Paul L. Child Jr., DMD, CDT and Gordon J. Christensen, DDS, MSD, PhD
Direct restorations have been placed in teeth for more than
a century. During that time, dental caries has been claimed to be
cured multiple times and/or definitively treated with numerous
ideal direct restorations. However, caries still remains to be the
most prevalent disease to affect mankind. Today, manufacturers,
"key opinion leaders," researchers, academics, sales representatives
and many experienced and inexperienced clinicians alike
repeat similar claims as in the past. The word "ideal" and "gold
standard" are used audaciously and casually in ads, lectures and
conversations to justify or explain why a dentist should buy
another "new and improved" product. Does the ideal direct posterior
restoration even exist?
Fig. 1: Gold inlay and gold foil restorations. Is gold still the "gold standard"?
Photo courtesy of Dr. Allan Rappold.
At one point, gold alloy and pure gold were considered to be
the ideal indirect and direct posterior restorations (Fig. 1). In
contrast, only a small percentage of the restorations currently
placed use these materials. Ironically, gold alloy and pure gold
restorations are often found to be the oldest and least carious in
the oral cavity. Currently, many dentists choose gold alloy as the
primary option for their own mouths, but are reluctant to offer
it to their patients. As tooth-colored direct resin-based composite
restorations and all-ceramic indirect restorations have
become popular with the lay public, clinicians rarely offer gold
restorations as an option to patients. The simple fact that tooth-colored
restorations offer better aesthetic results seems to imply
that they are superior in other aspects such as strength, wear and
longevity. This misconception has led to abuse of the currently
available aesthetic materials, cessation of proven techniques and
safeguards and general ignorance of the shortcomings of the new
and reportedly improved direct posterior restorations.
The purpose of this article is to examine the two most popular
types of direct posterior restorations – amalgam and resin-based composite – and provide direction on how they are best
used within current limitations. For those who believe that
amalgam or resin-based composite is the ideal direct posterior
restoration, this article might provoke thought and reconsideration
of product and technique selection.
Ideal Characteristics of
Direct Posterior Restorations
Presently, none of the available direct posterior restorations
possess all of the ideal characteristics listed below. It is interesting
to note the anxiety and controversy this statement involves, to
infer that the most common procedure provided by dentists does
not provide the optimal properties for restoration of teeth. Many
clinicians have been taught or misled to believe that whatever they
have placed in a patient's mouth is the ideal restoration because it
is the newest, most popular or touted by an expert. The following
list represents most of the ideal desired characteristics of direct
posterior restorations. Compare your current choice of direct
restorative material with the following list and see how many of
the characteristics are actually present in your clinical procedures.
Upon reading the above list, many will agree that there is no
direct posterior restoration that currently possesses all of these
characteristics. However, a few manufacturers continue to claim
that their product or technique possesses all the ideal characteristics.
Be cautious with claims that seem too good to be true.
This list is meant to encourage the following:
- Adhesive system: contained within the material or separate
(if simple and quick) while maintaining its strength continuously
over the lifetime of the restoration
- Bacteriostatic: over the lifetime of the restoration
- Biocompatible: non-allergenic among all people
- Color: tooth-colored, with color stability over time
- Cost: low for all patient use
- Aesthetics: simple shade systems that duplicate optical
properties of teeth; no color change over time and withstands
- Handling: simple, bulk placement, non-sticky, stays where
placed and easy to finish/polish
- Innovation: improve concept, such as color change that
alerts clinicians to defects or recurrent caries
- Longevity: proven over time with no defects; clinically predictable
- Non-technique-sensitive: works the same in every clinicians'
hands, regardless of situation
- Post-operative sensitivity: non-existent regardless of situation
- Preventive chemistry: releases chemicals/ions that promote
remineralization continuously at a level that is clinically
- Properties of tooth structure: mimics enamel and dentin
and resists breakdown and bacterial assault
- Radiopaque: easily identifiable on radiographs
- Setting and working time: fast snap-set and long working
time (minutes if necessary)
- Smoothness: similar to natural tooth structure, retains
smoothness over time and does not appear dull with wear
- Strength: able to withstand occlusal forces
- Wear, shrinkage and stress: similar to natural tooth structure
and low to non-existent
Manufacturers to develop a direct restorative material that
meets most of the above characteristics with the long-term goal
to provide all of the characteristics; ensure that marketing claims
are ethical, truthful and can be proven with both clinical and invitro
Clinicians to provide proper informed consent to patients
with all options for direct restoratives, their benefits and limitations
and average longevity in the oral cavity; recognize current
limitations with direct restoratives and to do your best to compensate
for the limitations with improved skill and proper technique.
