Nanoleakage related to bond strength in RM-GIC and adhesive restorations.

Abstract

This was to investigate the nanoleakage of Resin Modified Glass Ionomer Cement (RMGIC) and composite resin (CR) restorations in sound and caries-affected primary dentine, submitted to load cycling and cariogenic challenge in vitro.
Occlusal cavities were prepared in 60 sound exfoliated primary second molars and 30 specimens were subjected to chemical induction of artificial caries lesions and the others were restored without caries induction. All prepared teeth were divided into 2 groups according to restorative materials. From each dentine condition 5 restored teeth and restorative material were subjected to microtensile bond strength and nanoleakage tests immediately or after load-cycling or submitted to the pH-cycling procedure before testing.
The adhesive presented bigger areas of silver leakage at the interfaces on caries-affected dentine (2.46±0.47)mm2 than sound dentine (0.90±0.19)mm2. RMGIC nanoleakage was not influenced by the sound (1.75±0.11)mm2 or caries-affected (2.08±0.39) condition of the substrate. A significant moderate inverse correlation was revealed between the bond strength and silver leakage area at the interface, (r= -0.55, p<0.001).
Nanoleakage is greater in caries-affected primary teeth dentine than sound dentine in adhesive restorations although at the interfaces of RMGIC does not differ. As nanoleakage increases, bond strength decreases significantly.

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Introduction
Different causes that interact synergistically contribute to
restoration failures, with hydrolysis being the main event,
because of water entering at resin/dentine interface. Hydroly-
sis breaks not only the links between collagen fibers, but
those between the resinous polymers as well [Hashimoto et
al., 2000]. This process can be accelerxated by the action
of enzymes released by bacteria or dentine [Pashley et al.,
2004]. This intrinsic degradation was described in partially
demineralised dentine collagen and is attributed to the action
of matrix metalloproteinases (MMPs) [Hebling et al., 2005;
Carrilho et al., 2007].
The word nanoleakage was introduced to describe the occur-
rence of nanosized spaces inside the hybrid layer, even in the
absence of gaps at the interface [Sano et al., 1994; Sano et
al, 1995]. Nanoleakage can represent:
l incomplete collagen network impregnation by the adhesive;
l incomplete solvent evaporation;
l unpolymerized monomers;
l hydrolytic degradation of collagen;
l resin degradation.
Thus, silver deposition in specimens tested immediately
(within 24 hours) represents residual water from the adhe-
sive procedure, while in older specimens it represents water
absorption and consequent degradation [Breschi et al., 2008].
As nanoleakage represents the degradation of interfaces,
causing reduction in the adhesive bond strength, an inverse
correlation between bond strength and nanoleakage is
expected [Okuda et al., 2002]. Reis et al. [2007a] demon-
strated an inverse and significant relationship between bond
strength and nanoleakage.
Bond strength of caries-affected dentine is lower than that
of sound dentine; there is greater MMP activity in affected
dentine [Hebling et al., 2005], and the bond interface to caries
affected dentine is more susceptible to degradation [Erhardt
et al., 2008]. Thus, it is relevant to consider that when the
affected dentine layer is kept on the pulpal wall of the cavity,
chemical mechanism of bonding and fluoride release can be
beneficial to resistance against degradation [De Munck et al.,
2005], as well to as facing cariogenic challenge. In this sense,
it seems plausible to investigate the behaviour of restorations
in caries-affected dentine, made with Resin Modified Glass
Ionomer Cement (RM-GIC) and composite restorations (CR)
made with a bonding agent containing functional agents.
