1. VOLUME 43 1 2012 e1
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function.1,2
Fiber posts that are used after
endodontic treatment have some addition-
al advantages, including biocompatibility,
mechanical strength, resistance to corro-
sion, improvement of light transmission, and
the optical effects of esthetic restorations.3
An important characteristic of fiber posts
is a modulus of elasticity similar to dentin,
resin cement, and resin core materials4
so that the occlusal loads can be better
distributed along the root.5
In addition,
the restoration of endodontically treated
teeth with metal-free materials eliminates
the potential hazards of corrosion and aller-
gic hypersensitivity.6
Fiber-reinforced posts
also have the advantage of easy removal if
with prefabricated fiber post-and-core sys-
tems has been widely accepted as a treat-
ment option that offers both esthetics and
1
Associate Professor, Department of Prosthodontics, Faculty of
Dentistry, Ondokuz Mayıs University, Samsun, Turkey.
2
Assistant Professor, Department of Prosthodontics, Faculty of
Dentistry, Ondokuz Mayıs University, Samsun, Turkey.
3
Research Assistant, Department of Prosthodontics, Faculty of
Dentistry, Ondokuz Mayıs University, Samsun, Turkey.
4
Private Practice, Ankara, Turkey.
5Professor, Department of Prosthodontics, Faculty of Dentistry,
Selçuk University, Konya, Turkey.
Correspondence: Dr Ahmet Umut Güler, Ondokuz Mayıs
University, Faculty of Dentistry, Department of Prosthodontics
55139, Kurupelit, Samsun, Turkey. Email: auguler@omu.edu.tr
Effects of different acids and etching times on the
bond strength of glass fiber–reinforced composite
root canal posts to composite core material
Ahmet Umut Güler, DDS, PhD1
/Murat Kurt, DDS, PhD2
/Ibrahim Duran, DDS3
/
Altay Uludamar, DDS, MSc, PhD4
/Ozgur Inan, DDS, PhD5
Objective: To investigate the effects of different acids and etching times on the bond
Method and Materials:
in the other groups were acid etched with 35% phosphoric acid and 5% and 9.6% hydro-
polytetrafluoroethylene mold was placed around the treated posts and filled with dual-cure
After 24 hours of water storage, the specimens were sectioned perpendicularly to the
bonded interface under water cooling to obtain 2-mm post-and-core specimens. Eight
specimens were made from each group. Push-out tests were performed at a crosshead
speed of 0.5 mm/min using a universal testing machine. Data were analyzed by one-way
α Results: The
P
the highest bond strength values (P Conclusion: -
ing procedures tested showed significantly increased bond strength when compared with
the control group. Acid-etching with 5% hydrofluoric acid and 9.6% hydrofluoric acid for 2
minutes and with 35% phosphoric acid for 3 minutes (groups H5-120, H9-120, and P-180,
composite core material. Although the bond strength was increased by prolonged acid
(Quintessence
Int 2012;43:e1–e8
Key words: acid etching, bond strength, composite core material, etching time,
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2. e2 VOLUME 43 1 2012
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Güler et al
endodontic retreatment is required. These
systems can reduce the incidence of nonre-
trievable root fractures when compared with
prefabricated metallic posts or conventional
cast posts.9,10
If the bonding of the interface is poor,
debonding and/or fracturing of the core
and post can occur.11
A good adaptation
and reliable bonding between the post
surface and core buildup material must be
achieved.12
-
cal studies of fiber-based post systems that
present clinical failure rate. Glazer13
pub-
lished results of a study in which the results
for 52 teeth in 42 patients were analyzed.
