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 -2-
Dr. Hazem El Ajrami

3. • Cavity preparation:
Amalgam is a brittle restoration. It is
vulnerable to fracture by tensile and shear
stresses that predominate at critical isthmus
and marginal areas. In addition, it is a non-
bonded restoration that requires macro-
mechanical means of retention to retain
restoration in place. This reflects on cavity
preparation design (inverted truncated cone)
which incorporates distinct resistance and
retention forms.

4. • General features of cavity preparation:
1. Cavity preparations should have
conservative outlines. The outline should
exclude centric holding areas, whenever
possible.
2. The design should provide adequate bulk
for strength of material given through the
depth.
3. Cavity walls should be parallel or
perpendicular to direction of occlusal force
of mastication.

5. 4. Cavo-surface angle (CSA) should be 90
degrees to provide sufficient strength at the
margin for both the tooth and amalgam
restoration. If cavosurface angle is obtuse,
there will not be sufficient bulk for amalgam
at the margin and it may fracture under
loading while if it is acute, brittle unsupported
enamel rods may fracture. In both cases
marginal fracture (ditching) will occur.

7. 90° CSA provides bulk for tooth and restoration
(black arrow), incorrect CSA provides insufficient
bulk for amalgam (dotted arrow) or tooth (grey
arrow).

8. 5. Any undermined unsupported enamel should
be removed to avoid its fracture under load.
6. Elimination of stress concentration by
providing smooth walls and floor and
slightly rounded line angles.
7. Sufficient retention features, including
undercuts, grooves and slots.
8. Every portion of compound cavities should
be provided with adequate self retention and
resistance features.

10. 9. The isthmus area should have proportional
width to the occlusal and proximal bucco-
lingual width. An isthmus area of minimum
width of one quarter the bucco-lingual distance
between cusp tips and an increased depth. It
should also be given an increased depth to
provide bulk for the restoration at this critical
area. This is done through roundation of axio-
pulpal line angle and inclining the axial wall
towards the isthmus portion.

11. 10. In compound cavities, gingival seat should be
definite with proper width. The gingival
enamel wall should be given proper
inclination using GMT.
11. If a cusp is undermined, it should be reduced
to a minimum of 2 mm. for cusp building with
amalgam.

12. • Before starting amalgam manipulation, the
cavity should be checked for details of
preparation. If required, pulp protection by
cavity liners, varnish and/or bases is done.
Proper isolation, cleanliness and dryness of the
cavity preparation should be maintained.

13. • Matricing (if needed):
Amalgam should be well confined during
its condensation between four walls and a
floor. If any wall is missing it must be
substituted by a matrix which should be very
thin, rigid, well contoured, adapted to margins,
wedged to compensate for the thickness of
matrix and stabilized to prevent its movement
during condensation.

14. • A metallic matrix is indicated with amalgam
restorations. Several matrices can be used
according to the case. Ivory matrix number 1
or number 8 can be used. The most common
matrix used with amalgam is the Tofflemire
matrix. It should be properly placed and
wedged after contouring of the band.
Automatrix might also be used in extensive
preparations.

16. • Manipulation of amalgam:
The manipulation of amalgam is a multi-
variable set of procedures that should be
adequately controlled and standardized in
order to obtain consistent restorations of
clinical success and durable performance,
otherwise, poor quality restorations will be
obtained.
The technique of amalgam manipulation
consists of six distinct steps:

17. 1. Selection of the alloy and mercury.
2. Proportioning of alloy/mercury.
3. Trituration of alloy and mercury.
4. Condensation of the plastic amalgam mix.
5. Carving of the restoration.
6. Finishing and polishing of the restoration.

18. 1. Selection of alloy and mercury:
Several variables might be considered during
selection of the amalgam alloy, including the
shape and size of the alloy, its copper and its
zinc content.

19. • Shape of alloy particles:
Spherical alloys provide amalgam of
exceedingly soft consistency although they
contain the least mercury concentration. It cannot
be forcefully condensed and therefore
establishing of proper contours and proximal
contact would be too difficult, and development
of marginal overhangs would be more likely. It is
therefore, not recommended for extensive
restorations which involve the external line
angles of the tooth.

