references from these books, 1-Phillips' Science of Dental Materials,12th Edition 2-BASIC DENTAL MATERIALS,3rd Edition 3-Clinical Applications for Dental Assistants and Dental Hygienists,3rd ED I T I O N **slide 19 the link of atomizaion process is https://www.youtube.com/watch?v=ldP1sQnjWcc

1. g
g1
g2h
e
Ag-Sn
Ag-Cu
Hg

3. 9. Metallurgical phases and
amalgamation
10. Lowe copper alloys

4. Introduction
*In dentistry, amalgam has been successfully used for more than a
century as a restoration material for tooth decay.
*An amalgam is defined as a special type of alloy in which mercury is
one of the components.
*Mercury is able to react with certain alloys to form a plastic mass (
putty like consistency), which is conveniently packed into a prepared
cavity in a tooth. This plastic mass hardens and is stronger than any
dental cement or anterior filling material.
*Dental amalgam is the most widely used filling material for posterior
teeth.
*No other direct restorative material has the durability, ease of
handling, good physical characteristics, wear resistance and
compressive strength of amalgam.

5. Alloy a mixture of two metals or more .
Amalgam
A special alloy containing mercury
and any other metal (mercury is one
of the components) .
Dental Amalgam
an alloy of reacting Hg with Ag -Cu-
Sn and may contain other elements in
much smaller quantities Pd –Zn to
improve handling characteristics and
clinical performance.
Dental Amalgam Alloy
(alloy before combining or
reacting with mercury )
an alloy of Ag-Cu-Sn and
other elements(to be mixed
with Hg) processed in the
form of powder particles or
pellet.
Definition

6. Definition
Creep time - dependent plastic deformation
(When stress is applied to an
amalgam, it will undergo plastic
deformation).
Increases susceptibility to marginal
breakdown.
Corrosion is an actual deterioration of metal
by reaction with its environment .
‫الحشوة‬ ‫إنه‬ ‫يعني‬‫تآكل‬ ‫صارلها‬(‫شكل‬ ‫على‬ ‫تظهر‬
‫صدأ‬ ‫ليس‬ ‫و‬ ‫شقوق‬)‫األملغم‬ ‫لتفاعل‬ ‫نتيجة‬(‫المعادن‬
‫فيه‬ ‫الي‬)‫البيئة‬ ‫مع‬
Tarnish
is a surface observable
discoloration on a metal without
any loss of structure.
‫المعدن‬ ‫سطح‬ ‫لون‬ ‫في‬ ‫تغير‬(‫صدأ‬)

7.  Uses or Applications
 Class I,II and Class V(posterior)
restorations.
 In retrograde root canal fillings = filling of apices of roots after
apicectomies.
 As a core material
for badly broken
down teeth.

8.  Packing :-
 Trituration is achieved either by:
 Manually by hand with mortar and pestle
 Mechanical mixing by device
called amalgamator

9. The excess mercury was removed from the amalgam by
using a squeeze cloth to squeeze out the excess
mercury.
Advantages of mechanical trituration:
1. Shorter mixing time.
2. More standardized procedure.
3. Requires less mercury when compared to
hand mixing technique and hence less health
hazard.
Hand mixing
This older method of mixing the
amalgam has declined in use, because:-
*manual mixing often leak mercury into
the operatory during mixing,
*mixes are not as consistent ,
*health hazard.

10. classifications
10
Conventional =
=
traditional
High copper alloy

12. * Produces better proximal *Difficult to contour
contour as in class II.

18. Result

19. The spherical alloy is prepared by an atomization process.
Desired elements melted together to form molten alloy .The
molten alloy is sprayed under high pressure of an inert gas
through a fine crack into a large chamber.
If the droplets solidify before hitting a surface, the spherical
shape is preserved. Like lathe-cut, spherical powders are
given an annealing heat treatment and surface washing.