Patients to better understand the materials that are placed in
their teeth and to be informed of their choices.
Fig. 2: Well-placed and non-carious amalgam restorations at 25 years.
Amalgam as a Direct Posterior Restoration
Amalgam continues to be either loved or hated in all areas of
the world with many dental offices refusing to offer this type of
direct restorative. Tooth-colored resin-based composite is now
believed by many clinicians to be highly superior to amalgam.
Some clinicians make their income by removing non-carious,
unaesthetic, clinically acceptable amalgam restorations and promoting
the still-controversial allegations of mercury toxicity. This
practice of encouraging patients to remove sound amalgam
restorations by preying on public and patient anxiety for profit is
unethical and highly questionable of a "professional." Despite
their unaesthetic shortcomings, amalgam restorations are still supported
by the ADA, WHO, FDI and the FDA and are an acceptable
and viable treatment option for direct posterior restorations.
Fig. 3: Fractured DB and DL cusps of a mandibular molar with staining and
minor caries; an onlay or crown would be the optimal restoration.
Fig. 4: Fractured facial cusp of maxillary premolar with staining and minor
caries; an onlay would be the optimal restoration.
Fig. 5: Fractured maxillary MB cusp with an older mesio-occlusal amalgam
restoration; note the long-lasting gold inlay now forgotten but rarely taught.
Photo courtesy of Dr. Sameer Puri
Fig. 6: Removal of amalgam restoration demonstrates minor caries and staining;
a CEREC-fabricated onlay was the final restoration chosen.
Photo courtesy of Dr. Sameer Puri Fig.7: Twenty-year-old fractured and patched amalgam restorations, recurrent
caries and fractured cusps that require onlay or crown placement. Fig. 8: Questionable amalgam restorations more than 25 years in service; is it best
to leave them alone?
Fig. 9: Completed resin-based composite restorations demonstrating lack of severe
caries; will these new restorations last 25 years?
Observation of patients you or another dentist have treated
will reveal the following about amalgam restorations:
The main advantages of amalgam as clearly demonstrated and
proven over many years of successful use are: bacteriostatic, easy to
place and shape, durable, strong, have longevity and low cost. The
main disadvantages are: unaesthetic properties, staining of tooth
structure and propensity for fractured cusps due to preparation
technique (excessive tooth removal for retention) and expansion/
contraction characteristics dissimilar to tooth structure. In searching
for the ideal direct posterior restorative, it is evident that amalgam
has many of the ideal characteristics, namely bacteriostatic, longevity
and strength. Amalgam is often reserved for patients who are limited
in financial resources, have high caries risk or have minimal third-party
benefits. Ironically, it is these patients who might benefit most
from amalgam's bacteriostatic and longevity properties, while the
patients with more adequate insurance and financial resources
receive aesthetic but non-cariostatic materials.
- Many amalgams serve for several decades (Fig. 2).
- It is common to experience fractured cusps, due to preparation
technique of undercuts and the wedging effect of amalgam
(Figs. 3 & 4).
- Most amalgam restorations cause staining of dentin and
residual caries (due to the bacteriostatic properties of silver)
(Figs. 5 & 6).
- Large amalgam restorations that involve most of the tooth
with no other option but an onlay or crown still function relatively
well (preferable an onlay when at all possible) (Fig. 7).