The aims of this study were firstly to investigate the resist-
ance to degradation of RMGIC and adhesive/CR restorations
in sound and caries-affected primary dentine, submitted to
load cycling and cariogenic challenge in vitro, by evaluating
nanoleakage. The second aim was to verify the relationship
between nanoleakage and microtensile bond strength. The
null hypotheses tested were that the nanoleakage of the RM-
GIC and the adhesive/CR restorations does not differ when
these materials are applied in sound or affected dentine;
nanoleakage is not modified by the load and pH cycling; and
nanoleakage is not related to bond strength.
material and methods
In this study 60 sound exfoliated primary second molars
were used. The human primary molars were obtained after
the institutional informed consent from all donors. Teeth were
cleaned with pumice/water slurry, rinsed and stored in a solu-
tion of distilled water and thymol in a refrigerator (4°C) until
use. The pulp chambers of 60 crowns were filled with CR and
abstract
aIm: This was to investigate the nanoleakage of Resin
Modified Glass Ionomer Cement (RMGIC) and compos-
ite resin (CR) restorations in sound and caries-affected
primary dentine, submitted to load cycling and cariogenic
challenge in vitro. mETHOD: Occlusal cavities were
prepared in 60 sound exfoliated primary second molars
and 30 specimens were subjected to chemical induction
of artificial caries lesions and the others were restored
without caries induction. All prepared teeth were divided
into 2 groups according to restorative materials. From
each dentine condition 5 restored teeth and restorative
material were subjected to microtensile bond strength
and nanoleakage tests immediately or after load-cycling
or submitted to the pH-cycling procedure before testing.
REsulTs: The adhesive presented bigger areas of sil-
ver leakage at the interfaces on caries-affected dentine
(2.46±0.47)mm2 than sound dentine (0.90±0.19)mm2.
RMGIC nanoleakage was not influenced by the sound
(1.75±0.11)mm2 or caries-affected (2.08±0.39) condition
of the substrate. A significant moderate inverse correla-
tion was revealed between the bond strength and silver
leakage area at the interface, (r= -0.55, p<0.001). CON-
ClusIONs: Nanoleakage is greater in caries-affected
primary teeth dentine than sound dentine in adhesive
restorations although at the interfaces of RMGIC does
not differ. As nanoleakage increases, bond strength
decreases significantly.
Key words: nanoleakage, primary dentine, adhesion
Postal address: Dr. J.A. Skupien. Federal University of Santa Maria, RS,
Santa Maria, RS, 97015-372, Brazil.
E-mail: jovitoodonto@yahoo.com.br
M. Marquezan, J.A. Skupien, B.L. da Silveira, A.L. Ciamponi
Dept. of Paediatric Dentistry, University of São Paulo, São Paulo, SP, Brazil.
Nanoleakage related to bond strength in Rm-GIC
and adhesive restorations
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their cusps) flattened with 220-grit abrasive paper. Occlusal
Class I cavities (7mm x 5mm x 2mm deep) were prepared
using a high-speed handpiece with a cylindrical medium-grit
(100 µm) diamond bur (#842) (Komet, Lemgo, Germany)
under water irrigation. Each diamond bur was replaced every
five preparations. A sub-set of 30 specimens was subjected
to the induction of artificial caries lesions and the other 30
were restored without artificial caries induction.
Artificial caries induction. The entire surface of each speci-
men, except for the internal surfaces of the cavity, was painted
with two layers of an acid-resistant red varnish (Colorama,
São Paulo, SP, Brazil). Simulated dentine carious lesions
were created by a pH-cycling procedure, according to the
protocol described in a previous report [Mendes and Nicolau,
2004]. The demineralising solution contained 2.2 mM CaCl2,
2.2 mM NaH2PO4, and 50 mM acetic acid adjusted to a pH
of 4.8. The remineralising solution contained 1.5 mM CaCl2,
0.9 mM NaH2PO4, and 0.15 M KCl adjusted to a pH of 7.
Each specimen was cycled for 8 hrs in the demineralising
solution (10 ml) and 16 hrs in the remineralising solution (10
ml). This procedure was performed for 14 days with solutions
being renewed at each change, at 37ºC, and without shaking.
The depth of dentine demineralisation with this same method
has been reported to be over 100 μm deep [De Munck et al.,
2005]. After the induction period, a diamond bur with tapered
safe end was used to clean the walls surrounding the cavities
keeping the demineralised dentine layer at the bottom of the
cavities.
Restoration procedures. The prepared teeth were ran-
domly divided into 2 groups (Figure 1) according to the
restorative materials: a RM-GIC (Vitremer®) (3M ESPE, St.
