Key words: Adhesion - Class II - deep margin relocation - direct restoration - micro-computed
tomography CT - microleakage
INTRODUCTION
Nowadays, the resin composites are the main dental material used as direct fillings.
Their chemistry has evolved strikingly over the past years due to the use of different
novel filler particles along with innovative low shrinkage monomers.[1 ]
[2 ] These are only some of the advances in this field. An old major drawback of the
resin composite fillings was the excessive wear. However, some of the current materials
can present enamel like wear which decreases substantially the formation of gaps and
stairs along the outer enamel resin borders.[3 ] This border is fundamental for the durability of the restorations since it has higher
resistance against degradation.[4 ]
[5 ] The resin dentin interfaces are not as hydrolytically stable as the enamel margins
so that the practitioners should limit to enamel the boundaries of the cavities. Nevertheless,
in some cases, Class II cavities resulted from deep proximal caries below the cementum
enamel junction (CEJ) require restorations with gingival dentin margins. The dentin
bonded interfaces compromise the long lasting durability of the fillings due to the
faster degradation attained by hydrolysis of collagen which may be accelerated by
enzymatic activity.[6 ]
[7 ] In these cases, a suitable alternative would be, for instance, the indirect technique
which would be less compromising than the direct filling as the former exposes less
collagen. However, even the indirect restorative procedures may undergo marginal microleakage.
The microleakage is related to the seepage of molecules, fluids, and bacteria within
gaps between the cavity walls and the dental filling along the outer borders.[8 ] Some outcomes of microleakage are tooth sensitivity, pulpal inflammation, and secondary
caries.[9 ] Several strategies have been proposed to reduce the microleakage; for instance,
the use of ceramic inserts,[10 ] the use of glass ionomer cement as a base,[11 ] and the use of immediate dentin sealing or the so called resin coat technique.[12 ] The latter relies on the use of a bonding agent and a flowable resin composite after
the cavity preparations. The flowable composite may act as a stress relieving more
elastic liner and may provide better marginal integrity with less microleakage due
to its low viscosity.[13 ] Using such approach, the margins may be relocated upper to the enamel cavosurface
border. Therefore, the final direct restoration could have only enamel surrounding
borders. This relocation might be undertaken also with preheated composites which
showed improved degree of conversion and less shrinkage stress.[14 ] Nevertheless, there is little information on the use of preheated resin composites
as a liner for direct restorations. Thus, the purpose of the present work is to investigate
the microleakage attained after the use of flowable, preheated and micro hybrid composites
as a liner to relocate coronally gingival margins in the proximal boxes of the MOD
cavities. The null hypothesis chosen was that there is no difference between the resin
based materials on the microleakage along the borders of direct restorations.
MATERIALS AND METHODS
Specimen preparation
Thirty selected molars, removed for periodontal reasons, were used in this study (gathered
as approved by the Research Ethical Committee of the University of “Rome Tor Vergata”).
All teeth were sound, completely formed, and free from pathology. Specimens were kept
in distilled water for no >1 month at 4°C before being used. Mesio occluso distal
preparations were completed, with the interproximal margins located, respectively,
1.5 mm apically (dentin/cementum) and 1.5 mm coronally (enamel) to the CEJ. Standard
cavities were obtained with 4 mm in width and 2 mm in depth at the proximal boxes.
All walls were prepared straight with rounded internal line angles and no retentive
grooves. All II MOD cavities were completed using coarse diamond burs (846KR, Komet
Italia srl, Milano) under copious water spray and finished with fine grained burs
of the same shape (8846KR, Komet Italia srl, Milano). The 30 specimens were randomly
allocated to one of the three experimental groups, corresponding to the combination
of restorative materials as described in [Table 1 ].
Table 1:
Summary of the products used in the study
Groups
Adhesive
Relocation’s materials
Schematic representations of the restorative procedures used in the study. Specimens
under evaluation (n =10 samples per group). Groups divided based on the material used to relocate the
margins
Micro-hybrid composite (controll group)
Etch and Rinse
Premise Dentin A3 Kerr BN. 4396739
Preheated micro-hybrid composite
3 steps Optibond - FL
Premise Dentin A3 Kerr BN. 4396739
Flowable
BN. 4190785
Premise flowable Kerr BN. 4264444
Sample preparation
An adhesive system “Etch and Rinse” was used to treat dentin surfaces, according to
the manufacturer’s instructions, following groups of [Table 1 ]. With the exception of Group A (Control group), a layer of composite 1,0–1,5 mm
thick was applied on all the gingival floor (mesial and distal), using, respectively,
a flowable (Premise Flowable) or a preheated composite (Premise Dentin A3), to relocate
the margins coronally to the CEJ. The resin composite was applied after placing an
auto matrix (Dentsply Caulk) and light cured from the occlusal surface for 30 s with
a power density of 1200 mW/cm2 (Bluephase, Ivoclar Vivadent, Schaan, Liechtestein). The restoration was then completed
with 3–4 layers of the conventional composite using a horizontal placement technique
of 1–1.5 mm composite thickness and light cured for 30 s. Build ups were finished
and polished using diamond burs (40 μm) and discs of decreasing grain size (Optidisc,
Kerr, Orange) as shown in [Figure 1a and b ].
