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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 29  |  Issue : 1  |  Page : 47-52

Evaluation of residual root canal filling material after retreatment of canals filled with hydrophilic and hydrophobic obturating system: An in vitro scanning electron microscopy study


Department of Conservative Dentistry and Endodontics, YMT Dental College, Kharghar, Navi Mumbai, Maharashtra, India

Date of Web Publication25-May-2017

Correspondence Address:
L Murkey
801-A, Juhu Griha Swapna, Gulmohar Cross Road No. 4, Juhu Scheme, Mumbai - 400 049, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/endo.endo_14_17

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  Abstract 

Aims: The aim and objective of this in vitro study was to evaluate the remaining novel hydrophilic and conventional hydrophobic obturating material on the walls of root canals after retreatment under scanning electron microscopy (SEM).
Subjects and Methods: Sixty single-rooted human mandibular teeth were decoronated, prepared till F3 ProTaper (PTR) rotary files, and divided into three groups for obturation. Group 1 (control) – gutta-percha (GP) + AH Plus, Group 2 – C point + Smartpaste Bio, and Group 3 – GP + GuttaFlow 2. The teeth were retreated with PTR retreatment files and resin-based Endosolv R solvent. After final irrigation with 5 ml of 17% ethylenediaminetetraacetic acid followed by 5 ml of 5.25% sodium hypochlorite in all the samples, canals were dried using absorbent paper points and split into two halves using a diamond disk. The side of the root with the highest residual debris score was selected and each sample was divided into three equal parts as apical, middle, and coronal thirds. The samples were then evaluated using the SEM at ×1000 magnification. The data were tabulated and then subjected to statistical analysis using Kruskal–Wallis test and Mann–Whitney U-test (multiple comparisons).
Results: Results showed that PTR universal retreatment files along with Endosolv R solvent did not produce completely clean canals in any of the groups. Group 2 (Smart-Seal system) was difficult to retrieve from the middle and apical thirds of the root canal walls as compared to the Group 1 and Group 3 (hydrophobic groups).
Conclusion: None of the tested obturating systems could be completely removed from root canal walls however hydrophilic obturating system was difficult to retrieve as compared to hydrophobic system.

Keywords: GuttaFlow 2; hydrophilic; scanning electron microscopy; Smart-Seal system.


How to cite this article:
Hegde V, Murkey L. Evaluation of residual root canal filling material after retreatment of canals filled with hydrophilic and hydrophobic obturating system: An in vitro scanning electron microscopy study. Endodontology 2017;29:47-52

How to cite this URL:
Hegde V, Murkey L. Evaluation of residual root canal filling material after retreatment of canals filled with hydrophilic and hydrophobic obturating system: An in vitro scanning electron microscopy study. Endodontology [serial online] 2017 [cited 2019 Sep 21];29:47-52. Available from: http://www.endodontologyonweb.org/text.asp?2017/29/1/47/207000


  Introduction Top


Success of root canal treatment has been considered to rely on the control of pulp space infection. Dr. Schilder described the objective of root canal therapy as being “the total obturation of the root canal space” and “the sealing of the complex root canal system (RCS) from the periodontal bone that ensures the health of the attachment apparatus against breakdown of endodontic origin.”[1] The canal system should be sealed apically, laterally, and coronally, and various methods and materials are advocated for obturation.

An estimated 5.3% of patients experience tooth pain after nonsurgical root canal treatment.[2] This pain may be due to periapical inflammation caused by residual necrotic tissue or bacterial growth beneath the gutta-percha (GP) or sealer. The main causes of endodontic failure, making retreatment necessary, are insufficient cleaning and inadequate obturation. The endodontic failure cases can be treated in three ways: nonsurgical retreatment, surgical retreatment, or extraction. Among all these treatment alternatives, nonsurgical retreatment should be considered as the first choice of treatment. Success rates for orthograde retreatment are 65% to more than 80%.[3],[4] The main goals of orthograde retreatment are gaining access to the apical foramen by complete removal of the root canal filling material, thus facilitating sufficient cleaning and shaping of the complete RCS and final obturation.[5] Thus, new root canal filling materials have been introduced to increase the success of endodontic treatment; however, to fulfill the criteria of ideal materials they must be easily removable when retreatment is needed.[6]

Hence, the purpose of this study was to evaluate residual root canal filling material after retreatment of canals filled with GP + AH Plus, Smart-Seal system, and GP + GuttaFlow 2 with ProTaper (PTR) retreatment files and a resin-based Endosolv R solvent under scanning electron microscopy (SEM).