Paul, MN, USA) and a total-etch adhesive system (Adper
Single Bond 2®) (3M ESPE, St. Paul, MN, USA) followed
by a CR (Filtek Z100®) (3M ESPE, St. Paul, MN, USA). The
methods of application of these materials were in accord-
ance with the manufacturer’s instructions (Table 1). Filtek
Z100 was inserted using an incremental technique, and each
layer was light polymerized for 40 seconds with a Translux
EC (Kulzer GmbH, Bereich Dental, Wehrheim, Germany)
halogen light-curing unit. The output intensity was monitored
with a Demetron Curing Radiometer (Model 100) (Demetron
Research Corporation, Danbury, CT, USA). A minimal output
intensity of 600mW/cm2 was used for the experiments.
Figure 1. Distribution of teeth into experimental groups (SO: sound
dentine; CA: simulated caries-affected dentine; VI: Vitremer®; SB:
Adper Single Bond 2®; 24: control= test in 24h; PH: pH cycling; LO:
load cycling).
Table 1. Materials used in the experimental groups to investigate the nanoleakage of RM-GIC and composite resin restorations.
Product/
Manufacturer/ Batch #
ComponentsMode of application
Vitremer®
3M ESPE, St Paul, MN,
USA
Primer: #6BJ
Powder: #6EJ
Liquid: #6FN
Primer: methacrylate functional copolymer of
polyacrylic and polyitaconic acids, HEMA, ethanol and
photoinitiators.
Powder: fluoroaluminosilicate glass, microencapsulated
potassium persulfate and ascorbic acid, small amounts
of pigments.
Liquid: aqueous solution of a polycarboxylic acid
modified with pendant methacrylate groups,
methacrylate functional copolymer of polyacrylic and
polyitaconic acids, water, HEMA and photoinitiators.
1) Apply Primer for 30s, using a light scrubbing motion.
Mild air stream for 15s.
2) Light polymerize for 20s.
3) Hand-mixed manipulation
4) Insertion into a cavity using a syringe injector in a
single increment.
5) Light polymerize for 40s.
6) Apply light-polymerizing finishing gloss and light-
polymerize for 20s.
Adper Single Bond 2®
(Adper Scotchbond 1
XT in Europe)
3M ESPE, St Paul, MN,
USA
#5CW
HEMA, water, ethanol, Bis-GMA, dimethacrylates,
amines, methacrylate functional copolymer of
polyacrylic and polyitaconic acids, 10% by weight of 5
nanometer-diameter spherical silica particles.
1) Etch with phosphoric acid 37% for 15 s.
2) Rinse with water spray for 15s, leaving tooth moist.
3) Active application of two consecutive coats of the
adhesive with a fully saturated brush tip. Dry gently
for 2–5 s.
4) Light polymerize for 10 s.
Abbreviations: HEMA: 2-hydroxyethylmethacrylate; Bis-GMA: bis-phenol A diglycidyl methacrylate
M. Marquezan, et al.
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Nanoleakage and bond strength
After storage in distilled water 37°C for 24 hrs, the occlusal
surfaces of the restorations were ground in order to assure
exposure of enamel-restorative material interfaces. Then 5
restored teeth from each dentine condition and restorative
material were subjected to one of the following procedures:
1) Sectioned and tested for microtensile bond strength and
nanoleakage (control 24 hrs); or 2) mounted in plastic rings
using acrylic resin, for load-cycling (50,000 cycles, 90 N, 3 Hz)
under water, with a compressive load applied to the centre of
the restoration using a 5 mm diameter spherical stainless steel
plunger, attached to a cyclic loading machine (S-MMT-250NB)
(Shimadzu, Tokyo, Japan) before testing; or 3) submitted to the
pH-cycling procedure, being alternately placed into containers
with the demineralizing solution for 8 hrs and remineralizing
solution for 16 hrs. Solutions were the same as those described
above for carious lesion induction, but the cycling procedure
was performed for 10 days, as proposed by Rocha et al. [2007].