Figure 1: (a and b) Specimens restored using a preheated composite to relocate the margins
on dentin (a) and enamel (b). Restorations is completed with conventional composite
Thermocycling procedures
All specimens from each group were wrapped in gauze and placed in bag named with the
corresponding group. Specimens were thermocycled in distilled water for 1000 cycles
(5–55°C) with dwell time of 30 s and draining time of 10 s between cycles.
Dye penetration test
With the exception of 1 mm thick area around the restoration margin the specimens
where covered with two layers of nail varnish and the apex of each tooth was sealed
with epoxide cement. A 50% ammoniac AgNO3 solution was used as tracer and after 1
day of water storage at 37°C, all the specimens were infiltrated as described by Tay
et al .[15 ]
Micro ct analysis
Microleakage analysis was performed using a microtomography system Sky scan 1072 (SKYSCAN,
Kartuizersweg 3B 2550, Konitch, Belgium). The settings of the machine were as follow:
100 kV, 10 W and 98 μA, a standard aluminum filter and ×15 magnification were applied.
Final resolution was in the range of pixels 19.1 μm × 19.1 μm and around 3–5 h were
necessary to complete scan on each sample.
The data acquired were bi dimensional images processed into cross sectional images
with a resolution of 19.1 μm × 19.1 μm and a slice thickness of 13.0 μm.
The pattern of infiltration was digitally assessed with a dedicated system (TView
SkyScan, bvba), which allowed observing of all micro scans and detecting the leakage
of AgNO3 as shown in [Figures 2a‒c ] and [3 ]. Three dimensional 3D images were obtained by juxtaposition of 2D images of adjacent
slices [Figure 4 ]. Since the beginning and the end of the procedure, microleakage could be observed
in each scan and the infiltration was measured with the accuracy up to 0.001 mm. The
computed tomography analyzer (CTAan) (SkyScan, bvba) software was used for the determination
volume of the AgNO3. A desktop X-ray microfocus CT scanner (SkyScan 1072, bvba, Aartselaar,
Belgium) was used.
Figure 2: (a) X–ray projection image of the II MOD class of specimen C1 (Group C) obtained
with micro–computed tomography scan. (b and c) Coronal micros–computed tomography
scans of the same specimen showing presence of AgNO3 infiltration along the dentin
margin. Note that enamel margin (c) does not present any infiltration in this case
Figure 3: Axial view of C1 specimen, maximum intensity projection image, which is similar to
a two–dimensional radiograph of the Volume of Interest where is possible to appreciate
the presence of AgNO3 alongside the dentin margin
Figure 4: Three–dimensional volume rendering of specimen C1 post infiltration; in red volume
of AgNO3
RESULTS
The acquired data were evaluated on the basis of recorded volume from AgNO3 infiltration
expressed in mm3 [Table 2 ]. The evaluation was conducted to assess microleakage patterns in both enamel and
dentin margins. Statistical analysis was performed using t test (two tailed) to compare the differences in enamel and dentin/cementum margins,
and one way ANOVA was used to determine differences among groups. Microleakage’s mean
of all tested materials showed greater leakage in the cementum margins compared to
enamel margins. There were statistically significant differences in microleakage between
enamel and dentin margins [Table 3 ]. Descriptive statistical analysis depicts that flowable composite showed maximum
microleakage with a mean of 0.74 mm3 at the cementum margin [Table 4 ] and [Figure 5 ]. ANOVA test showed the presence of significant differences (P < 5%) within groups in both enamel and dentin margins.
