* Dr. Kugel is Professor and Assistant Dean for Research,
School of Dental Medicine, Tufts University, Boston, Massachusetts, USA
** Dr. García-Godoy is Professor and Director, Clinical
Materials Research, Department of Restorative Dentistry, University of
Texas Health Science Center at San Antonio, Texas, USA.
Esthetic direct alternatives to amalgam restorations include
glass-ionomers, resin-modified glass-ionomers, compomers and composite
restorations. Marked changes in the use of restorative materials have
occurred during the past 10 to 20 years1-5 and esthetic
considerations are growing in importance for the restoration of posterior
teeth.6 Alleged adverse health effects and environmental
concerns due to the release of mercury launched controversial discussions
about the continued use of amalgam as a contemporary restorative
In recent years, development and interest in esthetic
dentistry has dramatically increased. This is evident from dental
journals publications. Many of the articles and an increasing number of
entire journals are devoted to this topic. Along with the journals comes
an avalanche of advertisements with products claiming to be the new
breakthrough in esthetic restorative dentistry although many times there
is nt enough clinical evidence to support their use. The patient
population is not immune from this onslaught. They read about bleaching,
lasers and metal-free dentistry while standing in line at the supermarket.
These same patients are living in a youth oriented society, which places a
high value on appearance. Add to this the unsupported fear of mercury in
dental amalgams and is it any wonder that the dental professionals are
flocking to educational institutes and seminars all across America in
search of the esthetic revolution.
As amalgam replacements have become a primary focus of
dental materials research, the need for improved adhesion has also become
an area of major interest. The principles of adhesive dentistry date back
to 1955 when Buonocore,9 employing techniques of industrial
bonding, suggested that acids could be used as a surface treatment before
applying resins. In the late sixties Buonocore et al10
believed that resin tag formation was the cause of adhesion to acid etched
enamel. This principle is well accepted today.
As we advanced in our understanding of enamel and dentin
bonding we also sought to improve those materials we used with our new
bonding systems. We marched from our first generation of adhesives, which
yielded bond strengths of only 1-3 MPa with poor clinical results, to the
present use of fifth and sixth generation systems.11 For
example, ESPE's recent entry into the bonding arena is Prompt L-Pop. This
is a sixth generation self-etching adhesive system that incorporates the
etching of enamel and dentin in one application without a bottle
(A) Pre-op photo, teeth 12&13,
(C) Prompt-L Pop Bonding System,
(D) Immediate post-op, ESPE’s experimental fluoride-releasing composite,
(E) 6-month post-op,
(F) I-year post-op.
Esthetic restorative materials require a bonding
procedure in order to be durable and reliable. In order to accomplish
this, the bonding system must be biocompatible, bond similarly to both
enamel and dentin, have sufficient strength to resist masticatory forces,
have mechanical properties close to those of tooth structures, be
resistant to degradation in the oral environment and easy to use.
The longevity of dental restorations is dependent upon
many different factors including materials-, dentist-, and patient-related
factors. Main reasons for failure are predominated by the formation of
secondary caries, fracture of the bulk of the restoration or of the tooth,
marginal deficiencies, and wear.
The importance of direct placement esthetic tooth-colored
restorative materials is still increasing. Direct composite restorations
require a time-consuming and more costly treatment procedure.
Our laboratories reported the benefit of using
resin-modified glass-ionomers (RMGIs) as liners under posterior composites
and amalgams as a way to reduce cervical microleakage13,14 and
recurrent caries.15,16 This may be due to their fluoride
release.17,18 Glass-ionomers have also been shown to be
From an esthetic standpoint, glass-ionomers can only be
considered as "long-term" provisional restorations in stress-bearing
posterior cavities and will not be addressed in this review
Direct Adhesive Restorative
The availability of fluoride-releasing dental materials
have been increasing and the following outline highlights the amount of
Fluoride Releasing Restorative Fluoride
Conventional glass-ionomer High
Smart composite --> High-Med
Compomer --> Medium
Ceromers --> Low
Composite Resin --> Low
Packable composite --> Low
Flowable composite --> Low
Ormocer --> Low
Along with improved bonding the clinical performance of
direct and indirect restoratives has improved. The most commonly used
direct esthetic restorative material is composite resin. The
clinical performance of these materials has improved due to developments
in wear resistance, color stability, strength, radiopacity and percent
cure.20 There are three main factors affecting the properties
of composite resins: they are the filler, resin, and interface
characteristics. The fillers in composite resins are added to control
their handling characteristics, reduce shrinkage, increase strength and
decrease abrasive wear.
