Patients combination with sodium hypochlorite (NaOCl) has proven to

 

Patients who have had endodontic treatment frequently present with
problems such as extensive coronal damage from caries or trauma, thus requiring
intraradicular retentive strategies to stabilize the restoration as well as
restore the previous esthetic form and functionality of the teeth1. Prefabricated
fibre posts in combination with resin cements have been preferred to restore endodontically
treated teeth as an alternative to prefabricated metal posts or custom cast
post.2,3,4 Their main advantage is the elastic modulus which is very
close to that of dentin, thus resulting in a balanced stress distribution
pattern and reduced possibility of vertical root fractures. However, luting of
posts to interradicular dentin can pose to be a challenge owing to the high C-factor
inside the canal, limited access and moisture control. 5 The weakest link of the whole tooth-posts-restoration
system may be identified in the adhesion
between the substratum and the resinous cements. Adhesion grossly depends on:
removal of the  smear layer, which interferes with the formation
resin dentin interdiffusion zone; 6 also bond degradation may occur
due to water absorption or by proteolytic degradation (collagenolysis) of the
hybrid layer, by action of matrix metalloproteinases.7

Various post space treatment strategies have been explored in
order to preserve the resin-dentin adhesion. Irrigation with ethylenediaminetetracetic
acid (EDTA) in combination with sodium hypochlorite (NaOCl) has proven to
efficiently remove the smear layer. The chelating property of EDTA removes the
inorganic component and the tissue dissolving property of NaOCl eliminates the
organic component.8 Chlorhexidine digluconate (CHX) is a potent
antiseptic with a broad-spectrum antimicrobial activity and substantivity. It
is an also known to prevent collagenolysis by inhibition of the matrix
metalloproteinases (MMP) and thus secure the resin-dentin bond.9Another pre-treatment
strategy is the ethanol wet bonding technique. Ethanol coaxes hydrophobic
monomers into a demineralized collagen matrix without sacrificing any
additional matrix shrinkage.10 SmearOFF is a novel irrigant having synergistic
combination of both EDTA and Chlorhexidine. So it not only aids in removal of smear
layer but also inhibits the MMP related bond degradation. To the authors’ best
knowledge, no study has evaluated the effect of this irrigant on the bond
strength of prefabricated fibre posts to canal dentin.

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Furthermore, several studies have
appraised the use of self- adhesive resin cement to lute prefabricated fibre
posts to dentin. It does not require tooth surface pre-treatment for adhesion
as it is based on the chemical interactions between monomeric acidic groups and
hydroxyapatite, and on micromechanical retention. 11,12 However,
less literature is available about the effects of the pre-treatment
protocol prior post placement using self-adhesive resin cements.

Therefore, the aim of the
present study is to assess the
effect of different post space
irrigating agents on the push-out bond strength of prefabricated fiber
posts luted with self-adhesive resin
cement in different
root thirds (coronal, middle, and apical).  

 

 

 

 

MATERIALS AND
METHODS

Freshly extracted intact human mandibular premolars (for orthodontic
purpose) without caries, with
anatomically similar roots were selected. The teeth were examined with a stereomicroscope under 10x magnification
to detect craze lines or cracks which were excluded from the study. Performing
the above procedure resulted in 60 specimens. The teeth were stored in 0.1% thymol solution, and were
decoronated at the cement-enamel junction with a diamond-coated saw (Isomet
2000; Buehler Ltd, Lake Bluff, IL, USA). The roots were adjusted to 16 mm in
length and the working length was established 1 mm short of the apex. All the
root canals were instrumented using ProTaper Universal rotary instruments
(Dentsply Maillefer, Ballaigues, Switzerland), according to the manufacturer’s
recommendation. The master apical instrument was the ProTaper Universal F3.
Five milliliters of 2.5% sodium hypochlorite (NaOCL) was used for irrigation
between each instrumentation with a final rinse of 2 mL 17% aqueous ethylenediaminetetraacetic
acid (EDTA) for 1 min, followed by 5 mL of 2.5% sodium hypochlorite. Each root
canal was dried with paper points (Protaper® Universal Paper Points) size
F3 matching the final finishing file, and obturated with gutta-percha using
cold lateral condensation technique and AH Plus sealer (DeTrey Dentsply, York, PA, USA). The teeth were stored
at 37° C and 100% humidity for 7 days to allow for the setting of the sealer. All
the root canals were enlarged with a #2 Unicore Drill (Ultradent, South Jordan,
UT, USA), using a low-hand piece, to a depth of 10 mm. During preparation of
the canal, 5 mm of the endodontic filling was left at the apex of each canal. All
samples received a final rinse with 5 mL of distilled water and the excess was
removed using paper points (Protaper® Universal Paper Points).