-
cal pathology, while an additional two were
mechanical failures of the restoration. A
published prospective investigation14
dem-
onstrated a failure rate of glass fiber posts
of 12.8% after 24 months. The most frequent
types of failure were post fractures or loss
of retention. A retrospective study evaluat-
ing 1,304 teeth restored with three different
types of fiber posts from 1 to 6 years without
recording the loss of coronal tooth structure
reported a failure rate of 3.2%.15
smooth surface that limits mechanical inter-
is often recorded at the post-composite
guarantee a strong and durable fiber post-
to-composite bond.16
Therefore, several
methods for conditioning the post surface
were investigated, including infiltration of
bonding, silanization followed by bonding
of the post surface,11,18–21
airborne-particle
abrasion with corundum,20–23
tribochemi-
5,23
acid etching using
5% hydrofluoric acid followed by silani-
zation,5,23,24 and surface activation using
acetone, chloroform, hydrogen peroxide, or
hydrochloric acid followed by silanization.24
These treatments result in surface micro-
between the two surfaces and/or exposure
of the fiber by removal of the matrix, per-
mitting silanization with a silane coupling
agent. Some of these treatments may cause
detrimental effects when the treatment is
performed over a long period of time, such
as etching with hydrofluoric acid or blasting
with aluminum oxide particles.25
Mechanical
pretreatment of the glass fiber–reinforced
only is the matrix removed, but the fibers
might also be damaged, depending on the
particle size and abrasion time.26
To optimize the bonding of resin cements
the posts have been proposed, such as
etching with phosphoric or hydrofluoric
acid. The effect of etching varied depend-
ing on the acid-etching time and acid type.
The aim of this study was to investigate
the effects of different acids and etching
times on the bond strength of glass fiber–
reinforced composite root canal posts to
composite core material. It was hypoth-
esized that the bond strength achieved at
the post-core interface was affected by the
various acids and acid-etching times.
METHOD AND MATERIALS
Twenty-six fiber-reinforced composite root
being a control group that received no
The specimens in group P-30 were acid
etched with 35% phosphoric acid gel (Ultra-
30 seconds, the specimens in group P-60
were acid etched for 60 seconds, the speci-
mens in group P-120 were acid etched for
2 minutes, and the specimens in group
P-180 were acid etched for 3 minutes. After
the acid-etching procedures, all specimens
were rinsed with water for 30 seconds and
dried with oil-free air spray for 30 seconds.
The specimens in group H5-30 were
acid etched with 5% hydrofluoric acid gel
-
mens in group H5-60 were acid etched
for 60 seconds, the specimens in group
H5-120 were acid etched for 2 minutes, and
the specimens in group H5-180 were acid
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3. VOLUME 43 1 2012 e3
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Güler et al
etched for 3 minutes. After the acid-etching
procedures, all specimens were rinsed with
water for 30 seconds and dried with oil-free
air spray for 30 seconds.
The specimens in group H9-30 were
acid etched with 9.6% hydrofluoric acid
in group H9-60 were acid etched for 60
seconds, the specimens in group H9-120
were acid etched for 2 minutes, and the
specimens in group H9-180 were acid
etched for 3 minutes. After the acid-etching
procedures, all specimens were rinsed with
water for 30 seconds and dried with oil-free
air spray for 30 seconds.
-
allel in the coronal and tapered in the apical
part of its design. A polytetrafluoroethylene
tapered part of the posts. The tapered sec-
tion was placed in the PTFE mold, while
the parallel section was used for the core
foundation to simplify the calculation of
the surface area. Only the upper cylindric
the larger diameter of 2 mm was used. It is
ideal for the post diameter to be constant
throughout the post length. A cylindric PTFE
mold was placed around the coronal part of
Photoactivation was performed by using
a light-emitting diode unit with 1,550 mW/
cm2
The tip of the light unit was initially placed
at the top of the PTFE mold for 20 seconds
and then through the mold on each side for
20 seconds, for a total exposure of 60 sec-
-
tilled water, the specimens were attached
to the arm of a low-speed saw (IsoMet,
the bonded interface into 2-mm post-and-
core segments under water cooling. Four
segments were obtained from each post-
and-core specimen—each group of eight
post-and-core specimens provided a total
of 104 post-and-core segments. The exact
was measured using a digital micrometer
was calculated using the formula: A = 2r
× ∏ × h where r is the post radius, ∏ is the
constant 3.14, and h
coronal sections were used for core foun-
dations, the bonding area was equal for all
post segments and calculated as 2 × 3.14
× 1 × 2 = 12.56 mm2
.