20. • This soft amalgam is recommended for restoring
pulp-capped teeth where pressure in
contraindicated. They are also indicated in pin-
retained restorations, since they adapt well
around pins. On the other hand, blended or
admixed alloy shape is indicated in extensive
restorations especially those requiring cusp
building and extensive restoration of contact and
contouring.

21. • Copper content:
High copper alloys provide amalgam with
superior physical and chemical properties as
well as better handling characteristics and lower
mercury content. They are thus highly indicated
in extensive restorations and when margins
involve centric holding areas where marginal
integrity, strength and corrosion resistance are
more significant parameters of durability.

22. • Zinc content:
Zinc-free alloys are recommended in lesions
where moisture control is difficult, since they are
less adversely affected by moisture
contamination. In the past, zinc-free amalgam
alloys showed less plasticity and workability.
However, improved manufacturing procedures
have resulted in the elimination of zinc in most
high copper alloys.

23. • Form supply of alloy/mercury:
The alloy may be supplied in the form of:
Powder.
Tablets (pellets) of pre-weighed condensed
powder particles.
These two forms are supplied with highly
distilled mercury in a separate bottle to be
proportioned with the alloy powder or tablets.

24. • Capsules of pre-weighed alloy and mercury,
separated by a diaphragm or septum. Although
capsules are slightly more expensive, it is more
convenient. It eliminates the chance of mercury
spills and exposure to mercury vapor during
proportioning and mixing. In addition, it provides
a more reliable and higher alloy/mercury ratio. A
capsule may be supplied as slow, regular or fast
according to speed of the setting reaction. It is
supplied as one, two or three spills according to
amount alloy and mercury.

26. 2. Proportioning of alloy and mercury:
If powder alloy is used, the powder and
mercury should be accurately dispensed. Pre-
weighed tablets require dispensing of mercury
only while capsules are already pre-
proportioned. Although the use of capsules
ensures more accurate proportioning, yet, it
does not allow for individual variations in
amounts or alloy/ mercury ratio, if needed .

27. • Dispensing of alloy:
Gauging of the alloy is more accurately done
by weight rather than by volume, since the
volume is greatly affected by variations in the
shape and size of particles.
• Dispensing of mercury:
Volume dispensers are accurate enough for
measuring the liquid mercury. Care should be
taken to keep mercury dispensers upright while
dispensing mercury for accurate measuring, since
tilting may cause inaccuracy in proportioning.

28. • Alloy/mercury ratio:
The alloy/mercury ratio should be accurately
adjusted because of the critical influence of
mercury on the physical and mechanical
properties of amalgam. Excess mercury in the
final restoration causes marked reduction in
strength, increased expansion, decreased
hardness and increased flow and creep as a
result of increased formation of gamma 2 phase.

29. • An amount of mercury just sufficient to wet all
alloy particles is needed. If the amount of
mercury is excessively decreased, some particles
remain uncoated and will not be bound to the
rest of structure. A non-coherent, friable mix of
amalgam will be produced. This mix will have
low plasticity and workability and the resulting
restoration will be very weak and corrodible. On
the other hand, if excess mercury is used, there
will be excess mercury left in the final
restoration.

30. • Historically, in order to achieve smooth and
plastic amalgam mixes, it was necessary to use a
considerable amount of mercury in excess to that
desirable in the final restorations. This technique
was called high mercury or increased dryness
technique, where the alloy/mercury ratio was 5:6
by weight. Basically, the removal of excess
mercury was accomplished by squeezing the
mixed amalgam in a small piece of gauze
(squeeze cloth technique). However, it must
always be remembered that the higher the
mercury/alloy ratio, the higher the mercury
content of the final restoration regardless of every
effort to eliminate it.

31. • The most obvious method for reducing the
mercury content of the final restoration is to
reduce the original alloy/mercury ratio. This
method is known as the minimal (low) mercury
technique or Eames technique, where the
alloy/Hg ratio is 5:5 or 1:1 by weight. The ratio
could also be calculated in percent, so 5:5 and
5:6 alloy/mercury ratios indicate 50% and
54.5%, respectively.

32. • However, this ratio depends much on the type
of amalgam alloy, the particle size and shape
and previous heat treatment of the alloy. For
example, spherical alloys require only around
40% mercury and high-copper alloys require
around 45% mercury by weight, compared to
the lathe-cut conventional alloys which
required about 50-54% mercury, by weight.

