Dr. lama khaled El Banna Faculty of Oral and Dental Medicine Al – Azhar University operative dentistry part two

2. College of Dentistry
Operative Dentistry II
Amalgam Restorations -1-
Dr. Hazem El Ajrami

3. Contents ofContents of Operative Dentistry IOperative Dentistry I
• Scope and Objectives of Operative Dentistry.Scope and Objectives of Operative Dentistry.
• Structures of the Teeth.Structures of the Teeth.
• Tooth Form & Occlusion.Tooth Form & Occlusion.
• Carious & Non Carious Lesions.Carious & Non Carious Lesions.
• Cavity Classifications & Nomenclatures.Cavity Classifications & Nomenclatures.
• General Principles of Cavity Preparation.General Principles of Cavity Preparation.
• Instruments and Instrumentation.Instruments and Instrumentation.

4. • Cement Bases and Liners.Cement Bases and Liners.
• Amalgam Restorations.Amalgam Restorations.
• Introduction to Adhesive Dentistry.Introduction to Adhesive Dentistry.
• Direct Esthetic Tooth-Colored Restoration.Direct Esthetic Tooth-Colored Restoration.
Contents ofContents of Operative Dentistry IIOperative Dentistry II

5. Amalgam Restorations:
 Advantages & Disadvantages.
 Indications and Contraindications.
 Classification, Composition and Types.
 Manipulation of Amalgam.

6. • Amalgam has been an accepted part of dental
therapeutics for more than 150 years and is still
used for more than 75% of direct posterior
restorations. The reasons for its popularity lie in
its ease of manipulation, relatively low cost, and
long life. Some concern has been raised about
mercury toxicity from both a biologic and an
environmental point of view; however, it is
believed that dental amalgam presents an
acceptable risk-to-benefit ratio when properly
used.

7. • Amalgam could be defined as an alloy of
mercury together with one or more metallic
elements. Dental amalgam is a metallic alloy
that results from mixing mercury together with a
specially formulated alloy that is based on the
silver-tin compound. Mercury has a unique
characteristic; it is the only metal which is liquid
at room temperature. It is thus used to liquefy and
react with dental amalgam alloy constituents
producing a workable plastic mass that solidifies
at body temperature maintaining the form and
size of the restoration.

8. • The high rate of success and longevity of
amalgam restorations is owed to its inherent
superior characteristics which comply, to a
great extent, with the rigid requirements of the
oral environment. Its performance is considered
to be a standard for comparison of new
materials.

9. • These advantages include:
1. High compressive strength; enough to sustain
the range of compressive loads expected in
the mouth without fracture.
2. Superior adaptation to cavity walls, which
uniquely improves on aging through self-
sealing with corrosion products that deposits
into and occludes the critical tooth-restoration
interface and decreases micro-leakage.

11. 3. Fairly good form stability due to its
insolubility, high wear resistance and the
reasonably low creep value of modern high
copper alloys. This enables the restoration to
maintain surface polish, occlusal anatomy and
inter-proximal contact.
4. Low coefficient of thermal expansion which is
only about twice that of the tooth structure.
This property ensures the marginal integrity of
the restoration when subject to thermal
changes.

12. 5. Satisfactory handling characteristics and less
sensitivity to manipulative variables which
makes it possible for the average practitioner
to obtain successful restorations consistently.
However, as any other restorative material, its
technique involves many variables, which
should adequately be controlled to obtain
successfully lasting restorations and prevent
failure.
6. Fairly low cost and the relatively short time
required for the construction of restorations.

13. • Regardless of the various researches and
improvements achieved in material
formulation, amalgam still suffers certain
inherent weaknesses which require adequate
attention to details of cavity designs and
material manipulation in order to limit the
incidence of failure of the clinical restorations.

14. • These disadvantages include:
1. Low tensile and shear strength, averaging
about 25% its compressive strength. It is a
brittle restoration that is greatly vulnerable to
fracture under high tensile or shear stresses,
such as the isthmus and the margins.
2. Poor esthetics due to its objectionable metallic
color, which may be further complicated by
excessive discoloration due tarnish and
corrosion. This caused a marked decline in
popularity of amalgam in favor of tooth-
colored restorations.

