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ORIGINAL ARTICLE
Year : 2020  |  Volume : 23  |  Issue : 6  |  Page : 811-816

The effect of nonthermal plasma on the push-out bond strength of two different root canal sealers


1 Department of Endodontics, Eskisehir Osmangazi University, Faculty of Dentistry, Eskisehir, Turkey
2 Department of Endodontics, Necmettin Erbakan University, Faculty of Dentistry, Konya, Turkey
3 Department of Prosthodontics, Eskisehir Osmangazi University, Faculty of Dentistry, Eskisehir, Turkey

Date of Submission22-Oct-2019
Date of Acceptance03-Feb-2020
Date of Web Publication11-Jun-2020

Correspondence Address:
Dr. K Y Yeter
Department of Endodontics, Eskisehir Osmangazi University, Faculty of Dentistry, 26480 Eskisehir
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_578_19

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   Abstract 


Background: An optimum bonding between the sealer and dentin is important for impermeable root canal filling and many procedures were applied to improve root canal dentin and in turn the bond strength between the sealer and dentine. There is lack of sufficient data on the effect of nonthermal plasma application on the bond strength of sealers to the root canal dentin. Aim: The purpose of this study was to evaluate the effect of NAP on the push-out bond strength (PBS) of a bioceramic and resin-based root canal sealer (RCS) to root canal dentin. Materials and Methods: Forty single-rooted mandibular premolars were decoronated. After preparation and final irrigation, the specimens were divided into four groups (n = 10). Group AH: Root canals were filled with gutta-percha (GP) and AH Plus RCS, Group P-AH: Root canals were filled with GP and AH Plus RCS following the NAP application, Group BC: Root canals were filled with GP and Endosequence BC RCS, and Group P-BC: Root canals were filled with GP and Endosequence BC RCS following the NAP application. Then roots were sectioned horizontally to obtain ~1 mm thick dentin disks. PBS test was performed to the second (coronal) and fourth (middle) slices. Data were analyzed with the Kruskal–Wallis and t-test. Results: There was a statistically significant difference among the groups for both coronal and middle regions (P < 0.05). P-BC group showed higher PBS than AH and P-AH groups in the coronal region. P-BC group showed higher PBS than the other groups in the middle region. Conclusions: The use of NAP did not influence the push-out bond strength of AH-Plus sealer to the root canal dentin. The Endosequence-BC sealer showed a better bond strength than the AH-Plus sealer after NAP application.

Keywords: Bioceramic sealer, epoxy resin sealer, non-thermal atmospheric pressure plasma, push-out bond strength


How to cite this article:
Yeter K Y, Gunes B, Terlemez A, Seker E. The effect of nonthermal plasma on the push-out bond strength of two different root canal sealers. Niger J Clin Pract 2020;23:811-6

How to cite this URL:
Yeter K Y, Gunes B, Terlemez A, Seker E. The effect of nonthermal plasma on the push-out bond strength of two different root canal sealers. Niger J Clin Pract [serial online] 2020 [cited 2020 Jul 15];23:811-6. Available from: http://www.njcponline.com/text.asp?2020/23/6/811/286442




   Introduction Top


A complete debridement, elimination of microorganisms, and a fluid-tight seal filling of the root canal system is necessary to provide a successful root canal treatment.[1] This prevents recontamination of root canal syWstem with microorganisms and their by-products which are the main factors of pulpal and periapical pathosis.[2] Using gutta-percha (GP) with root canal sealers (RCSs) is the common procedure to fill the canals.[3] Bonding between the dentin and RCSs through micromechanical retention or frictional resistance is favorable in sustaining the unity of sealer–dentin interface.[4],[5]

Many types of RCSs are available in the market. Recently, bioceramic-based RCSs like mineral trioxide aggregate (MTA) are favored because of their biocompatibility and bioactivity.[6],[7]

