Copyright Ó Eur J Oral Sci 2005
Eur J Oral Sci 2005; 113: 525–530
Printed in Singapore. All rights reserved
European Journal of
Oral Sciences
Degree of conversion and permeability
of dental adhesives
Milena Cadenaro1, Francesca
Antoniolli1, Salvatore Sauro3,
Franklin R. Tay2, Roberto Di
Lenarda1, Carlo Prati3, Matteo
Biasotto1, Luca Contardo1, Lorenzo
Breschi1
Cadenaro M, Antoniolli F, Sauro S, Tay FR, Di Lenarda R, Prati C, Biasotto M,
Contardo L, Breschi L. Degree of conversion and permeability of dental adhesives. Eur J
Oral Sci 2005; 113: 525–530. Ó Eur J Oral Sci, 2005
1
The aim of this study was to analyse the extent of polymerization of different adhesive
films in relation to their permeability. One adhesive of each class was investigated:
OptiBond FL; One-Step; Clearfil Protect Bond; and Xeno III. Adhesive films were
prepared and cured with XL-2500 (3M ESPE) for 20, 40 or 60 s. Polymerization
kinetic curves of the adhesives tested were obtained with differential scanning calorimetry (DSC) and data were correlated with microhardness. The permeability of the
adhesives under the same experimental conditions was evaluated on human extracted
teeth connected to a permeability device and analysed statistically. The results showed
that the extent of polymerization obtained from DSC exotherms was directly correlated with microhardness. An increased level of polymerization after prolonged lightcuring was confirmed for all adhesives. Simplified adhesives exhibited a lower extent of
polymerization and showed incomplete polymerization, even after 60 s. An inverse
correlation was found between the degree of cure and the permeability. This study
supports the hypothesis that the permeability of simplified adhesives is correlated with
incomplete polymerization of resin monomers and the extent of light exposure. These
adhesives may be rendered less permeable by using longer curing times than those
recommended by the respective manufacturer.
Dentine adhesives may be classified as Ôetch-and-rinseÕ
and Ôself-etchingÕ systems. Etch-and-rinse systems are
characterized by the use of a separate etching agent,
usually 35% phosphoric acid, which is applied on enamel
and dentine and then rinsed off. This is followed by the
application of the primer/adhesive on smear layer-free
and demineralized dentine. Self-etching systems are
characterized by the application of an acidic primer/
adhesive solution on smear layer-covered dentine. The
adhesive may be applied either simultaneously (i.e. onestep self-etch systems), or after air-drying of the etching/
priming solution (i.e. two-step self-etch systems) (1).
Irrespective of the number of steps required, self-etching
systems are characterized by simultaneous hard tissue
demineralization and resin infiltration. Although onestep self-etch adhesives are user friendly, they exhibit
lower bond strengths (1) and a decline in clinical performance over time when compared with multistep
dentine adhesives (2, 3).
Recent morphological studies have revealed that
nanoleakage, identified by the use of silver tracers,
occurs in bonded interfaces of both etch-and-rinse and
self-etching adhesives. These results highlighted that the
complete infiltration of demineralized dentine cannot
easily be achieved (4). Incomplete polymerization of
adhesive monomers has been speculated as one of the
reasons for the occurrence of nanoleakage in self-etching systems. The compromise in the degree of conversion of adhesive monomers, in turn, may be caused by
Department of Dental Sciences, Biomaterials
and Bioimplants, University of Trieste, Trieste,
Italy; 2Department of Oral Biology &
Maxillofacial Pathology, School of Dentistry,
Medical College of Georgia, Augusta, GA,
USA; 3Department of Dental Sciences, Alma
Mater Studiorum, University of Bologna,
Bologna, Italy
Professor Lorenzo Breschi, UCO of Dental
Sciences, University of Trieste, Via Stuparich,
1, I-34129 Trieste, Italy
Telefax: +39–040–912579
E-mail: [email protected]
Key words: degree of conversion; dental
bonding systems; dentine; permeability; polymerization
Accepted for publication August 2005
the entrapment of residual water within adhesive–dentine interfaces (3, 5, 6). Previous studies have shown
that both hybrid layers and adhesive layers created by
simplified adhesives are porous, with water channels
and hydrophilic domains present in the latter that
permit water permeation through the resin–dentine
interfaces (7). Water permeation of these bonded
interfaces occurs rapidly, resulting in the expression of
fluid droplets over the adhesive surfaces. These fluid
droplets are observed either when trapped by slowcuring composites, or when polyvinylsiloxane impressions are taken of the bonded vital dentine (8, 9). As
this fluid transudation phenomenon may either be
caused by, or the result of, suboptimal polymerization
of the adhesive polymer matrix, there is a need to
examine the relationship between the degree of polymerization of dentine adhesives and their permeability
to fluid movements.
