Q U I N T E S S E N C E I N T E R N AT I O N A L
GENERAL DENTISTRY Effect of post diameter and cement thickness on bond strength of fiber posts Hesam Mirmohammadi, DDS, MSc, PhD1/Elie Gerges, DDS, MSc2/Ziad Salameh, DDS, PhD3/Paul Rudolf Wesselink, DDS, MSc, PhD4
Objective: This study evaluated the effects of different post diameter and oversized post spaces on the push-out bond strength of a fiber post to dentin. Method and Materials: Fifty extracted human maxillary central incisors and canines were divided into five groups and submitted to the push-out test (0.5 mm min-1). Groups 1, 2, and 3 were restored using a fiber post size that was identical to the drill size (sizes 1, 2, and 3, respectively), and groups 4 and 5 were both prepared with drill size 3, and restored using the size 2 and 1 fiber post, respectively. The fiber posts were cemented using self-adhesive dual-polymerized resin cement (RelyX Unicem). The data were analyzed using a one-way analysis of variance (ANOVA) and the Tukey test. Results: There were no significant differences in the mean values for push-out bond strength between groups with different post diameters (P > .05). However, the push-out bond strengths were significantly different between groups with different cement thicknesses, and group 4 yielded the highest bond strength (11.7 ± 0.4 MPa). For all groups, the apical third had the lowest bond strength value (P < .05). Conclusion: The highest push-out bond strength values were obtained when one incremental oversized post space was used. Clinically, fiber post space has to provide an optimum cement thickness (around 120 μm) for adequate cementation. (Quintessence Int 2013;10:801–810; doi: 10.3290/j.qi.a30179)
Key words: bond strength, cement thickness, fiber post, push-out, self-adhesive cement
Endodontically treated teeth that have
Adhesive resin composite cements,
reduced coronal tooth structure require a
which have an elastic modulus in the same
radicular post to retain the restoration of the
range as both the post and dentin, are rou-
tooth. Recently, the increasing demand for
tinely used to lute the post into the root.
esthetic posts and cores has led to the
Increased post retention and fracture resis-
development of metal-free post and core
tance and reduced microleakage have
systems, which serve as alternatives to cast
been reported for posts cemented with
post and core systems and metal posts.1-3
composite resin cements, as compared to conventional luting systems.4,5 However, the
1
Researcher, Department of Cariology Endodontology Pedo-
most common cause of failure in previous
dontology, Academic Centre for Dentistry Amsterdam (ACTA),
studies was due to pull-out of the cement-
Universiteit van Amsterdam and Vrije Universiteit, Amsterdam,
post-restoration assembly, which is caused
The Netherlands; and Assistant Professor, Department of Re-
by debonding between fiber post and resin
storative Dentistry, School of Dentistry, Esfahan University of Medical Sciences, Esfahan, Iran. 2
Assistant Professor, Department of Prosthodontics, School of Dentistry, Lebanese University, Beirut, Lebanon.
3
Associate Professor, Department of Prosthodontics, School of
cement and/or between resin cement and root canal dentin interface and inadequate bond strength.6,7 Thus, there is a need to investigate and improve the adhesion
Dentistry, Lebanese University, Beirut, Lebanon.
between the fiber post, resin cement, and
Em Professor, Department of Cariology Endodontology Pedo-
root canal dentin interfaces.
4
dontology, Academic Centre for Dentistry Amsterdam (ACTA),
The actual bond strength at the post-
Universiteit van Amsterdam and Vrije Universiteit, Amsterdam,
cement-root interface is influenced by many
The Netherlands. Correspondence: Dr S. Hesam Mirmohammadi, ACTA, Department of Cariology Endodontology Pedodontology, Gustav
factors, including the type of conditioning agent and the accompanying cement used,
Mahlerlaan 3004, 1081 LA Amsterdam, The Netherlands. Email:
the type of post, the cavity configuration of
[email protected]
the root canal, and the anatomic differences
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
801
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
in density and orientation of the dentinal
increase in retention when the diameter of
tubules at different levels of the root canal
the metallic posts was increased from
area.8-13 Furthermore, difficult moisture con-
0.5 mm to 1.1 mm at the apex. Moreover,
trol, polymerization stress inside of the root
when the length was increased from 9 mm
canal, and visualization difficulties can
to 15 mm, there was a 100% increase in
affect the bonding procedures as well.14,15
retention. Many in vitro studies suggested
Various adhesive systems and accom-
the influence of different resin cement thick-
panying resin cements have been used that
nesses on bond strength of fiber posts.27,29-
are able to remove or condition the smear
32
layer prior to luting fiber-reinforced compos-
offer a consensus as to the ideal thickness
However, to date, the literature does not
ite resin posts into root canals. Zicari et al16
of the resin cement or to the ideal fiber post
suggested that RelyX Unicem (RX) had a
diameter and length needed to improve
high tolerance for moisture because water
retention. As debonding is the most fre-
was formed during the neutralization reac-
quent cause of failed bonded fiber posts, a
tion of the phosphoric acid methacrylate,
better understanding of the factors that
basic fillers, and hydroxyapatite, which was
influence bond strength is required.
