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Year : 2018  |  Volume : 8  |  Issue : 2  |  Page : 128-132

Evaluation of push-out bond strength of GuttaFlow 2 to root canal dentin treated with different smear layer removal agents

Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Manipal University, Manipal, Karnataka, India

Date of Web Publication5-Apr-2018

Correspondence Address:
Dr. Tina Puthen Purayil
Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Manipal University, Manipal, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/sej.sej_69_17

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Aim: The purpose of this in vitro study was to evaluate and compare the effect of 7% maleic acid and QMix root canal irrigants on the push-out bond strength of GuttaFlow 2 to root canal dentin.
Materials and Methods: Thirty single-rooted maxillary incisors were taken and decoronated to a standardized root length of 15 mm. Canal patency was established and working length was determined using #15 K file. The root canals were then prepared to F3 size using nickel-titanium ProTaper rotary instruments with 3 ml of 2.5% sodium hypochlorite irrigation performed between each instrumentation. Then, based on the final irrigation regimen, the specimens were randomly divided into three groups (n = 10): Group 1: QMix, Group 2: 7% Maleic acid, and Group 3: 0.9% Saline (control group). The root canals were obturated using GuttaFlow 2 sealer and 2-mm horizontal thick sections of each root were prepared at three levels using a hard tissue microtome. Push-out bond strength was measured using a universal testing machine by application of compressive force to each root canal filling at a crosshead speed of 1 mm/min.
Results: Group 3 showed significantly higher bond strength values than Group 1 and 2 in all the three levels of the root canal.
Conclusion: The smear layer removal using 7% maleic acid and QMix as a final rinse did not enhance the bond strength of GuttaFlow 2 to radicular dentin.

Keywords: Endodontic irrigants, GuttaFlow 2, maleic acid, push-out bond strength, QMix

How to cite this article:
Upadhyay ST, Purayil TP, Ballal NV. Evaluation of push-out bond strength of GuttaFlow 2 to root canal dentin treated with different smear layer removal agents. Saudi Endod J 2018;8:128-32

How to cite this URL:
Upadhyay ST, Purayil TP, Ballal NV. Evaluation of push-out bond strength of GuttaFlow 2 to root canal dentin treated with different smear layer removal agents. Saudi Endod J [serial online] 2018 [cited 2023 Feb 3];8:128-32. Available from: https://www.saudiendodj.com/text.asp?2018/8/2/128/229356

  Introduction Top

Mechanical instrumentation of root canals during endodontic therapy usually results in the formation of a smear layer.[1] Smear layer is an amorphous irregular structure containing dentin debris, pulp remnants, bacteria, and endotoxins which covers the dentinal surfaces of root canal and plugs the dentinal tubules.[2] Several studies have demonstrated that the smear layer removal results in improving the root canal sealing ability,[3] and hence, its total removal facilitates the penetration of root canal irrigants, intracanal medicaments, and sealers into the dentinal tubules. Further, it also increases the sealing ability of root canal obturating materials by reducing their apical and coronal microleakage levels.[4]

Sodium hypochlorite (NaOCl) is an excellent antimicrobial agent with nonspecific proteolytic action, which is the most commonly employed irrigant in the root canal therapy.[5] However, it does not remove the inorganic part of the smear layer.[5] Hence, in addition to NaOCl, it is essential to remove the smear layer with the use of a chelating agent.[6] Thus, final irrigation with a chelating agent plays an important role in the success of an endodontic treatment. Numerous chelating agents such as ethylenediaminetetraacetic acid (EDTA), maleic acid, citric acid, peracetic acid, etridonic acid, mixture of tetracycline, acid, and detergent (MTAD) and tetraclean have been used for the removal of smear layer.[7]

Maleic acid is a mild organic acid, which has the property of smear layer removal.[8] Final irrigation of root canal system with 7% maleic acid was found to be more effective for the removal of smear layer in the apical third, when compared to 17% EDTA.[8],[9]

QMix 2 in 1 is a root canal irrigating solution for smear layer removal, it has a mixture of polyaminocarboxylic acid calcium-chelating agent (EDTA), bisbiguanide antimicrobial agent (chlorhexidine), water, and a surfactant.[10] QMix formulations have performed superior smear layer removal and exposure of root canal dentinal tubules compared to 17% EDTA.[11]

Various root canal obturating materials have been developed in recent times, for improving the root canal seal and to increase the resistance of root canal treated teeth against tooth fracture.[12] GuttaFlow 2 is a self-curing, injectable cold flowable obturation system, with a combination of sealer and gutta-percha. It has polydimethylsiloxane matrix containing very finely ground gutta-percha (less than 30 μm) along with platinum catalyst, zirconium dioxide, and microsilver. It has been reported that GuttaFlow 2 expands by 0.2%, providing adequate adaptability to root canal walls.[13]

