Dental Materials Lecture BDS II Year

Dr. Raghuwar D Singh Associate Professor

Prosthodontic Department King George’s Medical University UP, Lucknow

 Amalgam: is an alloy of mercury with one or more other metals.

 Dental amalgam alloy: is an alloy that contains solid metals of silver, tin, copper and some times zinc.

 Dental amalgam: is the alloy that results when mercury is combined with the previously mentioned alloys to form a plastic mass.

Advantages

• Inexpensive • Ease of use • Proven track record – >100 years • Familiarity • Resin-free – less allergies than composite

History

• 1833 – Crawcour brothers introduce amalgam to US • • 1895 powdered silver coins mixed with mercury – expanded on setting – G.V. Black develops formula for modern amalgam alloy • 67% silver, 27% tin, 5% copper, 1% zinc – overcame expansion problems

History

• 1960’s – conventional low-copper lathe-cut alloys • smaller particles – first generation high-copper alloys • Dispersalloy (Caulk) – admixture of spherical Ag-Cu eutectic particles with conventional lathe-cut – eliminated gamma-2 phase

History

• 1970’s – first single composition spherical • Tytin (Kerr) • ternary system (silver/tin/copper) • 1980’s – alloys similar to Dispersalloy and Tytin • 1990’s – mercury-free alloys

USES OF AMALGAM

• ANTERIOR TEETH – Class III = distal surfaces of Canine .

• POSTERIOR TEETH – Class I & Class II • OTHER USES – Retrograde root canal filling , Post & Core preparation .

Amalgam Capsules

• Contain (in separate compartments): – powdered amalgam alloy – liquid mercury • Some are manually activated, others self-activated • Pestle usually included

Amalgamator (Triturator)

• Speeds vary upward from 3000 rpm • Times vary from 5–20 seconds • Mix powder and liquid components to achieve a pliable mass • Reaction begins after components are mixed

Constituents in Amalgam

• Basic – Silver – Tin – Copper – Mercury • Other – Zinc – Indium – Palladium

Alloy Powder Composition

Type

Low copper

Ag Sn

63-72 26-28

Cu

2-7

Zn Other

0-2 — High-Cu admixed lathe-cut High-Cu admixed spherical 40-70 26-30 12-30 0-2 40-65 0-30 20-40 High-Cu unicomp ositional spherical 40-60 22-30 13-30

compositions in weight percent

0 0 — 0-1 Pd 0-5 In, 0-1 Pd

Basic Constituents

• Silver (Ag) – increases strength – increases expansion • Tin (Sn) – decreases expansion – decreased strength – increases setting time

Basic Constituents….

• Copper (Cu) – ties up tin • reducing gamma-2 formation – increases strength – reduces tarnish and corrosion – reduces creep • reduces marginal deterioration

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

Basic Constituents….

• Zinc (Zn) – used in manufacturing • decreases oxidation of other elements – sacrificial anode – provides better clinical performance • less marginal breakdown – Osborne JW Am J Dent 1992 – causes delayed expansion with low Cu alloys • if contaminated with moisture during condensation – Phillips RW JADA 1954 H 2  2

Other Constituents

• Indium (In) – decreases surface tension • reduces amount of mercury necessary • reduces emitted mercury vapor – reduces creep and marginal breakdown – increases strength – must be used in admixed alloys – example • Indisperse (Indisperse Distributing Company) – 5% indium

Other Constituents…

• Palladium (Pd) – reduced corrosion – greater luster – example • Valiant PhD (Ivoclar Vivadent) – 0.5% palladium

Basic Setting Reactions

• Conventional low-copper alloys • Admixed high-copper alloys • Single composition high-copper alloys

Conventional Low-Copper Alloys

• Dissolution and precipitation • Hg dissolves Ag and Sn from alloy • Intermetallic compounds formed

Ag-Sn Alloy Hg Hg Ag-Sn Alloy Ag Sn Sn Ag Sn Ag Ag-Sn Alloy Mercury (Hg)

Ag  3 Sn + Hg  Ag 3 Sn + Ag  2  Hg 1 3 + Sn 8  Hg 2

Conventional Low-Copper Alloys

• Gamma (  ) = Ag 3 Sn – unreacted alloy – strongest phase and corrodes the least – forms 30% of volume of set amalgam

Hg Ag-Sn Alloy Hg Ag-Sn Alloy Ag Sn Sn Ag Sn Ag Ag-Sn Alloy Mercury Hg

Ag  3 Sn + Hg  Ag 3 Sn + Ag  2  Hg 1 3 + Sn 8  Hg 2

Conventional Low-Copper Alloys

• Gamma 1 ( 

1

) = Ag 2 Hg 3 – matrix for unreacted alloy and 2nd strongest phase – 10 micron grains binding gamma (  ) – 60% of volume

Ag-Sn Alloy Ag-Sn Alloy



1

Ag  3 Sn + Hg  Ag 3 Sn + Ag  2  Hg 1 3 + Sn 8  Hg 2

Ag-Sn Alloy

Conventional Low-Copper Alloys

• Gamma 2 ( 

2

) = Sn 8 Hg – weakest and softest phase – – corrodes fast, voids form corrosion yields Hg which reacts with more gamma (  ) – – 10% of volume volume decreases with time due to corrosion

