AMALGAM Structure and Properties PPT

8/4/2019 AMALGAM Structure and Properties PPT

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DENTALAMALGAM

Stephen C. Bayne Department of Operative DentistrySchool of DentistryUniversity of North CarolinaChapel Hill, NC 27599-7450

2006, Bayne and Thompson



DENTAL AMALGAM

Where is it?



BEFORE REACTIONBEFORE REACTION AFTER REACTIONAFTER REACTION

AlloyAlloy

MercuryMercuryReactionReactionProductsProducts

AlloyAlloy

AMALGAM TERMINOLOGY

AMALGAM = an alloy containing Hg as the major ingredient.

DENTAL AMALGAM = an alloy of Hg with Ag-Sn.DENTAL AMALGAM ALLOY = a Ag-Sn alloy (to be mixed with Hg).



ALLOY PRODUCTION

Melting / Casting / Comminution IRREGULAR Particles

Melting / Spray Atomization SPHERICAL PARTICLES

“Cast ingots --> filed into powder” Irregular particles = lathe cut = filings

Hot alloy sprayed into cold airParticles spherodize and solidify

Polycrystalline particlesHomogenized by HT to remove coringAnnealing HT to relieve cold work in filings

Spheres are acid-washedGenerally spheres are HT



Hg / Alloy RATIOS

50:50

42:58



ALLOY MANIPULATION

Manual Trituration Procedures: Alloy + Hg mortar + pestle manual mixing

Mechanical Trituration Procedures: Powdered alloy + Hg capsule + pestle amalgamatorPelleted alloy + Hg capsule + pestle amalgamator

Powdered alloy + Hg pre-capsulated amalgamator



CLASSIFICATION

• Copper content = low copper, high copper• Particle size (and shape) = irregular, spherical• Number of particle types = 1 or 2• Zinc content = Zn-containing, Zn-free

Application of system of nomenclature

Alloy Copper Particle Number of Zinc Name: Content: Shape: Particles: Content:

New True Dentalloy Low Irregular 1 Particle No

Velvalloy Low Irregular 1 Particle No“Dispersalloy” High Both 2 Particles Yes“Tytin” High Spherical 1 Particle No



Rx and MICROSTRUCTURE

IrregularAlloy

SphericalAlloy

Ag Primary reactantSn Creates solubility, fluidityCu Reacts with SnZn Alloy processing aidHg Reactant with Ag (and Sn)



SETTING REACTIONS

Low-Copper Dental Amalgam:

2-Particle High-Copper Dental Amalgam:

1-Particle High-Copper Dental Amalgam:

S-Alloy + Hg Residual Alloy + Matrix-1 + Matrix-2 Ag3Sn/Cu+ Hg Ag3Sn/Cu + Ag2Hg3 + CuSn + Cu3Sn g + Hg g + g 1 + e + h

I-Alloy + Hg Residual Alloy + Matrix-1 + Matrix-2 g + Hg g (Ag3Sn) + g 1 + (g 2)

S-Alloy + Hg Residual Alloy + Matrix-1 + Matrix-2 Alloy + Hg Alloy (Ag-Cu) + g 1 + e + h

I/S-Alloy + Hg Residual Alloy + Matrix-1 + Matrix-2Ag-Sn + Hg Ag-Sn + Ag-Hg + Sn-HgAg3Sn + Hg Ag3Sn + Ag2Hg3 + Sn7-8Hgg + Hg g + g 1 + g 2




+ Hg + +

g g1 g2

BEFORE REACTIONBEFORE REACTION AFTER REACTIONAFTER REACTION

AlloyAlloy

MercuryMercuryReactionReactionProductsProducts

AlloyAlloy

Penetrating Corrosion



+ Hg + +

g g1+ spheres e + h


69 Ag

18 Sn12 Cu

1 ZnDISPERSALLOY



PHASE DIAGRAMS

Ag Hg

Ag3Sn + Hg >>>Ag2Hg3 = g1

(26Ag-74Hg)

g1g + b



Overview of Manipulation

Selection / Proportioning / Amalgamation / Manipulation / Polishing

Placement andCondensation

Carving Burnishing Polishing

Onset of

MIXING

Onset of

WORKING

Onset of

SETTING

End of

SETTING

24 hours

TIME



Amalgamators

SPEED TIME

ENERGY = Speed x Time



Unset amalgam

A

Setting amalgam

B

Ag-Hg crystalreaction products

Residual alloy

Excess Hg-rich matrixeliminated by condensation.