considered responsible for the greater
The aim of the present study was to
bond strength values in the apical sections
evaluate the effect of oversized post spaces
of the roots. Farina et al 17 also demon-
and the diameter of the posts on the push-
strated increased bond strength using RX
out bond strength of a fiber post. The null
for the cementation of glass fiber posts.
hypothesis was that post diameter and the
Pirani et al18 reported that the retentive
width of the gap between the root canal and
strength of a bonded post could be due to
post would have no influence on the push-
the combined result of micromechanical
out bond strength of the fiber posts.
interlocking, chemical bonding, and sliding friction. Recently, Dimitrouli et al19 suggested that the use of self-adhesive resin
METHOD AND MATERIALS
cement (SA) could provide bond strength values comparable to bond strength values
Fifty recently extracted human maxillary
of the etch-and-rinse systems. It has also
canines and central incisors (mean length
been shown that a modified application
23 ± 2 mm), which were stored in an aque-
procedure using SA in combination with
ous solution of 0.525% chloramine-T at 4°C
single-step self-etch dentin adhesives did
and used within 2 weeks of extraction, were
not improve the bond strength of the fiber
selected for this study. External debris was
post when compared to conventional SA.20
removed from the teeth using an ultrasonic
Although a significant body of informa-
scaler (Parkell Electronics Division). Radio-
tion has been published regarding the
graphs were used to eliminate specimens
retentive properties of prefabricated post
with irregular canals, pronounced canal
systems cemented with resin cements,21-24
curvatures, or evidence of internal resorp-
limited information is available regarding
tion. Teeth with roots shorter than 10 mm or
the effect of cement thickness and post
with defects or cracks were excluded. Teeth
diameter on the retention of fiber posts. On
were decoronated 2 mm coronally to the
the other hand, retrospective clinical stud-
most incisal point of the cementoenamel
ies have demonstrated that debonding
junction (CEJ) using a low-speed diamond
occurs
saw (Isomet 2000, Buehler) under copious
with
large
cement
film
thick-
nesses.25,26 One study also suggested that
water cooling.
resin cement film thickness influences the
Root canal preparation was performed at
pull-out strength of the fiber posts and
a working length of 0.5 mm from the apical
reported that the greatest bond strength
foramen (defined visually) using rotary
values were obtained when oversized post
instruments (FlexMaster, VDW) and a step-
spaces were used.27
back technique. Canals were prepared to
A previous study suggested that post
the ISO file size of 40 with a 6-degree taper.
diameter could affect retention of the metal
The root canals were irrigated between
posts. Nergiz et al 28 reported a 60%
analyses, and the canal spaces remained
802
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
filled with irrigation solution (5% NaOCl) dur-
a 22-gauge needle-irrigating tip (Ultradent)
ing analyses (approximately 10 ml per
and dried with sterile paper points. A self-
tooth). The root canals were rinsed with 17%
adhesive cement (RelyX UniCem Aplicap
ethylenediaminetetraacetic acid (EDTA) and
cement, 3M ESPE) was used for luting of the
final irrigation with 0.9% saline solution was
different posts. The capsule of the cement
performed. Root canals were dried with
was first activated for 2 to 4 seconds and
paper points (Coltene Whaledent), and
then mixed (Capmix, 3M ESPE) for 15 sec-
obturated with a thermoplasticized inject-
onds. The cement (2 to 3 mm) was dis-
able gutta-percha (Obtura II, Model 823-
pensed from an auto-mixing syringe that
600, Obtura) using AH Plus (Dentsply) as a
had been placed in the canal spaces with
canal sealer. The teeth were then stored in
an elongation tip (30 gauge), according to
water for 24 hours at 37°C. The gutta-per-
the manufacturer’s instructions.
cha was removed with a size 10 electrically
was introduced and held under digital pres-
heated endodontic plugger (Hu-Friedy).
sure. The excess cement was removed and
Three drill diameters (0.7 to 1.3 mm, 0.8 to
the specimen was left at room temperature
1.6 mm, and 0.9 to 1.9 mm) were randomly
for setting of the cement. The different post
combined with three fiber post sizes (RelyX
sizes used for each group were as follows:
fiber post, sizes 0.7 to 1.3 mm, 0.8 to
•
The post
Group 1: The canals for this group were
1.6 mm, and 0.9 to 1.9 mm; 3M ESPE) to
prepared with a size 1 low-speed post
yield five groups of 10 teeth each (Table 1).
drill (apical 0.7 mm, coronal 1.3 mm
Each drill was used to prepare the post
diameter) in combination with a size 1
space for 10 teeth and was then discarded.