For the microtensile test, 5 teeth per group were sequentially
sectioned with a water-cooled diamond disc (Isomet 4000)
(Buehler, Lake Bluff, IL, USA), along the mesiodistal and
buccolingual axis, in order to obtain beams with a square cross-
sectional area of about 1 mm2 for microtensile testing. 45 beams
were obtained per group. Each beam was attached to a modi-
fied Bencor Multi-T testing apparatus (Danville Engineering Co.,
Danville, CA, USA) with cyanoacrylate adhesive (Zapit) (Dental
Venture of America Inc., Corona, CA, USA) and stressed to fail-
ure under tension, in a universal testing machine (Instron 4411)
(Instron Corporation, Canton, MA, USA) at a crosshead speed
of 0.5 mm/min. Bond strength values were expressed in MPa.
Nanoleakage test. One section of each restoration, which was
not cut for the microtensile test, was prepared for the nanoleak-
age test. The sections were waterproofed with the nail varnish,
with the exception of the pulpal floor interface of the cavity,
and immersed in aqueous ammoniacal silver nitrate for 24 hrs.
The tracer was prepared by dissolution of 25g of silver nitrate
crystals in 25 mL of distilled water. Concentrated ammonium
hydroxide (28%) was used for titration of the black solution until
it became white and the ammonium ions were converted from
silver into silver diamine ions. This solution was diluted in 50 ml
of distilled water to reach a concentration of 50% (pH=9.5). The
specimens impregnated with silver were rinsed in distilled water
and immersed in photo developing solution for 8 hrs under
fluorescent light to reduce silver ions into metallic silver grains
within voids along the interface.
The cosmetic varnish was removed by the application of 600-grit
SiC paper, the sections were fixed and included in epoxy resin
to be polished with a sequence of SiC papers (1,000, 1,550 and
4,000), followed by felt that was impregnated with 1 and 0.25
μm grit diamond slurry used in an automatic polishing machine.
Between each granulation and at the end, the specimens were
cleaned and immersed in water in an ultrasonic vat. After this,
the slices were dehydrated in increasing concentrations of etha-
nol for five minutes in each concentration (30, 50, 70, 90, 96%).
The last bath was in absolute alcohol for 10 mins, repeated
twice. The specimens were immersed in HMDS for 30 minutes
and left to dry in laminar flow chapel equipped with an exhaust.
After this, each polished slice was mounted on a metallic stub
and covered with carbon. SEM was operated in the backscat-
tered mode, and silver presented white in the image. So that
the images would present a magnification suitable for verifying
the areas of silver impregnation, a 1 mm wide area in the depth
of the cavity was captured at 150x. White areas at the inter-
faces were checked by EDX sounding (energy dispersive x-ray
detector) for determining the chemical elements presented and
to discard the possibility of false-positives results. The captured
images were analysed in Leica QWin program (Leica Microsys-
tems, Heildelberg, Germany), which allowed leakage area to be
measured by the tracer through the number of pixels in white
colour (silver) converted into μm2.
Statistical analysis. The silver nitrate leakage area values in
μm2 were analyzed by descriptive statistics using SPSS soft-
ware. Normal distribution was verified with the Shapiro-Wilk test
and homogeneity by Levene’s test. The data were raised in log-
arithms in base 10 to equalize the variances. A multiple ANOVA
was carried out followed by multiple comparisons Tukey’s test.
The mean bond strength value for each tooth was correlated to
the silver leakage area at the interface by Spearman’s correla-
tion coefficient.
Results
The mean areas of silver nanoleakage at the interface and
their respective standard deviations for each experimental
group are presented in Table 2. The factor dentine (F=37.87;
p<0.001) significantly influenced silver nanoleakage at the inter-
face, whereas the other factors: material (F=1.69; p=0.20) and
challenge (F=0.51; p=0.60) did not affect leakage. The interac-
tion between the factors dentine and material were significant
(F=13.03, p<0.01).
