RESEARCH REPORTS
Biomaterials & Bioengineering
K.L. Van Landuyt1, J. De Munck1,
J. Snauwaert2, E. Coutinho1, A. Poitevin1,
Y. Yoshida3, S. Inoue4, M. Peumans1,
K. Suzuki3, P. Lambrechts1,
and B. Van Meerbeek1*
Monomer-Solvent Phase
Separation in One-step
Self-etch Adhesives
1 Leuven
BIOMAT Research Cluster, Department of
Conservative Dentistry, School of Dentistry, Oral Pathology
and Maxillo-Facial Surgery, Catholic University of Leuven,
Kapucijnenvoer 7, B-3000 Leuven, Belgium; 2Laboratory of
Solid-State Physics and Magnetism, Department of Physics,
Catholic University of Leuven, Celestijnenlaan 200D, B-3001
Heverlee, Belgium; 3Department of Biomaterials, Okayama
University Graduate School of Medicine and Dentistry, 2-5-1
Shikata-cho, Okayama 700-8525, Japan; and 4Division for
General Dentistry, Hokkaido University Dental Hospital, Kita
13 Nishi 7, Kita-ku, Sapporo 060-8586, Japan; *corresponding
author, [email protected]
J Dent Res 84(2):183-188, 2005
ABSTRACT
One-step adhesives bond less effectively to
enamel/dentin than do their multi-step versions. To
investigate whether this might be due to phase
separation between adhesive ingredients, we
characterized the interaction of 5 experimental and
3 commercial self-etch adhesives with dentin using
transmission electron microscopy. All adhesives
were examined for homogeneity by light
microscopy. Bonding effectiveness to dentin was
determined with the use of a micro-tensile bondstrength protocol. The lower bond strength of the
one-step adhesives was associated with lightmicroscopic observation of multiple droplets that
disappeared slowly. Interfacial analysis confirmed
the entrapment of droplets within the adhesive
layer. The prompt disappearance of droplets upon
application of a small amount of HEMA (2hydroxyethyl methacrylate) or a HEMA-containing
bonding agent, as well as the absence of droplets at
the interface of all HEMA-containing adhesives,
strongly suggests that the adhesive monomers
separate from water upon evaporation of
ethanol/acetone. Upon polymerization, the droplets
become entrapped within the adhesive, potentially
jeopardizing bond durability. This can be avoided
by strong air-drying of the adhesive, thereby
removing interfacial water and thus improving
bonding effectiveness.
KEY WORDS: adhesion, monomer, solvent, phase
separation.
Received June 15, 2004; Last revision November 1, 2004;
Accepted November 3, 2004
INTRODUCTION
ne-step self-etch adhesives are more commonly associated with lower
O
bonding effectiveness to both enamel/dentin than are their multi-step
counterparts (Bouillaguet et al., 2001; Frankenberger et al., 2001; Chan et
al., 2003). Since such adhesives theoretically combine the 3 functions of
three-step adhesives—etching, priming, and bonding—both hydrophilic and
hydrophobic monomers are blended, with a relatively high concentration of
solvent required to keep them in solution (Pashley et al., 2002; Tay et al.,
2002a). In this 'difficult' mixture, water is also essential as an ionization
medium to enable self-etching activity to occur. Due to their high
hydrophilicity, one-step self-etch adhesives behave as semi-permeable
membranes, allowing fluids to pass through and seriously jeopardizing bond
durability (Tay et al., 2002b; Shirai et al., 2005).
The objective of this study was to investigate whether the lower bonding
effectiveness of one-step self-etch adhesives should be attributed in part to
phase separation between adhesive ingredients. Therefore, we compared the
adhesive interaction of 5 experimental and 3 commercial self-etch adhesives
with dentin using transmission electron microscopy (TEM). All adhesives
were examined for homogeneity by light microscopy (LM). Bonding
effectiveness to dentin was determined with the use of a micro-tensile bondstrength (␮TBS) protocol. The actual hypothesis tested was that phase
separation may occur upon evaporation of primer solvents and may account
for the lower bonding effectiveness of one-step adhesives.
