Clinical Treatment Options
Sep 2007 —
Replacement Choices for the Worn-Out Amalgam Restoration
Not many years ago, the choices for replacement of a
large amalgam (Figure 1 View Figure) were relatively simple
because the choices were limited. Now there are
many more choices and the patient demand
for esthetics, as well as health issues, are eliminating some former choices. Many patients
today desire metal-free esthetic restorations.
The dental professional desires to maintain as much healthy tooth structure as possible
while maintaining the vitality of the pulp.
Sometimes this can lead to a conflict in the ideal treatment for the tooth. The potential replacement choices will
be discussed with the benefits and
disadvantages of each highlighted.
Even though amalgam has been getting a lot of bad
publicity in some circles, it still remains a viable replacement material
for an existing amalgam restoration. There have been some concerns about
health issues from the use of amalgam; however, studies have been
unable to find a link between chronic mercury toxicity and body burden of mercury in patient populations or dental personnel.1,2
Dental amalgam has many advantages when used as a
restorative material. It has a high compressive strength,
excellent wear characteristics, is easier to use
than other materials, is less technique-sensitive
(especially in unfavorable conditions), and has excellent long-term results. The
causes of postoperative sensitivity with amalgam are well understood and usually transient in nature. Of
the long-term restorative materials,
dental amalgam is the least time-consuming to
place and has the lowest overall cost.3
Dental amalgam is not the perfect replacement
material because it has some
disadvantages. Whal et al published data showing
that there was no significant difference in the prevalence of cusp fracture
rates in amalgam-restored teeth vs composite-restored teeth in
subjects aged 18 through 54 years.4 Some of the problems with
amalgam are that it is not tooth-colored (although this becomes an
advantage when removal of the amalgam is necessary), it does not bond to tooth structure (but can be
bonded using a separate step), and it contains
mercury, which may be more of a hazard to the dental staff and to environmental concerns than to the patient. The primary problem with amalgam is that it
is less conservative in its preparation requirements because of the need to remove more tooth structure during preparation for mechanical retention and resistance. The fact that it cannot
be repaired easily makes it a less
Composite is now used in more than 95% of all anterior
direct restorations and in 50% of all posterior direct restorations.5 This would mean that, as the choice of composite for the
replacement material for a large amalgam, a
composite would often be considered. This could
be problematic for the patient in the long run because of the physical
characteristics of the material and difficulties
in the bonding steps leading to postoperative sensitivity issues and potential for
extensive recurrent decay underneath the
subsequent composite restoration. Many patients are
requesting—in some cases demanding—that the replacement be
done with a tooth-colored material, but is this the best choice?
Composite materials should be considered as the first
choice for initial, small carious lesions;
however, the replacement of large amalgams can
lead to problems for the patient and disappointment for the dentist. The
large amalgam preparation was not designed with bonding in mind. It was
designed with the need for retention and
resistance. Ideally, composite should be used when all the margins are in
enamel. This is not usually the case when
replacing a large amalgam because the secondary decay usually extends the margins of the new preparation beyond enamel, especially interproximally.
One of the primary shortcomings of all composite materials is the
characteristic of polymerization shrinkage upon
curing. The larger
the restoration, the greater the polymerization
shrinkage of the composite (2.6% to 7.1% by
volume),6 because there is a greater chance that the restoration margins will lie beyond the enamel
surface, and there will be a greater potential for microleakage
and recurrent decay. Shrinkage stresses negatively influence the
mechanical properties and marginal integrity of the restorative material.7 There are numerous methods to
attempt to control these stresses, such as layering the material, use of polymerization tips, inserts, and soft-start polymerization. Any or all of these
methods should be used for these larger direct
In the final analysis, the ideal indications for
composite use in the
posterior are limited. The criteria should include: centric stops on tooth structure rather than
on composite material; patients who
exhibit little signs of bruxing or clenching; the ability to
isolate the area with a rubber dam; the
faciolingual width should be restricted to no more than one third of the intercuspal
distance;8 and all the cavosurface margins
should be on enamel.9 If the base of the proximal box extends into root dentin, it is extremely difficult, if not impossible, to ensure close marginal
adaptation and to obtain a perfect
marginal seal, even with the use of current
dentin bonding agents.10 When replacement restorations fall outside of these criteria, alternative materials and
techniques should be considered.
INDIRECT RESTORATIONS—TOOTH COLORED
Indirect inlays or onlays made of composite or
porcelain make ideal replacement restorations
for these large amalgam restorations. They offer the patient the esthetics
of a tooth-colored restoration while
conserving tooth structure (Figure 2 View Figure). The preparation for these restorations is
not conservative because enough tooth structure must be removed to give strength to the
material, but it is more conservative than a
crown because it maintains as much healthy
tooth structure as possible. Eventually, if necessary, it
can always be converted to a crown in the future if further deterioration of the tooth
The indirect restoration allows for improved
marginal fit and strengthening
of tooth structure because the restoration is bonded into place. Other advantages include: better control of
contacts, contours, anatomic form, color
matching, wear resistance, and, because
the polymerization shrinkage takes place outside the mouth, less stress on the bond to tooth structure. The
preparation is less
traumatic to the tooth and the surrounding tissue because it is more conservative
and the margins can be kept supra-gingival in many instances.