Figure 5: Graphic log–bar chart, microleakage of different formulations of composite in dentine
and enamel, measured in mm3
Table 2:
Results of microleakage distribution in each group
Group A Micro-hybrid composite
Group B Preheated composite
Group C Flowable composite
Enamel (mm3 )
Dentin (mm3 )
Enamel (mm3 )
Dentin (mm3 )
Enamel (mm3 )
Dentin (mm3 )
Volume of silver nitrate recorded (mm3 ) per specimen in each group at the enamel and dentin margins
0.017
0.123
0.015
0.023
0.019
1.877
0.013
0.119
0.013
0.19
0.022
1.168
0.012
0.056
0.012
0.16
0.023
1.158
0.010
0.045
0.00
0.15
0.018
1.221
0.010
0.040
0.00
0.02
0.018
1.10
0.011
0.043
0.00
0.02
0.015
0.53
0.008
0.032
0.00
0.00
0.013
0.45
0.00
0.013
0.00
0.00
0.012
0.023
0.00
0.00
0.00
0.00
0.010
0.021
0.00
0.00
0.00
0.00
0.010
0.00
Table 3:
t –test results
Groups
P
Significance
Two-tailed t -test. Comparison between enamel and dentin/cementum margins. S: Significant
Flowable
0.001
S
Micro-hybrid
0.011
S
Preheated micro-hybrid
0.047
S
Table 4:
Results of microleakage expressed as mean, deviation standard and interquartile percentage
ranges for each group
Group Margin location
A - Micro-hybrid composite
B - preheated composite
C -Flowable composite
Enamel
Dentin
Enamel
Dentin
Enamel
Dentin
Descriptive statistic - Microleakage distribution (mm3 ). SD: Standard deviation
Count
10
10
10
10
10
10
Mean
0.008
0.047
0.004
0.056
0.016
0.744
SD
0.006
0.043
0.006
0.078
0.005
0.635
Minimum
0
0
0
0
0.01
0
25%
0.002
0.018
0
0
0.012
0.130
50%
0.01
0.041
0
0.02
0.016
0.815
75%
0.012
0.053
0.009
0.118
0.019
1.149
Maximum
0.017
0.123
0.015
0.19
0.023
1.877
DISCUSSION
Microleakage is the undetectable passage of bacteria, fluids, molecules, and ions
at the interface between the cavity walls and the restorative material bonded to.
It can be used as a measure by which clinicians can evaluate the performance ability
of dental materials within the oral environment.[16 ] The most important aspect of microleakage is the direct link with the formation
of secondary marginal caries. Although a lot of methods and strategies have been used
to reduce this phenomenon, microleakage is still present and affect the longevity
of the restorations.[2 ] When facing a MOD II cavity with deep margins in dentin and/or cementum, with resin
composite, microleakage can frequent occur if a good dentin/bonding interface is not
achieved.[17 ] Restoration of a deep Class II cavities has always been a topic of debate. Adhesion
to dentin/cementum is still a challenge because the nature of the substrate so the
quality of the margins of a bonded restoration is questionable.[18 ] In 1998, Dietschi and Spreafico proposed a conservative approach to such challenge,
the deep margin elevation technique. The procedure consisted in the placement of composite
underneath indirect bonding restoration to relocate coronally the proximal margins.[19 ] The DME concept can also be used in direct restoration as reported by Magne in synergy
with the immediate dentine sealing technique.[20 ] There has been controversy on which material can be successfully used to relocate
the deep margin of II classes. Several authors reported that the use of flowable material
at the deep margin of Class II could show a good sealing ability and marginal adaptation.[14 ]
[21 ] Other authors revealed that flowable materials used at the dentin margin showed
high microleakage score when compared to nonflowable materials. The preheated composite
is also advocated for reducing microleakage at the dentin/cementum margins.[22 ]
[23 ] The study evaluated the microleakage of deep Class II cavities to determine the
bonding capacity of the given resin based materials in both enamel as well as cement
area. Thermocycling was done completely according to the ideal timing. The apical
extent of the Class II was intentionally placed into root surface on one side because
in this area, microleakage is known to be a clinical concern. Previous microleakage
studies have found significant differences in the amount of microleakage at enamel
versus cementum margins in relation to the material used with a huge variety of results.[24 ] This big diversity of results may be due to different methods used to detect the
microleakage, techniques, and protocols used to restore an II deep class. In this
study, microleakage was detected using a CT scan and a metal tracer. As reported by
Neves et al ., this technique has shown good sensitivity to evaluate the pattern of silver nitrate
infiltration at the resin tooth interface.[25 ] In all tested materials of this study, a degree of microleakage was observed. However,
the preheated composite showed less leakage compared to the others in cementum margins
and was possible to reject the tested null hypothesis. The flowable material showed
high infiltration in both margins, enamel, and dentin, and was possible to record
from the CT scan a maximum volume of 1.87 mm3 . The results of this study showed that the majority of the microleakage occur at
the cementum/dentin margin, and confirm that an optimal adhesion to dentin/cementum
is still a challenge. For instance, the results of this research indicate that the
use of a flowable material should be avoided in the dentin/cementum margin. Further
studies testing these materials in vivo are recommended o determine the potential clinical effect.
CONCLUSION
Within the limitations of this in vitro study, it can be concluded that a flowable composite should be avoided at the dentin/cementum
margin. Therefore, in clinical situation, if the cavity margin is placed below the
CEJ, it is advisable to line the cavity with preheated composite based material to
reduce the incidence of microleakage.
Financial support and sponsorship
Nil.