DIMENSIONAL CHANGES

Dimensional changes on setting: CONTRACTION during alloy dissolutionEXPANSION during impingement of reaction product crystals(EXPANSION if side reactions due to H2O contamination)

EXP (+)

CONT (--)

TIME

Dimensional changes on depend on reaction variables:

Particle size, Hg/alloy ratio, trituration time, condensation, ...

ADA =± 20 mm



AMALGAM PROPERTIES

2. Clinical Performancea. Longevity = 20-25 yrs ideally, 8-12 yrs practicallyb. Modes of failure = caries, marginal fracture, bulk

UNITEDSTATES

WORLD

ADA FDI

ISOANSI

B. Properties:

1. Physical

2. Mechanical3. Chemical4. Biological

A. Introduction:

1. Specifications for Amalgam Propertiesa. ADA / ANSI and ISOb. Determination of “safety and efficacy”



Physical Properties

1. Thermal conductivity =2. Electrical conductivity =3. Coefficient of thermal expansion =4. Radiopacity =

5. Color =

[>2 mm Aluminum]

[Lustrous, shiny, white]

25 ppm/ºC[High]

[High]



Mechanical Properties

Compressive Strength (psi) Tensile Strength (psi)15-min 1-hr 24-hr 15-min 1-hr 24-hr

LOW COPPER: Velvalloy 5,400 17,400 56,200 625 1,900 9,000Spheralloy 5,800 18,500 56,900 450 1,550 8,800

HIGH COPPER: Optalloy II 9,100 23,800 55,900 1,000 2,350 7,250Dispersalloy 6,200 22,400 59,900 575 1,750 6,990Indiloy 4,600 26,300 64,500 450 2,400 6,500Sybraloy 23,800 50,000 72,700 2,190 4,700 6,600Tytin 10,200 40,800 79,100 990 4,000 9,300



Mechanical Properties

TYTIN (Kerr Dental Mfg) = “tie up the tin” High-Copper, Spherical, 1 Particle, Zn-free42% Hg mixed with alloyFast-settingHigh early strength

PolishedSurface

Fracture

Surface



Chemical Properties

Clean Surface,High O2 Potential

(CATHODIC)

Plaque Buildup,Low O2 Potential

(ANODIC)

(a)

(b)

(a) (b)

PlaqueBuildup

Clean Surface,High O2 Potential

(CATHODIC)

Plaque Buildup,Low O2 Potential

(ANODIC)

(a)

(b)

(a) (b)

PlaqueBuildup

ELECTROCHEMICAL CORROSION:

• Galvanic corrosion• Local galvanic corrosion (structure selective)• Crevice corrosion (concentration cell)• Stress corrosion

Sn-O-ClSn-O

CHEMICALCORROSION: AgS



Biological Properties

Mercury Toxicity: OSHA maximum TLV = 50 mg/m3 (vapor) per 40 hr work week.Transient intraoral release (<35 mg/m3).

Mercury Hypersensitivity:

Low level allergic reaction.Estimated to be < 1 / 100,000,000

Amalgam Tatoo: Can occur during amalgam removal if no rubber dam.Embedded amalgam particles corrode and locally discolor gum.

No known adverse reactions.



Clinical Performance

Reasons for Failure: Low-copper amalgam – marginal fracture and secondary caries.High-copper amalgam – marginal fracture and bulk fracture.

Jorgensen theory of mercuroscopic expansion (and marginal fracture)

Internal corrosion

PenetratingCorrosion

Corrosion at margins

SuperficialCorrosion

Sn-O-Cl and Sn-O

CorrosionProducts



Clinical Evaluation

Mahler scale:

???

Hi-Cu, no Zn

Hi-Cu, +Zn

Low-Cu, +Zn

Low-Cu, no Zn

Hi-Cu Low-Cu



THANK YOU

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AMALGAM Structure and Properties PPT