  Subjects and Methods Top


Mechanical preparation of the teeth

Sixty human single-rooted teeth were extracted and decoronated with a diamond disk to standardize the length of the samples to 13 mm. The root canals were prepared using PTR rotary instruments (Dentsply Maillefer) to size F3 (30/0.06 taper). Irrigation protocol was followed using 5.25% solution of sodium hypochlorite alternating with 17% ethylenediaminetetraacetic acid (EDTA) for 1 min with a 5 ml syringe using 27-gauge side venting needle placed 2 mm short of the working length (WL). Final rinse was done with 5 ml of sterile saline. Canals were then dried with sterile paper points.

The teeth were divided into three groups, twenty samples in each group which were obturated with the following:

  • Group 1 (control) - Master GP cone size F3 was coated with AH Plus sealer and slowly inserted inside the canal till the full WL followed by lateral condensation
  • Group 2 - Smartpaste Bio preloaded syringe sealer was inserted deeply into the root canal and the sealer was dispensed into the apical portion. C point size F3 was coated with Smartpaste Bio and inserted into the canal to the appropriate length using single cone technique as per the manufacturer's instruction. Excess sealer was removed with a moisten cotton pellet and the coronal excess of C point was trimmed using a high-speed handpiece with a diamond bur
  • Group 3 - Master GP cone size F3 was lightly coated with GuttaFlow 2 sealer and obturation was done using lateral condensation.


The samples were stored at a temperature of 37°C and 100% humidity for 2 weeks in an incubator for complete setting of the sealer.

Root canal retreatment

All the three groups were subjected to first-stage retreatment procedure, which included bulk removal with rotary PTR files.

To create a small reservoir for the Endosolv R solvent, D1 (0.09/0.30 mm) file was used to remove a small amount of obturating material at the orifice. The D1 file was then gently pressed into the obturation material to remove it from the coronal one-third of the canal space. D2 (0.08/0.25 mm) file was used to remove material incrementally from the middle one-third of the canal. Finally, PTR D3 (0.07/0.20 mm) file was used to remove material from the apical third of the canal space in a brushing action. Retreatment was deemed completed when no debris of the obturating system was visible on the surface of instruments and canal walls were smooth. During retreatment, all instruments were used in three canals and were then discarded.

Irrigation was done with 5 ml of 17% EDTA followed by 5 ml of 5.25% NaOCl in all the samples. Final rinse was carried out with saline and the canals were dried using absorbent paper points.


  Observation and Results Top


After instrumentation, the roots were split vertically on the buccal and lingual surfaces, using a water-cooled diamond disk and taking care to avoid touching the root canal. The side of the root with the highest residual debris score was regarded for further statistical analysis. The samples were then evaluated using the SEM at ×1000 magnification.

A 4-point grading system was used with respect to residual obturation material, and debris at the coronal, middle, and apical third of each canal were evaluated. Two blinded reviewers categorized sixty SEM images according to the following criteria by Somma et al.[7] Variation in the scoring occurred rarely, and when discrepancy was observed, an average of the scores was considered and rounded.

  • 0: 0%–25% of residual debris covering the dentinal surface
  • 1: <50% of the dentin surface covered with obturation debris
  • 2: 50%–75% of the dentin surface covered with obturation debris
  • 3: 75%–100% of the dentin surface covered with obturation debris.


The data were tabulated and then subjected to statistical analysis using Kruskal–Wallis test and Mann–Whitney U-test. In the above tests, P ≤ 0.05 was considered statistically significant. All analyses were performed using SPSS Statistics for Windows, Version 17.0. Chicago: SPSS Inc.


  Results Top


The statistical analysis of this study indicated that the hydrophobic obturating material was difficult to retreat from the middle as well as apical thirds of the canal [Graph 1 [Additional file 1]],[Graph 2 [Additional file 2]],[Graph 3 [Additional file 3]].


