The bond strength of endodontic sealers to root /prosthodontic courses

The bond strength of endodontic
sealers to root dentine exposed to
different gutta-percha solvents
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

Introduction
• The success of root canal treatment depends
on completely cleaning and shaping, and then
filling the root canal systems.
• If these parameters are not achieved, post-
treatment disease may occur because of
persistence of bacteria in root canal system.
• When this occurs, non surgical root canal
retreatment is often indicated as the first
choice to eliminate the microbial infection.

• The retreatment aims to completely remove
the old filling material from the root canal
system to allow effective cleaning, shaping
and effective refilling of root canal.
• In root canal retreatment, solvents are often
used as an aid for removing gutta-percha.
• Chloroform, an organic solvent, has been
shown to be effective when used with gutta-
percha.

• However, it has carcinogenic potential and the
search for alternative solvents continues.
• Studies have shown that essential oils,
eucalyptol, orange oil and turpentine oil, may
be used in retreatment because they are safe
and useful for dissolution of gutta-percha and
root canal sealers.
• Several chemical agents change the chemical
structure of dentin and the ca/p ratio of
dentin surface.

• Alteration in the original ca/P ratio between organic
and inorganic components may change the
permeability and solubility of root dentin and can
affect the adhesion of dental materials to hard tissues.
• During root canal retreatment the root and coronal
dentin is exposed to GP solvents deposited in root
canals.
• Kaufman et al reported that solvents may alter the
chemical composition of dentin surface and affect
bond strength of restorative materials to dentin.

• Many studies have been conducted to evaluate the
effect of various endodontic procedures on bond
strength of root canal sealers.
• However, there is no information about the effects of
various GP solvents used over different application
times on the bond strength of sealers to root dentin.
• The purpose of this study was to compare the push-
out bond strength of different endodontic sealers to
root dentin exposed to various GP solvents for 2 to 5
min.
• The null hypothesis is that various GP solvents do not
affect the bond strength of several root canal sealers.

Materials and Methods
• 210 freshly extracted, straight, single-rooted
human mandibular premolar teeth were
selected and stored in distilled water untill
required.
• Preoperative mesiodistal and buccolingual
radiographs were taken to verify the presence
of single canal.

Inclusion criteria
• Completely formed apex
• Absence of previous root filling
• Absence of resorption or calcification

• To ensure standardization, crowns of the
selected teeth were partially removed to
achieve a final length of 21 mm for each
tooth.
• The crown served as a reservoir for the
solvent.
• Endodontic access cavities were prepared
using diamond burs (Diatech; coltene whale
dent, Switzerland) with a high speed hand
piece under water cooling.

• A size 10 k file was then placed in the canal until
it was visible at the apical foramen.
• The working length was determined by
subtracting 1 mm from this measurement.
• The 210 roots were instrumented with the
protaper rotary system up to size F4 (size 40, .06
taper) as the master apical file.
• During preparation the root canal was irrigated
with 5 ml of 2.5% NaOCl solution using a syringe
and 30 gauze needle (ultradent) between each
instrument change.

• A total of 210 roots were then randomly
assigned to six experimental groups (n=30)
according to the solvent type and time of
exposure and one control group (n=30) as
follows:
• Group 1: control (not exposed to any solvent)
• Group 2: chloroform for 2 min
• Group 3: Chloroform for 5 min
• Group 4: eucalyptol for 2 min

• Eucalyptol for 5 min
• Orange oil for 2 min
• Orange oil for 5 min
• A total of 0.2 mL of each solvent was placed in
the root canal and left in place up to
completion of the exposure time and then
removed with paper points.
• All canals received a final rinse of 5 ml 17%
EDTA for 1 min followed by 5 ml distilled water
and dried with absorbent paper point.

• The roots with in each of six experimental groups
and the control group were further randomly
assigned to three subgroups (n=10) according to
sealer used as follows:
1. AH plus
2. MTA Fillapex
3. Sealapex
• Each sealer was mixed according to the
manufacturer instructions for use.

