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Journal of Dentistry (2004) 32, 629–634
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Translucent fiber post cementation using
a light-curing adhesive/composite system:
SEM analysis and pull-out test
Luca Giachetti*, Daniele Scaminaci Russo, Fabio Bertini,
Valentina Giuliani
Department of Dentistry, Faculty of Medicine and Surgery, University of Florence,
Viale Morgagni 85, Florence 50134, Italy
Received 27 October 2003; received in revised form 10 June 2004; accepted 23 June 2004
KEYWORDS
Fibre posts;
Scanning electron
microscopy;
Pull-out test;
Cementation
Summary Objectives. The performance of both light-curing and dual-cured
adhesive/luting systems (as control), when used in combination with translucent
fibre posts, was evaluated by means of pull-out test and scanning electron
microscopy (SEM ) observation.
Methods. Forty root canal treated teeth were randomly divided into two groups of
20 specimens each. Group 1 light-curing system: Excite and Tetric Flow; Group 2 dual
cured system: All Bond 2CRelyX ARC. Translucent, double taper fibre posts were
used (2.1/1.4 mm diameter). The teeth were stored in NaCl 0.9% solution at 37 8C. A
week later, the pull-out test was carried out on all specimens. Ten tested specimens
for each group and their corresponding posts were processed for SEM observation.
Statistical analysis was performed applying one-way analysis of variance (ANOVA)
followed by T-test as post-hoc comparison at a significance level set at p!0.05.
Results. There is no statistically significant difference (p>0.05) between the lightcuring system group (275.2G58.9 N) and the dual cured one (301.4G40.1 N). SEM
observations confirm a good bond between the dentine and the post whatever the
curing method employed.
Conclusions. Dual curing of the All Bond 2CRelyX ARC system seems to be the most
appropriate method since it allows to cure even those areas which would not be
otherwise reached by light. On the other hand, in apical areas, the incomplete curing
of the ExciteCTetric Flow system could improve the post adaptation and allow the
achievement of both an improved apical seal and a more even distribution of the
stress along the canal walls.
q 2004 Elsevier Ltd. All rights reserved.
Introduction
* Corresponding author. Tel.: C390-554-15598; fax: C390554-11798
E-mail address: [email protected] (L. Giachetti).
The use of fibre posts in the restoration of
endodontically treated teeth has recently
0300-5712/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jdent.2004.06.004
630
L. Giachetti et al.
increased in popularity. This is due to two main
factors: first, fibre posts are ready to use, and
therefore save time; second, some studies have
demonstrated that their use reduces the risk of
fracture1–3 since their modulus of elasticity is
similar to that of dentine.
Since carbon fibre posts can jeopardize the
aesthetic appearance of direct restorations, white
and translucent fibre posts were introduced. Translucent fibre posts have high fatigue and tensile
strength and their modulus of elasticity can be
compared to that of dentine and of other fibre posts.3
Translucent fibre posts should allow light to be
transmitted into the root canal. This would increase
the conversion degree of dual-cured composite
resins with a consequent improvement of their
mechanical properties such as modulus of elasticity
and hardness. However, the ability to transmit light
through the post has still to be determined. The
exclusive use of dual-cured or self-curing composites to lute fibre posts is therefore recommended.4
Nevertheless, mechanical tests carried out in a
recent pilot study show no remarkable difference
between the use of light-curing and dual-cured
composites in the cementation of translucent
posts.5
The aim of this study, which was carried out by
means of a pull-out test and SEM observations, was
to compare the performance of light-cure cement
with a dual-cured adhesive/luting system (control
group) in the root canal dentine when used to
cement translucent fibre posts.
Materials and methods
Forty caries-free human maxillary anterior teeth,
extracted due to periodontal problems, were
selected for this study. These teeth were stored in
10% formaline solution at 4 8C, and were used within
1 month after the extraction.
Specimen preparation
The crown was removed by cutting it at the
amelocemental junction with a low speed diamond
saw (Isomet 1000, Buhler, Lake Bluff, NY, USA).