Teeth were
then randomly divided into 4 groups (n=15).

Group 1
(Control): The roots were
irrigated with 2 mL distilled water;

Group 2: The roots were irrigated with 2 mL of 17% aqueous EDTA over one minute, rinsed out by distilled
water and then irrigated with 2ml of 2.5%sodium hypochlorite over 15 seconds.
Final rinse was done with distilled water.

Group 3: The roots were irrigated with 2 mL of 99%
Ethanol over one minute

Group 4: The
roots were irrigated with 2 mL of SmearOFF solution (VistaDental) over one minute

All solutions were maintained in the root
canals for 60 s and dried with paper points. Fibre post placement was done
using RelyX U200 (3M ESPE), a self-adhesive resin cement. After excess was
removed light curing was performed using light-emitting diode unit
(Bluephase polywave LED, IvoclarVivadent) according to manufacturer’s
instructions. All specimens
were maintained in 100% humidity, for 24 h, at 37°C. Each root was then cut
horizontally to the longitudinal axis using a low-speed diamond-coated saw
(Isomet 2000, Buehler Ltd, Lake Bluff, IL, USA) under water cooling. Three
slices were prepared at a thickness of 2 mm in the coronal, middle, and apical
third of each root, which were taken respectively 1 mm, 5 mm, and 8 mm from the
cement–enamel junction.

Mechanical Testing

The push-out test was carried out by
applying a load using Instron Universal Testing Machine (Zwick, Germany, at a cross head speed of 0.5 mm/min in
the apex in the direction of the crown until the fiber post resin cement
segment was dislodged from the root slice. A cylindrical plunger was used to
dislodge with 1mm, 0.7mm, and 0.4 mm diameters to the coronal, middle, and
apical thirds, respectively.

 

 

Statistical
Analysis

Descriptive statistics were expressed as
means and standard deviation for each group. The effect of different post space
irrigation procedures on the push-out bond strength of the posts was assessed
by comparison of groups using ANOVA test with post hoc Bonferroni test (Table 1
and Table 2). In the above tests, p value less than or equal to 0.05 (p?0.05)
was taken to be statistically significant. All analyses were performed using
SPSS software version 17.

 

RESULTS

·     
The push-out bond strength was significantly affected by the
different irrigants (p 0.05).

·     
Treating the post space with ethanol (Group 3) showed the
highest bond strength regardless of the location inside the canal.

·     
No significant difference in push out bond strength was
noted when post space was treated with the combination of 17% aq. EDTA &
2.5% NaOCl (Group 2) or SmearOff (Group 4) (p = 1.000).

 

 

 

DISCUSSION

The results of the study revealed that the bond strength of
fiber posts inside the root canal differed significantly between different
pretreatment irrigating agents. In general, improvements in bond
strength values (MPa) were found in the following order: Ethanol > (17%EDTA+
2.5% NaOCl) = SmearOff >distilled water groups

Highest bond strength was achieved by Group 3 (99% Ethanol). This
could be attributed to ethanol’s “water-chasing” ability. It replaces the water in
the dentin, so the hydrophobic monomers are able to penetrate the dentin and
form a more stable hybrid layer.13 Previous studies have also indicated
that
insufficient moisture control in the depth of the root canal could be
compensated by ethanol wet bonding. It might increase the resin uptake and
sealing of the collagen matrix and probably also increase the degree of
conversion of hydrophilic adhesives.14 The results of this study are
in accordance with the study by Bitter et
al. 15 which concluded that ethanol significantly increased bond
strength in case of the etch-and-rinse adhesive approach and a self-adhesive resin
cement inside the root canal.

