Dental Amalgam: Part 1

Copyright © 2016 by Saunders, an imprint of Elsevier Inc. All rights reserved.
Dental Amalgam
• Combination of metals
• Easy to manipulate, has good clinical durability, and low cost
• In the United States, dental amalgam has been used
successfully for the restoration of teeth for more than 175
years.
• Millions of amalgam restorations are placed each year.
• Amalgam is a direct placement material that is used in the
posterior region of the mouth.
2

Dental Amalgam
• No other direct restorative material has the durability,
ease of handling, and good physical characteristics of
amalgam
• Wear resistance and compressive strength are
superior to composite resin and glass ionomer
cements
• 3

Dental Amalgam
• Insurance carriers have seen a reduction in the
use of dental amalgam for posterior restorations
by approximately 45% in the past 20 years.
• Probably because of concerns by patient about its
safety and its lack of esthetics have prompted patients
to request tooth-colored restorations.
• A study conducted by the National Institute of
Health (NIH) in 1991-1993 concluded that amalgam
is safe for human use.
• 4

Alloy Used in Dental Amalgam
•Alloy: Mixture of
two or more metals
5

Alloy Used in Dental Amalgam
• The alloy used to produce dental amalgam is
composed predominantly of silver but also contains
copper and tin.
• A variety of other metals, such as palladium, iridium,
or zinc, may be added in smaller quantities.
• When the silver-based alloy is mixed with mercury,
the reaction that occurs is called amalgamation and
the material that is produced is called dental amalgam.
• 6

Silver-Based Amalgam
Alloy Particles
• Classified according to the shape
of the particles in the powder
• Irregular
• Lathe-cut alloy
• Admixed
• Mixture of lathe-cut and spherical
• Spherical
• Spherical alloy
7
Courtesy of Grayson W. Marshall, University of
California School of Dentistry (San Francisco, CA).

Silver-Based Amalgam
Alloy Particles
• Each of these particle shapes contributes certain handling characteristics to
the amalgam.
• Irregularly shaped particles are formed by shaving fine particles of an ingot
of the alloy with a lathe (lathe-cut alloy).
• The particles are sifted to separate them into fine and ultrafine particles.
• Spherical particles are produced by spraying (atomizing) a mist of molten
alloy into an inert gas (spherical alloy).
• Spherical particles are formed as the atomized droplets cool.
• Require less mercury to wet the particles and generally set more quickly than lathe-
cut particles
• Admixed particles consist of a mixture of lathe-cut and spherical particles
(admixed alloy).
• 8

Spherical vs Admixed
• When spherical high-copper amalgam alloys are contrasted with admixed
dental amalgam alloys, the spherical alloy has very little resistance to
condensation into the cavity preparation and feels soft compared with an
admixed amalgam.
• The spherical alloy needs approximately 10% less mercury than the
admixed alloy for the amalgamation process.
• Spherical alloys do not displace a matrix band and keep it in contact with
the adjacent tooth in class II preparations as well as admixed amalgams
do.
• Spherical amalgams have higher 1-hour and 24-hour compressive
strengths than admixed amalgams do.
• 9

Composition
• Silver
• Tin
• Copper
• Indium
• Palladium
• Zinc
10

Dental Alloys- Composition
• Dental alloys for amalgam are composed mainly silver and tin.
• Copper is added to replace some of the silver to lessen the brittleness.
• Modern dental alloys are considered to be high in copper content (13% to
30%) compared with their predecessors, which had 4% to 6% copper by
weight.
• They generally contain 40% to 70% silver and 12% to 30% tin.
• Tin is used to control the rate of set of the amalgam.
• Both silver and tin dissolve into the liquid mercury until the solution becomes saturated
with them, they also absorb mercury.
• They are mixed with mercury 42% to 52% by weight.
• 11

Dental Alloys- Composition
• Manufacturers may also add indium, palladium, and zinc.
• Zinc may inhibit corrosion by reducing the oxidation of the
other metals in the amalgam.
• In low-copper amalgams, zinc is responsible for gradual
expansion for the amalgam over time when moisture
contamination is present during placement.
• Contact of the moisture with zinc caused the formation of hydrogen
gas within the amalgam, which caused it to expand
• Delayed expansion could cause the restoration to expand beyond the
cavity walls and could cause cracking in the adjacent enamel.
• 12