Table 1
A metal post was inserted into the root canal in
order to obtain a cutting surface perpendicular to
the longitudinal axis. The root canals were
mechanically enlarged by alternating Hero 6,4,2
endodontic files (Micro Mega SA, Geneva, Switzerland) operated at 400 rpm, and syringe irrigation
with 2.5% NaOCl. The definitive preparations had a
6-degree taper (as a result of the instrument shape)
and a diameter of 0.3 mm at the apex. The canals
were then rinsed with water, dried with paper
points (Kerr, Romulus, MI), and obturated with Pulp
Canal Sealer E.W.T. (Kerr) using the continuous
wave technique (System B, Analytic Technology,
Redwood, USA). The root canal walls of each
specimen were enlarged with low-speed drill tips
provided by the manufacturer (RTD, France) with
the fibre posts: the post space preparation was
9 mm in depth. The specimens were randomly
divided into two groups of 20 specimens each
(Table 1).
Group 1: 20 specimens were treated with Excite
(Vivadent-Ivoclar, Schaan, FL) and Tetric Flow
(Vivadent-Ivoclar) following the manufacture’s
instructions. The root canal walls were etched
with 37% phosphoric acid (Total Etch, VivadentIvoclar) for 10 s, rinsed using a water syringe and
then gently dried with paper points (Kerr). The
adhesive was applied into the root canals by means
of a microbrush (Plus Super Fine Roen, Pianezza TO,
Italy). After 20 s, the excessive adhesive solution
was removed with a paper point (Kerr) and then
gently air-dried, but it was not light cured. Finally,
the post was covered with flowable composite and
seated in the root canal; the excess resin was
subsequently removed. The resin cement and the
adhesive material were light-cured simultaneously
through the post for 60 s (Astralis 10, VivadentIvoclar pulse program for the first 20 s and high
power for the following 40 s).
Group 2 (control group): the other 20 roots were
treated with All Bond 2 (Bisco, Itasca, IL) and RelyX
ARC (3M ESPE, Dental Products, 3M Company,
St Paul, MN, US) according to the manufacturer’s
instructions. The root canal walls were etched with
37% phosphoric acid (Total Etch, Vivadent-Ivoclar)
for 10 s, rinsed using a water syringe and then
gently dried with paper point (Kerr). The primer
Tested materials and procedures of polymerisation.
Groups
Adhesive systems
Luting materials
Procedures of polymerisation
1.
2.
Excite (Ivoclar-Vivadent)
All Bond 2 (Bisco)
Tetric Flow (Ivoclar-Vivadent)
RelyX ARC (3M)
Light cured for 60 s
Self curedClight cured for 60 s
Translucent fiber post cementation
adhesive material was applied into the root canals
with a microbrush (Plus Super Fine Roen). Excessive
primer adhesive solution was removed with a paper
point (Kerr) and then gently air-dried. Then a layer
of bonding adhesive (included in All Bond 2
package) was applied into the root canals with a
microbrush. Excess bonding adhesive solution was
removed with a paper point. Finally, RelyX ARC
composite base and catalyst were mixed for 10 s
and applied as a layer on the fibre post surface. The
fibre post was subsequently seated and the excess
resin was removed. The polymerization of the resin
cement was completed by light-polymerizing it
through the post for 60 s (Astralis 10, VivadentIvoclar pulse program for the first 20 s and high
power for the following 40 s).
Translucent, double taper fibre posts (Light-Post
N83, RTD) were used (2.1/1.4 mm diameters).
The specimens were stored in NaCl 0.9% solution
at 37 8C for a week.
Pull-out test specimen preparation
The pull-out test was carried out on 20 specimens
for each group. The teeth were placed in acrylic
resin blocks with the tooth/post extruding from the
block horizontally. Parallelism between post, canal
and resin block was obtained using a parallel meter
(CL-MF2002S, Heraeus-Kulzer Inc.). Transverse cuts
had been previously made on the root surface in
order to increase resin retention. The pull-out test
was performed along the long axis of the post and
the tooth at a cross-head speed of 0.5 mm/min
using a universal testing machine (Instron Inc.,
model 4301, High Wycombe, UK). The force
required to dislodge each post was then recorded
in Newton.
Statistical analysis
Statistical analysis was performed applying oneway analysis of variance (ANOVA) followed by T-test
(JMP Version 5.0 2002, SAS Institute Inc., Cary, NC,
USA) as post-hoc comparison at a significance level
set at p!0.05.