Endosequence BC (Brasseler USA, Savannah, GA), a bioceramic-based RCS, is composed of tri- and di-calcium silicate, calcium hydroxide, calcium phosphates, and colloidal silica as inorganic components.[8] It can be used as a premixed paste as it contains water-free thickening vehicles. Zirconium oxide was added to the sealer as the radiopacifier.[9] It is a hydrophilic and insoluble material that uses the moisture in the dentinal tubules to accomplish the setting procedure.[10]

AH Plus (Dentsply, Konstanz, Germany), an epoxy resin-based RCS, is defined as the “gold standard” in literature. In addition, it is the most commonly used RCS [11],[12] which contains Bisphenol-A and Bisphenol-F epoxy resins, zirconium oxide, calcium tungstate, silica, aerosol, and iron oxide pigments in Paste A; N-Dibenziyl-5-oxanonane, silica, aminoadamantane, TCD-diamine, calcium tungstate, tricylodecane-diamine, silicone oil aerosol and zirconium oxide in Paste B. AH Plus has some advantages such as biocompatibility, low solubility, and adhesion to dentine.[12]

There are many applications that could change the surface properties of root canal dentine to improve the bond strength between the sealer and dentin. These procedures change the physical conditions of dentine by removing the smear layer, thereby opening the dentinal tubules and increasing the wettability of root canal dentin.[13],[14],[15]

Plasma that contains highly reactive particles such as electrons, ions, electronically excited neutrals, and free radicals is the fourth state of the matter. Nonthermal atmospheric plasmas (NAP) are partially ionized gases at room temperature.[16],[17] The highly energetic particles are carried to the plasma-treated surfaces after plasma application.[18] NAP treatment causes changes on the surface energy of the materials and increases the bonding ability of the plasma-treated surface.[19] In recent years, NAP has several applications in dentistry such as root canal disinfection,[20] tooth bleaching,[21],[22] changing dentinal conditions to improve adhesion.[23] NAP improves the adhesive properties between the enamel, dentinE and composites and also increases the wettability of enamel and dentin.[17] The dentin tubules were found to develop hydrophilic property upon NAP treatment and thus increase the penetration depth of the adhesive materials.[19],[24] Many studies [23],[25],[26] showed that NAP improved the bonding strength between dentin and adhesive materials. To our knowledge, no study has compared the effect of NAP application on the push-out bond strength (PBS) of Endosequence BC sealer.

The purpose of this ex-vivo study was to investigate the effect of NAP application on the PBS of a bioceramic- and a resin-based RCS to dentine. The null hypothesis was that nonthermal plasma has no effect on the PBS of sealers.


   Materials and Methods Top


Specimen selection

The protocol of this study was approved by the Ethics Committee of the Eskisehir Osmangazi University (80558721/G-56). Freshly extracted 40 human mandibular premolars were used. Inclusion criteria were: teeth with a single and straight root canal; a straight, nonresorbed, noncarious, and at least 15 mm length root without any cracks. Teeth were stored in distilled water and decoronated 15 mm from the apex with a high-speed handpiece under water cooling.

Root canal preparation

A #10 K file was inserted into the root canal until it was visible from the apical foramen to measure the working length. After working length determination, the root canals were prepared with a single file system (Reciproc R50, VDW, Munich, Germany). 5% NaOCl was used for irrigation during the preparation procedure. Final irrigation was performed with 5 mL of 17% EDTA, 5 mL of 5% NaOCl, and 5 mL of distilled water, respectively. The root canals were dried with paper points before the filling procedure.

Splitting the specimens

Specimens were divided into four experimental groups: (n = 10)

Group AH: Root canals were filled with AH Plus sealer and GP,

Group P-AH: Root canals were filled with AH Plus sealer and GP following the NAP application,

Group BC: Root canals were filled with Endosequence BC sealer and GP,

Group P-BC: Root canals were filled with Endosequence BC sealer and GP following the NAP application.

NAP application

For plasma application, a plasma jet equipment with Argon gas (Kinpen 11, Neoplas, Germany) was used with a flow rate fixed as 5 L/min. [Figure 1]. The pressure of argon gas was stabilized at 2.5 bars and the length between the root canal orifice and the nozzle of plasma was fixed and standardized as 5 mm throughout the whole plasma application process. Plasma application was performed to each root canal for 30 sec with a 15-mm-length plasma stream.
Figure 1: Application of NAP into the root canal

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All root canals were filled with the cold lateral compaction technique. After the procedure, the orifices of the root canals were sealed with a temporary filling material (CavitG, 3M ESPE, Germany).