(0.7 to 1.3 mm diameter) fiber post, as
To ensure standardization of post inser-
provided by the manufacturer (control
tion and removal, all post-space preparations were performed by the same oper-
group). •
Group 2: This group received the same
ator using a dental surveyor (Fedi 18
procedure as group 1, but the size 2 drill
Mariotti). The roots were transferred into an
(0.8 to 1.6 mm diameter) was used in
acrylic mount using an autopolymerizing
combination with size 2 (0.8 to 1.6 mm
resin (LD Caulk Division, Dentsply) that extended 1 mm below the buccal side of
diameter) fiber posts. •
Group 3: The group received the same
the CEJ. Immediately after the acrylic resin
procedure as group 1, but the size 3 drill
reached its doughy stage, the specimens
(0.9 to 1.9 mm diameter) was used in
were detached from the surveyor and
combination with size 3 (0.9 to 1.9 mm diameter) fiber posts.
placed in a cool water bath. Subsequently, the mounted specimens were secured in the
•
Group 4: This group received a similar
dental surveyor, and the coronal 9 mm of
procedure to group 3 (0.9 to 1.9 mm drill
each root canal was prepared with a drill of
diameter), but size 2 (0.8 to 1.6 mm
the same size to leave a minimum apical seal of 4 mm for the gutta-percha. Following
diameter) fiber posts were used. •
Group 5: The group received a similar
the preparation of the post space, the
procedure to group 3, but size 1 (0.7 to
canals were rinsed with saline solution using
1.3 mm diameter) fiber posts were used.
Table 1
Group
Distribution of specimens according to drill diameter, post diameter, and cement thickness Drill diameter (mm)
Post diameter (mm)
Approx. cement thickness (μm) 20
Group 1
0.7–1.3
0.7–1.3
Group 2
0.8–1.6
0.8–1.6
20
Group 3
0.9–1.9
0.9–1.9
20
Group 4
0.9–1.9
0.8–1.6
120
Group 5
0.9–1.9
0.7–1.3
210
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
803
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
Preparation of specimens for the push-out bond strength test
Failure mode analysis
After 24 hours of water storage at 37°C, the
assessed initially using a stereomicroscope
roots were cut into three 2-mm-thick slices
(Swift Stereo Eighty microscope, Swift
perpendicular to the long axis of the tooth
Instruments International) and then at a
using the Isomet saw under conditions of
higher magnification (500× magnification)
water cooling. The first cut was initiated
using scanning electron microscopy (SEM)
2 mm below the CEJ and was followed by
to determine the mode of failure, which was
two additional cuts that were 2 mm thick.
classified as follows:
Thus, the slices represented coronal, mid-
•
After the push-out test, the specimens were
dle, and apical sections of the post-space
post and the cement without visible
preparation. A 1-mm-thick slice was then removed from each sample using the same
cement around the post •
saw. These slices were fixed onto slides
Mode II: adhesive failures between the cement and the root dentin with cement covering the post surface
and polished up to 600 grit. The specimens were then subjected to a push-out test
Mode I: adhesive failures between the
•
Mode
III:
mixed
failures
(adhesive
using a universal testing machine (Accu-
between the cement and dentin and
force Elite Test Stand, Ametek, Mansfield &
cohesive in the resin cement) with
Green Division) and a cross-head speed of 0.5 mm/min. Due to the tapered design of the posts, three different sized punch pins
cement covering the post surface •
Mode IV: cohesive failures inside the dentin.
(0.5 mm, 0.8 mm, and 1.2 mm) were used
For SEM evaluation, the samples were ultra-
for the push-out testing.33
sonically cleaned using alcohol 90%, air-
The maximum stress was calculated by
dried, mounted on a metallic stub, gold
dividing the recorded peak load by the inter-
sputtered (JEOL, Fine Coat, Ion Sputter
facial area (SL) of the post fragment. To cal-
JFC-1100), and then observed under SEM
culate the exact bonding surface, the tapered
(XL 20; Philips).
design and the respective portions of the posts were considered. Therefore, each
Cement thickness evaluation
specimen was measured using a micrometer
Before push-out bond strength testing, two
screw (Ultra-Cal IV, Ted Pella), and the SL
sample specimens from the second apical
was calculated using the following formula:
slices of each group were evaluated by SEM
SL = π (R + r) [h2 + (R − r)2]0.5
(500× magnification) to compare the cement
where π = 3.14, R = coronal post radius,
thicknesses between groups. As the cement
r = apical post radius, and h = specimen
thickness surrounding the post was variable,
slice thickness.
the lowest thickness was reported as the cement thickness for each group (see Fig 1).