The indirect restoration does have some disadvantages.
takes longer to complete because it may mean an impression, a temporary, and two
appointments if it is fabricated by the laboratory. Thus the cost to the
patient is increased because of the additional
time and the laboratory bill. It is a technique-sensitive restoration because it is bonded
to place and all the steps for proper bonding
must be followed. The porcelain restoration does not allow for the possibility of intraoral repair. If some
part were to fracture, the entire restoration
would need to be removed and replaced
with another restoration.
This problem has been somewhat addressed with the
design/computer-assisted manufacturing (CAD/CAM) unit from Sirona Dental (CEREC® 3D, Sirona Dental Systems, Charlotte,
NC) and the newly introduced unit from D4D Technologies (E4D Chairside CAD/CAM
System, D4D Technologies, Richardson, TX). The CEREC unit
has been in service for over 20 years and has
many long-term studies to support its use.11 The survival
probability of a CEREC-generated restoration has been reported to be
approximately 97% for 5 years and 90% for 10 years.11 The disadvantage of this
type of restoration is the large initial
investment for the equipment and the initial learning
curve for the use of the computer program and the demands for specific preparation criteria. Once the criteria and the computer program have been mastered, a very
well-fitting, long-lasting restoration can be delivered to the
patient in one appointment that is both conservative and
PARTIAL COVERAGE INDIRECTRESTORATIONS—GOLD
For centuries, an alternative to complete-coverage
restorations has been
the partial gold coverage restoration. This type of restoration was the standard of care for conservative, high-quality, long-term restorations12 (Figure 3 View Figure). These would include gold inlays, onlays,
and partial veneer crowns. Gold restorations have excellent mechanical and
biocompatibility properties and do not deteriorate
over time. The mechanical properties of gold include proper stiffness, strength,
ductility, hardness, and coefficient of expansion
for a long-term dental restoration.13 Some of the properties of gold
described in one article12 include: gold does not corrode,
leaving the tooth discolored as amalgam often
does; it has nearly
an identical wear factor as a natural tooth; it protects and supports the
remaining tooth structure even when placed in
a thin layer; if properly placed, the margins are almost
imperceptible; the restoration exhibits a high degree of
polishing and finishing, which results in less plaque retention; and it
enables the reproduction of normal tooth anatomy and esthetics.
Although there are a few articles in the literature
that do not show support for the longevity of
gold inlays and onlays,14,15 the literature for the most part has supported the
longevity of intra- and extra-coronal gold
restorations.16-19 A more recent article20 reported the
longevity results of 1,314 cast-gold restorations placed in 114 patients by one
practitioner. All restorations were cemented with zinc phosphate cement. The survival rate ranged from 97% at 9 years
to 94.1% in place for more than 40 years.
There was an overall failure rate of 4.6%.
Gold inlay indications are basically the same as those
of medium-sized amalgam restorations. They are not indicated for
restoration of small carious lesions. Amalgam or composite are
better suited in these instances. Because gold inlays are more expensive than amalgam or composite
restorations, they need to be placed in patients who have better oral hygiene. The
teeth restored with this type of
restoration should have sufficient bulk to provide adequate
resistance and retention form. They are not for use where the missing tooth
structure is greater than one third of the
buccal-lingual cusp tip distance. Nor are they generally
indicated in mesial-occlusal-distal situations because of in increased risk of cuspal fracture.
Gold onlays have the same mechanical and biologic
benefits of gold inlays plus the added
advantage of providing cuspal coverage for
teeth that have a more extensive loss of tooth structure. Before bonded ceramic restorations became widely
available they were seen as one of the
most conservative treatment options available
Many dentists would agree that if it were not for
esthetic considerations, gold restorations
would still be the treatment option of choice.
If a tooth to be restored meets the indications for a gold restoration,
oftentimes it can still be prepared in a manner so that the restoration is
not visible. This is especially true in the maxillary posterior region.
Patients who desire long-term and esthetic
restorations should still consider gold inlays
and onlays when the display of the gold can be
minimized. Gold restorations have the potential to provide unparalleled long-term function and tissue compatibility.
INDIRECT CROWN RESTORATIONS
If a tooth has had extensive proximal and
facial-lingual caries, a conservative restoration may not be
indicated. In these cases a complete crown may be indicated. The crown may
be metal-ceramic, all-ceramic, or full cast, depending on esthetic
considerations. The tooth should be relatively intact with sufficient
coronal structure to support the restoration. This is particularly
important in the incisal and occlusal areas where the
porcelain thickness should not exceed 2 mm.21 Full-coverage restorations have better retention than
partial coverage cast restorations, and they are generally
required to serve as a retainer for a fixed partial denture.
Although full-coverage restorations will always
be the treatment of choice for extensively damaged teeth, they should not be routinely
used in place of a more conservative treatment
option simply because they are easier to place than partial coverage restorations.
The dentist and the patient have many choices for the
replacement of an old, defective amalgam restoration. The
cost/benefit ratio of each choice must be weighed against the
desires of the patient and the correct
treatment for the tooth. Sometimes, compromises
must be made to satisfy these desires; however, the choice must be made after having considered the advantages
and disadvantages of each material and based on sound clinical
judgment. Maximum retention of healthy tooth structure with the most conservative restoration possible should be
the primary concern in any decision.
The author is a consultant for Sirona Dental
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