybe done before carving

to further condense amalgam andto further condense amalgam andremove excess mercuryremove excess mercury

Carving is done soon after amalgam isCarving is done soon after amalgam is

placed in cavityplaced in cavity

Finishing and polishing is done after 24Finishing and polishing is done after 24

hours.hours.


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Bonding amalgamBonding amalgam

Amalgam is conventionally retained inAmalgam is conventionally retained in

cavities mechanically.cavities mechanically.

Low copper amalgamLow copper amalgam High copper amalgamHigh copper amalgam

Expand as they setExpand as they set shrink slightlyshrink slightly

Produce corrosionProduce corrosion corrode slowlycorrode slowly

Reduce microleakageReduce microleakage postoperative sensitivitypostoperative sensitivity


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Bonding amalgamBonding amalgam

Using resin bonding agents:Using resin bonding agents:

Etching of cavity preparationEtching of cavity preparation Bonding is done with one or twoBonding is done with one or two

bonding resins:bonding resins:

11stst technique: bonding agent applied totechnique: bonding agent applied to

enamel and dentine, followed by chemicalenamel and dentine, followed by chemical

cured resin. Amalgam is condensed againstcured resin. Amalgam is condensed against

the wet resin.the wet resin.

22ndnd technique: a single chemical curetechnique: a single chemical cure

bonding agent is applied before placementbonding agent is applied before placementof amalgam.of amalgam.


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Mercury safetyMercury safety

Mercury is toxic, but released inMercury is toxic, but released in

small amounts from set amalgam.small amounts from set amalgam. Safety should be considered for:Safety should be considered for:

PatientPatient OperatorOperator

EnvironmentEnvironment

How does mercury enter the humanHow does mercury enter the human

body?body?


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Continue,Continue,

Skin contactSkin contact

Vapor inhalationVapor inhalation IngestionIngestion

To protect the patient:To protect the patient: Use high volume suctionUse high volume suction

Rubber dam isolationRubber dam isolation


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Continue,Continue,

How are the operator or dental staffHow are the operator or dental staff

exposed to amalgam:exposed to amalgam:

Placing or removing amalgamPlacing or removing amalgam

Sterilizing instrumentsSterilizing instruments

Improper disposal of amalgamImproper disposal of amalgam Carpeted clinics, or tile floors that can collectCarpeted clinics, or tile floors that can collect

mercury spellsmercury spells

OSHA: acceptable level of mercuryOSHA: acceptable level of mercuryexposure 0.005 mg/mexposure 0.005 mg/m33


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Safety proceduresSafety procedures

Adequate ventilationAdequate ventilation

Avoid heating instruments to>80Avoid heating instruments to>80CC Floors should be nonporous and easyFloors should be nonporous and easy

to cleanto clean Use gloves, masks, glassesUse gloves, masks, glasses

Amalgam scrap stored under waterAmalgam scrap stored under waterin airtight containersin airtight containers

Recycling of amalgam scrapRecycling of amalgam scrap

appropriatelyappropriately


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Continue,Continue,

Reduction of mercury vapor:Reduction of mercury vapor:

Use amalgam capsulesUse amalgam capsules Use amalgamator with enclosed mixingUse amalgamator with enclosed mixing

armarm

Store amalgam scrap under waterStore amalgam scrap under water

Clean instruments from any amalgamClean instruments from any amalgam

before sterilizationbefore sterilization Avoid ultrasonic condensersAvoid ultrasonic condensers

Clean mercury spills promptly with spillClean mercury spills promptly with spill

kitkit


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MercuryMercury--free amalgamfree amalgam

Gallium as a substitute for mercuryGallium as a substitute for mercury

Similar handling characteristics toSimilar handling characteristics totraditional amalgamtraditional amalgam

Not a good alternative due to highNot a good alternative due to highcorrosion and lower strengthcorrosion and lower strength

Not commonly usedNot commonly used


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Reference:Reference:

Chapter 8. Dental Materials, clinicalChapter 8. Dental Materials, clinicalapplications for dental assistants andapplications for dental assistants and

dental hygienistsdental hygienists

Documents

Lecture 1 & 2- Dental Amalgam (Slides)