FP 210 μm
FP 40 μm
D
Rc
Rc 120 μm
FP
20 μm D a
Rc b
D
c
Figs 1a to c SEM images comparing the cement thicknesses across different groups (D, dentin; FP, fiber post; Rc, resin cement). (a) The image represents the cement thickness in groups 1, 2, and 3 showing the 20 μm thickness at the thinnest part of the resin cement. (b) The image indicates the cement thickness in group 4 (one oversized post space), which represents a cement thickness of 120 μm. (c) An image of the specimen from group 5 (two oversized post spaces) showing a cement thickness of 210 μm. The arrows indicate air bubbles, which were larger in this group.
804
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
Table 2
Mean values for push-out bond strength (MPa) by group
Bond strength (mean ± SD)
Group 1
Group 2
Group 3
Group 4
Group 5
9.2b ± 1.00
10b ± 0.7
9.5b ± 0.6
11.7a ± 0.4
9.5b ± 0.63
a,b
The same lower case letters indicate no significant difference between each group (P < .05).
Statistical analysis After performing the tests of normality of data
Table 3
distribution and homogeneity of group variances, a one-way ANOVA was performed to examine the effect of post diameter on interfacial strength for groups 1, 2, and 3 and to assess the effect of cement thickness on
Mean values for push-out bond strengths by root section (MPa) Root section
Group Group 1
post-hoc multiple comparisons were performed using the Tukey test (P < .05).
Group 2
For the variable regional bond strength, identical statistical tests were performed, although a Welch test was used for group 5
Group 3
because the variances were not homogenous. Therefore, a post-hoc analysis was
N
10.266 ± 0.931
20
Middle
9.179a ± 1.265
20
Apical
7.962b ± 0.927
13
Coronal
10.366a ± 0.619
20
Middle
10.685a ± 1.2
20
b
Apical
8.524 ± 0.975
14
Coronal
9.825a ± 0.839
20
Middle
9.826a ± 0.835
20
Apical
performed using Dunnett’s C test. The
a
Coronal
interfacial strength for groups 1, 4, and 5. For comparisons with significant differences,
Push-out bond strength (mean ± SD)
b
8.358 ± 0.570
12
Coronal
13.201a ± 0.673
20
region of each group was measured in
Middle
12.577b ± 0.601
20
order to find the mean push-out bond
Apical
9.431c ± 0.643
13
mean between coronal, middle, and apical
strength for each group. All statistical analy-
Group 4
Group 5
ses were performed using statistical soft-
Coronal
10.639a ± 0.547
20
Middle
9.832b ± 0.490
20
Apical
8.056c ± 0.839
13
ware (SPSS Windows Standard Version 15.0; SPSS). a,b
The same lower case letters indicate no significant dif-
ference within each group (P < .05).
RESULTS Push-out test
groups demonstrated significantly higher
The overall mean bond strength values and
bond
standard deviations for each group are pre-
(P < .05, Table 3). By optical microscopy
strengths
than
the
apical
third
sented in Table 2. The results indicated that
and SEM, most of the failures (approxi-
there were no significant differences in
mately 59% to 62%) were found to occur
mean push-out bond strength between
between the post and the resin cement
groups
diameters
without any visible cement around the post
(P < .05; group 1, 9.2 ± 1 MPa; group 2,
(mode I). Group 4 was the exception, as
10 ± 0.7 MPa; group 3, 9.5 ± 0.6 MPa).
this group demonstrated 45% mode I failure
However, the push-out bond strengths
and 39% mode III failure (Table 4).
with
different
post
between groups with different cement thicknesses (groups 3, 4, and 5) were found to
Microscopic observation
be significant, and group 4 yielded the
An analysis of the specimens under SEM
highest bond strength (11.7 ± 0.4 MPa).
revealed that the cement thicknesses were
Regarding the variable root regions, the
of the same order for groups 1, 2, and 3
coronal and middle thirds from each of the
(approximately 20 μm), whereas those of
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
805
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
Table 4
Distribution and percentage of failure modes following push-out test
Failure mode
Group 1
Group 2
Group 3
Group 4
Group 5
Mode I
33 (62%)
33 (61%)
31 (59%)
24 (45%)
32 (61%)
Mode II
6 (11%)
7 (13%)
6 (12%)
5 (10%)
7 (13%)
Mode III
10 (19%)
11 (20%)
12 (23%)
21 (39%)
10 (19%)
Mode IV
4 (8%)
3 (6%)
3 (6%)
3 (6%)
3 (6%)
53 (100%)
54 (100%)
52 (100%)
53 (100%)
52 (100%)
Total
groups 4 and 5 were significantly larger at
clinical success on the luting procedure. RX
approximately 120 μm and 210 μm, re-
is recommended for the cementation of the
spectively (Fig 1). Residual gutta-percha
fiber post; this newly developed self-adhe-
was found in some sections, which were
sive and dual-cure resin cement does not
associated with areas of debonding at the
require conditioning or bonding of the tooth
interface around the gutta-percha.