The fillers used include:
Amorphous silica (microfiller)
Radiopaque glasses, barium, strontium, others
Fluoride containing fluorosilicates, ytterbium and yttrium
(A) Pre-op photo, teeth 12&13, (B) Preparation,
(C) Prompt-L Pop Bonding System, (D) Immediate post-op, ESPE’s
experimental fluoride-releasing composite, (E) 6-month post-op, (F)
One of the major improvements in composite resin has
resulted from increased filler loading along with varying its
distribution, size, shape and composition.
|Table I - Filler Classification|
|Type||Average (mm)||Large (mm)||Vol % |
|Microfill||0.04 - 1||0.1 - 5.0||38 - 50|
|Minifill||0.4 - 0.8||1.0 - 5.0||56 - 66|
|Midifill||1.0 - 3.0||5.0 - 15.0||70 - 77|
|Conventional||5.0 - 15.0||50 - 70||60 - 70|
The microfilled composite resin direct restoratives are
highly polishable but are subject to increased marginal
breakdown.21 Most of the mini-filled composites have a small
amount of amorphous silica added to the monomer to improve the handling
characteristics. Midifilled composite resins employ zirconium silicate,
strontium, or barium fillers and they have an average particle size of 1-3
µm (Table 1). Along with particle size, one must be concerned with filler
content. Filler content is the quantity of filler in a composite. It has
been demonstrated that filler volume and filler load correlate with the
strength of the composite resin. Increased filler volume results in an
increase in fracture, toughness (Figure 2), along with an increased
flexure modulus22 (Figure 2). The wear of composite
restorations depends on filler particle size, interparticle spacing, and
filler loading.23 There is reduced wear with smaller particles
due to less plucking and therefore fewer voids. Smaller interparticle
spacing allows for matrix protection by having the matrix areas smaller
than the abrasive particles.
The filler particles of composite resins are silanated in
order for the hydrophilic filler to bond to the hydrophobic resin matrix.
The importance of silanation is significant. Good silanation will result
in a stable composite resin that is resistant to wear with a homogenous
The matrix of most composite resins is a mixture of
di-functional monomers containing Bis-GMA, TEGDMA, or UDMA in some
combination. More recent materials such as the ormorcers (organically
modified ceramic) employ multi-functional methacrylates.
Also included in the category of composite resins are the
flowable composite resins. These resins have lower filler volumes than the
conventional direct composite resin restorative materials. As a result of
this lower filler volume, these materials have a decreased viscosity,
which makes them a good choice as a pit and fissure restorative. However
they also have increased shrinkage and increased wear along with decreased
strength. They have been recommended as a class V restorative or as a
liner under posterior composites.
In vitro evidence does not support their use as a
liner in order to reduce microleakage.25
Recent Composite Resin
Compomers are defined as polyacid-modified resins. These
materials are basically light-cured, low fluoride releasing composite
resins. The difference between compomers and composites is that the
compomers monomers contain acidic functional groups that can participate
in an acid/base glass ionomer reaction following polymerization of the
resin molecule. The term compomers is the result of the hybridization of
the words composite and glass ionomer.
However, they are not glass-ionomer materials. A true glass-ionomer must
be a two-component system or else the acid/base reaction would take place
immediately.24 Conventional glass-ionomers must be mixed just
prior to use. With the compomers, there is a single component system which
cannot contain any water in order to prevent a premature glass-ionomer
A resin polymerization takes place with the compomers
after the material has set completely. The glass-ionomer reaction may then
occur in the presence of water. Water is a necessary medium for the
acid/base reaction. In the presence of water from the oral cavity, the
acid functional groups, which are attached to the monomer units, and have
now become part of the polymerized material are able to react with the
base (glass) to stimulate the glass ionomer reaction. Fluoride is released
as a result of this reaction. The level of fluoride release from the
compomers is significantly lower than what is seen for conventional
glass-ionomers or RMGIs.26 When they were introduced, acid
etching was not required by the manufacturers. This was seen as an
advantage over the use of composites along with the suggested fluoride
release. It was subsequently demonstrated that the use of an acid etched
procedure significantly improves both the retention and marginal leakage
of the compomers.27-29
In summary, compomers:
Consist of a paste containing Ca, Al, F silicate glass
filler in dimethacrylate monomers with acrylic acid like molecules;
Are set by polymerization of C=C of methacrylate (delayed
acid/base reaction between glass and acid molecules);
Promote adhesion to teeth, mediated by the adhesive.
Offer good strength, biocompatible, low solubility
Have higher wear than composite, lower F release than
conventional glass-ionomers and packable composites.
As the dental profession searched for an amalgam
substitute it found limitations in the composite materials on the market.
These limitations included: resistance to wear, fracture of the
restoration within the body and at the margins, marginal leakage due to
polymerization shrinkage and the technique sensitivity including the
ability to obtain adequate proximal contact in the final restoration.