Preparation of specimens for push-out test

Specimens were incubated at 37°C and 100% humidity for 1 week to allow setting of the RCSs. Then the specimens were buried perpendicularly in autopolymerized acrylic resin (Meliodent, Bayer Dental, Leverkuser, Germany) and the roots were sectioned horizontally with a low speed, water-cooled diamond saw (Buehler, IL, USA) to obtain ~1 mm thick slices. The first two slices from the corona were termed as coronal and the third and fourth were termed as middle. [Figure 2]
Figure 2: Schematization of the preparation of the dentin disks for the push-out test and implementation of push-out test

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PBS test

PBS test was performed on the second and fourth slices. A metallic plunger with the speed of 0.5 mm/min was used in the apical–coronal direction [Figure 2] until the root filling material was displaced from the root canal with a universal testing machine (Instron). The maximum load was quantified in Newtons (N). The N value was converted to megapascals (MPa) for each segment by dividing the N value into the total bonding area. The total bonding area was calculated with this equation for each dentin disk: π(r1+ r2) h, where h is the thickness of disk, r1 apical radii of the root canal, r2 is the coronal radii of the root canal, and π =3.14.

Statistical analysis

Data were statistically analyzed with the statistical package program SPSS 18.0 (SPPS Inc, Chicago, IL, USA). The significance threshold was determined as 5%. According to the Kolmogrov–Smirnov test, the data was not normally distributed. So, the Kruskal–Wallis test and t-test were performed for the statistical analysis of the obtained data.


   Results Top


The mean and standard deviation values of each experimental group are shown in [Table 1]. There was a statistically significant difference between the groups with regard to both coronal and middle regions (P < 0.05). In the coronal region, while the P-BC group showed higher PBS than the AH and P-AH groups, no statistically significant difference was found between the P-BC and BC groups. In middle region, the P-BC group showed higher PBS than all the other groups. Upon comparison of the bond strength values of the coronal and middle regions, a significant difference was found only in the P-AH group (P < 0.05). The coronal region showed higher PBS than the middle region in the P-AH group. However, there was no significant difference with respect to the different root regions in the AH, BC and P-BC groups. (P > 0.05)
Table 1: Mean bond strength values of coronal and middle thirds in MPa

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The failure modes were determined under stereomicroscope as adhesive, cohesive, and mixed failures. Adhesive failure is the failure at the sealer–dentin interface; cohesive failure is the failure within the filling material, and mixed failure is the occurrence of both adhesive and cohesive failures in a specimen. Representative SEM images were obtained for each failure mode. The examples of failure modes are shown in [Figure 3]. The distribution of the percentage of failure modes are shown in [Table 2]. In the AH group, the most dominant failure mode was mixed for both coronal and middle regions. In the P-AH group, the most common failure mode was mixed for coronal region but mixed and adhesive failure modes occurred evenly in the middle region. In the BC group, mixed failure mode was the dominant mode for both coronal and middle regions. In the P-BC group, cohesive failure mode was the most common mode for coronal region and the percentage of cohesive and mixed failure modes were equal.
Figure 3: SEM images for each failure mode. (a) Adhesive failure mode, (b) cohesive failure mode, (c) Mixed failure mode

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Table 2: Distribution of failure modes in percentages (%)

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   Discussion Top


NAP application is a contemporary subject in endodontics. Excited atomic, molecular, ionic, and free-radical species are included in NAP which is a partially ionized gas.[26] These species can enhance the surface energy of the applied area, making it perform better molecular interactions.[27] This characteristic of cold plasma could improve the adhesion of dentin surface/adhesive material.[26] In this study, the effect of 30 s NAP application on the PBS of AH Plus and Endosequence BC sealers was evaluated.