Different methods have been employed to investigate
the extent of polymerization of resin monomers. Differential scanning calorimetry (DSC) is a direct method that
analyses the extent of polymerization based on the
assumption that heat generated during resin polymerization (i.e. the heat of polymerization) is proportional to
the percentage or concentration of reacted monomers
(10–12). Microhardness has been shown to be a simple
(13) and reliable indicator of double bond conversion
and it is used as an indirect measurement of the extent of
polymerization (14, 15).
526
Cadenaro et al.
The aim of this study was to correlate the extent and
kinetics of adhesive polymerization with adhesive permeability by the combined use of direct (DSC) and
indirect (microhardness) evaluation methods. Adhesive
permeability was investigated with the use of a permeability device for each of the four adhesive classes (i.e.
three-step and two-step etch-and-rinse adhesives, and
two-step and one-step self-etching adhesives) using a
quartz-tungsten-halogen unit. The null hypotheses tested
were that the extent of polymerization of dentine adhesives has no effect on adhesive permeability and that
increasing curing times have no effect on adhesive permeability reduction.
Table 1
Composition of dental-bonding systems tested in the study
Adhesive
Composition
OptiBond FL
Etching
Primer
)37% phosphoric acid
)2-hydroxyethylmethacrylate (HEMA)
)Glycerophosphate-dimethacrylate
(GPDM)
)MMEP
)Ethanol
)water
)initiators
)Bis-phenol A diglycidylmethacrylate
(Bis-GMA)
)2-hydroxyethylmethacrylate (HEMA)
)Glycerophosphate-dimethacrylate
(GPDM)
)Barium–aluminum borosilicate glass
)Disodium hexa-fluoro-silicate
)Fumed silica
Bond
Material and methods
The adhesives tested in this study were: OptiBond FL
(Sybron-Kerr, Orange, CA, USA), a three-step etch-andrinse adhesive; One-Step (Bisco, Schaumburg, IL, USA), a
two-step etch-and-rinse adhesive; Clearfil Protect Bond
(Kuraray Medical, Tokyo, Japan), a two-step self-etching
adhesive; and Xeno III, (Dentsply DeTrey, Konstanz,
Germany), a one-step self-etching adhesive. Their compositions are listed in Table 1. For not-simplified adhesive
systems, only bonding agents were used for DSC analysis
and microhardness evaluation.
One-Step
Etching
Bond
Clearfil Protect Bond
Etching/Primer
DSC analysis
Each adhesive was cured with XL-2500 (XL; 3M ESPE,
St Paul, MN, USA) (at 600 mW cm)2). The irradiance of
the unit was previously verified by means of a radiometer
(3M ESPE).
Curing was performed in a Ôheat fluxÕ differential scanning
calorimeter (Q10 TA Instruments, New Castle, DE, USA)
at a constant temperature of 35°C and in a nitrogen atmosphere to avoid formation of an oxygen-inhibition layer.