The use of 17% aqueous EDTA (ethylenediaminetetracetic acid) in
conjunction 2.5% NaOCl (Sodium hypochlorite), as a post space irrigant has showed
better bond strength values as compared to that of the control group in the
present study. EDTA, acts as a calcium chelator that dissolves the smear layer.7
Also, the relatively low surface tension of aqueous EDTA might improve the
dentine wettability. 17 Sodium hypochlorite, dissolves the
organic components (mainly collagens) of the smear layer, and increases the
penetration monomers into the demineralized dentin structure. However, on
application of 5% NaOCl to dentin’s surface, it breaks down to sodium chloride
and oxygen. The released oxygen causes strong inhibition of the interfacial
polymerization of resin bonding materials, resulting in decreased bond strngth.16
However, a study by Arisu et al.18
concluded that increased dentin bond
strengths were demonstrated when post space irrigation was performed with NaOCl
and EDTA, with use of self-etching adhesives, as compared to pretreatment with NaOCl
alone and diode laser.

SmearOFF is a recently introduced
irrigant contains a synergistic combination of both EDTA and Chlorhexidine
digluconate (CHX). The manufacturer claims that, EDTA enhances the demineralization
of radicular dentin due to its chelating effect, whilst disinfecting  the canal at the same time due to presence of
CHX. Matrix metalloproteinases
(MMPs) and cysteine cathepsins present in mineralized dentin contribute to
collagen fibrils degradation, hindering the quasi-static mechanical
properties of the collagen matrix. Therefore, the use of MMP inhibitors; such
as chlorhexidine, prior to the bonding appears to be a rational step for
extending the longevity of the hybrid layer.14 Yet, in the present
study, comparable bond strengths were recorded by Group 2 (17% EDTA + 2.5%
NaOCl) and Group 4 (SmearOFF). Hence, it can be said that the bond strength achieved
in Group 4 ( SmearOFF) can be mainly attributed to EDTA’s chelating property
which leads enhanced smear layer
removal, rather than the MMP inhibition by CHX. Also, previous studies by
Bitter et al. 6, Cecchin et al. 15 have
concluded that, irrigation of the post space by chlorhexidine displayed results
comparable to  that of  the control group. In addition, Lindblad et al. 19investigated the
efficacy of chlorhexidine in increasing the resin cement bond strength, indicated
that no negative effects were observed.

The bonding
mechanism of adhesive systems to root canal dentin is based on hybridisation of
the demineralised surface and on resin tags and lateral branch formation.20Tubule
density and diameter of the tubules decreases in the apical direction, which
may influence the micromechanical bonding mechanism of the adhesive systems.21
 Other reasons for variable bond strengths
in different root regions  have been stated to
be,  technical sensitivity, the
difficulty of applying an adhesive in a narrow post space, and limited light
transmission to the apical region. 22 In the past decade,
self-adhesive resin cements were introduced to provide easier clinical
application compared with regular resin cements. RelyX U200 (3M ESPE), is the
most widely used self-adhesive resin cement. Its adhesive properties have been
based on acid monomers that demineralize and simultaneous infiltration by
methacrylate monomers of the tooth substrate, creating micromechanical
retention and chemical bonding to hydroxyapatite.23 The results
of this study  also indicate that
different root regions (coronal,
middle, apical) exhibited comparable push-out bond strengths, this could
be attributed to the above mentioned properties of the self-adhesive resin
cement.  However, future studies must be conducted to examine the long-term
effects of different post space irrigation 
procedures on the bond strength of self-adhesive resin cement to inter
radicular dentin.

 

CONCLUSION

Within the limitations of this
in-vitro study it can be concluded that; pretreatment of the post space using 99%
Ethanol can be recommended as a final rinse prior to luting of pre-fabricated fiber
posts. SmearOFF can be used as a viable single solution alternative to use of
the combination of EDTA +NaOCl, with respect to post space irrigation.

 

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