Ag-Sn Alloy Ag-Sn Alloy



2 Ag-Sn Alloy

Ag  3 Sn + Hg  Ag 3 Sn + Ag  2  Hg 1 3 + Sn 8  Hg 2

Admixed High-Copper Alloys

• Ag enters Hg from Ag-Cu spherical eutectic particles – eutectic • an alloy in which the elements are completely soluble in liquid solution but separate into distinct areas upon solidification • Both Ag and Sn enter Hg from Ag 3 Sn particles

Ag-Cu Alloy Hg Ag-Sn Alloy Hg Ag Sn Ag Ag Ag Sn Ag-Sn Alloy Mercury

Ag  3 Sn + Ag-Cu + Hg  Ag  3 Sn + Ag-Cu + Ag 2  Hg 1 3 + Cu 6 Sn  5

Admixed High-Copper Alloys

• Sn diffuses to surface of Ag-Cu particles – reacts with Cu to form (eta) Cu 6 Sn 5 (  ) • around unconsumed Ag-Cu particles 

Ag-Sn Alloy Ag-Cu Alloy Ag-Sn Alloy

Ag  3 Sn + Ag-Cu + Hg  Ag  3 Sn + Ag-Cu + Ag 2  Hg 1 3 + Cu 6 Sn  5

Admixed High-Copper Alloys

• Gamma 1 ( 

1

) (Ag 2 Hg 3 ) surrounds (  ) eta phase (Cu 6 Sn 5 ) and gamma (  ) alloy particles (Ag 3 Sn) 

Ag-Sn Alloy Ag-Cu Alloy Ag-Sn Alloy



1

Ag  3 Sn + Ag-Cu + Hg  Ag  3 Sn + Ag-Cu + Ag 2  Hg 1 3 + Cu 6 Sn  5

Single Composition High-Copper Alloys

• Gamma sphere (  ) (Ag 3 Sn) with epsilon coating (  ) (Cu 3 Sn) • Ag and Sn dissolve in Hg 

Ag-Sn Alloy Ag Ag-Sn Alloy Sn Ag Sn Ag-Sn Alloy Mercury (Hg)

Ag  3 Sn + Cu 3  Sn + Hg  Ag 3  Sn + Cu 3  Sn + Ag 2  Hg 1 3 + Cu 6 Sn  5

Single Composition High-Copper Alloys

• Gamma 1 ( 

1

) (Ag 2 Hg 3 ) crystals grow binding together partially dissolved gamma (  ) alloy particles (Ag 3 Sn) • Epsilon (  ) (Cu 3 Sn) develops crystals on surface of gamma particle (Ag 3 Sn) in the form of eta ( 

)

(Cu 6 Sn 5 ) – reduces creep – prevents gamma-2 formation 

Ag-Sn Alloy Ag-Sn Alloy



1 Ag-Sn Alloy

Ag  3 Sn + Cu 3  Sn + Hg  Ag 3  Sn + Cu 3  Sn + Ag 2  Hg 1 3 + Cu 6 Sn  5

Classification of dental amalgam alloys REGULAR ADMIXED UNICOMPOSITION BASED ON Cu CONTENT HIGH Cu ALLOYS > 6% Cu SINGLE COMPOSITION LOW Cu ALLOYS < 6% Cu

BASED ON Zn CONTENT Zn CONTAINING > 1% Zn Zn FREE ALLOY < 1% Zn

LATHECUT BASED ON SHAPE OF ALLOY SPHERICAL ADMIXED

BASED ON NUMBER OF ALLOY METAL BINARY Ag,Sn TERTIARY Ag,Sn,Cu QUATERNARY Ag,Sn,Cu,Zn

BASED ON SIZE OF ALLOY MICROCUT \FINE CUT MACROCUT \COURSE CUT

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 9 to 30% Cu • at expense of Ag

Particle Shape

• Lathe cut – low Cu • New True Dentalloy – high Cu • ANA 2000 • Admixture – high Cu • Dispersalloy, Valiant PhD • Spherical – low Cu • Cavex SF – high Cu • Tytin, Valiant

Method of Adding Copper

• Single Composition Lathe-Cut (SCL) • Single Composition Spherical (SCS) • Admixture: Lathe-cut + Spherical Eutectic (ALE) • Admixture: Lathe-cut + Single Composition Spherical (ALSCS)

Single Composition Lathe-Cut

• More Hg needed than spherical alloys • High condensation force needed due to lathe cut • 20% Cu • Example – ANA 2000 (Nordiska Dental)

Single Composition Spherical

• Spherical particles wet easier with Hg – less Hg needed (42%) • Less condensation force, larger condenser • Gamma particles as 20 micron spheres – with epsilon layer on surface • Examples – Tytin (Kerr) – Valiant (Ivoclar Vivadent)