Two aluminum pans (diameter ¼ 4 mm, 1.2 mm thick)
were placed in the sample holder of the calorimeter furnace:
one with the tested adhesive and the other empty as a reference. Adhesive films (n ¼ 10 for each adhesive) of 15 mg
weight were prepared in the aluminum pan and gently airdried for 5 s, at a constant distance of 10 cm, to evaporate
solvent prior to exposure to light. The DSC chamber was
covered by an aluminum cover with a round hole (8 mm
diameter) and a thin quartz glass to allow light to pass
through and permit curing of the specimen inside the calorimeter at a minimum distance (5 mm). A custom-made
support was built to hold the lamp during polymerization
and to fully irradiate the adhesive-containing pan. Calorimetric analysis consisted of two consecutive light exposures:
the first one onto the adhesive specimens up to complete
polymerization (varying from 60 to 150 s depending on the
adhesive) and the second one onto the same fully cured
specimens to evaluate irradiation heat flow from the lamp
(10). The heat of reaction obtained from the first scanning
represented the sum of the exothermic effect caused by
monomer conversion and heat flow from the lamp, while the
second was attributed to the irradiation heat output of the
lamp. The extent of polymerization percentage (EP), normalized by the sample weight, was determined, at 20, 40 and
60 s time-points, from the following equation:
)37% phosphoric acid
)2-hydroxyethylmethacrylate (HEMA)
)Biphenyl-dimethacrylate (BPDM)
)Bis-phenol A diglycidylmethacrylate
(Bis-GMA)
)Acetone
Bond
Xeno III
Liquid A
Liquid B
)2-hydroxyethylmethacrylate (HEMA)
)hydrophilic dimethacrylate
)10-methacryloyloxydecyl
)dihydrogen phosphate
)12-methacryloyloxydodecylpyridinium
)bromide
)water
)10-methacryloyloxydecyl dihydrogen
phosphate (MDP)
)Bis-phenol A diglycidylmethacrylate
(Bis-GMA)
)2-hydroxyethylmethacrylate (HEMA)
)Hydrophobic dimethacrylate
)camphorquinone
)N,N-diethanol-p-toluidine
)Silanated colloidal silica
)Surface treated sodium fluoride
)2-hydroxyethyl methacrylate (HEMA)
)Butylated hydroxy toluene (BHT)
)Highly dispersed silicon dioxide
)Purified water
)Ethanol
)Phosphoric acid-modified methacrylate
resin
)Mono fluoro phosphazene modified
methacrylate resin
)Urethane dimethacrylate resin
)Butylated hydroxy toluene (BHT)
)Camphorquinone (CQ)
)Ethyl-4-dimethylaminobenzoate
Rtx
Ep ¼
0
tRtot
0
Wg ðtÞdt
100
Wg ðtÞdt
Polymerization of adhesives
where Wg ¼ heat flow normalized by sample weight, t ¼
time, and x ¼ 20, 40, 60 s.
Microhardness evaluation
Microhardness measurements were performed with a Leica
VMHT microhardness tester (Leica Microsystems, Milano,
Italy) equipped with a Vickers indenter. Adhesive specimens
(n ¼ 10 for each adhesive at each curing time) were prepared and cured using three different irradiation times (20,
40 or 60 s), following the same protocol as in the DSC
analysis, in a fully saturated nitrogen atmosphere at 35°C.
Microhardness was immediately measured on the exposed
surface at three randomized points (for a total of 30 measurements) using a Vickers indenter at 25 gf of load and 20 s
dwell time.
Permeability evaluation
Recently extracted human third molars (patient age: 25–
45 yr) were collected after informed consent was obtained
under a protocol approved by the Review Board of the University of Bologna, Italy. Crown segments (2.5 ± 0.5 mm
thick) were obtained by removing occlusal enamel (2 mm
above the cementoenamel junction) and roots using a low
speed water-cooled diamond saw (Remet, Bologna, Italy).
Fluid flow was measured using a permeability set up
incorporating a 2.5-ll capacity microcapillary tube (0.9 mm
internal diameter) (Microcaps, Fisher Scientific, Atlanta,
GA, USA) positioned between the pressure reservoir and
the horizontally mounted crown segment (16). An air bubble was created inside the glass capillary to assist the
detection of the fluid flow. Dentin permeability (DP) was
calculated as ll cm)2 min)1. The experimental design
involved three measurements of DP under 20 cm H2O
pressure, each measurement consisting of a 3-min measuring
period. Ten dentine disks were used for each adhesive at
each curing time. A smear layer was created on the dentine
surface using a 400-grit silicon carbide paper for 30 s and
DP was measured to establish the baseline (minimum)
permeability of each specimen. The smear layer was then
removed by etching the dentine surface with 35% phosphoric acid (3M ESPE) for 15 s (without a simulated pulpal
pressure) and DP was remeasured under a pulpal pressure
of 20 cm H2O to evaluate the maximum permeability of
each specimen (a DP maximum of 100% was arbitrary
assigned). The two etch-and-rinse adhesives were applied on
527
the etched dentine. For the two self-etching systems, a smear
layer was recreated and DP was measured under a simulated
pulpal pressure of 20 cm of H2O pressure. All the adhesives
were used in accordance with the manufacturers’ instructions, applied without simulated pulpal pressure, and irradiated for 20, 40 or 60 s. Dentin permeability across the
bonded interfaces was expressed as percentage (DP %) of
maximum permeability (acid-etched dentine), which was
assigned as 100% flow rate (17).