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specimen was treated with 15% EDTA (Largal Ultra,
Septodont) for 60 s then rinsed with water and air–
water spray for 30 s. In order to carry out a more
correct analysis of the hybrid layer and of the resin
tag formation, the other half of each specimen was
partially deprived of its organic and mineral
components. To this aim, the sectioned surface
was treated using 37% H3PO4 (Total Etch, VivadentIvoclar) for 120 s, then rinsed with water and
air–water spray for 30 s. The specimens were
subsequently immersed in NaOCl (7G2%) for
15 min, and rinsed again with tap water for 30 s.
The specimens were first dehydrated in alcohol–
acetone and then the Critical Point Dry process was
carried out (CPD 030, BAL-TEC AG, Balzers FL).
Subsequently, the specimens from each group
were mounted on aluminum stubs coated with
colloidal silver paint, and sputter-coated (SCD 005
BAL-TEC AG, Balzers FL) with 200 Å gold–palladium
alloy. Each specimen was examined by SEM (Philips
515, Philips Co., Amsterdam, The Netherlands) at a
15 KV accelerating voltage. A computer program
(Analysis, Soft Imaging System, GMBH) was used to
convert microscope images.
Results
Pull-out tests
Data from the pull-out tests are presented in
Table 2. No statistically significant difference
(p>0.05) between the light-curing system group
and the dual cured group was found (Fig. 1).
SEM observations
SEM images of Group I specimens were similar to
those of Group II specimens.
In all specimens ‘debonding’ mainly occurred at
the dentine–cement interface and the extracted
posts were almost entirely covered with a consistent resin cement layer (Fig. 2A). Nevertheless, very
large voids were found in the apical third of some
posts (Fig. 2B). Furthermore, both groups showed
several small bubbles on the cement layer that
SEM specimen preparation
Ten randomly selected specimens from each group,
with their corresponding posts, were prepared for
SEM observation. After the removal of the resin, the
roots were longitudinally sectioned using a low
speed diamond saw under water coolant. Each half
was then smoothed under running water with
600 grit silicon carbide paper. One half of each
Table 2
Pull-out test results.
Groups
Mean
SD
Min.
Max.
EXCTF
ABCRX
275.2(a)
301.4(a)
58.9
40.1
171
234
351
378
Means with similar superscript symbols indicate non-significant differences (pO0.05).
632
L. Giachetti et al.
Figure 1
Box plot representation of the pull-out test between fibre posts and luting materials.
Figure 2 (A) Scanning electronic microscope image of a Group 2 extracted post. It is almost entirely covered with a
consistent resin cement layer; (B) Scanning electronic microscope image of a Group 1 extracted post. The resin cement
layer covers the coronal and middle thirds of the post; a very large void can be observed in the apical third. This fault is
probably due to the fact that the lentulo was not used.
covered the apical and middle thirds of the posts
(Fig. 3A). Large areas with many fractured resin
tags were found on the post surface (Fig. 3B).
Some of the dentinal tubules that were visible on
the dentinal walls appear to be obstructed by resin
material (Fig. 4A), while others were open (Fig. 4B).
It was possible to see some glass fibres that
probably came off the post surface and were
trapped in the cement residue (Fig. 5A–B).
Discussion
According to the results of this study, dual curing
of the All Bond 2CRelyX ARC system seems to be the
most appropriate method since it allows even those
areas which would not otherwise be reached by light
to be cured. Consequently, cement acquires a
higher conversion rate even in the most apical
areas with an improvement of the mechanical
Figure 3 (A) Scanning electronic microscope image of a Group 1 extracted post. Several small bubbles are present in
the cement layer. They were probably due to a persistent humidity along the canal root walls during the cementation
process; (B) Scanning electronic microscope image of a Group 2 extracted post. Several short resin tags, which were
probably fractured during the mechanical test, can be observed on the post surface.
Translucent fiber post cementation
633
Figure 4 (A) Scanning electronic microscope image showing the canal wall of a Group 2 specimen, which was
longitudinally sectioned and then treated using EDTA. A homogenous adhesive layer covers the dentinal surface and fills
the dentinal tubules; (B) Scanning electronic microscope image showing the canal wall of a Group 2 specimen, which was
longitudinally sectioned and then treated using EDTA. The dentine surface is not covered by any adhesive material and
most tubules appear to be open.
properties. This, however, involves a higher contraction stress and a higher modulus of elasticity as
well as the possibility of a reduced bonding and the
consequent loss of the apical seal. In addition,
longer preparation times are required and it is
generally difficult to completely fill the apical third
of the canal root. Last but not least, the manual
mixing procedure, which is necessary in the case of
two-paste systems, could produce bubbles.