• All canals were filled using the single cone
technique with F4 gutta-percha cones.
• After the canal filling, mesiodistal and
buccolingual radiographs were taken to confirm
complete filling.
• The coronal 1mm of the filling material was then
removed, and the spaces were filled with a
temporary filling material.
• After being wrapped in pieces of sponge, all the
specimen were stored at 370c in 100% humidity
for 2 weeks

Push-out Testing
• The specimens were sectioned horizontally in
to three 1+_ .1 mm thickness serial slices
using a low speed precision diamond saw
under continuous water irrigation.
• The thickness of each slide was measured with
a digital calliper with an accuracy of .001 mm.
• Both apical and coronal aspects of the
specimens were then examined
microscopically to confirm a circular canal
shape.

• The push out test was performed in a
universal testing machine by applying a
continuous load to the apical side of each slice
using 0.7, 0.8, and 0.9 mm diameter
cylindrical plungers matching the canal
diameter of each third.
• The diameter of each plunger was approx 90%
of the canal diameter.

• Loading was applied at cross-head speed of 1
mm min from the apical to the coronal
direction until the bond fracture occurred.
• The maximum load applied to filling material
before fracture was recorded in newtons and
converted to megapascals according to
following fourmula.
• Pushout bond strength (Mpa)= N/A

Analysis of failure modes
• After measurement of bond strength both
sides of the failed bond were examined under
a stereomicroscope at 30X magnification to
determine the mode of fracture.
• The fracture mode was classified according to
following criteria:
• Adhesive fracture at sealer-dentin or sealer-
core interface, cohesive fracture with in sealer
and mixed sealer in both sealer and dentin.

• Two specimens that were representative of
the fracture modes from each group were
further evaluated under a SEM.
• Statistical analysis was carried out using four
way factorial ANOVA.
• All statistical analysis was carried out using
SPSS 16.0 software.

Results
• All variables had a significant effect on the
push-out bond strength of sealers (p< 0.001).
• The use of chloroform for 5 min significantly
reduced the push out bond strength of all
sealers when compare with other groups.
• There was no significant differences between
the control, orange oil, eucalyptol groups.

• Under all conditions, a statistical ranking or
bond strength values was obtained as follows
(P < 0.001):
• AH plus > Sealapex > MTA Fillapex
• The bond strength values were highest in the
coronal and lowest in the apical thirds
(P<0.001).

Discussion
• Adhesion, one of the required physical
properties of filling materials, is a desirable
property in root canal sealers.
• Adhesion of endodontic sealer is defined as its
capacity to adhere to the root canal walls and
the ability to promote the union of the core
filling material to each other and to the
dentin.

• Shokouhinejad et al (2010) evaluated push out
bond strength of resilon/epiphany self-etch to
root dentin after retreatment.
• They filled the canals and then removed the
initial root filling with a combination of
retreatment files and solvent.
• After retreatment roots were filled with
resilon/epiphany self-etch

• The results of the present study revealed that
most interaction was between solvent type
and time.
• The use of chloroform for 5 min had a
negative effect on the bond strength of all the
sealers.
• Erdemir et al reported that chloroform and
halothene had an effect on the mineral
content of root dentin.

• In the current study, the decreased bond
strength in the roots exposed to chloroform
for 5 min may be explained by compositional
changes in dentin that may affect the bond
strength of filling material.
• However, the use of orange oil and eucalyptol
for 2 and 5 min did not affect bond strength of
the root sealers.

• In the present study, AH plus had the highest
push-out bond strength under all conditions.
• The superior results of AH plus may be due to
better adhesion to root dentin and deeper
penetration in to dentinal tubules.
• In the current study, three plunger sizes were
used to match the diameter of each of the
root third.

• This avoids excessive pressure on the
surrounding root canal walls and any notching
effect of the plunger into GP surface.
• According to the root thirds, bond strength
values in all specimens were
• Coronal > Middle > Apical
• This is because penetration of endodontic
sealers in dentinal tubules achieves
mechanical interlocking and may increase
retention of the root filling.

• The decreasing bond strength in the corono-
apical direction can be explained by the
decreasing tubule density in a coronal to apical
direction, which reduces sealer penetration into
smaller tubules in the apical third.
• In the present study, inspection of the root slices
revealed that the fracture modes were mainly
adhesive (sealer-dentin interface).
• This result may be due to changes likely in the
chemical structure of root dentin exposed to
solvents.

conclusions
• The bond strength of AH plus, MTA fillapex
and sealapex was negatively affected by the
use of chloroform for 5 min.
• Further study should evaluate the effect of
different solvents for various periods of time
on the bond strength of different sealers.

The bond strength of endodontic sealers to root /prosthodontic courses

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