In this study, for testing the bond strength of resin cement to the root dentin, the push-out test was used. The PBS test provides uniform stress distribution throughout the resin–dentin interface of the dentin disk and lessens the occurrence of premature failures. Also, it allows to examine the bond strength of different root canal regions. The thickness of the dentin disk is also important for push-out testing. The optimum thickness for the disks was reported to be 1 mm because with decreased thickness of dentin disks, the risk of friction and stress distribution decreased.[28] Diameter of the plunger is another factor that can affect the results of PBS test. The ratio of the diameter of the plunger and GP must be more than 60%.[29] All of these factors that may affect the results of PBS test were considered throughout the study and the thickness of the dentin disks were determined as 1 mm. The tip of the plungers was determined as 0.8 mm for coronal region and 0.6 mm for middle region in accordance with the apical diameter of the coronal and middle sections.

Ritts et al. (2010) found that NAP application for 30 s increased the bonding of the dental composite to dentin while prolonged application of plasma adversely affected the bond strength.[23] Also, Abreu et al. evaluated the effect of 15 s, 30 s and 45 s NAP application on the microtensile bond strength of adhesives and the results showed that 30 s NAP application improved the microtensile bond strength.[30] A study by Chen et al. stated there was no significant difference between 30 s and 45 s plasma application on the wettability of dentin surface [31] and after 30 s NAP treatment, the water contact angle values decreased to <5°, which was close to a value of super hydrophilic surfaces. So, in this study, the application time was determined as 30 s.

According to the results of this study, plasma application has significant effects on the PBS of calcium silicate-based Endosequence BC sealer in such a way that in the coronal region AH and P-AH groups showed lower PBS value than the P-BC group. Although the P-BC group showed higher PBS values than the BC group in the coronal region, the difference was not statistically significant. The P-BC group showed higher PBS than all the other groups in the middle region. So, the null hypothesis was rejected. Endosequence BC sealer is a tricalcium silicate-based and hydrophilic RCS. During the setting process, the sealer creates a chemical bond with root canal dentine by producing hydroxyapatite. In addition, it can easily spread over the dentinal walls due to its low contact angle.[32] Changes on the root canal dentin surface after NAP application such as wettability, chemical interactions, and grafting hydrophilic groups on to the surface could increase the dentinal tubule penetration of BC sealer. After 30s plasma application, the contact angle values decrease and the low contact angle values define the hydrophilic surface properties.[16] However, carbonyl groups of dentin surface increase after argon plasma application. These carbonyl groups enhance the hydrophilic property of dentin surface.[25] This might be an advantageous factor for BC sealer besides chemical bonding to dentin. The reason of the higher bond strength values of Endosequence BC sealer after NAP treatment might be this surface modification.

It has been previously reported that plasma application caused lower bond strength value of MTA-Fillapex group and plasma application did not affected the bond strength value of AH Plus.[33] The finding of our study partly in agreement with this study. According to our result there is no difference on PBS of AH-Plus RCS with or without NAP application. However, our conflicting results about MTA Fillapex and Endosequence BC sealer could be arising from different ingredients, different physical properties such as fluidity of the sealers and different application methods of nonthermal plasma.

Failure mode results indicate that P-BC group has a higher percentage of cohesive failures than the other groups which means better bond strength to root canal dentin. This failure mode result is compatible with push-out bond strength test results of the present study.

Future studies are needed to say accurate information about effects of plasma application to root canal dentin for improving the bond strength of RCSs.


   Conclusion Top


Under the limitations of the present ex-vivo study, NAP application had no effect on the PBS of AH Plus to the root canal dentin for both coronal and middle regions. NAP application positively affects the PBS of Endosequence BC sealer in middle region but it was not effective in coronal region.

Acknowledgements

This study was presented as an oral presentation at CED-IADR/NOF Oral Health Congress in Vienna, Austria, 2017. The authors would like to thank to Dr. Yasin ALTAY from Eskisehir Osmangazi University, Faculty of Agriculture for statistical analysis.

Clinical relevance

The application of nonthermal plasma into the root canal walls provides a better bond strength while using bioceramic-based root canal sealers for obturation procedure.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Tables

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