20. Components of dental amalgam
and the function of each constituent

22. Mercury
3-
4-

23. *Major element
*whitens alloy
*Decreases creep
*Increases strength
*Increases expansion on setting
*Increases tarnishing resistance in resulting
amalgam
Silver (Ag)

24. *Controls the reaction between Ag and Hg
*Reduces strength and hardness
*reduces tarnish and corrosion resistance
Tin (Sn)

25. Copper (Cu)

26. Summarize the functions in schedule
SILVER COPPER TIN
Increases strength Increases Strength Controls reaction rate
Increases expansion Increases expansion Decreases strength
Decreases flow(creep) Decreases flow(creep) Decreases expansion
Decreases setting
time
Decreases setting time Increases Flow(creep)
Increases corrosion
resistance
Increases corrosion
resistance
Decreases corrosion
resistance
Decreases plasticity Increases lasticity
Increases hardness

27. Other elements that are present in small
amounts
function
Zinc (Zn)
*Act as scavenger(deoxidizer) during manufacture, thus
prevents the oxidation of important elements like silver,
copper or tin.
*Decreases brittleness
*Increases plasticity
*causes delayed expansion in the presence of
moisture so amalgam with Zn free is preferred in cases of
difficult isolation.
(others eg.
palladium,
Indium ,…..)
*whiten, hardens the alloy
*increase resistance to corrosion and tarnish.
*reduce creep

28. Metallurgical phases

29. 1*
2*
3*
4*
5*
6*

31. *Matrix= γ1 & γ2
* Filler = γ

32. Ag3Sn + Hg Ag2Hg3(γ1) +Sn8Hg ( γ2)+
unreacted Ag3Sn (γ )

33. Low-copper Alloys (1)
• When a powder (Ag3Sn, g) is triturated, the Ag
and Sn in the outer portion of the particles
dissolve into Hg (mercury).
• Hg also diffuses into the alloy particles.
– Solubility for Ag < Sn
33

34. Low-copper Alloys (2)
• When the solubility is exceeded, crystals of two
binary metallic compounds precipitate into the
mercury.
– Ag2Hg3 compound (g1) precipitates first.
– Sn7-8Hg compound (g2) precipitates later.
34
As the remaining mercury dissolves the alloy particles, g1
and g2 crystals grow.
trituration condensable, carvable

35. Low-copper Alloys (3)
 As the mercury disappears, the amalgam hardens.
Particles become covered with newly formed
crystals, mostly g1.
35
Unconsumed particles (smaller after being partly
dissolved) = γ , are surrounded and bound together by
solid g1 and g2 phases.

37. Low-copper Alloys (4)
 In summary,
Alloy particles (b + g) + Hg  g1 + g2 + unconsumed alloy
particles (b + g)
 Physical properties
1. g-phase  strongest,
2. g2 phase  weakest
3. Hardness: g > g1 >>> g2
4. g2  poor corrosion resistance
37

38. • The physical properties of the
hardened amalgam depend on
the relative percentage of each of
the microstructural phases.
• The more unconsumed Ag-Sn
particles found in the final
structure , the stronger the
amalgam.
• The weakest component is
the g₂ phase.
38

39. High copper alloys contain between 13 to 30% wt. copper. They are
preferred because of their :
 improved mechanical properties,
 resistance to corrosion and
 better marginal integrity
Types:
1. Admixed alloy(mixture of lathe-cut and spherical particles ‫اسمها‬ ‫)من‬
2. Single-composition alloy.

40. High copper alloys or low copper alloys?? ‫أفضل‬ ‫مين‬
reduction or elimination of g2 and high copper
particles aid to :-
*improved mechanical properties,
*resistance to corrosion and
*better marginal integrity.
‫باختصار‬...

