Comparison of Dentin Pretreatment Protocols on Fiber Post Bond Strength

Comparison of Different Dentin
Pretreatment Protocols on the
Bond Strength of Glass Fiber
Post Using Self-etching
Adhesive
 INDIAN DENTAL ACADEMY
 Leader in continuing Dental Education
JOURNAL CLUB
www.indiandentalacademy.com

INTRODUCTION
 Tooth with large structural loss usually requires the use of an
intraradicular post for improving the retention of additional
restoration .
 Fiber posts have led to greater advantages compared with
the traditional cast metal and core systems, especially
regarding mechanical properties, such as high flexural
strength and elasticity modulus, similar to those of dentin.
 This minimizes the transmission of stresses to the root walls,
decreasing the possibility of fractures and improving the
esthetic appearance with no risk of gingival discoloration or
alteration of the root surface by corrosive products, especially
at the anterior region. .

 Composite luting cements are used to bond
the fiber post to root canal dentin because
they provide mechanical retention to dentin
with a hybrid layer and mechanical and/or
chemical bonding to the post .
 Studies have shown that self-etching
adhesive, commonly used in dentin, is
capable of promoting a favorable bond
strength between composites and dentin
structure.

 The most common failure associated with fiber
posts is their debonding at the adhesive resin-
dentin interface caused by difficulties regarding
dentin hybridization.
 Studies have shown that dentin hybridization can
be affected by modifications in the dentin substrate
caused by irrigants , obstruction of the dentin
tubules during instrumentation, post space
preparation ,and type of adhesive system ,
including the limited action of light-curing units that
can be

 Although sodium hypochlorite (NaOCl) is the most
commonly used irrigant in endodontics , it interferes
with the organic/inorganic constituents of the dentin
, which is of concern regarding the adhesion of
luting agents
 On the other hand, chlorhexidine (CHX) is an
alternative irrigant that does not seem to interfere
with the collagen present in the organic matrix of
root dentin , thus maintaining the quality of the
dentin substrate
 It has been determined that ultrasound and laser
techniques contribute to both disinfection and
elimination of residual tissue , and it has been
argued whether they can contribute to bond
strength by altering the dentin layer .

 This study compared the influence of
different irrigants with and without
ultrasound or laser irradiation on the bond
strength of glass fiber posts using a self-
etching adhesive system in a
supplementary dentin pretreatment.

MATERIALS AND METHOD
 Ninety freshly extracted bovine incisors with
anatomically similar root segments and fully
developed roots were selected.
 Teeth were stored in 0.02% thymol solution and
prepared within 1 month of extraction.
 Each tooth was decoronated below the
cementoenamel junction perpendicularly to the
longitudinal axis by using a slow-speed, water-
cooled diamond saw (90 mm; Microdont, S~ao
Paulo, SP, Brazil) at low rotation.
 The roots were cut in a uniform length of 16 mm
from the apical end. The apices of the teeth were
sealed with a temporary filling material (CavitW;
Premier Dental Produtos, Rio de Janeiro, RJ, Brazil

 All root canals were prepared by 1 trained operator.
 Pulp tissue and predentin were removed, and the
root canals were enlarged up to #80 file size
(Dentsply Maillefer, Ballaigues, Switzerland).
 The apical end (1 mm) was left unprepared to
prevent apical extrusion of both solutions and luting
cement.
 Roots were rinsed with 5mL saline solution to
remove the remaining debris, dried with paper
points, and filled with gutta-percha (Dentsply Ind E
Com Ltd, Petropolis, RJ, Brazil) by lateral
condensation and Sealer 26 (Dentsply DeTrey,
Konstanz, Germany).

 Roots were embedded vertically with acrylic
resin (Jet; S~ao Paulo,SP, Brazil) using a
prosthetic liner to ensure orientation in the
long axis of the root.
 After this procedure, the filling material was
removed from the root canal by using drills
until leaving a remnant of 3mm in the apex
before the use of the fiberglass post system
(White Post DC4; FGM, Joinville,SC, Brazil).
 The specimens were divided into 3 groups
according to the irrigant

 The specimens were divided into 3 groups
according to the irrigant solution: saline
solution (n = 30), 2% CHX (n = 30), and
2.5% NaOCl (n = 30).
 Each group was randomly divided into 3
subgroups according to the supplementary
dentin pretreatment: ultrasound,Nd:YAG
laser, and nonsupplemented (control). The
canals were irrigated with 5 mL of the
irrigant solution according to the irrigants
tested.