Adhesion of the obturating materials on to the root canal dentinal walls is essential both in static and dynamic situations, and it depends on multiple factors such as surface tension and wettability of the sealers, surface free energy of the core materials or dentin, and the cleanliness of the root canal surface. In addition, the adhesive bond can be affected by stresses caused by dimensional changes during setting of the sealers and differences in their thermal expansion coefficients.[14]

Different studies have reported that irrigation with various chelating agents resulted in improved bond strength values for root canal obturating materials.[15] A few studies have reported the bond strength and sealing ability of GuttaFlow 2 to radicular dentin [16] but, till date, no study has investigated the push-out bond strength of GuttaFlow 2 to root canal dentin after final irrigation with different smear layer removal agents. Thus, the aim of the study was to evaluate and compare the influence of 7% maleic acid and QMix root canal irrigants on push-out bond strength of GuttaFlow 2 to radicular dentin.

  Materials and Methods Top

Ethical clearance was attained from the Institutional Ethical Committee (IEC 709/2014) of Manipal University, Manipal. Thirty noncarious, single-rooted human maxillary incisors with fully formed apex, and single canal were selected for this study. Teeth with incompletely formed root apex, fractured/restored or cracked teeth, teeth with development defects, endodontically treated teeth, teeth with bifurcating canals, or calcified canals were excluded from the study. After surface debridement with scaling instruments, the samples were kept in 0.2% sodium azide (Sigma-Aldrich, London) at 4°C till used. Crown portion of each tooth was decoronated using diamond disc (Horico, Germany) to standardize the root length to 15 mm. Pulpal tissue was removed using barbed broach (Mani, Japan), and working length was determined using number 15 K file (Mani, Japan). Root canal orifice was enlarged using Gates Glidden drills (Dentsply Tulsa dental specialties, Switzerland) up to number 3 size. The root canals were then enlarged to F3 size using ProTaper nickel-titanium rotary instruments (Dentsply Tulsa dental specialties, Switzerland) with 3 ml of 2.5% NaOCl (Ricca chemical company, Arlington) irrigation performed between each instrument change for 1 min.

Based on the final irrigation regimen, the specimens were then divided randomly into three groups (n = 10):

  • Group 1: 3 ml of QMix (Dentsply Tulsa dental specialties, United States of America) for 1 min
  • Group 2: 3 ml of 7% Maleic acid (Sigma-Aldrich, London) for 1 min
  • Group 3: 3 ml of 0.9% Saline (Shijiazhuang No. 4 Pharmaceuticals, Hebei, China) for 1 min (control group).

After final irrigation, 5 mL of distilled water (David Gray, Western Australia) was used to rinse the root canal, to remove any precipitates that have formed.

The root canals were coated with GuttaFlow 2 (Coltene/Whaledent AG, Switzerland) using lentulo spirals (Dentsply Maillefer, Switzerland) after drying with sterile paper points (Dentsply Tulsa dental specialties, Switzerland). Then, F3 ProTaper GP (Dentsply, United Kingdom) was inserted into root canal up to the working length. The excess cone was sheared off using a heated instrument and vertically condensed with a plugger. All samples were then stored for 2 days at 37°C and 100% humidity to facilitate complete sealer setting.

Then, each root was vertically positioned and fixed in a cold cure acrylic resin (DPI-RR Cold Cure, DPI, Mumbai, India) using a custom-made mold (1.5 cm diameter and 3 cm height). After the setting of the cold cure resin, three horizontal sections were taken from coronal, middle, and apical thirds of each root using a hard tissue microtome (Leica SP1600 saw microtome, Leica Biosystems Nussloch GmbH, Heidelberger Str). This resulted in thirty 2-mm thick horizontal sections per each group with a total of 90 horizontal sections for all the three groups. Each section thickness was further measured and confirmed using a Pro-Max Electronic Digital Calliper (Fowler High Precision, Newton, Mass).

Push-out bond strength evaluation

The coronal and apical diameter of the obturated area of each section was measured under a stereomicroscope using Olympus DP2-BSW software (Olympus Corporation, Shinjuku-ku, Tokyo, Japan). 3 plungers of different sizes (0.9 mm, 0.7 mm, and 0.5 mm) were made each for coronal, middle, and apical third root sections based on the measured average diameters of the obturated areas.

Each section was then carefully positioned on a customized jig, and the plunger was positioned in such a way that it contacts only the root canal filling. The push-out test was executed at a crosshead speed of 1 mm/min using a universal testing machine (Instron 3366, Inston corp., Canton, USA) where compressive force was applied in an apico-coronal direction (because of the convergence of root canal sections) until the occurrence of bond failure. This was exhibited as a sudden drop along the load deflection with the extrusion of the obturation material. The maximum failure load was recorded in Newtons and push-out bond strength was measured using the formula:

The adhesion area was calculated using the following formula:

Where “r1” denotes coronal radius, “r2” denotes apical radius, and “h” represents the slice thickness.