Statistics
Data obtained from microhardness were analysed by oneway analysis of variance (anova) and posthoc Tukey’s tests,
and extent of polymerization and permeability were analysed by two-way anova, with a global significance level of
0.05. Correlations among microhardness, the extent of
polymerization percentage (EP), and the permeability
(expressed as percentage DP) were analysed using the
Pearson product moment correlation test at a ¼ 0.05.
Results
Table 2 shows the mean and standard deviations of the
total reaction time, extent of polymerization (EP), and
Vickers hardness (VH) values of the four tested adhesives
that were polymerized at various irradiation times (20, 40
and 60 s). Figure 1 shows DSC exotherms with each
tested adhesive up to maximum polymerization.
The total reaction time (i.e. the time taken for each
adhesive to reach the maximum extent of polymerization)
differed among the tested adhesives, as follows: OptiBond
FL < Clearfil Protect Bond < One-Step < Xeno III.
The difference among the adhesive was statistically significant (P < 0.05).
The EP increased for all tested adhesives (P < 0.05)
when the curing time was prolonged (to 40 and 60 s). Only
OptiBond FL revealed no difference in EP between 40- and
60-s curing times. At a curing time of 20 s, OptiBond FL
showed the highest extent of polymerization, while the
lowest values were obtained with One-Step and Xeno III.
Differences between OptiBond FL and Clearfil Protect
Bond were not significant when the adhesives were poly-
Table 2
Mean (± standard deviation) values of total reaction time, extent of polymerization (EP) and Vickers microhardness (VH) values of
the tested adhesives at each time of curing
EP (%)
Adhesive
Total reaction
time (s)
OptiBond FL
One-Step
Clearfil Protect Bond
Xeno III
47.9
119.3
58.1
150.1
±
±
±
±
3.0a
1.5b
2.4c
2.8d
20 s
94.8
21.7
86.2
27.3
±
±
±
±
0.7a
1.0c
0.6f
2.7h
40 s
99.8
53.7
99.0
67.3
±
±
±
±
VH
60 s
20 s
40 s
60 s
0.3b 100.0 ± 0.0b 27.1 ± 0.7A 28.4 ± 0.2B 28.7 ± 0.1B
2.4d 83.0 ± 3.9e
0.6 ± 0.5A 3.2 ± 0.4B 3.5 ± 0.7B
0.3b 99.9 ± 0.0b 16.1 ± 0.2A 16.7 ± 0.0B 16.8 ± 0.0B
3.4i
88.8 ± 4.0f
1.6 ± 0.4A 6.3 ± 0.3B 7.6 ± 0.6C
Pearson
correlation
0.863*
0.962*
0.837*
0.926*
Mean (± standard deviation) values followed by the same lower case letter indicate no statistical difference at the 95% confidence
level (P < 0.05) between adhesives for the total reaction time and EP. Mean (± standard deviation) values followed by the same
capital letter indicate no difference (P < 0.05) among adhesives for VH (because microhardness data can be compared only within
the same adhesive system). Pearson correlation (two-tailed) between VH and EP (%) indicates significant correlation (*95% confidence level).
528
Cadenaro et al.
Discussion
Fig. 1. Representative polymerization exotherms, obtained
with differential scanning calorimetry (DSC), for each of the
tested adhesives up to complete polymerization reaction. m,
Optibond FL; d, One Step Plus; n, Clearfil Protect Bond; and
X, Xeno III.
