Dental amalgam is an alloy used in dental fillings that is created by mixing mercury with silver, tin, and copper. The document discusses the composition of dental amalgam alloys, including low-copper, high-copper, and gallium-based alloys. It also covers the properties, clinical use, and safety of dental amalgam, including how it is manipulated during dental procedures, its strength, creep, and corrosion resistance over time. The typical service life of a dental amalgam filling before needing repair or replacement is 7 to 15 years.

1. DENTAL AMALGAM
DR ASHWINI M PATIL
Reader
Navodaya dental college
Raichur

2. ⚫Amalgam—Analloycontaining mercury.
⚫Dental amalgam—Analloy that is formed by reacting
mercury with silver, copper, and tin, and which may
also contain palladium, zinc, and other elements to
improve handling characteristics and clinical
performance.
⚫Dental amalgamalloy (alloy fordental
amalgam)—Analloyof silver, copper, tin, and other
elements that is processed in the form of powder
particlesoras a compressed pellet.

3. amalgam alloys
irregularly
shaped
as
spherical
particles
as a
mixture of
both lathe-
cut and
spherical
particles

4. composition of amalgam alloy:
⚫Low-Copper Alloys
Silver-tin alloys are quite brittle and difficult to blend
uniformly unless a small amount of copper is
substituted for silver. Within the limited range of
coppersolubility, an increased coppercontent hardens
and strengthens the silvertin alloy.

5. High-Copper Alloys
⚫The first high-copperalloy
This modification raises thecoppercontent to 11.8%
byweight. This is often called “dispersed-phasealloy”
or “admixed high-copperalloy.”
⚫A second typeof high-copperalloy
This processyieldsa singlecomposition system. The
coppercontentof thisgroupof alloyscan beas
high as 30% byweight.

6. Gallium-Based Alloys
In an attempttoeliminate mercury from direct
metallicrestorative materials.
gallium , has been considered as a substitute
which is also a liquid when alloyed with indium
and tin at room temperature. Like mercury, this
metal element can be triturated with alloys for
high-copperamalgam.

7. POWDER CONFIGURATION
⚫the physical configuration and condition of the
particles will have a significant influence on the
setting process.

8. Lathe-Cut Powder versus Spherical
Powder
⚫Amalgams made from lathe-cut powdersoradmixed
powders tend to resist condensation better than
amalgams made entirely from spherical
powders.(why?)
⚫Spherical alloys require less mercury than typical
lathe-cutalloys(why?)

9. Particle Size
⚫Smaller particles greatly increase the surface area per
unitvolumeof the powder. A powdercontaining tiny
particles requires agreateramountof mercury to form
an acceptableamalgam.
⚫During carving, the larger particles may be pulled out
of the matrix, producing a rough surface. Such a
surface is probably moresusceptibletocorrosion than
a smooth surface. A smalleraverage particlesize tends
to produce a more rapid hardening of the amalgam
with greaterearly strength.

10. ⚫The physical propertiesof the hardened amalgam depend on
the relative percentagesof each of the microstructural
phases.
⚫The greater the numberof unconsumed Ag-Sn particles
retained in the final structure, the strongertheamalgam will
be.
⚫The γ2 phase is the weakest and least stable in a corrosive
environment and may suffer corrosion attack especially in
crevicesof the restorations.
⚫ the addition of more than 6% of copper by weight can
reduceoreliminate theγ2 phase by formation of the Cu-Sn
phase.

11. Clinical manipulation of amalgam
for restorations
⚫The amountof alloyand mercury to be used can be
described as the mercury/alloy ratio.
⚫The mercury content of the lathe-cut alloy is about
50% byweightand that forspherical alloys is 42% by
weight.

12. Triturators
⚫A trituratorshould be used at the speed recommended
by thealloy manufacturer.
⚫For a given alloy and mercury/ alloy ratio, increased
trituration timeand/orspeed shorten theworking and
setting times.

13. appears rounded with a smooth shiny surface ,
the strength will be optimal and the smooth
carved surface will retain its luster long after
polishing.
has low strength and poor resistance to corrosion.
the rough surface left after carving of the
granular amalgam will increase its susceptibility
to tarnish ,The mixture may appear in solid mass,
but the surface remains without luster as shown.
is shinier than that of the properly triturated one,
and because of more fluid consistency the mass
appears flattened by the force of trituration.

14. Condensation
⚫The goal of condensation is to compact the alloy into the
prepared cavity so that the greatest possible density is
attained, This results from a reductionof excess mercuryand
porositywithin the setamalgam.
⚫The field of operation must be keptabsolutelydry during
condensation.
⚫ Sufficient pressureshould be used toremovevoidsand to
adapt the material to thewalls.
⚫The longer the time thatelapses between mixing and
condensation, theweaker theamalgam will be(why?)

15. Carving and finishing
⚫The objectiveof carving is tosimulate theanatomy
ratherthan to reproduceextremely fine
details.(why?)
⚫Carving should not be started until theamalgam is
hard enough to offer resistance to the carving
instrument. (why? )

17. PROPERTIES OF AMALGAM
1-dimensional stability
⚫Amalgamcan expand orcontract, depending on its
manipulation.
⚫ Severecontractioncan lead to microleakage , plaque
accumulation, and secondarycaries.
⚫Excessive expansion can produce pressure on the pulp and
postoperativesensitivity. Protrusionof a filling can also result
from excessiveexpansion.

