| Abstract|| |
Aim: To evaluate the effect of different irrigating solutions on postspace treatments on the push-out bond strength of glass fiber posts.
Materials and Methods: Thirty mandibular premolar roots were decoronated and endodontically treated. Postspaces were prepared and roots were divided into three groups: In group 1: 2.5% sodium hypochlorite irrigation (control), group 2: 17% ethylenediaminetetraacetic acid (EDTA) with hand activation, group 3: 17% EDTA irrigation with photon-induced photoacoustic streaming (PIPS) has been done to the postspaces. Scanning electron microscope (SEM) analysis has been made for two samples of each group. Fiber posts were then luted with resin cement. Each root was prepared for push-out test. Data have been statistically analyzed.
Results: SEM results showed clean postwalls with both group 2 and group 3, whereas group 1 showed adhesion of resin cement to intraradicular dentine. When all groups were compared, the bond strength values are higher with group 2 followed by group 3.
Conclusion: Within the limitations of the study, clean postwalls and the highest bond strength values were obtained from 17% EDTA with hand activation and 17% EDTA with PIPS.
Keywords: Ethylenediaminetetraacetic acid; glass fiber posts; photon-induced photoacoustic streaming; push-out test; scanning electron microscope
|How to cite this article:|
Vangala A, Hegde V, Sathe S, Dixit M, Jain P. Effect of irrigating solutions used for postspace treatment on the push-out bond strength of glass fiber posts. J Conserv Dent 2016;19:82-6
|How to cite this URL:|
Vangala A, Hegde V, Sathe S, Dixit M, Jain P. Effect of irrigating solutions used for postspace treatment on the push-out bond strength of glass fiber posts. J Conserv Dent [serial online] 2016 [cited 2020 Feb 28];19:82-6. Available from: http://www.jcd.org.in/text.asp?2016/19/1/82/173206
| Introduction|| |
Posts and cores are commonly used in endodontically treated teeth suffering from excessive loss of the coronal tooth structure. Specially, fiber posts play a significant role in the restoration of such teeth. 
Bond strength between the postmaterial and a resin luting agent, as well as the bond strength between the resin luting agent and postspace dentin remains an important factor for the retention of fiber posts in the roots. ,
After the preparation of postspace, heavy smear layer gets deposited on the dentine walls and creates hybrid layer. Removal of smear layer and debris from dentinal walls is necessary. This increases the retention when resin cement is used.  Previous studies have shown the use of various chemical irrigants, such as solutions of sodium hypochlorite (NaOCl) or ethylenediaminetetraacetic acid (EDTA) in combination with NaOCl to clean the postspaces.  EDTA was reported to be effective in the removal of the smear layer in root canals. Studies have shown that after irrigation with EDTA the dentine surface is clean and the dentinal tubules open widely, which facilitates adhesive resin to penetrate. This improves the push-out bond strengths of the post. 
Recent technologies such as laser irradiation have been investigated for the treatment of root canal dentine along with the routinely used chemicals.
An erbium-doped yttrium aluminum garnet (Er:YAG) laser equipped with the newly designed radial and stripped tip, when used in combination with 17% EDTA solution, with a very low pulse duration (50 μs) and low energy (20 mJ) results in effective debris and smear layer removal causing minimal or no thermal damage to the organic dentinal structure through a photoacoustic technique called photon-induced photoacoustic streaming (PIPS™).  Based on the available literature, this study was formulated to evaluate the effect of different irrigating solutions on postspace treatments on the push-out bond strength.