Amalgamation
• When the alloy in powder form is mixed with the mercury, a chemical
reaction occurs.
• The setting transformation is also known as amalgamation.
• The mixture has a putty-like consistency that can be packed into the cavity
preparation.
• Over the next several minutes the mix becomes firmer.
• During the firming phase, the amalgam can be carved to the anatomic shape of the
tooth.
• Once it reaches its initial set, it no longer can be carved.
• It is firm but is not fully reacted.
• It is relatively brittle at this point.
• It takes up to 24 hours for most amalgams to gain their maximal strength.• 13

Dental Amalgam
• Many of the high-copper spherical amalgams gain
approximately 50% of their compressive strength in the
first hour
• Some gain approximately 80% of their strength in the
first 8 hours
• High and low-copper amalgams are comparable in
compressive strength once they have completely set at
about 24 hours.
• Once fully set, they are hard, strong and durable
restorations.
• 14

Setting reaction phases
• The first phase, called the gamma phase, is the silver alloy phase.
• It is the strongest phase and involves the least corrosion.
• The second phase is the gamma-1 phase, which consists of
mercury reacting with silver.
• It is strong and corrosion resistant.
• Not as resistant as the gamma phase
• The third phase is the gamma-2 phase, which consists of the
reaction of mercury with tin.
• Gamma-2 is weak and corrodes easily.
• High-copper amalgams DO NOT have this phase, and are superior in
their clinical performance to low-copper amalgams.
• 15

High-Copper and Low-Copper
Amalgams
• High-copper amalgams are more durable than low-copper
amalgams
• The higher copper content of newer alloys eliminates the
formation of the gamma-2 reaction product that caused
weakening of the amalgam.
• High-copper alloys have virtually replaced low-copper
alloys because high-copper have:
• Less deterioration at the margins
• Less corrosion
• Greater strength
• 16

Tarnish
• Oxidation that attacks the surface and slightly below
the surface making it discolor
• Results from contact with:
• Oxygen
• Chlorides
• Sulfides
17
Courtesy Dr. Steve Eakle.

Tarnish
• Tarnish causes a dark, dull appearance that is not
destructive to the amalgam.
• The rougher the surface, the more it tends to tarnish.
• Polishing of amalgams is best done after the restoration has
set for a period of 24 hours or longer.
• Why??
• 18

Corrosion
• Chemical reaction between amalgam and substances
in saliva or food, resulting in oxidation of the
amalgam
• Galvanism
19

Corrosion
• Corrosion can occur when two dissimilar metals interact
in a solution that contains electrolytes (saliva).
• An electrical current is generated between the metals
(much like a battery) in a process called galvanism,
resulting in corrosion.
• It weakens the amalgam over time, can stain surrounding
tooth structure as corrosion products enter the dentinal
tubules, and can lead to deterioration of the margins.
• 20

Creep
• Gradual change in shape of the restoration
• Creep in dental amalgams refers to the gradual change in
shape of the restoration from compression by the
opposing dentition during chewing or by pressure from
adjacent teeth.
• This phenomenon is associated with the gamma-2 phase
seen with low-copper alloys and results in deterioration of
the margins.
• High-copper alloys exhibit far less creep and have
superior marginal integrity
21

Dimensional Change
• Some expansion and contraction occurs during the setting reaction
of the amalgam.
• If it contracts excessively, it will open gaps at the margins and contribute
to microleakage of fluids and bacteria, and cause sensitivity
• If the material expands excessively, it puts pressure on the cusps
and cause pain with biting pressure, or it may cause fracture of the
cusps.
• Low-copper amalgams containing zinc are prone to expansion over
time if they are exposed to moisture during placement.
• The gradual expansion after placement is called delayed expansion.
• 22

Dimensional Change
• Ideally, the dimensions of a newly placed amalgam
should not change.
• Some expansion and contraction occur during the
setting reaction of the amalgam.
• It is the net effect of these two processes that is important.
23
Courtesy Dr. Steve Eakle.

Strength
• Amalgam: Strongest of the directly placed restorative
materials
• Amalgams are stronger in compression than composite or
glass ionomer.
• They are relatively weak in tension and shear
• Therefore require adequate bulk to resist breaking.
• If amalgams are too thin in areas, they may be broken by the
biting forces.
24

Thermal Conductivity
• Amalgam: Good conductor of heat and cold
• In shallow cavity preparations, the thickness of the
dentin remaining over the pulp is usually adequate to
dissipate the heat or cold.
• In deeper cavity preparations or in teeth that were
sensitive prior to the placement of the amalgam
restorations, a base or liner should be used for the
comfort of the patient.
25

Dental Amalgam: Part 1

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Dental Amalgam: Part 1