MATERIALS & METHODS
Five experimental 'mild' one-step self-etch adhesives containing a carboxylateand phosphate-based functional monomer were prepared (Table). Three
experimental adhesives differed in composition for the solvent used, being either
ethanol/water (Exp-Eth), acetone/water (Exp-Ac), or 2-hydroxyethyl
methacrylate/water (Exp-HEMA). Two experimental adhesives were applied
differently, with Exp-Ac/SA representing the acetone-based adhesive strongly airdried before samples were light-cured. Exp-Eth/UB transformed the master onestep adhesive (Exp-Eth) into a two-step self-etch adhesive when Exp-Eth (that
served as a self-etching primer) was not light-cured, and a HEMA-containing
bonding agent was additionally applied (UB; from Unifil Bond, GC, Tokyo,
Japan). One commercial one-step self-etch adhesive (iBond, Hereaus-Kulzer,
Hanau, Germany) and 2 commercial two-step self-etch adhesives (Clearfil SE
Bond, Kuraray, Osaka, Japan; Unifil Bond, Tokyo, Japan, GC) served as controls.
TEM Interface Characterization
Each adhesive was applied to bur-cut dentin following the prescribed application
procedure (Table). The specimens were processed for TEM according to the
procedure previously described in detail (Van Meerbeek et al., 1998). Nondemineralized and lab-demineralized (10% formaldehyde-formic acid for 36 hrs)
ultrathin sections were cut (Ultracut UCT, Leica, Vienna, Austria) and examined
183
Van Landuyt et al.
184
unstained and positively stained (5% uranyl acetate for 20
min/saturated lead citrate for 3 min) by TEM (Philips CM10,
Eindhoven, The Netherlands).
LM of Adhesive Homogeneity
All adhesive solutions were examined (uncured) by LM for
homogeneity (Olympus BH2, Hamburg, Germany). A drop of each
self-etching solution was dispensed onto a glass plate, and imaged
real-time at different magnifications (140-280x) by means of a
digital camera (JVC TK-870E, Yokohama, Japan).
␮TBS Testing
Human third molars (gathered from patients following informed
consent obtained according to a protocol approved by the
J Dent Res 84(2) 2005
Commission for Medical Ethics of KU Leuven) were used within
1 mo of extraction. They were stored in 0.5% chloramine/water
(4°C) until used. The occlusal crown third was removed with a
diamond saw (Isomet 1000, Buehler, Lake Bluff, IL, USA),
thereby exposing a flat mid-coronal dentin surface. A bur-cut
smear layer was produced by removal of a thin layer of the surface
by means of a Micro-Specimen Former (University of Iowa, Iowa
City, IA, USA), equipped with a high-speed regular-grit (100 ␮m)
diamond (842, Komet, Lemgo, Germany). After application of the
experimental and control adhesives according to the manufacturers'
instructions (Table), dentin was immediately built up with Gradia
Direct Anterior (GC).
After samples were stored overnight in distilled water (37°C),
Table. Adhesives Investigated and Their Composition, pH, and Application Procedure
Adhesive
Manufacturer
Classa
Compositionb,c
pHd
(primer) Application
Experimental Adhesives
Exp-Eth
GC, Tokyo, Japan 1-SEA
4-MET, phA-m, DMA, ethanol, water,
filler, photo-initiator, stabilizer
~2
(1) Apply adhesive to the entire dentin surface
with a disposable applicator; (2) keep dentin
wet (shiny surface) with adhesive for at least 10 sec
and gently air-dry; (3) light-cure for at least 10 sec.
Exp-Ac
1-SEA
4-MET, phA-m, DMA, acetone, water,
filler, photo-initiator, stabilizer
~2
As above.
Exp-HEMA
1-SEA
4-MET, phA-m, DMA, HEMA, water,
filler, photo-initiator, stabilizer
~2
As above.
Exp-Ac/SA
1-SEA
4-MET, phA-m, DMA, acetone, water,
filler, photo-initiator, stabilizer
~2
(1) Apply adhesive to the entire dentin surface with
a disposable applicator; (2) keep dentin wet (shiny
surface) with adhesive for at least 10 sec, then
strongly air-dry (strongest possible air pressure);
(3) light-cure for at least 10 sec.
Exp-Eth/UB
2-SEA
Primer: 4-MET, phA-m, DMA, ethanol,
water, filler, photo-initiator, stabilizer
Bonding: UDMA, HEMA, TEGDMA, photoinitiator (bonding agent of Unifil Bond, GC)
~2
(1) Apply primer to the entire dentin surface with a
disposable applicator; (2) keep dentin surface wet
(shiny surface) with primer for at least 10 sec, then
gently air-dry but do not light-cure; (3) apply
bonding agent UB and light-cure for 20 sec.