structure, which therefore reduces the highly technique-sensitive nature of multiple-step cementing procedures. RX con-
DISCUSSION
tains multifunctional hydrophilic monomers with phosphoric acid groups, which can
The aim of this study was to determine
react with hydroxyapatite and infiltrate and
whether
strengths
modify the smear layer. 39,40 It has been
between glass fiber posts and root canal
shown that light activation of the dual-cured
dentin depended on resin cement thickness
resin cement from the canal orifice offers
or post diameter. The tested null hypothesis
the advantage of establishing an immediate
must be partially rejected, as the push-out
coronal seal, although this technique also
the
push-out
bond
bond strength of the tested fiber post was
blocks the pathway for stress relief.8 There-
significantly influenced by the resin cement
fore, in the present study, RX was not light-
thickness; however, post diameter had no
cured. Compared to the results of this
significant influence.
study, previous studies reported lower bond
Regarding the method and materials,
strength values when using RX for the
the main disadvantage of using human
cementation of fiber posts.16,41 Goracci et
teeth was the relatively large variation in
al41 reported a mean bond strength value of
morphology, size, and mechanical proper-
5.1 MPa, and speculated that the self-adhe-
ties of the specimens.34,35 Previous studies
sive resin cement was ineffective for etch-
have reported that intact natural central
ing through the thick smear layer produced
incisors and canines are optimal for clini-
during the post-space preparation. How-
cally simulating the treatment of endodonti-
ever, Dimitrouli et al19 found greater bond
cally treated teeth with an endodontic post
strength values (11.3 ± 8.8 MPa) by strictly
system.36-38 The post system used in this
following the manufacturer’s recommenda-
study, which consisted of the RelyX fiber
tions for luting the fiber posts. This differ-
post, involves a parallel, tapered-end glass
ence may be explained by the non-uniform
fiber post that offers the potential advan-
resin-cement interface formation, by the
tages of reduced stress concentration at
application of cement only to the post sur-
the apex and the preservation of tooth
face (in the study of Goracci et al41), or by
structure. This system also allows for a uni-
variation in the resilience of the testing
form progressive increase in cement thick-
machines at different laboratories.
ness and post diameter when used with
The stress distribution for the push-out
standardized incremental intervals. As
test is expected to be more uniform than for
these are passively inserted inside of the
conventional shear or tensile tests. This dis-
root canals, the dislocation resistance
tribution leads to a shear stress that is com-
mainly depends on the luting agent and the
parable to the stress created under clinical
806
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
conditions.42 The fracture occurs parallel to
3, and approximately 210 μm for group 5).
the dentin-adhesive interface, which makes
In spite of a theoretical decrease in the
it a true shear test; therefore, the test mea-
C-factor for group 5, one may expect relax-
surements truly express the interfacial bond
ation to be more efficient as the unbonded
strength between the dental tissue and the
area becomes thicker. However, when the
material.43
cement thickness is too great, more air is
In this study, no significant differences
incorporated into the surface area, and this
were found when the matched drill and post
may inhibit the polymerization of the resin
sets were used (groups 1, 2, and 3). More-
around the minuscule air bubbles.47 The
over, the post diameter had no significant
incorporation of air bubbles may also
influence on the push-out bond strength,
weaken the resin cement substantially,
which is represented by the ratio of the
which perhaps explains the relatively low
debonding force (F) to the surface (SL). As
bond
the radius increased from group 1 to group
(Fig 1c).48
strength
recorded
for
group
5
3, there was a proportional increase in the
Regarding the root level, specimens
debonding force, which led to similar bond
from the apical third of the roots showed
strengths in group 1, group 2, and group 3.
significantly lower bond strengths, which is
bond
in agreement with previous studies.14,35,49
strength were significant when an oversized
This can be explained by a lower number of
post space was used (group 4). These find-
dentinal tubules and the more sclerotic
ings are in agreement with previous studies
structure of dentin in the apical part of the
that reported greater bond strengths for
roots. It has been recently reported that the
oversized post spaces.27,30 The intimate fit
higher C-factor in the apical part can nega-
that was produced with the matching drill
tively influence cohesive strength of resin
and post sets may not have provided ade-
cement, which could be another explana-
quate space for the resin cement to
tion for lower push-out bond strength in the
develop its maximum strength. Moreover,
apical part.50
The
differences
in
push-out
the relative lack of oxygen in such a narrow
Approximately 62% of the specimens in
space may have quickened the setting of
groups 1, 2, 3, and 5 showed a mode I fail-
the resin and prevented the complete inser-
ure at the post-cement interface (Table 4).