Packable or "condensable" composites have recently been
introduced to the profession as an amalgam substitute. They contain a
higher filler load as well as filler distribution. This results in a
stiffer consistency than hybrid composites. These changes in the
properties of the packable composites result in improved handling
characteristics, at least as seen by the manufacturers of these products.
The major advantage to these materials is that they make it easier to
establish inter-proximal contacts while placing class II restorations.
Some of these materials also claim that they may be cured
in bulk. Recent studies have indicated that some of the packable
composites claiming bulk fill to 5 mm depth fall short of these
One study using a halogen light demonstrated at a
40-second cure that the uncured values are 39.08% for Prodigy, and 39.61%
for Surefil, both of which claim to be bulk fill materials. The results
for the two materials, which recommend incremental cure, were 33.76% for
P60 and 33.19% for Tetric Ceram30 (Figure 4).
Bingham JDR 1518A:2000
The term ceromer stands for Ceramic Optimized
Polymer and was introduced by Ivoclar to describe their composite Tetric
Ceram. This material consists of a paste containing barium glass (< 1
µm), spheroidal mixed oxide, ytterbium trifluoride, and silicon dioxide
(57 vol%) in dimethacrylate monomers (Bis-GMA and urethane dimethacrylate.
They are set by a polymerization of C=C of the methacrylate. They must be
bonded to tooth structure. The properties of the ceromers are identical to
those of composites and they exhibit fluoride release lower than
conventional glass-ionomers or compomers.
Ormorcer is the acronym for Organically Modified
Ceramics. This class of material represents a novel inorganic-organic
copolymer in the formulation that allows for modification of its
mechanical parameters. The inorganic-organic copolymers are synthesized
from multi-functional urethane- and thioether(meth)acrylate alkoxysilanes
as sol-gel precursors. Alkoxysilyl groups of the silane permit the
formation of an inorganic Si-O-Si network by hydrolysis and
poly-condensation reactions. The methacrylate groups are available for
photochemical polymerization.3,31 The filler particles are
1-1.5 µm in size and the material is 77% filler weight and 61% filler
This class of composites was introduced as the product
Ariston pHc in 1998. Ariston pHc is an ion-releasing composite material.
It releases fluoride, hydroxyl, and calcium ions as the pH drops in the
area immediately adjacent to the restorative material. The drop in pH
values is the result of active plaque which results in a corresponding
increase in the release of functional ions.3 Smart composites
work based on the newly developed alkaline glass filler which will reduce
secondary caries formation at the margin of a restoration by inhibiting
bacterial growth. This results in a reduced demineralization and a
buffering of the acid produced by caries forming
The paste consists of Ba, Al, and F silicate glass filler
(1 µm) with ytterbium trifluoride, silicon dioxide and alkaline Ca
silicate glass (1.6 µm) in dimethacrylate monomers: it is filled 80% by
weight and 60% by volume. The use of an adhesive to tooth is not
recommended. However dentin should be sealed to reduce sensitivity. The
fluoride release from this material is claimed by the manufacturer to be
lower than conventional glass-ionomers but more than that of
In an effort to address the disadvantages of the direct
adhesive restoratives such as technique sensitivity, anatomic form,
polymerization shrinkage, wear and interproximal contacts, the indirect
composite resins were introduced. These materials were also seen as having
advantages over PFM and all ceramic restorations. PFM restorations require
a metal substructure, although reliable and time-tested, they are often
considered as esthetic as the all-ceramic or indirect composite
restorations. It is difficult to obtain the translucency seen in natural
teeth when using a metal substructure.
While the all-ceramic restorations are more translucent than
PFM, they have other problems, such as abrasion of the natural dentition
and they are not easily repaired.
The first generation of the composite–based indirect
adhesive restoratives were introduced in the early 1980’s. These included
Visio-Gem (ESPE) and Dentacolor (Kulzer) followed in 1987 by Concept
(Ivoclar). These materials were developed in an effort to overcome the
polymerization shrinkage and accelerated wear experienced with the direct
adhesive restorative materials. These new materials offered the advantages
of chairside repair, esthetics, improved anatomy and interproximal contact
along with ease of fabrication. However, this first generation of
materials suffered from low flexural strength, low modulus of elasticity
and low resistance to wear abrasion. These poor physical properties were
the result of low filler load and high matrix load.
It was not until the mid-1990’s that the second
generation of indirect composite restorative were introduced. These new
materials included Artglass (Heraeus-Kulzer), BelleGlass HP (Kerr), Targis
(Ivoclar), Colombus (Cendres et Mataux) and more recently, Sinfony
The effect of heat curing these newer composite materials
on the degrees of conversion was demonstrated by Ferracane and Condon in
199232 (Figure 5). They demonstrated that heat treatment, in
addition to a 60-second light cure, will increase the degree of
conversion. This increase in degree of conversion will improve the
fracture toughness of the indirect composite materials (Figure 6).