- Old amalgam restorations that have discolored and stained
the tooth, but with little evidence of recurrent caries (clinically
or radiographically) (Figs. 8 & 9); these restorations
should be carefully examined over time and potentially
replaced when necessary.
When deciding about your continued use of amalgam, carefully
consider each characteristic. If you must choose to use amalgam for
a highly visible first pre-molar, discuss with your patient the benefits
and limitations of all of the restorative options. When considering
the potential graying of tooth structure if amalgam is used,
against its proven longevity and known bacteriostatic properties,
you might decide resin-based composite is the best option.
However, when treating a maxillary second molar that is not visible
when smiling, you might recommend an amalgam restoration.
It is equally important to consider each patient's caries risk potential
and estimated needed longevity in his or her oral cavity based
upon their habits, history and health.
Resin-based Composite as a
Direct Posterior Restoration
Resin-based composite (RBC) has been continuously improved
over the years and manufacturers are striving to meet the ideal characteristics
listed above. However, two of the most important characteristics
have not been adequately met, bacteriostatic properties
and increased longevity. It is known through both research and
observation that posterior direct resin-based composite restorations do not possess the same longevity and bacteriostatic properties
as amalgam (Fig. 10). Yet, they can be highly aesthetic and have
revolutionized the aesthetic/cosmetic desires of dentistry. In
which clinical situations are the aesthetic characteristics of a
material more important than the other properties?
The emphasis of resin-based composite material by both
manufacturers and key opinion leaders as a solution for most
restorative dental needs is unfortunate. The resultant overuse
of RBC is at the expense of patients. Adequate informed consent
is required, including candor regarding its longevity in
comparison to other restorative materials. Many third-party
benefit providers in the U.S. will reimburse a portion of the
allowable amount after only five years. Despite this, each time
a restoration is replaced more tooth structure is removed with
a decrease in strength and an increase in microbiological
assault. As a result, many of the "first composite replacements"
become crowns instead of onlays or another resin-based composite
Fig. 10: Is it radiolucent flowable resin-composite or recurrent caries after only four
years in service? All restorations exhibited recurrent caries with two direct pulp caps
in this 32-year-old moderate-caries risk patient.
Fig. 11: How long will these well-placed, large resin-based composite restorations last
before recurrent caries is detectable?
Fig. 12: Recurrent caries was evident under both restorations (first molar example of
Observation of patients you or another dentist has treated will
reveal the following about resin-based composite restorations:
Despite the limitations mentioned above, including high
cost, technique sensitivity of the product, high overhead for
time spent, poor reimbursement rate and an always-changing
choice of materials claiming to be superior to the previous versions;
resin-based composite restorations for direct posterior use
are improving. Manufacturers are making sincere efforts to solve
some of the challenges that have continued to plague these
restorations for decades. New "universal" adhesives that can be
used with or without phosphoric acid etching for direct and
indirect restorations are being introduced to simplify the race to
be the next superior "generation." Flowable resin-based composites,
which have been one of the most abused dental materials,
are being changed to include stress-reducing properties at a
lower shrinkage rate. Some companies have redesigned their
flowables in response to practitioners placing it in increments
that are larger than original recommendations of less than
0.5mm. The new flowables compensate for practitioner abuse
by decreasing stress and shrinkage at a larger placement depth.
Bulk fill or "dentin replacement materials" are being introduced
that actually meet manufacturers' claims. Adhesives are being
combined with resin-based composite to simplify procedures.
Many of these new introductions are major steps in the right
direction (as middle stage products) but presently manufacturers
have not truly addressed the issues concerning bacteriostatic
properties, longevity and lifetime maintenance of dentin bond
strength over time. If these three limitations were presently met
by any system, we would not observe the higher caries rates
among this class of restoration.