  Discussion Top


Various techniques have evolved to remove filling material from the canal such as the use of hand, rotary, reciprocating, heat-carrying instruments, chemical agents, ultrasonic device, and laser. Wilcox et al. suggested that removing all obturating materials from the root canal space is very difficult, and some traces of GP and sealer remain inadvertently in the canal after instrumentation regardless of the technique used.[8] In the current study, nickel–titanium (NiTi) retreatment rotary instruments along with Endosolv R solvent were used for the removal of the obturating material. It was reported that the PTR files could remove the obturating material from the coronal aspect of RCS [Table 1]. This was due to its convex triangular cross-section, a continuously changing helical angle, and pitch over their 14 mm of cutting blades. Tasdemir et al. have stated that the NiTi rotary files has 3 times more elastic flexibility than stainless steel files due to its very low modulus of elasticity and superior resistance to torsional fracture.[9] However, PTR files showed poor efficacy in removal of the obturating materials from the middle and apical thirds of the root canal space. This can be attributed to the fact that the middle and apical thirds of the RCS had greater compaction and penetration of obturating material into the dentinal tubule resulting in more remaining debris. This finding is similar to the study conducted by Madani et al. who evaluated the efficacy of D-RaCe, PTR, and hand H-files in the removal of GP and AH Plus with the aid of chloroform and reported that no statistical difference was seen with rotary and hand files.[10] EndoSolv R is a phenolic resin-based solvent composed of 66.5% formamid and 33.3% phenyl-ethylic alcohol. Hülsmann and Stotz have stated that solvents do not remove the GP per se, but rather create a thin film of GP, which adheres to the canal wall, making it difficult to detect and eliminate.[11] This is in agreement with the findings of our study in which the use of Endosolv R along with the PTR files led to incomplete removal of obturating material from the middle and apical thirds of the RCS.
Table 1: Comparison of the root canal-filled material after retreatment of canals filled with Smart-Seal system, gutta-percha/AH Plus sealer, and gutta-percha/GuttaFlow 2 in the coronal third

Click here to view


GP cones and AH Plus resin sealer have proven to be a gold standard combination for endodontic fillings.[12] However, GP lacks the ability to completely seal the root canal surfaces, which may result in leakage of bacteria. In the control group, the result of our study is in agreement with the study conducted by Piskin et al. who reported that the major demerit evaluated with GP is its inability to reinforce endodontically treated tooth and failure to form a monoblock even with the utilization of a resin-based sealer such as AH Plus.[13] Moreover, due to the hydrophobicity of the GP cones, the sealer tends to pull away from it on setting. In Group 1, both the middle and apical thirds had significant amount of remaining debris [Figure 1]. This observation is consistent with that of Zmener et al. who concluded that epoxy resin-based sealers adhere better to the dentin walls and penetrate 10–80 μm into the dentinal tubules, making their removal with rotary instruments difficult.[14]
Figure 1: Scanning electron microscopy images of Group 1 at ×1000. (a) Coronal, (b) middle, (c) apical

Click here to view


A new trend toward the use of bondable obturating materials is gaining popularity due to its biocompatibility and greater adherence to the root dentin. Smart-Seal System is a novel methacrylate-based endodontic obturating material that utilizes premade obturation points (C points) containing a polyamide core with an outer bonded hydrophilic polymer coating and an accompanying resin-based bioceramic sealer. These points are designed to expand laterally without expanding axially by absorbing residual dihydrogen monoxide from the instrumented root canal space and the naturally present moisture in the dentinal tubules.[15] In Group 2, the findings of our study stated that almost 75%–100% of Smart-Seal obturating remnants were retained in the middle and apical parts of the RCS [Figure 2]. A statistical difference was seen when the three groups were compared as shown in [Table 2] and [Table 3]. This can be attributed to the fact that C point showed an approximately 14% of expansion after 20 min [16] and enhanced biocompatibility with the root dentin. Furthermore, the addition of bioceramics to the resin-based Smartpaste Bio sealer produces a calcium silicate hydrate gel and calcium hydroxide when hydrated, giving it exceptional dimensional stability, biocompatibility, and nonresorbable ability inside the root canal.[17],[18] Therefore, the property of expansion in conjunction with the bioceramic nanoparticles led to a greater penetration of the polymer and sealer into the dentinal tubules, especially due to the greater diameter of dentinal tubules present in the middle and apical thirds of the RCS as seen in the SEM images (Group 2). The results of our study are in accordance with the study conducted by Hess et al. who evaluated the retreatability of an EndoSequence Bioceramic root canal sealing material and reported that the WL was not regained in 70% of samples obturated with Bioceramic sealer (BCS)/master cone short of the WL. Patency was not re-established in 20% of samples obturated with BCS/master cone to the WL or in 70% of samples filled with BCS/master cone short of the WL. Considering that bioceramic materials are known to be hard upon setting, the ability to retreat canals obturated with BCS is a current concern for practitioners.[19]
Figure 2: Scanning electron microscopy images of Group 2 at ×1000. (a) Coronal, (b) middle, (c) apical

Click here to view
Table 2: Comparison of the root canal-filled material after retreatment of canals filled with Smart-Seal system, gutta-percha/AH Plus sealer, and gutta-percha/GuttaFlow 2 in the middle third