 For the laser subgroups, the Nd:YAG laser handset
(300-D Laser;American Dental Technologies,
Corpus Christi, TX) was used in the pulsed mode
and high power.
 Irradiation was set to 100-mJ energy,a repetition
rate (frequency) of 15 Hz, and a maximum power of
1.5 W.

 For the ultrasound subgroups, the ultrasonic device
used was the CVDent 1000 (Clorovale, S~ao Jose
dos Campos, SP, Brazil), with TOS-E2 tips running
all root canal walls during 15 seconds, totaling 10
laps around them, with 10% of power.

 The canals were dried with paper points. Then, a
dual-curing selfetch adhesive system (Futurabond
DC; VOCO GmbH, Cuxhaven, Germany) was
actively applied with a microbrush for 20 seconds,
and the solvent was dispersed with air for 5
seconds.
 According to the manufacturer’s recommendation,
the adhesive layer was not polymerized

 The dual-cured radiopaque resin-based adhesive
luting system (Bifix QM, VOCO GmbH) was applied
by using the root canal tip of the double syringe
 The cement was injected into the root from the
apical end toward
the entire length of the root canal, with the
fiberglass post (White
Post DC4, FGM) placed on the canal to ensure
only a slight excess.

Before luting, the fiberglass posts were cleaned
with alcohol for disinfection and silanized with a
silane coupling agent (Prosil, FGM)
The post was held in place with firm pressure for
5–10 seconds and cured for 40 seconds by
placing the light guide onto it.
The specimens were kept at 37C and relative
humidity for 7 days.

PUSH-OUT TEST
 For the bond strength test, the roots were horizontally
sectioned into 3 slices of 2.0 0.1 mm in thickness by
using a slow-speed saw (LabCut 1010; EXTEC-ERIOS,
S~ao Paulo, SP, Brazil) with a 4 * 0.12 * ½–inch
diamond blade (EXTEC-ERIOS) under continuous water
cooling.
 Each slice represented 1 of the root thirds: cervical,
middle,
and apical.
 The first slice of 1 mm in thickness was discarded to
avoid imperfections on the adhesive interface specially
caused by the oxygen presence.
 The other slices represented each 1 of the root thirds:
cervical,middle, and apical.

 The push-out test was performed using a universal
testing machine (DI-1000; EMIC, Curitiba, PR, Brazil) at
a crosshead speed of 1.0 mm/min and a load cell of 50
kgF.
 Specimen was carefully positioned over a rigid basis,
with the apical face facing the punch tip with the
diameter corresponding with the diameter with the set
post/cement.
 The push-out bond strength of each specimen (MPa)
was calculated as the force (N) of failure divided by the
adhesive area (mm2).

The means and standard deviations of
bond strength were calculated, and
data were analyzed by using 3-way
analysis of variance followed by the
post hoc Tukey test (P < .05).

FAILURE MODE PATTERN
 After the push-out test, the slices were
analyzed with a stereomicroscope (50) to
verify the failure mode, which was divided
as follows:
 adhesive between resin cement and post,
 adhesive between resin cement and dentin,
mixed with resin cement covering less than
50% of the post, mixed with resin cement
covering more than 50% of the post, and
 cohesive in dentin.

RESULTS
 The mean and standard deviation values of the push-out test,
showing the bond strength for each group, are shown in Table
.
 A significant bond strength decrease was found after the use
of 2.5% NaOCl in all root thirds (P < .05).
 CHX showed no difference in the mean bond
 strength value compared with saline solution (P > .05).
 The supplementary dentin pretreatment using either the
Nd:YAG laser or ultrasound did not improve the bond strength
values regarding both NaOCl and CHX (P > .05).
 Moreover, the apical third exhibited the lowest mean bond
strength values (P < .05).

 Analysis indicated that the predominant failure
mode was the mixed type.
 However, the control group showed more mixed
failures with resin cement covering less than 50%
of the post, and the groups with supplementary
treatments had predominance of the mixed failure
with more than 50% of cement covering the
post.
 No cohesive failures were identified in dentin.

Scanning electron microscopic illustrative images of failure mode pattern: (A) adhesive
failure between resin cement and dentin (100 magnification),(B) interface of dentin
marked in A with 500 magnification, (C) mixed failure with resin cement covering less
than 50% of the post (arrow shows cement in dentin interface) (100 magnification), and
(D) interface of cement/dentin marked in C with 500 magnification.