tion of the posts. Another factor that
Similar findings were reported by Le Bell et
strongly interferes with the development of
al,51 Perez et al,29 and Dimitrouli et al. 19
high bond strength is the cavity configura-
RelyX fiber posts contain epoxy resin (3M
tion, or C-factor.44 One method that is used
ESPE, technical information); therefore,
to estimate the C-factor is to divide the free
lower interfacial strength is expected due to
surface area by the total bonded area, as
the absence of a chemical bond between
described
by
Bouillaguet
et
al 45
and
the methacrylate-based RX luting agent
Jongsma et al,46 who reported that the
and the epoxy resin, a highly cross-linked
C-factor is greater than 200 for post cemen-
matrix of fiber posts that does not have
tation. In the present study, groups 1, 2,
functional groups available for reactions.51
and 3 exhibited small unbonded surfaces
Furthermore, during the RX setting reaction,
due to the thin layer of cement. Thus, there
the negatively charged phosphoric acid
could have been insufficient stress relief by
groups of the methacrylate monomers bond
flow and a high probability that one or more
to calcium ions in the tooth structure, there-
of the bonded areas would pull off or
fore shrinkage stress causes debonding of
debond. In groups 4 and 5, the resin
the cement from the post surface. Simulta-
cement may have had the opportunity to
neously, the setting of the cement takes
flow due to the oversized post space, which
place through a radical polymerization
may have resulted in the relaxation of poly-
reaction of the methacrylate monomers that
merization stresses. On the other hand, no
is started by the initiator system to provide
significant differences were found between
a highly cross-linked, three-dimensional
group 5 and the first three groups, although
network,
the cement thicknesses were different
remaining functional groups to react with
(approximately 20 μm for groups 1, 2, and
the resin of the fiber post. In addition, the
and
this
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
process
leaves
no
807
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
a
b
c
d
e
f
Figs 2a to f Example showing the clinical implications of one incremental oversized post space. The maxillary right second premolar was obturated using a warm-vertical technique. (a) The palatal canal was prepared for fiber post placement using RelyX drill size 2 (red, 0.8 to 1.6 mm), immediately after down packing of the gutta-percha. The post space was irrigated with normal saline, applying EDTA for 2 min, and then 5 ml of distilled water. (b) The RelyX fiber post (yellow, 0.7 to 1.3 mm) was examined for length fit. (c) RelyX Unicem cement was applied in the prepared space from the bottom to the top. (d) The tested fiber post was placed and the tooth restored using dental composite resin. (e) The final radiographic image (parallel). (f) The final radiographic image with mesial angulation.
intimate fit between the post and the dentin
CONCLUSION
walls may have resulted in the complete escape of the resin cement from the post
The greatest push-out bond strength values
space during post insertion. However, when
were obtained when one incremental over-
the resin cement was placed in an over-
sized post space was used.
sized space, as in group 4, sufficient func-
The apical third of the root canals pre-
tional groups became available for reaction
sented the lowest bond strength potential,
at the post-cement and dentin-cement
suggesting that the length of the post should
interfaces. This, in addition to less shrink-
be limited to the coronal half of the root.
age stress, may explain the higher percentage of mode III failures in this group. Traditionally, post spaces are prepared
Post diameter had no influence on the push-out bond strength of the tested fiber posts.
after finishing the root canal obturation. This may result in residual gutta-percha around
CLINICAL SIGNIFICANCE
the post space, which will decrease the
Fiber post space has to provide an opti-
bond strength. In the present study this was
mum cement thickness (around 120 μm) for
confirmed under SEM evaluation. It can be
adequate cementation (Fig 2). For the
suggested to place the fiber post immedi-
RelyX fiber post system, this can be
ately after the down packing of gutta-per-
reached by using a post one size smaller
cha in the apical part. Hence, residual
than the size of the post drill to create the
sealer on the root canal walls needs to be
post space. Bond strength of fiber post to
removed by rinsing and drying.
root canal dentin will be lowered by too thick or too thin cement thickness.
808
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
REFERENCES 1. Paul SJ, Werder P. Clinical success of zirconium oxide
14. Ferrari M, Mannocci F, Vichi A, Cagidiaco MC, Mjor IA. Bonding to root canal: structural characteristics of the substrate. Am J Dent 2000;13:255–260.
posts with resin composite or glass-ceramic cores in
15. Van Meerbeek B, De Munck J, Yoshida Y, et al.
endodontically treated teeth: a 4-year retrospective
Buonocore memorial lecture. Adhesion to enamel
study. Int J Prosthodont 2004;17:524–528.
and dentin: current status and future challenges.