16. 3. Creep tendency (time-dependent deformation
of set material in the mouth) may result in form
instability in term of marginal deterioration,
flattening of contacts, saucering of occlusal
anatomy and formation gingival overhang.
However, creep values are markedly decreased
in recent high copper alloys.

17. Marginal deterioration and ditching
due to amalgam creep

18. 4. High thermal conductivity, which may cause
pulp irritation unless it is adequately protected
by adequate thickness of remaining dentin
bridge or by an intermediary insulating base
material if the cavity preparation is deep.
5. Lack of adhesion to tooth structure which
dictates the use of mechanical means of
retention like undercuts and grooves in the
cavity preparation.

19. 6. Electrical irritation through galvanism can
occur if another metallic restoration with
different degree of electro-negativity was
placed in its close proximity, e.g. cast gold.
The resultant currents can cause patient's
discomfort or leave a metallic taste in the
mouth, and can accelerate the corrosive
breakdown of the electro-negative metal.
7. Potential health hazards due to presence of
mercury in dental amalgam have raised
concerns over its safety along many years.

20. • Indications and contraindications:
The primary application of amalgam in
dentistry is in the restoration of posterior teeth
and, to some degree, for core buildups in fixed
prosthetics. Amalgam is considered together
with posterior resin composite and indirect
restorations as a restorative for Class I and Class
II (Si/Sta 1.1 to 1.4 and 2.1 to 2.4). Meanwhile,
amalgam is used, to a lesser degree, for the
restoration of the distal surface of cuspids and
for Class V in posterior teeth.

22. Material selection in such cases will depend on:
The extent of the lesion.
Esthetics.
Caries incidence.
Economics.

23. 1. The Extent of the lesion:
The most suitable indication for amalgam
are the small and medium sized Class I and II
cavities (Si/Sta: 1.2, 1.3, 2.2, 2.3) especially
those with four walls and a floor where the
amalgam will be confined not subjected to
tensile loads. In extensive lesions (Si/Sta: 1.4
and 2.4), the amount of remaining tooth
structure dictates a material with higher
strength requirements.

24. • Indirect restorations will thus serve better in
such cases, since they provide tooth support
against high loads including tensile stresses as
well as easier contouring outside the patient
mouth. In Si/Sta 1.1 and 2.1 resin composite
may be favored to avoid unnecessary cutting
in tooth structure that would be inevitable to
provide the resistance features required with
amalgam.

26. 2. Esthetics:
For esthetic conscious patients, amalgam
will be objectionable particularly in
conspicuous areas of teeth. Resin composite
restorations may thus be favored.

28. 3. Caries incidence:
Amalgam may be favored in patients with
moderately high caries incidence in view of its
superior adaptation, low cost and easier repair.
4. Economics:
Costing per se is mostly in favor of
amalgam, except if, on the long run, repeated
remakes are likely to occur.

29. • Classification, Composition and Types:
The major approaches for classification of
amalgam and amalgam alloys are based on:
amalgam alloy particle shape and size, copper
content and zinc content.

30. • Until the 1960s, the chemical composition and
micro-structure of available amalgam alloys were
essentially the same as those of the most
successful systems investigated by G.V. Black.
Traditional or conventional alloys were delivered
to the dentist as filings, which were lathe cut from
a cast ingot. Milling and sifting produced the
ultimate particle-size distribution, as well as the
final form of the alloy particles. Filings of
traditional lathe-cut alloy were irregular in shape
and were gradually produced in finer sizes to
control the reaction, produce smoother mixtures
and enhance the final properties.

31. Lathe-cut amalgam alloy

32. • Conventional amalgam alloys were thus
commonly classified on basis of particle size.
Lathe-cut particles could be purchased in
regular-cut, fine-cut and microfine-cut versions.
The commercial alloy evolved into a blend of
different particle sizes to optimize the
packaging efficiency.