Table 3
Mean (± standard deviation) values of dentin permeability
(DP) for each adhesive after curing for 20, 40, and 60 s
DP (%)
Adhesive
OptiBond FL
One-Step
Clearfil Protect
Bond
Xeno III
20 s
40 s
60 s
23.8 ± 0.1a
41.8 ± 0.4d
26.8 ± 0.7e
11.1 ± 1.2b
26.2 ± 0.3e
12.7 ± 0.6b
8.3 ± 1.2c
19.9 ± 1.6f
9.8 ± 0.6c
41.9 ± 0.4d
25.9 ± 0.9e
20.2 ± 1.7f
The DP of each bonded tooth is expressed as a percentage of
the maximum DP for each respective tooth, with the latter
defined as the DP of the unbonded tooth after removal of the
smear layer with phosphoric acid etching.
Values that are followed by the same letters are not statistically
significant (P < 0.05).
merized for 40 or 60 s (P > 0.05), while One-Step and
Xeno III exhibited lower mean EP values (P < 0.05).
The VH value showed a statistically significant increase between 20 and 40 s for all adhesives (P < 0.05).
Conversely, when the curing time was further increased
from 40 to 60 s, only Xeno III demonstrated a further
significant increase in VH (P < 0.05). The Pearson
product moment correlation test showed a strong
(Table 2) and significant (P < 0.05) correlation between
EP and VH for all adhesives at each curing time.
The results of the permeability test are reported in
Table 3. All adhesives exhibited a reduction in the percentage DP with increased curing time (P < 0.05). The
differences among the adhesives are summarized as follows: OptiBond FL < Clearfil Protect Bond < OneStep < Xeno III, with the one-step self-etch adhesive
exhibiting the highest permeability at all curing times
(P < 0.05). An inverse correlation (P < 0.05; data not
shown) was found between permeability and DSC and
microhardness values (i.e. direct and indirect indicators
of the extent of polymerization).
Simplification of dentine adhesives necessitates increases
in the concentration of hydrophilic resin components in
contemporary simplified adhesives. As resin monomers
with increased hydrophilicity are less hydrolytically
stable (18), these simplified adhesives exhibit increased
permeability and higher water sorption within the
hybrid layer and adhesive layer, resulting in reduced
bond durability (19–23). Simplified adhesives have been
shown to be permeable to fluid movements across the
cured adhesive layers in the presence of increased concentrations of dissolved inorganic ions (7). This phenomenon is probably related to the presence of
incompletely polymerized adhesive resin monomers (5)
or to the presence of oxygen inhibition layers (3, 24).
For this purpose, we correlated microhardness and
extent of polymerization (i.e. DSC analysis) with permeability of the hybrid and adhesive layer in the absence
of oxygen inhibition layers by curing the adhesives
under a nitrogen atmosphere in this study. This eliminates the possibility of oxygen-inhibition layers affecting
our direct and indirect assessment of the extent of
polymerization of the adhesives.
The results obtained with DSC analysis (EP) clearly
demonstrated that polymerization of adhesive films is
compromised, even under a nitrogen atmosphere, for
simplified dentine adhesives that combine the adhesive
agent with either a primer (i.e. the two-step etch-andrinse adhesive One-Step) or an etching/primer solution
(i.e. the one-step self etching adhesive Xeno III). Of
particular clinical relevance is the observation that, at the
20 s curing time recommended for these adhesives by
their respective manufacturers, the extent of polymerization was in the order: OptiBond FL > Clearfil Protect
Bond > One-Step > Xeno III (DSC curves, Fig. 1,
Table 2). The DSC results also highlighted that incomplete polymerization occurs for all adhesives if these
adhesives are irradiated for 20 s, and that prolonged
light exposure contributes to reducing the percentage of
uncured oligomers. Prolonging the irradiation time,
however, only enabled OptiBond FL and Clearfil Protect
Bond, the two conventional adhesives, to reach optimal
polymerization, while One-Step and Xeno III, the two
simplified adhesives, were still suboptimally polymerized,
even after 60 s of light irradiation. These differences in
the curing kinetics should be directly related to the resin
composition of the adhesives (Table 1). On the contrary,
differences in microhardness may be simultaneously
affected by the differences in filler type and concentration
in these adhesives. Xeno III was the least polymerized
among the adhesives investigated; the high percentage of
hydrophilic monomers and the presence of water in a
one-step self-etching adhesive may compromise its
polymerization. Another factor that affects Xeno III
polymerization may be related to the presence of the
retarder butylated hydroxyl toluene (BHT) in the
adhesive solution, which slows down the polymerization
reaction but doesn’t compromise the final conversion
(25). Polymerization of this adhesive was completed only
after 150 s of light exposure. Using micro-Raman
Polymerization of adhesives
spectroscopy, incomplete polymerization was previously
reported on a one-step self-etching adhesive (Prompt
L-Pop; 3M ESPE) (26). Recent morphological analysis
suggested that as a result of incomplete polymerization,
the acidic nature of these one-step self-etching adhesives
was retained in the water-filled dentinal tubules and that
the walls of these tubules were susceptible to continuous
etching by the incompletely cured acidic monomers
during aqueous storage (6).