On the other hand, in apical areas, the incomplete curing of the ExciteCTetric Flow system (the
light radiation transmitted by the post is moderate
and decreases as depth increases) could improve
the post adaptation due to a lower contraction
of the cement. Moreover, single-paste systems
reduce the risk of bubbles to a greater extent
than two-paste systems and allow the use of
flowable composites, which are easier to apply
inside the root canal, thus reducing the formation
of voids.
The pull-out test showed that the bond strength
in the specimens prepared using the EXCTC lightcuring system was only slightly inferior to that
recorded in the specimens prepared with
the ABCRX dual cured system. However, no
statistically significant differences were found
between the two groups.
SEM observations of longitudinal sections and of
extracted posts confirm a good bond both between
the dentine and the cement as well as between the
cement and the post regardless of the curing
method employed.
Contraction stress induced by resin cement
curing should also be taken into account. The
composite flow is hindered by the confinement of
the material bonded to the tooth in the pre-gel
phase, and, as a result, contraction manifests
itself as stress at the adhesive interface. There is
a relationship between the configuration of the
cavity and stress development. If the composite can
shrink without any restriction within a cavity, no
problems may be expected. When the contraction is
hindered in three dimensions, the stress will be less
compensated for by flow.6 Feilzer et al.7 developed
the concept of the C-Factor, the ratio of the free
and restrained composite surface area of a dental
restoration. In general, an increasing rate of
shrinkage stress development with an increasing
C-value leads to a decreasing flow capacity.7
Whereas the C-factor typically varies from 1 to 5
in intracoronal restorations,7 it exceeded 200 in the
cementation of endodontic posts to root canal
dentine (the worst case scenario).8 Therefore,
shrinkage stress in the confinement of the intact
Figure 5 Scanning electronic microscope images showing the dentine-cement interface of a Group 1 specimen that
was longitudinally sectioned and then treated using ortophosphoric acid and sodium hypochlorite (c: composite; d:
dentine). Cement residue can be observed on the dentinal wall (A). The cement residue contains glass fibres (arrow) that
probably came off the post surface (B).
634
root canal may exceed the cement–dentine bond
strength, causing debonding of the cement from the
dentine. The composition of the material is a factor
that can influence the amount of shrinkage produced after polymerization. In fact, according to
Hooke’s rule, resin cements with a low modulus of
elasticity produce low contraction stress.
As a result, in order to evenly distribute the
stress generated by functional load, minimize the
contraction stress and ensure a good bond between
dentine and post, the composite cement should
have a low conversion rate and, consequently, a low
modulus of elasticity while maintaining a good
mechanical resistance.
When a post restored tooth undergoes stress, the
most rigid element of the tooth shifts the mechanical stress to the most flexible one9; this may result
in a root fracture or debonding of the post. For this
reason, in order to obtain a homogenous tooth
structure, the various restorative materials used
should have a similar modulus of elasticity, which
should also be approximately the same as dentine.
It is therefore advisable to use cement with a low
modulus of elasticity, which would not negatively
affect the fracture resistance of the restored tooth.
The presence of voids or bubbles in the cement
should also be taken into account. These faults
reduce the modulus of elasticity and create a larger
free contraction surface area thus contributing to
reduce the contraction stress of the composite.10,11
However, due to their unpredictability, voids and
bubbles cannot be considered an advantage. In
addition, voids impede an appropriate cementation
of the post, thus causing its debonding.
Since the presence of coronal dentine can
increase retention to a considerable degree,8 the
bond strength obtained using light-cure systems
could guarantee good clinical success to restore
teeth that retain a significant quantity of coronal
tissue.
Conclusions
Currently, dual cured systems still represent the
most reliable choice for post cementation. On the
other hand, light cure systems may allow an
improved apical seal as well as a more even
distribution of the stress along the canal walls.
Since light cure systems do not require mixing
L. Giachetti et al.
and can be cured at any time they undoubtedly
represent a considerable advantage for clinicians.
Acknowledgments
The authors wish to thank Mr Mauro Mauri, Department of Dentistry, University of Florence, and
Mr Elia Ladani for their technical assistance. This
work was partially supported by Leone S.p.a.
Firenze, IT.
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