UDMA, 4-MET, glutaraldehyde, acetone,
water, photo-initiator, stabilizer
~2
(1) Apply 3 layers of adhesive and wait for 30 sec,
while agitating the sample slightly; (2) gently air-dry
for a few sec; (3) light-cure for 20 sec.
Control Adhesives
iBond
Hereaus-Kulzer,
1-SEA
Hanau, Germany
Clearfil SE Bond Kuraray,
Osaka, Japan
2-SEA
Primer: 10-MDP, HEMA, hydrophilic DMA, 1.9
photo-initiator, aromatic tertiary amine, water
Bonding: 10-MDP, Bis-GMA, HEMA,
hydrophobic DMA, photo-initiator, aromatic
tertiary amine, silanated colloidal silica
(1) Apply primer for 20 sec, then gently air-dry;
(2) apply bonding agent; (3) light-cure for 20 sec.
Unifil Bond
2-SEA
Primer: 4-MET, HEMA, ethanol, water
Bonding: UDMA, HEMA, TEGDMA
(1) Apply primer for 20 sec, then gently air-dry;
(2) apply bonding agent; (3) light-cure for 10 sec.
a
b
c
d
GC, Tokyo, Japan
2.2
According to classification proposed by Van Meerbeek et al. (2003). 1-SEA, one-step self-etch adhesive; 2-SEA, two-step self-etch adhesive.
Abbreviation of monomers in numerical/alphabetical order: 4-MET, 4-methacryloxyethyltrimellitic acid; 10-MDP, 10-methacryloyloxydecyl
dihydrogen phosphate; Bis-GMA, bisphenol-glycidyl methacrylate; HEMA, 2-hydroxyethyl methacrylate; DMA, dimethacrylate; phA-m,
phosphoric acid ester monomer; TEGDMA, triethylene glycol dimethacrylate; UDMA, urethane dimethacrylate.
Underlined words refer to difference in either composition or application procedure of the experimental adhesive as compared with the Exp-Eth
master adhesive.
pH of self-etching solution according to the manufacturer.
J Dent Res 84(2) 2005
Monomer-Solvent Phase Separation
185
rectangular sticks (2x2 mm wide; 8-9
mm long) were sectioned
perpendicular to the adhesive-tooth
interface by means of the Isomet
saw. Only the 4 central sticks were
used, to eliminate substrate regional
variability (Yoshiyama et al., 1998).
The sticks were trimmed at the
interface into an hourglass shape
(diameter of ± 1.1 mm) by means of
the MicroSpecimen Former,
equipped with a fine-grit (30 ␮m)
diamond (5835KREF, Komet) in a
high-speed handpiece under air/water
coolant. The specimens were fixed to
a Ciucchi's jig with cyanoacrylate
glue (Model Repair II Blue,
Dentsply-Sankin, Ohtawara, Japan)
and stressed in tension at a crosshead
speed of 1 mm/min in a universal
testing device (LRX, Lloyd,
Hampshire, UK). We derived the
␮TBS by dividing the imposed force
at the time of fracture by the bond
Figure 1. Microscopic examination of the experimental adhesives Exp-Eth and Exp-Ac. (a) Nondemineralized, non-stained TEM of Exp-Ac revealing a multitude of entrapped droplets, particularly at
area (mm2). When a specimen failed
the bottom of the adhesive layer (Ar). The droplets are round or oval, with various sizes. A distinctive
during processing (pre-testing
oxygen-inhibition layer (O2-I) was present in the top of the adhesive layer. C = flowable composite; Hy
failure), the ␮TBS was set at 0 MPa
= hybrid layer; Ud = unaffected dentin. (b) Demineralized stained TEM of the submicron hybrid layer
(De Munck et al., 2004; Nikolaenko
formed by Exp-Eth. (c) Feg-SEM of a ␮TBS failure pattern of Exp-Ac that exhibited mixed adhesive
et al., 2004). Statistical differences
failure (dentin side). Note the high distribution of droplets at the bottom of the adhesive layer, while no
droplets are seen near the top. (d) LM image of a drop of uncured adhesive solution of Exp-Ac
were examined by Kruskal-Wallis
dispensed on a glass plate. This drop contains many droplets centrally, and is bordered by a dropletnon-parametric statistics (␣ = 0.05).
free halo, which becomes wider with time. The time indication indicates the time elapsed after the
The mode of failure was determined
adhesive was applied.
with a stereomicroscope at 50x
magnification.