As microhardness data are comparable only within the
same resin system (27) because they are not linearly
correlated to degree of cure if compared across different
materials, the data derived from the present study were
useful in comparing the polymerization achieved with
different exposure times in a particular adhesive (28).
The results supported the hypothesis that prolonged light
exposure improves the microhardness of each adhesive
by increasing the degree of conversion. It should be
pointed out that simplified adhesives (i.e. One-Step and
Xeno III) exhibited very low microhardness values when
they were irradiated at the manufacturers’ recommended
curing time of 20 s, to the extent that the microhardness
values were sometimes not even recordable by the
microhardness testing unit.
It is prudent to reiterate that, in this study, differences
in EP and microhardness values among the adhesives
were not related to the oxygen-inhibition layer, as the
latter was absent when polymerization was performed
under a nitrogen atmosphere. Previous investigations
revealed that the thickness of the oxygen-inhibition layer
depends on the resin viscosity (29) and on the concentration of HEMA in co-monomer blends (30). Thus, the
presence of oxygen-inhibition layers in vivo would
adversely affect simplified adhesives more than hydrophobic films (31) and may further compromise the
polymerization kinetics in simplified adhesive systems.
This important issue has to be investigated in future
studies. For a similar reason, to minimize thick oxygeninhibition layers generated by single-step self-etching
adhesive, a second adhesive coat compromising more
hydrophobic resins has been recommended following the
application of these simplified adhesives to reduce their
permeability as well as absorbing the uncured acidic
monomers into the overlying adhesive layer where they
would co-polymerize with the more hydrophobic resin
monomers (5,31).
As EP and VH values were inversely correlated with
DP, we have to reject the first null hypothesis (i.e. that
the extent of polymerization of dentine adhesives has no
effect on adhesive permeability). OptiBond FL and
Clearfil Protect Bond exhibited the lowest permeability,
One-Step exhibited intermediate permeability and Xeno
III exhibited the highest permeability, which correlated
well with their extent of polymerization. These data
confirm that simplified adhesives (i.e. One Step and Xeno
III) exhibit higher permeability than dentin bonding
systems characterized by separated non-solvated,
relatively hydrophobic, bonding agents (i.e. OptiBond
FL and Clearfil Protect Bond) (32–34). Interestingly,
even though data from not-simplified adhesives were
obtained using dentin bonding agents, in accordance
529
with the manufacturers’ instructions (i.e. both primer
and bonding solutions were used) the presence of the
primers did not affect the inverse correlation between the
extent of polymerization and dentin permeability.
Moreover, as the permeability of the four classes of
adhesives was all significantly reduced with increased
irradiation times, we have to conclude that extended
curing beyond the time period of 20 s recommended by
the manufacturers does lead to permeability reduction of
the bonded dentine. This requires a rejection of the second null hypothesis. Jacobsen & Söderholm (35) and
Miyazaki et al. (36) demonstrated that water may
interfere with polymerization of the dentin adhesives and
resin composites. As partially cured adhesives have been
reported to be more permeable to fluid movement (37),
they may expedite water sorption and compromise the
long-term integrity of the adhesive–composite bond.
Moreover, the entrapment of water or incompletely
removed solvents within the adhesive resin may result in
the subsequent hydrolytic degradation of hybrid layers
and resins via the cleavage of ester bonds.
