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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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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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Physical propertiesPhysical properties
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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Physical propertiesPhysical properties
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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Physical propertiesPhysical properties
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%28/4/2019 Lecture 1 & 2- Dental Amalgam (Slides)
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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