41. 1- High-Cu: Admixed Alloys
• Spherical silver-copper
(Ag-Cu) eutectic alloy
particles are added to
lathe-cut low-copper
amalgam alloy particles
(Ag-Sn or g ).
• The final powder is
composed of two kinds of
particles.  “admixed”
• Ag-Cu particles act
as strong fillers,
strengthening the
amalgam matrix.
41

42. 42

43. 43

44. 44

45. High-Cu:Admixed Alloys
 A layer of h forms around
unconsumed Ag-Cu
particles.
 g1 phase is the matrix.
 The final structure
composes of the g phase,
Ag-Cu particles, e particles,
g1 matrix, and h reaction
layers.
45
h

46. Note that …
ε phase ) Cu3Sn) is part
of lathe-cut particle
( low copper content Ag3-Sn)
while h phase (Cu6Sn5)
surrounds the spherical
particles of high
copper content
(Ag-Cu)

47. High-Cu:Admixed Alloys
 In summary:
Alloy particles (g) + Ag-Cu eutectic + Hg  g1 + h + unconsumed
alloy of both types of particles
 g2 has been eliminated in this reaction,
being replaced by h.
 The effectiveness in eliminating g2
depends on % of copper-containing
particles.
47

48.  These are high copper amalgam alloys. Unlike admixed
alloy powders, each particle of the alloy powder has
the same composition.Therefore they are called single
composition or unicompositional alloys.
 Major components:Ag-Cu-Sn
48
2- High-Cu: Single-composition Alloys

50. Admixed vs spherical single composition

51. High-Cu: Single-composition Alloys
• Phases found in each
single-composition alloy
particle are b (Ag-Sn), g
(Ag3Sn), and e (Cu3Sn).
• h crystals are found as
meshes of rod crystals
at the surfaces of alloy
particles , as well as
dispersed in the matrix.
51
g1
h
P

52. Final set material consists of :-
*Particles of
— Unreacted Ag3Sn (γ phase) and surrounded by a mesh of
rod shaped η)Cu6Sn5).
*Embedded in a matrix made up of
— γ1(Ag2Hg3)

53. High-Cu: Single-composition Alloys
 In summary:
 Little or none of g2 phase can form.
 Copper presents in the form of Cu3Sn)ε)
not Ag-Cu eutectic ( as in admixed alloy).
53

54. **Functions of η)Cu6Sn5) phase:
*strengthen the bond between alloy particles
and g1
*interlocks the γ1 phase thus improving the
amalgams resistance to deformation.

56.  Occurs due to penetration of fluids or debris around the
margins that can lead to secondary caries.
1- Microleakage

57. formation of corrosion products
they seal the interface and
reduce leakage
 Amalgam is a self sealing restoration:
self sealing by formation of corrosion
Products.
Both low and high copper amalgams are capable of sealing
against microleakage but the accumulation of corrosion
products is slower with the high-copper alloys

58.  Both low and high copper amalgams are capable of
sealing against microleakage but the accumulation
of corrosion products is slower with the high-
copper alloys.
 Microleakage can be reduced through the
application of varnish on the cavity walls.

59. 2- Dimensional Change
 The earliest amalgams exhibited expansion while
setting. This was because of the greater
mercury/alloy ratio used .
 Amalgams may expand or contract, depending on
its manipulation.
 Ideally, dimensional change should be small.
 Excessive contraction can lead to microleakage,
sensitivity and secondary caries.
 Excessive expansion can produce pressure on
the pulp and postoperative sensitivity.
Protrusion of the restoration can also occur.

60.  ADA Sp. no. 1 requires that amalgam should not expand more than
20 μm/cm or contract less than 15 μm at 37°C, between 5 minutes
and 24 hours from the start of trituration.
 Mechanically triturated modern amalgams, both low and high
copper, prepared from low mercury/alloy ratios show a slight
contraction.

61.  Theory of Dimensional Change
 Contraction
When the alloy and mercury are mixed contraction results
initially as the particles dissolve and the γ1 grows. The final
volume of γ1 is less than the initial volumes of silver and
mercury that go into making the γ1.
Therefore, contraction will continue as long as growth of γ1
continue.