| Materials and Methods|| |
Thirty human mandibular premolar teeth with single roots were collected and used in the present study. All teeth were extracted for orthodontic reasons and kept according to Jainaen et al.,  in 1% chloramine T (pH 7.8) (Sigma-Aldrich Co. LLC) at 4°C until use. To standardize the root canal lengths, the roots were cut to a uniform length of 14 mm. The roots were endodontically instrumented by using rotary system (Protaper, Dentsply India Pvt. Ltd.) at a working length of 0.5 mm from the apex to F3 rotary file. Irrigation was performed using 2.25% NaOCl solution after each change of file size. The canals were dried with paper points (Sure Dent Corporation, Korea) and obturated with Gutta-percha (Sure Dent Corporation) and root canal sealer (AH plus, Dentsply, Dentsply India Pvt. Ltd.) using cold lateral condensation technique. The root canal of each sample was enlarged with a low-speed drill provided by the post system's manufacturer (reamers size #3, Mani Inc., Tochigi, Japan) to a depth of 10 mm. The roots were then randomly divided into four groups according to the postspace treatments. Group 1 was irrigated with 5 mL 2.5% NaOCl (UPS Hygienes Pvt. Ltd., Mumbai) for 1 min, group 2 was irrigated with 5 mL 2.5% NaOCl for 1 min followed 5 mL 17% EDTA (hand activation) (EDTA DeSmear, Ahmedabad, Gujarat, India) for 1 min and final irrigation was done with distilled water for 1 min, and group 3 was irradiated with a 2940-nm Er:YAG laser (Fotona Slovenia, EU) - PIPS (Fotona from Lightwalker; Fotona LLC USA). For this group, a coronal tooth structure has been restored with composite resin to simulate the pulp chamber for the placement of the PIPS tip. During laser irradiation, the root canals were continuously irrigated with 5 ml of 17% EDTA for 40 s in a sterile syringe, positioned above the laser tip in the coronal aspect. Laser settings were 20 Hz, 40 mJ, with air/water spray off. After finishing the treatment, wet postspaces were dried with paper points. From each group, two samples were split along the long axis in the linguo-buccal direction using a chisel and a hammer to expose the entire extent of the root canal and processed for scanning electron microscope (SEM) (Quanta 200, company FEI, The Netherlands; Marketed by Icon analytical equipment Pvt. Ltd.) assessment to observe the morphological changes of the root canal dentine after different postspace treatments.
A glass fiber post (Angeles DT, 308, Andheri West, Mumbai) 2 mm in diameter, was cemented into the remaining postspaces with a resin cement (RelyX TM ARC - made in USA by 3M ESPE dental products, St. Paul, USA) according to the manufacturer's instructions for the remaining samples. All samples were stored in saline solution in light proof boxes for 1 week at 37°C. The roots were then sectioned transversely starting 1 mm below the cement-enamel junction using diamond points on a low-speed drill and mounted in methacrylate resin. Push-out test was performed at a cross-head speed of 3 mm/min using a universal testing machine (computerized software based. Company - Star Testing Systems, India). The data were statistically analyzed using one-way analysis of variance (ANOVA).
P values were obtained using one-way ANOVA with post-hoc Tukey's correction for multiple group comparisons Software - XLSTAT 2015.1.
Values on push-out bond strength across three study groups at each level are shown using mean ± standard deviation.
The comparison of distribution of average push-out bond strength is done using one-way ANOVA with post-hoc Bonferroni's test for multiple group comparisons. The intra-group comparison (comparison of levels) is done using independent sample t-test. The underlying normality assumption was tested before subjecting the push-out data to the parametric statistical analysis. The entire data were entered in MS Excel before it was statistically analyzed in SPSS (version 11.5). All the results are shown in tabular form as well as graphical format to visualize the statistically significant difference more clearly.
The P < 0.05 are considered to be statistically significant. All the hypotheses were formulated using two-tailed alternatives against each null hypothesis (hypothesis of no difference). The entire data were analyzed statistically using Statistical Package for Social Sciences (SPSS version 11.5, Inc., Chicago, USA) for MS Windows.
| Results|| |
In the present study, the morphological changes in intraradicular dentine at the middle region after different postspace treatments were evaluated. The control (NaOCl) group was covered by a thick smear layer and debris, and no dentine tubule openings were present [Figure 1]a. In EDTA group with hand activation, all of the dentinal tubules were opened and widened tubular dentine was seen [Figure 1]b. In EDTA group with PIPS activation, the dentine surface was cleaner compared with the control group with less smear layer and debris and some dentinal tubules were open [Figure 1]c. The push-out bond strength was evaluated [Table 1]a and b and Graph 1].
|Figure 1: (a) Group 1: Scanning electron microscope image — thick smear layer, no dentinal tubule openings (b) Group 2: Scanning electron microscope image - open dentinal tubules, widened tubular dentine (c) Group 3: Scanning electron microscope image — less smear layer, debris, dentinal tubules open|
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| Discussion|| |
Fiber posts play a role of crucial importance in the restoration of endodontically treated teeth with a large amount of coronal tooth structure missing to retain a core for definitive restoration.  Fiber posts showed a reduced risk of failure and more favorable outcomes when compared with the traditional metallic posts because of their Young's modulus closely matching to that of tooth structure. 
Unlike metal or cast posts, where failure has been reported from the root fracture, the fiber posts resulted in lack of retention due to the pull out of the cement. Bond strength between the postmaterial and a resin luting agent, as well as the bond strength between the resin luting agent and postspace dentin dictates the retention of fiber posts in the roots. 