33. • Amalgam allows a working time of 3-5
minutes after which it must be discarded.
Therefore, large cavities may require multiple
mixes to ensure overfilling of cavities without
exceeding the working time for each mix. The
amount of alloy and mercury to be used will
thus depend on:
The amount required to slightly overfill the
cavity.
The amount which can be condensed within
its limited working time.

34. 3. Trituration:
This refers to the process of mixing or
amalgamation of mercury and alloy particles to
produce a coherent, plastic and homogenous mass
of condensable amalgam. It serves to rub the film
of oxides off the surface of alloy particles to
expose its clean surface to mercury. This dissolves
both silver and tin. While in solution, silver reacts
with mercury producing AgHg or Gamma-1
phase, while tin reacts with mercury in case of
conventional alloys producing Sn8Hg7 or Gamma-
2 phase or with available copper in case of high
copper alloys forming Cu3Sn or eta-phase and
Cu6Sn5 or epsilon-phase.

35. • This process of progressive dissolution and
formation of phases continues during trituration
and to a limited extent during condensation and
results in:
Decrease in size of remaining non-consumed
silver-tin particles (gamma-phase). This is the
strongest and hardest phase of dental amalgam.
Production of the hard, strong and non-
corrodible gamma-1 phase which covers
intermeshes and bonds the unconsumed powder
particles and other phases together. It is the only
new phase produced in high copper amalgam as
a result of Hg and alloy reaction.

36. Production of the soft weak and corrodible
gamma-2 phase (in conventional alloys only).
In high copper amalgam copper-tin phases are
precipitated which increase the hardness,
strength and rigidity of amalgam.
An amount of residual mercury remains giving
the amalgam mix its plastic consistency.
Progressive consumption of mercury will
occur with corresponding decrease of
plasticity.

37. • Variables of mixing:
The amount of trituration is a function of
Time (minutes), Speed (rpm) and Pressure
(F/A). It should be accurately timed and
standardized according to the instructions of the
manufacturer.

38. • If it is inadequate, the amalgam is
undertriturated. In this case, some alloy
particles will remain covered with oxides and
uncoated with or bound to the structure, with
excess of residual mercury remaining. The mix
will appear dull, friable and too soft. The
resulting amalgam will be exceedingly weak,
corrodible and exhibits excessive setting
expansion, flow and creep.

40. • Overtrituration, on the other hand, produces a less
plastic yet homogenous and coherent mix of shiny
bright amalgam. It sets fast as a result of rapid
mercury consumption and crystallization of
produced phases. This results in less setting
expansion or rather an insignificant setting
contraction of the amalgam which shows fast-
setting with higher early strength and smoother
surface.
• Under- or over-triturated amalgam should be
discarded. Properly mixed amalgam will look
bright, homogenous and coherent.

41. • Methods of trituration:
Mechanical trituration ensures standard
optimum results if done according to manufacturer
directions. This can be done using:
Amalgamators (mechanical triturators) which
use pre-weighed amalgam capsules to be mixed
for the accurate time and speed of
amalgamation specified by the manufacturer for
each type of capsules.
Amalgamirers are used for accurate
proportioning as well as trituration of alloy and
mercury.

42. AmalgamatorsAmalgamators

43. AmalgamizersAmalgamizers

44. • Manual trituration involves use of mortar and
pestle and a steady constant force for a standard
time and rate of mixing. Care should be taken to
use a clean and moderately rough mortar and
pestle of a corresponding form to keep the mix
always under the pestle pressure. Properly mixed
amalgam will start climbing along the walls of the
mortar (curling). This old manual method of
trituration could offer similarly good
amalgamation but is subject to human variables. It
should be noted that amalgam should never be
touched with bare hands because it is moisture-
sensitive and mercury is toxic.

46. • Mulling:
It is actually a continuation of the manual
trituration and can still be used following
mechanical trituration to improve the
homogeneity of the mass and to assure a
consistent mix. The mix is enveloped in a dry
piece of rubber material and vigorously rubbed
between the index finger and the thumb or the
thumb of one hand and the palm of the other hand
for 2-5 seconds. The mass regains its plasticity
and workability, which is claimed to be due to the
redistribution of its mercury contents.

47. Thank You