33. • Spherical alloys were then introduced on the
market. These alloys have lower mercury-alloy
ratios and dramatically reduced condensation
pressures by providing less resistance to
particle sliding. The maximum particle size in
a spherical alloy powder is generally 40 to 50
µm or less, although there usually is a particle
size distribution.

34. Spherical alloy

35. • The distinction between irregular (lathe-cut)
and spherical particle geometries became the
next major classification for amalgam alloys.
The third category has mixed geometries or
blended shapes or admixtures of both lathe-cut
and spherical. These are widely used in recent
alloy's.

36. Blended alloy

37. Setting reaction:
Ag3Sn (γ)+ Hg Ag2Hg3 (γ1) + Sn7Hg (γ2) +
un-reacted Ag3Sn (γ) + Hg + voids
By weight, traditional alloys contain 66% to
73% of silver and 25% to 29% of tin, with
about 6% of copper, up to 2% of zinc, and up to
3% of mercury.

38. • During the late 1960s, alloys with higher copper
content (more than 4% by weight) were
introduced on the market. Classification of
amalgam based on its copper content became the
most commonly used (high copper and low
copper amalgams). Almost all amalgams used
nowadays are high copper since they show higher
strength properties, lower creep and better
resistance to tarnish and corrosion. They thus
produce restorations with superior performance
and longer life span.

39. • Two types of high copper alloys are known;
admixed and unicompositional alloys. The
admixed type was first introduced by mixing
conventional alloys and 30-55% of a spherical
silver-copper eutectic alloy containing 71.9%
silver and 28.1 % copper by weight, thus
increasing the total copper content of the alloy to
9-20% by weight. This allows the copper to
consume compositional tin and thus prevents the
formation of the tin-mercury (γ2) phase.

40. • This phase (γ2) was found to be the weakest,
softest, most brittle and corrodible phase in
amalgam. It forms inter-connected blade-like
crystals which weakened the microstructure of
low copper amalgams.

41. Setting reaction:
Ag3Sn (γ)+ Hg Ag2Hg3 (γ1) + Sn7Hg (γ2)
+ un-reacted Ag3Sn (γ) + Hg +voids
Sn7Hg(γ2)+ Ag3Cu (eutectic) Ag2Hg3 (γ1)
+Cu6Sn5 (Ƞ) + Cu3Sn ( )ɛ

42. • Unicompositional alloys are produced by
melting together all components of a high-
copper system (silver, copper and tin) and
creating a single-composition spherical or lathe-
cut alloy, rather than mechanical mixture of two
distinct powders. Thus, each particle in these
alloys has exactly the same composition. Copper
is present at higher concentrations (13-30% by
weight) and thus becomes more able to consume
at tin and virtually eliminate all gamma 2 phase.

43. • The unicomposition contain higher total of the
copper content of 13-30 wt. % than the admixed
type and differ also in the each of its particles, it
has the same composition including the Ag3Sn
(γ), the Cu3Sn ( ) and may be some traces ofɛ
the Cu6Sn5 (Ƞ).

44. Setting reaction:
Ag2CuSn + Hg Ag2Hg3 (γ1) + Cu6Sn5 (Ƞ) /
Cu3Sn ( ) + un-reacted particles + Hg + voidsɛ

45. • Zinc is another important additive to amalgam
alloy. Zinc (1% or more) tends to oxidize
preferentially forming a zinc oxide film that
covers the surface of alloy during manufacturing
and prevents oxidation of other elements. A
detrimental side effect of residual zinc is that
moisture contamination during setting converts
zinc to zinc oxide and the produced hydrogen gas
could accumulate in considerable amounts within
the amalgam, exerting pressure and resulting in
delayed expansion of the set amalgam. This could
result in pain and marginal fracture or ditching of
the amalgam restoration.

47. • Although many noble metals have been added or
investigated on experimental basis, at present
only palladium, iridium, selenium, and indium
are used as commercial additives. Palladium and
iridium are added in less than 1 % concentration
to improve strength and corrosion resistance.
Selenium has been added in an attempt to
improve biocompatibility, and indium has been
admixed in large concentrations (10% by weight)
in metallic form to high-copper amalgam to
consume the mercury vapor released during
mastication.

48. Thank You