Push-out tests were performed at a
crosshead speed of 0.5 mm/min using a
loaded with a 1.5-mm–diameter cylindric
stainless steel plunger. The tip of the equip-
ment was positioned to contact only the
of extrusion of the post segment from the
Push-out bond strength values in MPa were
then calculated by dividing this force by the
bonded area of the post segment.
using statistical software (SPSS for Windows
effect of acid-etching procedures on bond
core material. The means were then com-
-
α
each group was prepared and evaluated by
observed for surface irregularity under a
scanning electron microscope at 250× and
500× magnification.
Tip of
apparatus
FRC Postec Plus
MultiCore Flow
Fixation apparatus
of sample
Space for displaced
filling material
F
Fig 1 Schematic drawing of push-out test of the
specimens.
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Güler et al
RESULTS
The bond strengths were shown to be sig-
P <
standard deviations, and group differences
for the 13 groups are shown in Table 2.
In the study groups, the lowest bond
Group P-30 demonstrated a high-
P -
cant difference was observed among group
P
groups demonstrated higher bond strength
values when compared with group P-30
-
ference was observed among group H5-60
P
groups demonstrated higher bond strength
values when compared with the above
mentioned groups (P
significant difference was observed among
(P
the highest bond strength values in this
study. The differences among all groups
are listed in Table 2.
The SEM studies revealed that the
surface irregularities of the glass fiber–
reinforced composite root canal post corre-
sponded to the results of the bond strength
DISCUSSION
Within the limitations of the present study,
it can be concluded that our hypothesis
was confirmed—that the bond strengths of
significantly affected by the investigated
acid-etching procedures.
Flowable and hybrid composites have
been reported to have good adaptation at
-
ical properties of flowable composites are
generally inferior to those of conventional
composites. Therefore, a dual-cure com-
also recommended as an adhesive luting
agent and core buildup material was used
in the present study.
Table 1 One-way ANOVA table for study groups
Variable (source) df Sum of squares Mean squares F P
12 88.036 .001*
Within groups 91 51.405 0.565
Total 103
df, degrees of freedom. *Significant difference at P < .05.
Table 2 Mean bond strengths (MPa),
standard deviation (SD) values,
and group differences for the
study groups (each n = 8)
Group Mean (MPa) SD Difference*
12.51 a
P-30 13.85 .95 b
H5-30 15.38 .99 c
H9-30 15.64 .88 c
P-60 c
P-120 16.14 .43 c
H5-60 .83 d
H9-60 .59 d
H5-180 .64 d
H9-180 18.10 .53 d
H5-120 20.31 .66 e
H9-120 20.55 .54 e
P-180 .94 e
*Different letters indicate dissimilarity of groups (P
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5. VOLUME 43 1 2012 e5
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Güler et al
A number of studies focused particularly
on the possibility to improve adhesion at the
fiber post–composite interface through vari-
ous treatments of the post surface.1,6,28–30
Mechanical and chemical treatments of
the post surfaces and changes in the
post matrix composition seemed to affect
the bond strength of resin materials to
been evaluated to dissolve the epoxy resin
matrix or methacrylate-based resin matrix
and expose fibers and filler particles so that
silanization could be effective.