Representative dentin and
much resin tag formation. Residual hydroxyapatite was clearly
composite ␮TBS-fracture planes, exhibiting the most frequently
present throughout the hybrid layer.
observed failure mode and a ␮ TBS close to the mean, were
LM of adhesive drops revealed multiple droplets in all oneprocessed for field-emission-gun scanning electron microscopy
step self-etch adhesives (Exp-Eth, Exp-Ac, iBond), causing the
(Feg-SEM; Philips XL30, Eindhoven), by a common specimendrop to lose its transparency shortly after being dispensed.
processing procedure described previously (Perdigão et al., 1995).
RESULTS
TEM revealed that the specimens bonded with Exp-Eth and
Exp-Ac showed adhesive layers full of droplets (Fig. 1). The
presence of droplets was confirmed by Feg-SEM (Fig. 1). ExpAc showed more droplets than Exp-Eth. These droplets were
round/oval, with various sizes (0.5-10 ␮m), and localized
mostly at the bottom of the adhesive layer. Smaller droplets
were seen to coalesce into larger ones. Only at the occurrence
of defects in the TEM section were the droplets filled with
embedding resin. No droplets were entrapped in the adhesive
layer when ethanol/acetone was replaced by HEMA (ExpHEMA), and when a HEMA-containing bonding agent was
applied to the non-cured Exp-Eth primer according to a twostep application procedure (Exp-Eth/UB) (Fig. 2). Strong airdrying of the experimental adhesive (Exp-Ac/SA) substantially
reduced the number of droplets, though it never completely
eliminated them (Fig. 2). Among the commercial adhesives,
only iBond revealed droplets with features/localization similar
to those observed with the experimental adhesives (Fig. 2). All
adhesives created a hybrid layer of 0.5-1 ␮m thickness, without
After 1-2 sec for iBond and Exp-Ac, and after about 1 min for
Exp-Eth, heavy turbulence streams gave rise to the formation
of multiple droplets that coalesced and emerged relatively
slowly at the surface. This reaction was more vigorous in iBond
and Exp-Ac than in Exp-Eth. After about 4 min, droplets could
no longer be observed in iBond, in contrast to the experimental
adhesives, in which droplets could still be observed after 10
min. As the solvent evaporated, the drop returned to its
transparent state, first at the boundary and gradually toward the
center. While drops of Exp-Eth and Exp-Ac remained blurred
in the center, iBond became totally transparent again. Agitation
did not help the droplets disappear faster, while strong airdrying removed most droplets and did return the transparency.
All droplets were resolved at once when a drop of pure HEMA
(2-hydroxyethyl methacrylate; Sigma-Aldrich, Bornem,
Belgium) or the HEMA-containing UB bonding agent was
added. In the two-step self-etch adhesives, convection streams
could be viewed as a result of solvent evaporation, but no
droplets appeared.
No significant difference was found among the ␮TBSs of
the 5 experimental adhesives (Fig. 3). They bonded
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Van Landuyt et al.
J Dent Res 84(2) 2005
liquid chromatographic analysis
showed that both functional
monomers appeared more stable
in acetone/water (unpublished
data). HEMA was omitted
because of its high allergenic
potential (Wrangsjo et al., 2001).