- Highly aesthetic for both anterior and posterior
restorations (Fig. 11)
- Susceptible to recurrent caries, even under sealants
(Fig. 12). Dr. Rella Christensen has demonstrated
through clinical research that more than 90 percent of
sealants have active caries at 10 years when the sealants are
removed. (TRAC Research)
- Staining of the margins often becomes evident after a
short period of time
- If carious, the lesions tend to be more severe (in comparison
- Moderate to high recurrent caries rate interproximally
- Tend to chip and some might stain bodily over time
- Might last several years in a patient with low caries risk,
good oral hygiene and excellent technique in placement;
however, in a patient with moderate-to-high caries risk,
longevity can be markedly less
Fig. 13: Rubber dam isolation is still the gold standard!
Fig. 14: Properly contoured, finished and polished resin-based composites on
mandibular premolars. Note the existence of occlusal embrasures and marginal ridges
on the premolars, unlike the second molar.
Compensation for Limitations
Through Improved Technique
It appears that resin-based composites will continue to dominate
and replace amalgam, despite their limitations. Another
factor contributing to the decline of amalgam is worldwide
political pressure to discontinue its use. Until ideal solutions can
be addressed with the composite itself and the adhesive systems manufactured for them, it is the responsibility of clinicians to
perfect their techniques in placing restorations to improve
longevity and decrease recurrent caries. The following are suggestions
to improve outcomes of direct posterior resin-based
- Rubber dam isolation: still the gold standard in reducing
contamination from blood, saliva and other contaminants
- Conservative preparation: extension for prevention is
no longer the accepted treatment standard, nor is the
preparation technique for amalgam the same as for
- Disinfection: TRAC Research (Dr. Rella Christensen) has
demonstrated that two one-minute coats of a 5%
Glutaraldehyde/35% HEMA product (i.e. Gluma by
Heraeus Kulzer, MicroPrime by Danville, etc.) disinfect
tooth preparations and eliminate bacterial contamination.
- Adhesive: use a well-proven adhesive that maintains consistent
bond strength under varying conditions. CR
research has demonstrated in pilot studies and unpublished
research that procedures as simple as varying the
amount of air pressure and time thinning an adhesive can
change bond strengths from 2MPa to 50MPa.
- Flowable: use of a resin-based flowable composite in the
box of a preparation, based on the claim it adapts better to
walls, is not a reason to use this high-stress, high-shrinking
product. If flowable is used, use it at 0.5mm increments,
or use a product that has research to prove it can be placed
in thicker increments with decreased stress (i.e. SureFil
SDR by Dentsply Caulk).
- Glass ionomer products: use of a resin-modified glass
ionomer as a liner or base is recommended for its preventive
chemistry, decreased sensitivity and insulating properties.
- Placement of composite: place the material in minimal
depth increments (usually 2mm or less) while being careful
to avoid pull-back or introduction of voids. Some
newer bulk-filling composites allow for placement up to 4-
5mm, while maintaining low shrinkage and stress.
- Finishing and polishing: take time to carefully finish
restorations, providing adequate marginal ridges, simple
occlusal anatomy, avoiding sharp angles (that usually chip
within one year), avoiding heavy occlusal contacts and
overfinishing of the margins (which creates gaps and another
area for micro-leakage and bacterial assault) (Fig. 14).
- Follow-up: monitor the restorations and check them
radiographically and clinically on a routine basis.
Examine the restorations for excessive wear, chips, open
margins, staining and caries. If you have to repair, do it
sooner rather than later.
Both amalgam and resin-based composite for direct posterior
restorations have advantages and limitations. However, neither
material has all the ideal characteristics. Providing patients
with adequate informed consent for choice of treatment, materials,
benefits, risks and limitations is not only ethical, but realistic
as to how these new advanced materials hold-up over time.
Exciting new products will continue to inundate the profession
with claims of being superior. We advise caution. Providing
patients with resin-based composites is not a high-revenue procedure
for most dentists, yet it is imperative that we improve our
techniques to compensate for the limitations of the products
until the ideal direct restorative material is introduced.