The RM-GIC Vitremer presented no difference in the nanoleak-
age pattern as a function of sound or affected substrate;
whereas, the adhesive Single Bond 2 presented larger areas of
silver nanoleakage at the interfaces with caries-affected dentine
in comparison with sound dentine. This was valid for baseline
(24hrs) and after pH cycling.
The pH or load cycling challenges did not promote difference in
silver nanoleakage in comparison with baseline (24 hrs) for any
of the materials and substrates. Figures 2 and 3 represent the
nanoleakage pattern found in the experimental groups. Figure
4 presents the dispersion graph between the bond strength val-
ues (MPa) and measurements of the silver nitrate nanoleakage
area at the interface (μm2). Spearman’s correlation coefficient
revealed a significant moderate inverse correlation between
the bond strength and silver nanoleakage area at the interface,
which means that as nanoleakage increases, bond strength
decreases significantly (r= -0.55, p<0.001).
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Table 2. Mean (SD) and Log10 mean (Log10SD) values for silver nanoleakage at the interface of Vitremer® and Adper Single Bond 2® submitted
to loading or pH cycling on sound or affected primary dentine.
Challenge Material Vitremer®
Adper Single Bond 2® + Filtek Z100®
Dentine Sound Dentine Affected DentineSound DentineAffected Dentine
24 hours Mean (SD)57.90 (15.35) 151.50 (90.46) 8.55 (3.77)345.12 (193.26)
Log10Mean
(Log10SD)
1.75 (0.11) Bab
2.08 (0.39) BCa
0.90 (0.19) Aa
2.46 (0.47) Ca
Load CyclingMean (SD) 25.92 (20.66) 79.60 (57.10)60.26 (58.30) 214.32 (185.88)
Log10Mean
(Log10SD)
1.29 (0.37)Aa
1.77 (0.47) Aa
1.08 (1.32) Aa
2.19 (0.39) Aa
pH CyclingMean (SD) 88.40 (60.62) 152.40 (99.08) 7.70 (9.21)397.20 (220.81)
Log10Mean
(Log10SD)
1.88 (0.27) Bb
2.13 (0.23) Ba
0.44 (0.89) Aa
2.55 (0.24) Ba
Means are shown in μm2. Means followed by the same small letters in columns and capital letters in rows did not differ significantly in Tukey’s test (p<0,05).
Figure 2. Micrographs showing a: A. Vitremer in sound dentine,
24h. Presented a medium pattern of infiltration of silver nitrate and
presents ‘water trees’; B. Vitremer in simulated caries-affected
dentine, at 24h presenting a medium pattern of infiltration of silver
nitrate and presents ‘water trees’; C. Vitremer in simulated
caries-affected dentine, load cycling. Presented a medium pattern
of infiltration of silver nitrate and presents ‘water trees’.
Figure 3. Micrographs showing: A. Single Bond 2 in simulated
caries-affected dentine, at 24h presenting a high pattern of infiltration
of silver nitrate; B. Single Bond 2 in simulated caries-affected
dentine, load cycling and presenting a high pattern of infiltration
of silver nitrate and presents numerous tags; C. Single Bond 2 in
simulated caries-affected dentine, pH cycling and presenting a high
pattern of infiltration of silver nitrate and presents numerous tags.
M. Marquezan, et al.
A
B
C
A
B
C
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Nanoleakage and bond strength
Discussion
As the hybrid layer is a mix of dentine organic matrix,
hydroxyapatite crystals, resin monomers and solvents, age-
ing can affect each one of these components individually or
in combination [Breschi et al., 2008]. Hydrolysis is the main
mechanism of resin degradation in the hybrid layer. Water is
also responsible for the collagen degradation. The combined
effect of degradation of the resinous portion and collagen
increases the presence of water at the interface, leading to
an additional deleterious effect on the longevity of the bond
[Breschi et al., 2008]. As hydrolytic degradation only occurs
in the presence of water, the hydrophilicity of the bonding
agent, its water sorption, and the subsequent degradation
are related [Tay et al., 2002a; Tay et al., 2003]. This means
that irrespective of the adhesive strategy (total-etching or
self-etching), the presence of a hydrophilic monomer in the
adhesive leads to the formation of hybrid layers that behave
as permeable membranes that allow the water to flow, even
after adhesive polymerization [Tay et al., 2002b].