2. Fernandes AS, Shetty S, Coutinho I. Factors determining post selection: a literature review. J Prosthet Dent 2003;90:556–562. 3. Fernandes AS, Dessai GS. Factors affecting the fracture resistance of post-core reconstructed teeth: a review. Int J Prosthodont 2001;14:355–363. 4. Cohen BI, Pagnillo MK, Newman I, Musikant BL, Deutsch AS. Retention of three endodontic posts cemented with five dental cements. J Prosthet Dent 1998;79:520–525. 5. Hagge MS, Wong RD, Lindemuth JS. Retention strengths of five luting cements on prefabricated
Oper Dent 2003;28:215–235. 16. Zicari F, Couthino E, De Munck J, et al. Bonding effectiveness and sealing ability of fiber-post bonding. Dent Mater 2008;24:967–977. 17. Farina AP, Cecchin D, Garcia Lda F, Naves LZ, Sobrinho LC, Pires-de-Souza Fde C. Bond strength of fiber posts in different root thirds using resin cement. J Adhes Dent 2011;13:179–186. 18. Pirani C, Chersoni S, Foschi F, et al. Does hybridization of intraradicular dentin really improve fiber post retention in endodontically treated teeth? J Endod 2005;31:891–894.
dowels after root canal obturation with a zinc
19. Dimitrouli M, Geurtsen W, Luhrs AK. Comparison of
oxide/eugenol sealer: 1. Dowel space preparation/
the push-out strength of two fiber post systems
cementation at one week after obturation. J Prosth-
dependent on different types of resin cements. Clin
odont 2002;11:168–175.
Oral Investig 2012;16:899–908.
6. Cagidiaco MC, Goracci C, Garcia-Godoy F, Ferrari M.
20. Erdemir U, Sar-Sancakli H, Yildiz E, Ozel S, Batur B. An
Clinical studies of fiber posts: a literature review. Int
in vitro comparison of different adhesive strategies
J Prosthodont 2008;21:328–336.
on the micro push-out bond strength of a glass
7. Aksornmuang J, Foxton RM, Nakajima M, Tagami J. Microtensile bond strength of a dual-cure resin core material to glass and quartz fibre posts. J Dent 2004;32:443–450. 8. Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometric factors affecting dentin bonding in root canals: a theoretical modeling approach. J Endod 2005;31:584–589. 9. Tay FR, Suh BI, Pashley DH, Prati C, Chuang SF, Li F. Factors contributing to the incompatibility between
fiber
post.
Med
Oral
Patol
Oral
Cir
Bucal
2011;16:e626–634. 21. Cantoro A, Goracci C, Vichi A, Mazzoni A, Fadda GM, Ferrari M. Retentive strength and sealing ability of new self-adhesive resin cements in fiber post luting. Dent Mater 2011;27:e197–204. 22. Schmage P, Cakir FY, Nergiz I, Pfeiffer P. Effect of surface conditioning on the retentive bond strengths of fiber-reinforced composite posts. J Prosthet Dent 2009;102:368–377.
simplified-step adhesives and self-cured or dual-
23. D’Arcangelo C, D’Amario M, Prosperi GD, Cinelli M,
cured composites. Part II. Single-bottle, total-etch
Giannoni M, Caputi S. Effect of surface treatments
adhesive. J Adhes Dent 2003;5:91–105.
on tensile bond strength and on morphology of
10. Cheong C, King NM, Pashley DH, Ferrari M, Toledano
quartz-fiber posts. J Endod 2007;33:264–267.
M, Tay FR. Incompatibility of self-etch adhesives
24. Nergiz I, Schmage P, Platzer U, Ozcan M. Bond
with chemical/dual-cured composites: two-step vs
strengths of five tapered root posts regarding the
one-step systems. Oper Dent 2003;28:747–755.
post surface. J Oral Rehabil 2002;29:330–335.
11. Suh BI, Feng L, Pashley DH, Tay FR. Factors contribut-
25. Fredriksson M, Astback J, Pamenius M, Arvidson K. A
ing to the incompatibility between simplified-step
retrospective study of 236 patients with teeth
adhesives and chemically-cured or dual-cured com-
restored by carbon fiber-reinforced epoxy resin
posites. Part III. Effect of acidic resin monomers. J Adhes Dent 2003;5:267–282.
posts. J Prosthet Dent 1998;80:151–157. 26. Ferrari M, Mason PN, Goracci C, Pashley DH, Tay FR.
12. Bolhuis PB, de Gee AJ, Kleverlaan CJ, El Zohairy AA,
Collagen degradation in endodontically treated
Feilzer AJ. Contraction stress and bond strength to
teeth after clinical function. J Dent Res 2004;83:414–
dentin for compatible and incompatible combina-
419.
tions of bonding systems and chemical and light-
27. D’Arcangelo C, Cinelli M, De Angelis F, D’Amario M.
cured core build-up resin composites. Dent Mater
The effect of resin cement film thickness on the
2006;22:223–233.
pullout strength of a fiber-reinforced post system. J
13. Farina AP, Cecchin D, Garcia Lda F, Naves LZ, Pires-
Prosthet Dent 2007;98:193–198.
de-Souza Fde C. Bond strength of fibre glass and
28. Nergiz I, Schmage P, Ozcan M, Platzer U. Effect of
carbon fibre posts to the root canal walls using dif-
length and diameter of tapered posts on the reten-
ferent resin cements. Aust Endod J 2011;37:44–50.
tion. J Oral Rehabil 2002;29:28–34.