For measuring the adhesion of fiber posts to root canal walls, a valid method is the thin-slice push-out strength test than the microtensile technique. This test makes it easy to fabricate several specimens out of one root, as well as testing for regional differences between root sections. And hence, in the present study, effects of different postspace treatments on adhesion of glass fiber post using a push-out test has been evaluated. ,
On postspace preparation, heavy smear layer is created. It is necessary to remove this smear layer so that a hybrid layer is achieved to increase the retention when resin cement is used. Several studies have shown the effectiveness of NaOCl to dissolve the organic tissues and neutralize the toxic products whereas aqueous EDTA has a calcium ion chelating capacity and showed to have high efficiency in removing smear layer. It is still a challenge to create a favorable environment for clinical success in root canal treatment. 
Studies have reported that near infrared lasers (up to 750 μ with the 810 nm diode laser and up to 1 mm with the 1064 nm neodymium-doped yttrium aluminum garnet laser) are efficient in disinfecting the root canal surfaces and dentinal walls. However, these wavelengths still fall short in debriding and cleansing the root canal surfaces effectively as well as cause characteristic morphological alterations of the dentinal wall. The smear layer was only partially removed and the dentinal tubules primarily closed as a result of the melting of inorganic dentinal structures. Recent studies have reported how the use of an Er:YAG laser using "PIPS™," in combination with 17% EDTA solution, with a very low pulse duration (50 μs) and low energy (20 mJ) resulted in effective debris and smear layer removal with minimal damage to the organic dentinal structure.  In the present study, no thermal damage was observed in any of the samples during the procedure.
According to the results of the present study, the NaOCl group was covered by a thick smear layer and debris and no dentine tubule openings were present [Figure 1]a. In EDTA group with hand activation, all of the dentinal tubules were open, and widened tubular dentine was seen [Figure 1]b. In EDTA group with PIPS activation, the dentine surface was cleaned compared with the control group with less smear layer and debris and most of the dentinal tubules were open [Figure 1]c, which may facilitate the penetration of adhesive resin. This might improve the push-out bond strengths of the post. In the current study, the lowest bond strength results were obtained from the NaOCl group. SEM observations certified that the dentine surface on the postspace walls was not clean. Negative effect of NaOCl irrigation on the adhesion of resin cement to intraradicular dentine has also been reported in some studies. NaOCl breaks down into sodium chloride and oxygen. This liberation of oxygen inhibits the polymerization of resin bonding materials which interferes with resin infiltration into demineralized dentine. The residual chemical irrigants and their products are likely to diffuse into the dentinal tubules, this affects the infiltration of the resin into the demineralized dentine or interferes with the complete polymerization of the adhesives. ,
In each study group of this study, the average push-out bond strength did not differ significantly between cervical and middle levels. However, the cervical level has shown better push-out bond strength when compared. It has been shown that tubule density is greater in the coronal and middle thirds than in the apical region of the root canal, and the diameter of the tubules decreases in the apical direction. The difference in the number of tubules suggests the strongest adhesion which is achieved in the coronal regions. ,,
Due to this, the push-out bond strength values of the cervical segments of the root canal dentine were significantly higher than the middle segments. The bonding mechanism of adhesive systems to intraradicular dentine is based on the hybridization of the demineralized surface and on resin tags and lateral branch formation. As we go apically in the root canal, the tubule density and diameter of the tubules decreases. This has an influence on the micromechanical bonding of the adhesive systems.  As previously verified, decrease in the adhesive values of root middle segments might probably be caused by difficulty in the adhesive polymerization by the halogen light in deeper regions of canal. A reduction of strength in middle third is related to the distribution of resin cement with void formation or traces of Gutta-percha and endodontic sealer that may remain in these thirds after postspace preparation. The coronal portion of the canal is the most accessible part of the canal space. Hence, it is easy to etch and apply the adhesive agents and hence showed maximum bond strength values.
| Conclusion|| |
Within the limitations of the study, it has been concluded that:
- At each level, the average push-out bond strength is significantly higher in groups 2 and 3 compared to group 1.
- At each level, the average push-out bond strength did not differ significantly between groups 2 and 3.
- In each study group, the average push-out bond strength did not differ significantly between cervical and middle levels.
We express special thanks to Mr. Sayyed Mehmood for his kind advice in the statistical analysis of the research.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. Amulya Vangala
M A Rangoonwala Dental College, Azam Campus, Camp, Pune - 411 001, Maharashtra
Source of Support: None, Conflict of Interest: None