TEM clearly revealed the
entrapment of droplets throughout
the adhesive, in particular at the
bottom of the adhesive layer. LM
of adhesive drops dispensed on a
glass plate showed that the
droplets were caused by turbulent
mixing reactions after exposure to
surrounding air. Due to the
formation of droplets, the solution
promptly lost its transparency and
turned opaque. Since this
happened a few seconds after the
drop was dispensed, solvent
evaporation must have triggered
this reaction. While turbulence
streams, though varying in
Figure 2. Microscopic examination of Exp-Eth/SA, Exp-Eth/UB, Clearfil SE Bond, and iBond. (a) Nondemineralized, non-stained TEM of Exp-Ac/SA. Strong air-blowing before light-curing reduced the number
intensity, continued in larger
of droplets considerably. Ar = adhesive resin; Hy = hybrid layer; Ud = unaffected dentin. (b) Nonglobules for a few minutes, the
demineralized, non-stained TEM of Exp-Eth/UB. Following a two-step self-etch approach with the HEMAsingle droplets disappeared only
containing UB bonding agent, the adhesive layer was free of droplets. The hybrid layer resembled that of
very slowly with time, suggesting
Exp-Eth. (c) LM of uncured Clearfil SE Bond (Kuraray) primer dispensed on a glass plate. Note the
transparency of the drop, some curves representing convection streams caused by solvent evaporation, and
that they represent water. Upon
the absence of droplets. Original magnification 5x. (d) LM of uncured iBond (Hereaus Kulzer) applied on a
further solvent evaporation, the
glass plate, showing an extensive phase-separation reaction (time after dispensing of adhesive is indicated in
drop of adhesive became
sec). Original magnification 5x. (e) Non-demineralized, non-stained TEM of the resin-dentin bond produced
transparent again, beginning
by iBond. A partially demineralized hybrid layer and hybridized smear plug (HySp) were formed. Note the
gradually from the outside, where
presence of small droplets entrapped in the adhesive resin adjacent to the hybrid layer. (f) Feg-SEM of a
␮TBS failure pattern of iBond (composite side). The bond failed between the adhesive and composite (C) and
the solution film was thinnest,
near the bottom of the adhesive layer, which appeared to be very porous due to the droplets entrapped after
toward the thickest film at the
the sample was light-cured.
center of the drop. We accepted
our hypothesis, because the
following evidence strongly
significantly better than the one-step self-etch adhesive iBond,
suggests that the droplets are due to phase separation: (1) the
significantly worse than the two-step self-etch adhesive Clearfil
particular dynamic behavior of the adhesive observed
SE Bond, and equally as effective as the two-step self-etch
microscopically; the prompt disappearance of droplets (2) upon
adhesive Unifil Bond. All adhesives proved to fail mainly
the addition of pure HEMA and (3) upon application of a
according to a 'mixed' failure pattern, which was confirmed by
HEMA-containing UB bonding agent; (4) the entrapment of
Feg-SEM (Figs. 1, 2).
droplets within the adhesive layer of the HEMA-free Exp-Eth,
Exp-Ac, and iBond, as observed by TEM; and (5) the dropletDISCUSSION
free adhesive layer of the HEMA-containing adhesives ExpHEMA, Exp-Eth/UB, Clearfil SE Bond, and Unifil Bond. Once
In the search for an efficient, easy-to-use adhesive, we prepared
ethanol/acetone starts to evaporate, the solvent-monomer
an experimental one-step self-etch adhesive that combines a
balance is broken, with water separating from the other
carboxylate and phosphate-based functional monomer. The
adhesive ingredients. This phase separation was also observed
rationale was that both functional monomers, combined
with another commercial one-step self-etch adhesive, AQ-Bond
synergistically, would improve bonding efficacy (unpublished
(Sun Medical, Shiga, Japan; unpublished LM observation).
observations). TEM observations confirmed that these
Droplet entrapment within the adhesive layer was confirmed by
monomers demineralized dentin only partially, and that there
Tay et al. (2002a), who also mentioned phase separation as a
were remaining hydroxyapatite crystallites available for
possible explanation. Droplets were also identified at the
additional chemical interaction following a so-called 'mild' selffracture planes of fatigued iBond (Hereaus-Kulzer) specimens,
etch approach (Van Meerbeek et al., 2003). Both functional
and were considered to be responsible for its low fatigue
monomers have recently been shown to be capable of
resistance as compared with that of a two-step self-etch
interacting ionically with hydroxyapatite (Yoshida et al., 2004).
adhesive and three-step etch & rinse adhesive (De Munck,
Regarding solvent, no difference in bonding effectiveness was
2004).
found between the ethanol/water (Exp-Eth) and acetone/water
The earlier onset of the separation reaction and the faster
(Exp-Ac) combinations, though the latter is preferred, since
J Dent Res 84(2) 2005
Monomer-Solvent Phase Separation
187
return of transparency in Exp-Ac
and iBond, as compared with ExpEth, must be explained by the
differences in solvents. Since the
vapor pressure (at 25°C) for
acetone is 200 mm Hg, as
compared with 54.1 mm Hg for
ethanol, acetone is more volatile
than ethanol. Although occurring in
slightly different patterns, the fact
that phase separation was apparent
in all 3 one-step adhesives indicates
that it is solvent-induced, but not
solvent-specific.