DISCUSSION
 The data obtained in the present study revealed
that regardless of the irrigant used (NaOCl or CHX),
the supplementary dentin pretreatment with
ultrasound or laser irradiation showed no
improvement in bond strength.
 Also, the use of NaOCl decreased the bond
strength of glass fiber posts using a self-etching
adhesive system, whereas CHX preserved it.
 Moreover, the failure analysis indicated that the
predominant failure mode was the mixed type.

 Our findings are in agreement with previous studies showing
that NaOCl (the most commonly used irrigant) ,decreases the
bond strength of glass fiber posts cemented with a composite
luting agent.
 This causes degeneration of the dentin because of
dissolution of collagen by breaking down the bonds between
carbon atoms, thus disorganizing the protein primary
structure.
 On the other hand, CHX did not affect negatively the push-out
bond strengthin post bond cementation, showing no
significant difference compared with saline solution.
 According toMoreira et al (9), CHX does not interfere with the
collagen present in the organic matrix of root dentin as it
maintains the quality of the dentin substrate.
 Typically, results showed that the use of CHX had no negative
effect on the push-out bond strength in post bond
cementation.

 Moreover, previous studies have shown that CHX
improves the longevity of the composite adhesive bonded
to dentin by inhibiting matrix metalloproteinase in the
hybrid layer, which are collagen-degrading enzymes.
 Considering the implication of irrigants on the dentin
substrate, in particular, NaOCl (the most frequently used
one), and the limited enamel and denting etching provided
by self-etching systems along with the ability of ultrasound
and the Nd:YAG laser in yielding a cleaner dentin surface
and modifying the dentin layer, the present study
hypothesized whether supplementary dentin pretreatment
with such devices would improve the bond strength of
glass fiber posts using a self-etching adhesive associated
with NaOCl or CHX.

 Regarding the supplementary dentin pre
treatment, the chemical vapor deposition
(CVD) ultrasound burs were shown to be an
option for the cleaning of root canals and they
did not interfere with bond strength values.
 Ultrasound has gained ground in dentistry by
presenting good efficiency in root canal
irrigation, such as chemical disinfection, debris
cleaning, and smear layer removal .
 Its efficiency on root dentin is assigned to the
improvement in the fabrication of burs that
present a diamond covered by CVD (34) and
new designs, thus allowing its use inside the
root canal .

 The Nd:YAG laser was tested as a supplementary dentin
pretreatment to improve bond strength. Although it has been
shown that the dentin structure can be changed according to
the Nd:YAG laser energy used, causing the dentinal tubules
to be sealed and the formation of fungiform projections that
aid in the mechanical adhesion of the dentin and thus
possibly improving the bond strength, the present
studyshowed lower bond strength values.
 Additionally, Nagase et al showed that the use of the
Nd:YAG laser negatively affects the post retention force.
 It might be argued that the use of the Nd:YAG laser before
adhesive application might have caused the melting of the
dentin, consequently sealing the dentin tubules and affecting
the formation of resin tags for a proper smear layer.

 Regarding post cementation, the adhesive systems are also of
concern, with different generations of adhesive systems being
presented in the literature (40).
 Particularly, the self-etching adhesive system used in this study is
characterized by acid etching, primer, and adhesive stages
occurring at the same time. Such an adhesive system modifies
the smear layer, which is essential for the formation of a quality
hybrid
layer.
 It has been reported that a self-etching adhesive system is
capable of performing etching of the dentin.
 The epoxy-based resin cement used (Bifix QM) is a dual-cure
luting agent, which requires the previous use of an adhesive
system.
 The lower values found in the apical region are usually reported
in the literature; thus, they are associated with the difficulties in
the adhesion protocol, such as the many steps for dentin
hybridization and the type of resin cement used.

 Also, there is always a risk of the presence of gutta-
percha and endodontic cement waste, which weakens
the adhesion .
 The lack of light fully reaching the interior of the root
canals is also a factor that influences the bond strength
of fiberglass posts because this affects the proper cure
of the resin cements.
 Fracture analysis showed a predominance of mixed
fractures with less than 50% of cement around the post
for the control groups.
 For ultrasound and laser groups, the adhesive failures
between resin cement and dentin and mixed failures
with more than 50% of cement around the post summed
more than 50% of the failures types, indicating that the
interface between resin cement and dentin was
compromised

 Overall, the present study has revealed that
regardless of the irrigant used, the supplementary
dentin pretreatment with ultrasound or laser
irradiation showed no improvement in bond
strength.
 Also, the use of NaOCl decreased the bond
strength of glass fiber posts using a self-etching
adhesive system, whereas CHX preserved it.

THANK YOU

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