62.  Theory of Dimensional Change
 Expansion
The γ1 crystals as they grow, impinge against one another, and
produce an outward pressure tending to oppose contraction.
If there is sufficient mercury present to provide a plastic matrix,
an expansion will occur when γ1 crystals impinge on each other.
After a rigid γ1 matrix has formed, growth of γ1 crystals cannot
force the matrix to expand.
Therefore, reducing mercury in the mix will favor
Contraction.

63.  Thus factors favoring contraction are:
 Low mercury/alloy ratio
 Higher condensation pressure (squeezes out mercury)
 Smaller particles (consumes more mercury because of increased
surface area)
 More trituration (accelerates setting).
 New amalgams or modern amalgams exhibit a net
contraction on setting.
 older amalgams always showed expansion ( due to high
mercury/alloy ratio + hand trituration was used)

64.  Effect of moisture contamination (delayed expansion)
 If a zinc-containing-low-copper or high-copper amalgam is contaminated by
moisture during trituration or condensation, a large expansion can take place.
 It usually starts after 3-5 days and may continue for months, This is known
as delayed expansion or secondary expansion .
 The expansion is caused by the releases of hydrogen gas from
the reaction of zinc with water.
H2O + Zn ZnO + H2 (gas)
 Indications for Zinc Free Alloys
Amalgam without zinc tends to be less plastic and
less workable.
These alloys are used only for cases
where it is difficult to control moisture.

65. Moisture ( saliva ,…etc) + zin-containing
=
amalgam

66.  Well designed amalgam restorations have sufficient
compressive strength to withstand normal intraoral
masticatory forces.
3- compressive strength
 Resistance to compression forces is the most favorable
strength characteristic of amalgam.
 compressive strength of high-Cu single alloy is the highest(after 24
hrs, reaches 510 MPa) > high-Cu admixed > low-Cu

67.  Amalgam cannot withstand high tensile or bending stresses
and can fracture easily in improperly designed restorations.
 Therefore, the cavity should be designed so that the restoration will
receive minimal tension or shear forces in service.
4- Tensile strength

68. Amalgam is

69. 
 Effect of Rate of Hardening

70.  When stress is applied to an amalgam, it will undergo
plastic deformation this characteristic refers to as creep.
 It is a time dependent plastic deformation.
 Creep of dental amalgam is a slow progressive permanent
deformation of set amalgam which occurs under constant
stress (static creep) or intermittent stress (dynamic creep).
 The γ2 phase is associated with higher creep rates.
 In general lathe-cut low-copper alloys show the highest
creep values.
4- Creep

71. 5- Tarnish and corrosion
 Corrosion :
is an actual deterioration of metal by reaction with its
environment .
 Tarnish: is a surface observable discoloration on a metal
without any loss of structure. ‫المعدن‬ ‫سطح‬ ‫لون‬ ‫في‬ ‫تغير‬
‫تآكل‬ ‫صارلها‬ ‫الحشوة‬ ‫إنه‬ ‫يعني‬(‫صدأ‬ ‫ليس‬ ‫و‬ ‫شقوق‬ ‫شكل‬ ‫على‬ ‫تظهر‬)
‫األملغم‬ ‫لتفاعل‬ ‫نتيجة‬(‫فيه‬ ‫الي‬ ‫المعادن‬)‫البيئة‬ ‫مع‬.

72. Note that…
*low copper amalgam is more susceptible to corrosion
(due to greater γ2content) than high copper.
*Also η (Cu6Sn5) phase of high copper is less
susceptible to corrosion.
* y1 has the corrosion resistance > y2 (has the lowest).

73. Effect of Particle size

74. Free mercury should not be sprayed or exposed to the
atmosphere.
This hazard can arise during trituration, condensation and
finishing of the restoration, and also during the removal of old
restorations at high speed.
Mercury vapors can be inhaled. Skin contact with mercury
should be avoided as it can be absorbed.
The clinic should be well ventilated. All excess mercury and
amalgam waste should be stored in well-sealed containers.
Proper disposal systems should be followed, to avoid
environmental pollution.

75. 75