The higher concentration of
droplets at the bottom of the
adhesive layer adjacent to the
hybrid layer must be attributed to
the upward movement of droplets
toward the surface, where they
emerge. The short 10-second
Figure 3. Box-whisker plot (min-[lower quartile-median-upper quartile]-max) of the ␮TBS to dentin
application time is not enough to
(mean ± standard deviation; n = total number of specimens; ptf = pre-testing failure). The diamond
allow all droplets to move upward,
represents the mean ␮TBS. Means with unlike superscript letters are statistically significantly different.
and subsequent light-curing
entrapped the droplets within the
adhesive layer. LM showed that
formulation of the one-step adhesive, separating water from the
complete disappearance of droplets through evaporation was
other ingredients upon ethanol/acetone evaporation, may be
achieved only after 4-10 min, depending on the adhesive. Both
advantageous by removing most of the water that would
the oval/circular shape of the droplets and the fact that they
otherwise only weaken the bond. Very strong air-drying
were not filled with embedding resin during TEM specimenappeared sufficient to blow the droplets out, leaving only a
processing suggest that they contain fluid. The disappearance
transparent film of co-monomers behind, as observed by LM.
of droplets upon the application of a small drop of HEMA or
Reduced droplet entrapment in such heavily dried adhesive
the HEMA-containing UB bonding agent must be ascribed to
layers was observed by TEM. Especially in the long term, a
HEMA acting as a solvent and bringing all adhesive ingredients
void-free adhesive layer should be beneficial to bond integrity.
back into solution. TEM confirmed the absence of droplets
This obviously should be confirmed by durability testing.
within the adhesive layer for Exp-HEMA and Exp-Eth/UB. In
Nevertheless, AQ-Bond (Sun Medical), with a composition
the HEMA-containing two-step self-etch adhesives, only
similar to that of the experimental one-step adhesive and
convection streams representing rapid solvent evaporation were
proven to be sensitive to phase separation (see above),
seen without any droplet formation or phase separation. The
maintained the best marginal adaptation after 1 yr of water
fact that droplets could be viewed by LM when the adhesive
storage and 2 thermo-cycling sessions among all one-step selfwas dispensed on a glass plate (no water-containing dentin
etch adhesives studied (Blunck, personal communication), and
tissue underneath), and that TEM of the one-step self-etch
performed as well as two-step self-etch adhesives and even the
adhesive Exp-HEMA did not reveal any droplet entrapment in
generally best-performing three-step etch & rinse adhesives. A
the adhesive layer, exclude any other origin, such as waterprerequisite is 'air-blowing the adhesive with full power', which
uptake from the tooth or from the specimen storage medium, as
is a less ambiguous instruction than 'gently air-drying'.
has been demonstrated before under different circumstances
In conclusion, although one-step self-etch adhesives
(Tay and Pashley, 2003).
appear to be easy to use, some stringent problems remain.
Conventional adhesives usually contain HEMA in a
Since HEMA-free one-step adhesives are complex blends of
concentration between 35 and 55 vol% (Pashley et al., 1998).
hydrophilic/hydrophobic ingredients, water and solvents, they
In etch & rinse adhesives, HEMA acts as a wetting agent and
are prone to phase separation, which accounts partially for
helps monomers to diffuse into the relatively deeply (3-5 ␮m)
their lower bonding effectiveness. In contrast, strongly airexposed collagen network within a clinically manageable time,
drying the phase-separated adhesive might be a clinical
thereby improving bond strength (Toledano et al., 2001).
technique for removing substantial interfacial water, thereby
Besides the drawback of potential allergenic effects, HEMA
improving bonding effectiveness. How successfully this can be
may also retain water within the adhesive, thereby weakening
done in complex cavity preparations in vivo remains to be
the mechanical strength of the adhesive itself and potentially
determined.
jeopardizing bond durability (Jacobsen and Söderholm, 1995;
De Munck et al., 2003; Shirai et al., 2005). The submicron
ACKNOWLEDGMENTS
hybrid layer produced by mild self-etch adhesives should make
diffusion of monomers easier, decreasing the need for HEMA.
K. Van Landuyt is appointed as Aspirant of the Fund for
In this respect, the omission of HEMA in the adhesive
Scientific Research of Flanders. This study was supported by a
188
Van Landuyt et al.
fund of the Toshio Nakao Chair for Adhesive Dentistry,
inaugurated at the Catholic University of Leuven with B. Van
Meerbeek and P. Lambrechts awarded as Chairholders. We
thank Hereaus Kulzer, GC, and Kuraray for providing the
commercial adhesives.
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