18. ⚫expansion will occur if sufficient mercury is present in the
mix.
⚫manipulation with less mercury in the mix, as occurs for
lower mercury/alloy ratios and higher condensation
pressures, will favorcontraction. In addition, manipulative
procedures that accelerate setting and consumption of
mercuryalso favorcontraction, including longertrituration
timesand useof smalleralloy particles.

19. ⚫What isdelayed expansionorsecondary
expansion?
⚫When a zinc-containing, low-copperor high-copper
amalgam is contaminated by moistureduring
triturationorcondensation, a largeexpansion can take
place. This expansion usually starts 3 to 5 days after
placement and may continue for months, reaching
valuesgreater than 400 μm/cm (4%) .

20. 2-strength
⚫The strengthof amalgam is more than adequate
under compressive loads. However, amalgam is
muchweaker in tension than in compression.
⚫Morecommonare defects at the margins of
amalgams.

21. factors
affecting
amalgam
strength :
Trituration
Mercury
Content
Condensation
Porosity
Amalgam
Hardening
Rate

22. 3-creep
⚫occurswhen a solid material slowlydeforms plastically
underthe influence of stresses.
⚫Creep rate has been found tocorrelatewith marginal
breakdown of conventional low-copperamalgams;
that is, the higher theamountof creep, thegreater is
thedegree of marginal deterioration.

23. 4-tarnish and corrosion resistance
⚫tendency toward tarnish, does notaffector hange the
mechanical propertiesof theamalgam.
⚫ Corrosion, on theother hand, has a negativeeffecton the
properties.
⚫Every effort should be made to produce a smooth,
homogeneous surface on a restoration in order to
minimize tarnish and corrosion.
⚫ Whenevera gold restoration is placed in contactwith an
amalgam, corrosion of the amalgam can be expected as a
result of the large differences in electromotive force
(EMF) of the two materials. The corrosion process can
liberate free mercury, which can contaminateand weaken
the gold restoration. Biological effects such as galvanism
can also result.

24. Clinical performance of amalgam
restorations
⚫Amalgam does not adhere to the tooth structure. At best it
affordsonlya reasonablycloseadaptation to thewallsof the
prepared cavity. For this reason cavity varnishes are used to
reduce thegross leakage thatoccursaround a new filling.
⚫The useof dentin bonding agents with amalgam is another
relatively new method toreduce microleakage.
⚫If theamalgam is properly inserted, leakagedecreases as the
restorationages in the mouth.(how?)

25. marginal breakdown
⚫Although theditching of a margin may not have progressed
to the pointwhere secondarycaries may havedeveloped, the
restoration is unsightly and further deterioration may be
anticipated.

26. Survival of amalgam restorations
⚫ The median survival times forposterioramalgam
restorationswere 7 to 15 years in general practices. Larger,
morecomplex restorations fall within the lowerrange.

27. Repaired amalgam restorations
⚫The important factorrelated to thequalityof theamalgam
repair is the interfacial bond between the new and the
existing amalgam.
⚫The surface of an old amalgam to be bonded should be
roughened to removecorrosionand salivacontaminantsand
freed of loosedebris.
⚫ When a freshly triturated amalgam is condensed directly
onto the roughened surfaceof an existing amalgam, the
flexural strength of the repaired structurecan reach 50% of
thatof unrepaired amalgam.

28. ⚫Making a sloton theexisting amalgam toestablish
mechanical interlocking between the two materialsalso
improves thequalityof the repair joint.
⚫Another repair option for areas that exhibit minor marginal
breakdown—gaps thatare 250 μm or less in width—is toetch
the enamel adjacent to the restoration and, after rinsing and
drying the marginal gap area, sealing the gap with a dentin
bonding adhesive.
⚫When secondarycaries is diagnosed, it inevitably requires
the replacement of the restoration, but an alternative
treatment is to remove part of the restoration to the full
depth at the siteof thedefect.

29. ⚫The repair should be attempted only if the area
involved is one that will not be subjected to high
stresses orone in which the two restorationparts
areadequatelysupported and retained.

30. Safety of amalgam fillings
Toxicity
total amount of mercuryvapor
released during occluding on
amalgam restorations is far
below the “no effect” level
Allergy
areexperienced by less than
1% of the treated population

31. Mercury hygiene in dental offices
⚫Theoperatory should bewell ventilated.
⚫ All excess should becollected and stored in well-sealed
containers.
⚫Properdisposal through reputabledental vendors is
mandatory topreventenvironment pollution.
⚫ The useof an ultrasonicamalgam condenser is not
recommended.
⚫Instrumentscan be used thatyield a time-weighted average
for mercuryexposure tosample theair in theoperatory.
⚫Film badges are also available that can be worn by office
personnel in a mannersimilar toradiation exposure badges.
⚫Biological determinationscan be performed on officestaff to
measure mercury levels in blood or urine.