Adhesives with a higher percentage of hydrophilic monomers
(simplified) show a higher degree of permeability after polym-
erization, and consequently, more nanoleakage expression
[Tay et al., 2002b]. The hydrophilic monomer HEMA is a
common component of adhesive agents to improve their
infiltration into moist substrates. However, HEMA decreases
the water vapour pressure, making it difficult to remove, and
then retaining water at the interface. This makes the hybrid
layer act as a hydrogel, absorbing and releasing water, con-
tributing to nanoleakage [Tay et al., 2002c]. The Vitremer
primer is a light polymerizable liquid with high concentration
of HEMA (46%) [Pereira et al., 2000]. The presence of a
high concentration of this hydrophilic monomer can produce
incomplete polymerization and water permeability, causing
dissolution and degradation of resinous components, as also
occurs with the simplified adhesive systems [Breschi et al.,
2008]. Navarra et al. [2009] found a relationship between a
low degree of conversion and the presence of nanoleakage,
and this could affect the quality and durability of the adhesive
interface over the course of time.
In seeking a resistant and lasting bonding, the addition of
functional agents to adhesive systems has been suggested.
Thus, the composition of the bonding agent also influences
the effectiveness of bonding. The Adper Single Bond 2 con-
tains a functional monomer, the copolymer of polyalkenoic
acid, which has some degree of interaction with the calcium
ions of dentine through acid-based reactions. Preventing
calcium loss from dentine matrix can contribute to stability
of the adhesive interface over the course of time [Osorio et
al., 2002].
However, silver deposits were detected throughout the hybrid
layer and also in the adhesive layer of Adper Single Bond
[Osorio et al., 2002; Reis et al, 2007b], as an amorphous
phase that was identified as the copolymer of polyalkenoic
acid, which does not infiltrate into the collagen network, due
to its high molecular weight [Osorio et al., 2002]. After ageing
for 6 months in water, Erhardt et al. [2008] and Reis et al.
[2007b] found an increase in silver leakage into the hybrid
and adhesive layers, suggesting that water comes from an
external source oriented to the copolymer mass by self prop-
agable water channels. Although these results are similar to
the present study for Single Bond 2 in affected dentine, the
interaction between dentine-material seems to explain better
the occurrence of nanoleakage, as nanoleakage at the base-
line represents residual water retained at the interface, and
the challenges used did not have any effect on the amount
of silver nitrate leakage. However, in sound dentine it was
not possible to observe the details described by Reis et al.
[2007b] because of the lower resolution and the use of scan-
ning electron microscopy instead of transmission electron
microscopy.
The presence of fluorides in the bonding agent has also been
reported as a component to improve the durability of bond-
ing. Sodium fluoride crystals were observed in the adhesive
layer of Clearfil Protect Bond. These fluoride crystals can be
extracted from the adhesive and inhibit the enzyme action
in the interface, being responsible for its better long-term
behaviour in vitro [Reis et al., 2007b]. GIC by nature liberates
fluoride, which, in accordance with the hypothesis previ-
ously cited, would contribute the longevity of the restoration.
Although, in our study, the pattern of silver leakage observed
for sound dentine specimens restored with Vitremer was
higher than that for adhesive restorations. Thus, the first
null hypothesis was rejected. Two reasons can be related to
this fact: 1) GIC are materials prone to hydric imbalances,
which possibly contributed for a high water presence in the
interface; and 2) the presence of great amount of HEMA in
the Vitremer can have contributed for a higher retention and
permeability to water.
None of the challenges used was able to intervene in the
pattern of silver infiltration. Li et al. [2002] also verified that
the pattern of infiltration was not affected by load cycling,
when applied over flat interfaces. Although porosities
existed in the adhesive interfaces, it did not increase with
simulated occlusal stress. Those authors emphasise that the
Figure 4. Dispersion graph between bond strength values (MPa)
and silver leakage area (μm2) at the interface.