In conclusion, the null hypotheses were rejected as all
adhesives exhibited variable degrees of incomplete
polymerization that were correlated with their permeability to fluid movement. Improvement in polymerization by extended curing also reduced the permeability
exhibited by these adhesives when they were bonded to
sound dentine. Incomplete polymerizations and adhesive
permeability were more extensive in simplified etch-andrinse and self-etching adhesives as a result of the presence
of higher concentrations of hydrophilic monomers.
Extending the curing times of simplified adhesives
beyond those recommend by the manufacturers resulted
in improved polymerization and reduced permeability,
and appeared to be a possible means for improving the
performance of these adhesives. Such a hypothesis
requires further validation in vivo.
References
1. Van Meerbeek B, De Munck J, Yoshida Y, Inoue S, Vargas
M, Vijay P, Van Landuyt K, Lambrechts P, Vanherle G.
Buonocore memorial lecture. Adhesion to enamel and dentin:
current status and future challenges. Oper Dent 2003; 28: 215–
235.
2. De Munck J, Van Landuyt K, Peumans M, Poitevin A,
Lambrechts P, Braem M, Van Meerbeek B. A critical review
of the durability of adhesion to tooth tissue: methods and
results. J Dent Res 2005; 84: 118–132.
3. Tay FR, Pashley DH. Have dentin adhesives become too
hydrophilic? J Can Dent Assoc 2003; 69: 724–731.
4. Sano H, Shono T, Takatsu T, Hosada H. Microporous dentin
zone beneath resin-impregnated layer. Oper Dent 1994; 19: 59–
64.
5. Pashley EL, Agee KA, Pashley DH, Tay FR. Effects of one
versus two application of an unfilled, all-in-one adhesive on
dentine bonding. J Dent 2002; 30: 83–90.
6. Wang Y, Spencer P. Continuing etching of an all-in-one
adhesive in wet dentin tubules. J Dent Res 2005; 84: 350–
354.
7. Chersoni S, Suppa P, Grandini S, Goracci C, Monticelli F,
Yiu C, Huang C, Prati C, Breschi L, Ferrari M, Pashley
DH, Tay FR. In vivo and in vitro permeability of one-step selfetch adhesives. J Dent Res 2004; 83: 459–464.
530
Cadenaro et al.
8. Tay FR, Pashley DH, Suh BI, Carvalho RM, Itthagarun
A. Single-step adhesives are permeable membranes. J Dent
2002; 30: 371–382.
9. Chersoni S, Suppa P, Breschi L, Tay FR, Pashley DH, Prati
C. Water movement in the hybrid layer after different dentin
treatments. Dent Mater 2004; 20: 796–803.
10. Maffezzoli A, Terzi A. Thermal analysis of visible-lightactivated dental composites. Thermochim Acta 1995; 269/270:
319–335.
11. Tanimoto Y, Hayakawa T, Nemoto K. Analysis of photopolymerization behavior of UDMA/TEGDMA resin mixture
and its composite by differential scanning calorimetry. J Biomed Mater Res B Appl Biomater 2005; 72: 310–315.
12. Imazato S, McCabe JF, Tarumi H, Ehara A, Ebisu S. Degree
of conversion of composites measured by DTA and FTIR. Dent
Mater 2001; 17: 178–183.
13. Yap AU, Soh MS, Siow KS. Effectiveness of composite cure
with pulse activation and soft-start polymerization. Oper Dent
2002; 27: 44–49.
14. Ferracane JL. Correlation between hardness and degree of
conversion during the setting reaction of unfilled dental
restorative resins. Dent Mater 1985; 1: 11–14.
15. Rueggeberg FA, Craig RB. Correlation of parameters used to
estimate monomer conversion in light-cured composite. J Dent
Res 1988; 67: 932–937.
16. Prati C, Erikson R, Tao L, Simpson M, Pashley DH.
Measurement of dentin permeability and wetness by use of the
Periotron device. Dent Mater 1991; 7: 268–273.
17. Prati C, Ferrieri P, Galloni C, Mongiorgi R, Davidson
CL. Dentine permeability and bond quality as affected by new
bonding systems. J Dent 1995; 23: 217–226.