Use of hydrogen peroxide24 and differ-
ent chemical agents (followed by silaniza-
resin core materials with dissolving of the
resin matrix of the post’s surface and con-
comitant exposure of undamaged fibers.31
The use of hydrofluoric acid and tribo-
chemical coating followed by silanization
resulted in damaged fibers at the surface of
24,32
Different concentrations and etching
times of acid agents were used in the
studies investigating the effect of surface
with hydrofluoric acid5,24,33,34
and phosphor-
ic acid5,35 since clear information regarding
the most appropriate etching conditions is
In the present study, 35% phosphoric
acid and 5% and 9.6% hydrofluoric acid
Fig 2 (right) SEM images of untreat-
ed specimen (control) at 250× magni-
fication. The undamaged glass fibers
and resin matrix around the fibers can
be seen (a, glass fiber; b, resin matrix).
Fig 3 (below) SEM images of treated
specimens at 500× magnification.
The cracks and damages on the glass
fibers and dissolved resin matrix
around the remaining fibers due to
the different acid treatments can be
seen.
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6. e6 VOLUME 43 1 2012
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Güler et al
gel with four different etching times (30,
evaluate time and concentration effects on
the bond strength of glass fiber–reinforced
composite root canal posts to composite
core material. Even though there is no sta-
tistical significance between 5% and 9.6%
hydrofluoric acid treatments for all etching
times, the hydrofluoric acid groups showed
greater bond strength values than phos-
phoric acid groups with the exception of the
180-second etching time. According to the
images obtained with SEM, the post surface
etched with phosphoric acid was not modi-
epoxy matrix and fibers was observed on
the surfaces etched with hydrofluoric acid
This is a minority finding: The study
indicated that conditioning with hydroflu-
oric acid seemed to be very aggressive
5
Acid-
etching treatment resulted in roughness
of the post surface, which might have
the luting cement and post surfaces. The
authors attributed the roughness to frac-
tured glass fibers and partial removal of the
epoxy matrix.35
The bond strength values of the phos-
phoric acid groups increased with longer
etching times. This was also similar for
the 30- and 60-second etching hydroflu-
oric acid groups. Hydrofluoric acid–treated
groups for 120 seconds showed higher
bond strength values than those of groups
treated for 180 seconds.
Schmage et al stated that previously
performed pretests with 120-second hydro-
fluoric acid etching had shown that the
described effect of increased surface tex-
ture could be observed with increased
etching time.36
However, any conditioning
method including prolonged acid etch-
ing would reduce the post diameter and
cause misfitting posts with a wider cement
gap, resulting in lower retentive bond
strengths.26,36
while other chemical conditioning methods
affect only the glass fibers.18
This is due to
the corrosive effect of hydrofluoric acid on
the glass phase of a ceramic matrix. These
findings were confirmed when hydrofluoric
acid was used for conditioning methacry-
late-based fiber posts. Despite the improve-
ment in post-to-composite bond strength, a
noteworthy surface alteration ranging from
fiber layer was detected.16,24
Although the bond strength was increased
with longer etching times, the microstructure
thus also damaging its physicomechanic
properties. Hence, even though this method
of conditioning improved the bond strength,
other studies to evaluate the effects of this
surface treatment on the physicomechanic
-
bility and integrity of the posts.
The current study is limited to one
better understanding of the effects of dif-
ferent acids and acid-etching times on the
bond strength of core buildup materials to
-
ating the effects of different post and core
materials using artificial aging methods are
recommended. To assess long-term dura-
bility and for improved simulation of the in
vivo environment, further treatments such
as mechanical loading and thermal cycling
could be applied.
CONCLUSION
Within the limits of the present study, it was
concluded that both the different acids
and acid-etching times significantly influ-
enced the push-out bond strength between
the composite core buildup material and
P
posts, all acid-etching procedures tested
significantly increased bond strength when
compared with the control group. Although
the bond strength was increased by pro-
longed acid etching, the microstructure of
The use of acid treatments seems to be
more practical than the other applications.
However, type and concentration of acid
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7. VOLUME 43 1 2012
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Güler et al
gels and application time is an essential
factor to achieve optimal bond strength
application. Additionally, acid etching the
need for additional chairside treatments.
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