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load-cycling machine reproduces axial loads, while the
chewing movements have a three-dimensional pattern. This
condition of specificity of the simulated challenge in vitro
must be considered for interpretation of results.
Reis et al. [2004] demonstrated an increase of silver particles
into the hybrid layer formed by Single Bond® after six months
in water. Literature is unanimous in pointing out that speci-
men storage in water is the best method to simulate ageing
that restorations suffer in an oral environment [De Munck et
al., 2005]. The pH cycling, however, aimed to simulate the
cariogenic challenge that the restorations are subjected to in
an environment characterized by caries activity. The deleteri-
ous effect of pH cycling over bond strength values of Adper
Single Bond 2® and not over nanoleakage could be explained
by the loss of minerals that weakened the union, without
however, having perceivable effect on hydrolytic degrada-
tion visualized by the penetration of silver. Perhaps it would
occur if pH cycling were extended to a longer period of time,
a determinate factor for nanoleakage increase. Meanwhile,
Vitremer® presented a silver leakage pattern coherent with
its bond strength values, which did not vary as result of chal-
lenges. Thus, the second null hypothesis was accepted.
As nanoleakage is the expression of areas with potential
depletion of the interface and the degradation per se, it is
reasonable that there is an inverse association between
the leakage pattern and bond strength [Okuda et al., 2002].
However existence of this relationship is not unanimously
recognised in the literature, probably due to technical difficul-
ties of obtaining data referring to leakage that is possible to
measure, and which is representative of the interface; and
at the same time, has morphologic details of the bond. Thus
most studies make only qualitative analyses of nanoleakage
[Erhardt et al., 2008]. Reis et al. [2007a] demonstrated an
inverse and significant correlation between bond strength
and nanoleakage after ageing of specimens for two years.
Those authors believed that the results were able to express
its inverse correlation because of ageing, which allowed the
expression of degradation by nanoleakage and reduction in
bond strength.
Otherwise the study of Hashimoto et al. [2004], which did
not evaluate these properties in the long-term, did not find
a correlation; and Ding et al. [2009] also found no statisti-
cally relevant relationship between nanoleakage and bond
strength. In the present study, although the challenges did
not influence the area of silver leakage, they did influence the
bond strength, and a moderate negative correlation between
the two properties was found, which denotes the influence of
substrate and material characteristics on the bond effective-
ness. Thus, the third null hypothesis was rejected.
The final aim of the adhesive procedures is for bonding agent
to completely envelop the collagen fibers, to protect the inter-
face from degradation. As the effectiveness and durability of
the bond seems to depend on the hybrid layer quality, some
strategies have been suggested to improve monomer infil-
tration; reduce the degree of water absorption and reduce
collagen degradation, such as: 1) use of systems in which
the primer and bond are separate; 2) increase polymerization
time; 3) improve of impregnation by a longer application time
and friction, and 4) use a MMP inhibitor [Breschi et al., 2008;
Ricci et al., 2010]. Furthermore, with the intention of protect-
ing restorations from degradation, it seems coherent to use
bonding agents with an additional chemical mechanism, such
as GIC. Neelakantan et al. [2009] found a lower amount of
nanoleakage for glass ionomer based bonding agents com-
pared with dentine adhesives.
The method of using of bonding agents is appropriate to
verify interface degradation and the results herein demon-
strated an inverse correlation between bond strength and
nanoleakage. The use of restorative material with chemical
mechanism of bonding is encouraged in patients with caries
activity, because these materials are resistant to cariogenic
challenge.
Conclusion
Nanoleakage is greater in caries-affected dentine than sound
dentine in adhesive restorations although at the interfaces
of RMGIC does not differ. As nanoleakage increases, bond
strength decreases significantly. Load cycling and cariogenic
challenge do not modify the pattern of silver nitrate leakage at
the interfaces of both RMGIC or adhesive/composite.
acknowledgements
The research was approved by the Research Ethics Commission of University
of São Paulo. We thank Dra. Célia Rodrigues, who passed away during the
preparation of this research, for all her knowledge.
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