18. Yiu CK, King NM, Pashley DH, Suh BI, Carvalho RM,
Carrilho MR, Tay FR. Effect of resin hydrophilicity and
water storage on resin strength. Biomaterials 2004; 25: 5789–
5796.
19. Sano H, Yoshikawa T, Pereira PN, Kanemura N, Morigami
M, Tagami J, Pashley DH. Long-term durability of dentin
bonds made with a self-etching primer, in vivo. J Dent Res
1999; 78: 906–911.
20. Hashimoto M, Ohno H, Sano H, Tay FR, Kaga M, Kudou
Y, Oguchi H, Araki Y, Kubuta M. Micromorphological
changes in resin-dentin bonds after 1 year of water storage.
J Biomed Mater Res 2002; 63: 306–311.
21. Takahashi A, Inoue S, Kawamoto C, Ominato R, Tanaka T,
Sato Y, Pereira PN, Sano H. In vivo long-term durability of
the bond to dentin using two adhesive systems. J Adhes Dent
2002; 4: 151–159.
22. De Munck J, Van Meerbeek B, Yoshida Y, Inoue S, Vargas
M, Suzuki K, Lambrechts P. Vanherle G. Four-year water
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
degradation of total-etch adhesives bonded to dentin. J Dent
Res 2003; 82: 136–140.
Armstrong SR, Vargas MA, Fang Q, Laffoon JE. Microtensile bond strength of a total-etch 3-step, total-etch 2-step,
self-etch 2-step, and a self-etch 1-step dentin bonding system
through 15-month water storage. J Adhes Dent 2003; 5: 47–56.
Nunes TG, Ceballos L, Osorio R, Toledano M. Spatially
resolved photopolymerization kinetics and oxygen inhibition in
dental adhesives. Biomaterials 2005; 26: 1809–1817.
Braga RR, Ferracane JR. Contraction stress related to degree
of conversion and reaction kinetics. J Dent Res 2002; 81: 114–118.
Wang Y, Spencer P. Physiochemical interactions at the interfaces between self-etch adhesive systems and dentine. J Dent
2004; 32: 567–579.
Tantbirojn D, Versluis A, Cheng Y, Douglas WH. Fracture
toughness and microhardness of a composite: do they correlate?
J Dent 2003; 31: 89–95.
Toledano M, Osorio R, Osorio E, Prati C, Carvahlo RM.
Microhardness of acid-treated and resin infiltrated human
dentine. J Dent 2005; 33: 349–354.
Rueggeberg FA, Margeson DH. The effect of oxygen inhibition on an unfilled/filled composite system. J Dent Res 1990;
69: 1652–1658.
Finger WJ, Lee KS, Podszun W. Monomers with low oxygen
inhibition as enamel/dentin adhesives. Dent Mater 1996; 12:
256–261.
King NM, Tay FR, Pashley DH, Hashimoto M, Ito S,
Brackett WW, Garcı́a-Godoy F, Sunico M. Conversion of
one-step to two-step self-etch adhesives for improved efficacy
and extended application. Am J Dent 2005; 18: 126–134.
Gregoire G, Guignes P, Millas A. Effect of self-etching
adhesives on dentin permeability in a fluid flow model. J Prosthet Dent 2005; 93: 56–63.
Elgalaid TO, Youngson CC, McHugh S, Hall AF, Creanor SL, Foye RH. In vitro dentine permeability: the relative
effect of a dentine bonding agent on crown preparations. J Dent
2004; 32: 413–421.
Hashimoto M, Ito S, Tay FR, Svizero NR, Sano H, Kaga M,
Pashley DH. Fluid movement across the resin–dentin interface
during and after bonding. J Dent Res 2004; 83: 843–848.
Jacobsen T, Söderholm KJ. Some effects of water on dentin
bonding. Dent Mater 1995; 11: 132–136.
Miyazaki M, Onose H, Lida N, Kazama H. Determination of
residual double bonds in resin–dentin interface by Raman
spectroscopy. Dent Mater 2003; 19: 245–251.
Tay FR, Suh BI, Pashley DH, Prati C, Chuang SF, Li F.
Factors contributing to the incompatibility between simplifiedstep adhesives and self-cured or dual-cured composites. Part II.
Single-bottle, total-etch adhesive. J Adhes Dent 2003; 5: 91–105.