Statistical analysis

Intra- and inter-group comparisons were made using two-way analysis of variance with post hoc Games–Howell test and post hoc Tukey's tests. The significance level was set at P < 0.05 (95% confidence level) and all the analysis was done using SPSS 18.0 software (SPSS Inc., Chicago, IL, USA).

  Results Top

The mean and standard deviations of push-out bond strength of GuttaFlow 2 to root canal dentin are represented in [Table 1]. Out of all the groups tested, Group 3 (Control) showed significantly higher push out bond strength when compared to Group 1 and Group 2 at coronal third (P = 0.001); middle third (P< 0.001); and apical third (P = 0.006) of the root canal system. When Groups 1 and 2 were compared, there was no significant difference between them at all the thirds of the root canal system (P > 0.05).
Table 1: Intergroup comparison of mean push-out bond strength of Guttaflow 2

Click here to view

  Discussion Top

Root canal irrigation with various solutions can alter radicular dentin's structural and chemical composition, leading to variation in its permeability and solubility characteristics.[17] This affects the adhesion of root canal filling materials to radicular dentin surfaces.[18] The intimate contact between the substrate and the adhesive material is required for optimum adhesion, either by micromechanical or chemical bonding. Consequently, the adhesion process is influenced by the relative surface free energy of the solid surface.[18]

As the chelating agents act on calcium ions present in the dentin, any alteration in its calcium content can considerably change the proportions of its organic and inorganic components. This results in altering the dentin wettability, permeability, solubility, microhardness, and can also affect the bonding of root canal filling materials to the radicular dentin.[14]

Some amount of interaction between sealers and irrigating solutions can be expected as both of these are chemicals.[19] The main objective of this study was to determine whether this interaction is synergistic or antagonistic or does not affect each other in either way. In the present study, the push-out bond strength of GuttaFlow 2 was considerably affected by the various irrigation regimens tested.

The bonding of root canal sealers to radicular dentin is prerequisite for maintaining the integrity of the dentin-sealer interface.[20] Among the various tests available to measure the bond strength of an obturating material, push-out bond strength was selected in the present study as this test is more reliable, reproducible and effective in better reflecting the clinical status of the bond strength failure.[21] This is less sensitive to small variations among specimens, discrepancies in stress distribution during load application and can evaluate materials even with low bond strength values.[22]

The wettability of root canal sealers to radicular dentin can be affected by sealer-related and dentin-related factors. Sealer-related factors include its surface tension and its hydrophobic or hydrophilic nature. The dentin-related factors are its surface free energy, hydration state, tubule density, homogeneity, roughness, and presence or absence of smear layer.[23]

To attain optimal wettability, the surface energy of the dentin needs to be as high as possible and the surface tension of the sealer contacting it should be as low as possible.[18],[24] The wettability of dentin by a sealer further depends on the surface treatment of root canal dentin by various irrigating solutions.[25]

Root canal irrigation with chelating agents, either alone or in combination with NaOCl reduces the surface free energy of the root canal dentin leading to decrease in its wettability. This in turn interferes with the bonding of root canal sealers to the dentin.[26] The chelating agents remove the inorganic portion of dentin, exposes the collagen fibers with low surface free energy, and makes the dentin surface hydrophobic.[27] The less bond strength values of GuttaFlow 2 when the root canal irrigated with maleic acid and QMix in the present study can be attributed to this hydrophobic nature of radicular dentin interfering with the wettability of GuttaFlow 2.

The chelating agents not only removes the smear layer but also causes demineralization of peritubular and intertubular dentin.[25] This makes the dentin tubules patent and also increases the surface roughness of dentin.[28] The coarser dentin surface might have resulted in poor wetting of GuttaFlow 2 to the root dentin surface. This can be attributed to the presence of silicone content in GuttaFlow 2, producing high surface tension forces and making the flow of this material more difficult.[25]

Final irrigation with maleic acid and QMix along with usage of NaOCl during root canal instrumentation had showed comparable smear layer and debris removal ability,[29] thus exhibiting similar radicular dentin surface for sealer interaction and penetration. This justifies the similar results of push-out bond strength of GuttaFlow 2 to radicular dentin in the two experimental groups of the present study.

5.25% NaOCl increases the wettability of root canal dentin significantly [27] because it dissolves proteins and removes organic portion of smear layer making the dentin surface hydrophilic.[24] The improved push-out bond strength values obtained for the control group can be attributed to better wettability of GuttaFlow 2 on the hydrophilic dentin surface created by NaOCl irrigation, which was performed in between each file size.

The bond strength values of the control group decreased in corono-apical direction as the apical dentin is more sclerotic than the other thirds of root canal.[30]

  Conclusion Top

Within the limitations of this in vitro study, it can be concluded that final irrigation with 7% Maleic acid and QMix did not improve the bond strength of GuttaFlow 2 to radicular dentin.


We would like to acknowledge Dr. Kishore Ginjupalli, Associate professor, Department of Dental Materials, Manipal College of dental sciences, Manipal University, for his assistance in push-out bond strength measurement.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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