Admixture: Lathe-cut + Spherical Eutectic

• Composition – 2/3 conventional lathe cut (3% Cu) – 1/3 high Cu spherical eutectic (28% Cu) – overall 12% Cu, 1% Zn • Initial reaction produces gamma 2 – no gamma 2 within two years • Example – Dispersalloy (Caulk)

Admixture:

Lathe-cut + Single Composition Spherical • High Cu in both lathe-cut and spherical components – 19% Cu • Epsilon layer forms on both components • 0.5% palladium added – reinforce grain boundaries on gamma 1 • Example – Valiant PhD (Ivoclar Vivadent)

Manufacturing Process

• Lathe-cut alloys – Ag & Sn melted together – alloy cooled • phases solidify – heat treat • 400 ºC for 8 hours – grind, then mill to 25 - 50 microns – heat treat to release stresses of grinding

Manufacturing Process

• Spherical alloys – melt alloy – atomize • spheres form as particles cool – sizes range from 5 - 40 microns • variety improves condensability

Alloy Selection

• Handling characteristics • Mechanical and physical properties • Clinical performance

Handling Characteristics

• Spherical – advantages • easier to condense – around pins • hardens rapidly • smoother polish – disadvantages • difficult to achieve tight contacts • higher tendency for overhangs

Handling Characteristics

• Admixed – advantages • easy to achieve tight contacts • good polish – disadvantages • hardens slowly – lower early strength

Amalgam Type

Amalgam Properties

Compressive Strength (MPa) 1 hr 7 days % Creep Tensile Strength (24 hrs) (MPa) Low Copper 1 Admixture 2 145 137 343 431 2.0

0.4

60 48 Single Composition 3 1 Fine Cut, Caulk 2 Dispersalloy, Caulk 3 Tytin, Kerr 262 510 0.13

64

Material-Related Variables

• Dimensional change • Strength • Corrosion • Creep

Dimensional Change

• Most high-copper amalgams undergo a net contraction • Contraction leaves marginal gap – initial leakage • post-operative sensitivity – reduced with corrosion over time

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

Strength

• Develops slowly – 1 hr: 40 to 60% of maximum – 24 hrs: 90% of maximum • Spherical alloys strengthen faster – require less mercury • Higher compressive vs. tensile strength • Weak in thin sections – unsupported edges fracture

VI. Properties of Dental Amalgam

1.

Compressive strength

-Amalgam is strongest in compression and much weaker in tension and shear.

-HCU materials have the highest compressive strength.

Properties of Dental Amalgam

2.

Tensile Strength:

-Amalgam is strongest in compression and much weaker in tension and shear.

-HCU materials have the highest early tensile strength.

Properties of Dental Amalgam

• Strength of various phases:

1. Unreacted Ag 3 Sn (  ) phase. (strongest) 2. Ag 2 Hg 3 (  1 )phase.

3. Sn 8 Hg (  2 )phase.(weakest)

Properties of Dental Amalgam

3. Elastic Modulus:

-High- copper alloys are stiffer than low-copper alloys.

-Amalgam are viscoelastic.

Corrosion

• Reduces strength • Seals margins – low copper • 6 months – – SnO 2 , SnCl gamma-2 phase – high copper • 6 - 24 months – SnO 2 , SnCl, CuCl – eta-phase (Cu 6 Sn 5 )

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

Creep

• High-copper amalgams have creep resistance – prevention of gamma-2 phase • requires >12% Cu total – single composition spherical • eta (Cu 6 Sn 5 ) embedded in gamma-1 grains – interlock – admixture • eta (Cu 6 Sn 5 ) around Ag-Cu particles – improves bonding to gamma 1

MCQs

1. Dental situation in which Silver amalgam is most commonly used: a) Anterior Class 4 b) Posterior Class 1 c) Root canal feeling d) Pit and fissure

2. Zn containing Amalgam contains: a) .001% Zn b) .01% Zn c) More than .o1% Zn d) More than .001% Zn

3. Epsilon phase in dental amalgam is: a) Ag-Sn b) Cu 3 Sn c) Ag 3 Sn d) Cu 6 Sn

4. Beta phase in dental amalgam is: a) Ag-Sn b) Cu3Sn c) Ag3Sn d) Cu6Sn5

5. The weakest phase in amalgam is: a) Gamma- 1 b) Beta c) Beta- 1 d) Gamma

6. Gamma -2 phase in dental amalgam is: a) Cu 6 Sn 5 b) Sn 7 Hg c) Ag-Cu d) Ag 3 Sn

7. Pain, after delayed expansion of amalgam is produced by: a) Presence of Zn b) Hydrogen gas c) Presence of H 2 O d) Improper cavity preparation

8. Which phase of amalgam promotes tarnish and corrosion: a) Gamma b) Gamma- 1 c) Gamma- 2 d) Eta

9. Low copper dental amalgam alloy contains maximum amount of copper upto: a) 3% b) 11% c) 6% d) 19%

10. All of the following are feathers of the high Cu alloys, except: a) Low dimensional changes b) Low compressive strength c) Lower creep values d) Less susceptible to corrosion