This second generation of materials incorporated ceramic
fillers with mean particle sizes of less than 1 µm of smaller diameter,
silanized and with a narrow distribution. The filler is commonly barium
silica. They have a high filler load (70-80% by weight and 50-60% by
volume) and they have a lower resin content (approximately 33% resin
matrix by volume.) As discussed earlier, the filler volume and filler load
correlate with the strength of a composite resin.22 The higher
filler load will help reduce the polymerization shrinkage, while it
increases the modulus of elasticity.
Wear data from the manufacturer is reported as being
quite low. BelleGlass is reported by the manufacturer as having wear of
1.2 µm for 1 year. The CRA in 1998 reported their findings as being quite
different. Belleglass was shown to wear at 62 µm per year, Targis, 106 µm,
and Artglass, 77 µm (Figure 7).
In an attempt to expand the use of these materials,
Kulzer attempted to bond their polymer glass, Artglass to a metal
substructure. The results were less than satisfactory. Depew and
Sorensen33 demonstrated that of 49 units placed, at year 1, 32%
failed and at year 2, they had a 39% failure rate. Ninety percent of these
failures occurred by the composite veneer debonding from the metal. They
also reported mean maximum wear depth of 113 µm (SD56-480 µm). Their
conclusion was that Artglass to metal is unreliable with high failure
rates and wear. More recently ESPE has entered this arena with their
product, Sinfony. This composed of 48% monomers, 1% initiator, 40%
ultrafine glass, 5% pyr. silica acid, 5% glass-ionomer and 1% silane. This
material shows promise but needs further evaluation.
This second generation of indirect composite resins may
be combined with fiber-reinforced substructure. This technology was used
for periodontal splinting as well as temporary bridge reinforcement to its
introduction as a reinforcement for indirect composite
restoratives.34 The fibers used for this purpose are composed
of carbon Kevlar, polyethylene and glass fibers (Table 2).
|Connect - Kerr||Weave, polyethylene (PE)
|DVA - Dental Ventures||Tufts, PE
|Fibreflex - Biocomp||Tufts, Kevlar
|FibreKor - Jeneric/ Pentron||Unidirectional, Glass
|FibreSplint - Inter Dental||Weave, Glass
|GlasSpan - GlasSpan||Weave, Glass
|Ribbond - Ribbond||Lock-stitch, Woven PE
|Splint-It - Jeneric/ Pentron||Weave, Glass
|Vectris - Ivoclar||Weave, Glass
These fibers may be preimpregnated with resin. The
preimpregnated fibers are silanized and coated with resin. This will
provide a cohesive bond to the resin matrix.
Indications for indirect composite restoratives
- Metal free dentistry
- Decreased wear of opposing dentition (as compared to
- Conservative tooth preparation35
-Long span fixed partial dentures
-High caries rate
-Difficult moisture control during adhesion
The CRA Newsletter reported in 1998 surface degradation
of the initial polish with significant wear rates. They also noted high
levels of post insertion sensitivity. Finally, delamination from the fiber
reinforcing substructure due to layering techniques used during the
fabrication process have been reported.36,37
This group of materials include the press ceramics such
as IPS-Empress, OPC, Finesse, Creepers and VitaPress along with the
reinforced core materials such as In-Ceram and Procera. These offer
improved esthetics and strength but they are more difficult to fabricate
and they cannot be repaired. The additional issue arises that the
reinforced core materials cannot be bonded. In addition to the pressed and
reinforced ceramics, there are the ceramic adhesive restoratives that are
ground from preformed blocks. These are machined by use of computer-aided
design/computer-aided manufacturing (CAD/CAM) or by a copy milling
There is a plethora of direct and indirect adhesive
restorative materials on the market. The average dentist is often
overwhelmed by the choices. Many times one material offers little
advantage over another. However, as the push for improved esthetics
continues to grow, so will our list of materials. So long as there is a
market, the manufacturer will introduce new products.
As dentists we must not only rely on the materials but on
our own ability to treatment plan and diagnose based on a multifactorial
situation. We must be careful in our preparation, design, communication
with a skilled laboratory technician and be meticulous in our bonding
techniques. Failures in dentistry are frequently blamed on the materials.
In reality, “user error” is often the culprit. Interpreting the research
data and understanding our options based on the patients’ caries risk
status are the first steps toward success.
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3. Manhart J, Kunzelmann KH, Chen HY, et al.
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4. El-Kalla IH, García-Godoy F. Mechanical properties
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5. Hickel R, Manhart J, García-Godoy F. Clinical
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6. Burke EJ, Qualtrough AJ. Aesthetic inlays: Composite
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7. Manhart J, Hickel R. Esthetic compomer restorations
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