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013
809
Q U I N T E S S E N C E I N T E R N AT I O N A L Mirmohammadi et al
29. Perez BE, Barbosa SH, Melo RM, et al. Does the thick-
40. Moszner N, Salz U, Zimmermann J. Chemical aspects
ness of the resin cement affect the bond strength of
of self-etching enamel-dentin adhesives: a system-
a fiber post to the root dentin? Int J Prosthodont 2006;19:606–609.
atic review. Dent Mater 2005;21:895–910. 41. Goracci C, Sadek FT, Fabianelli A, Tay FR, Ferrari M.
30. Hagge MS, Wong RD, Lindemuth JS. Effect of dowel space preparation and composite cement thickness on retention of a prefabricated dowel. J Prosthodont 2002;11:19–24.
Evaluation of the adhesion of fiber posts to intraradicular dentin. Oper Dent 2005;30:627–635. 42. Frankenberger R, Kramer N, Petschelt A. Fatigue behaviour of different dentin adhesives. Clin Oral
31. Coniglio I, Garcia-Godoy F, Magni E, Carvalho CA,
Investig 1999;3:11–17.
Ferrari M. Resin cement thickness in oval-shaped
43. Goracci C, Grandini S, Bossu M, Bertelli E, Ferrari M.
canals: oval vs. circular fiber posts in combination
Laboratory assessment of the retentive potential of
with different tips/drills for post space preparation. Am J Dent 2009;22:290–294.
adhesive posts: a review. J Dent 2007;35:827–835. 44. Feilzer AJ, De Gee AJ, Davidson CL. Setting stress in
32. da Rosa RA, Bergoli CD, Kaizer OB, Valandro LF. Influence of cement thickness and mechanical cycling on the push-out bond strength between posts and root dentin. Gen Dent 2011;59:e156–161.
composite resin in relation to configuration of the restoration. J Dent Res 1987;66:1636–1639. 45. Bouillaguet S, Troesch S, Wataha JC, Krejci I, Meyer JM, Pashley DH. Microtensile bond strength
33. Bitter K, Meyer-Lueckel H, Priehn K, Kanjuparambil JP, Neumann K, Kielbassa AM. Effects of luting agent and thermocycling on bond strengths to root canal dentine. Int Endod J 2006;39:809–818.
between adhesive cements and root canal dentin. Dent Mater 2003;19:199–205. 46. Jongsma LA, Bolhuis PB, Pallav P, Feilzer AJ, Kleverlaan CJ. Benefits of a two-step cementation proced-
34. Heydecke G, Peters MC. The restoration of endodontically treated, single-rooted teeth with cast or direct posts and cores: a systematic review. J Prosthet Dent 2002;87:380–386.
ure for prefabricated fiber posts. J Adhes Dent 2010;12:55–62. 47. Alster D, Feilzer AJ, De Gee AJ, Mol A, Davidson CL. The dependence of shrinkage stress reduction on
35. Perdigao J, Gomes G, Augusto V. The effect of dowel space on the bond strengths of fiber posts. J Prosthodont 2007;16:154–164.
porosity concentration in thin resin layers. J Dent Res 1992;71:1619–1622. 48. Boschian Pest L, Cavalli G, Bertani P, Gagliani M.
36. Newman MP, Yaman P, Dennison J, Rafter M, Billy E.
Adhesive post-endodontic restorations with fiber
Fracture resistance of endodontically treated teeth
posts: push-out tests and SEM observations. Dent
restored with composite posts. J Prosthet Dent 2003;89:360–367. 37. Sirimai S, Riis DN, Morgano SM. An in vitro study of the fracture resistance and the incidence of vertical root fracture of pulpless teeth restored with six post-and-core
Mater 2002;18:596–602. 49. Lopes GC, Ballarin A, Baratieri LN. Bond strength
systems.
J
Prosthet
Dent
1999;81:262–269.
and fracture analysis between resin cements and root canal dentin. Aust Endod J 2012;38:14–20. 50. Jongsma LA, Kleverlaan CJ, Pallav P, Feilzer AJ. Influence of polymerization mode and C-factor on cohesive strength of dual-cured resin cements. Dent
38. Mendoza DB, Eakle WS, Kahl EA, Ho R. Root reinforcement with a resin-bonded preformed post. J Prosthet Dent 1997;78:10–14.
Mater 2012;28:722–728. 51. Le Bell AM, Tanner J, Lassila LV, Kangasniemi I, Vallittu P. Bonding of composite resin luting cement to
39. Mormann W, Wolf D, Ender A, Bindl A, Gohring T, Attin T. Effect of two self-adhesive cements on mar-
fiber-reinforced composite root canal posts. J Adhes Dent 2004;6:319–325.
ginal adaptation and strength of esthetic ceramic CAD/CAM
molar
crowns.
J
Prosthodont
2009;18:403–410.
810
VOLUME 44 • NUMBER 10 • NOVEMBER/DECEMBER 2013