Click here to view
Table 3: Comparison of the root canal-filled material after retreatment of canals filled with Smart-Seal system, gutta-percha/AH Plus sealer, and gutta-percha/GuttaFlow 2 in the apical third

Click here to view


In Group 3, GuttaFlow 2 was used which is a polydimethylsiloxane-based sealer/GP combination that is flowable at room temperature. The manufacturer claims a better seal and good adaptability because of good flowability and the fact that this material expands slightly (0.2%) on setting, enhancing its adaptation to root dentin walls.[20],[21] In our study, the remaining filling material after removal of GuttaFlow 2 was significantly less when compared to the other subgroups as shown in the SEM images [Figure 3] which showed open dentinal tubules in the middle and apical thirds of the RCS [Table 4] and [Table 5]. This is due to the inability of GuttaFlow 2 to exhibit chemical bonding to the canal wall and it is frequently “peeled off” in the canal during retreatment.[22] Nakashima and Terata also stated that GuttaFlow 2 showed poor wetting on the root dentin surface because of the presence of silicone, perhaps producing a high surface tension force, resulting in poor bonding of the material to the root dentin.[23]
Figure 3: Scanning electron microscopy images of Group 3 at ×1000. (a) Coronal, (b) middle, (c) apical

Click here to view
Table 4: Comparison of the root canal-filled material after retreatment of canals filled with Smart-Seal system and gutta-percha/GuttaFlow 2 in the middle third

Click here to view
Table 5: Comparison of the root canal-filled material after retreatment of canals filled with Smart-Seal system and gutta-percha/GuttaFlow 2 in the apical third

Click here to view


The method of evaluating the remaining root-filled obturating materials after retreatment was done using SEM. The usage of SEM technology in endodontics allows visualization of root/dentin structures, with different heights, without altering the focus. In addition, since SEM figures are in gray scale, the color of dentin does not influence in obtaining a correct focus, a limitation that is found in optical stereomicroscopes.[24]

After evaluating the parameters associated with retreatment, it was concluded that among the materials tested, GuttaFlow 2 (Group 3) was easily removed leaving clear and open dentinal tubules in the root canal space.

Further research should be directed to formulate the best methods to retreat curved canals which can pose a challenge in failed endodontic cases.


  Conclusion Top


Within the limitation of the present study, it can be concluded that:

  • PTR Universal retreatment files along with Endosolv R solvent did not produce completely clean canals in any of the groups
  • PTR files and Endosolv R solvent exhibited easy removal of the obturating material from the coronal part of the RCS in all the three groups
  • Silicon-based GuttaFlow 2 (hydrophobic system) was easily retreatable as compared to the other groups since it did not bond to the surface dentin
  • Smart-Seal obturating materials (hydrophilic system) were difficult to retrieve from the middle and apical thirds of the root canal walls as compared to the hydrophobic groups.


Although the novel obturating materials introduced today aim at producing osseoconductivity, hydrophilicity, adhesiveness, and chemical bonding to form an ideal monoblock in the RCS, a microspace if present can act as a potential place for possible microbial growth, which can cause reinfection leading to a re-treatment procedure.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Schilder H. Filling root canals in three dimensions. Dent Clin North Am 1967;11:723-44.  Back to cited text no. 1
    
2.
Pallarés A, Faus V, Glickman GN. The adaptation of mechanically softened gutta-percha to the canal walls in the presence or absence of smear layer: A scanning electron microscopic study. Int Endod J 1995;28:266-9.  Back to cited text no. 2
    
3.
Allen RK, Newton CW, Brown CE Jr. A statistical analysis of surgical and nonsurgical endodontic retreatment cases. J Endod 1989;15:261-6.  Back to cited text no. 3
    
4.
Sjogren U, Hagglund B, Sundqvist G, Wing K. Factors affecting the long-term results of endodontic treatment. J Endod 1990;16:498-504.  Back to cited text no. 4
    
5.
Stabholz A, Friedman S. Endodontic retreatment – Case selection and technique. Part 2: Treatment planning for retreatment. J Endod 1988;14:607-14.  Back to cited text no. 5
    
6.
Good ML, McCammon A. An removal of gutta-percha and root canal sealer: A literature review and an audit comparing current practice in dental schools. Dent Update 2012;39:703-8.  Back to cited text no. 6
    
7.
Somma F, Cammarota G, Plotino G, Grande NM, Pameijer CH. The effectiveness of manual and mechanical instrumentation for the retreatment of three different root canal filling materials. J Endod 2008;34:466-9.  Back to cited text no. 7
    
8.
Wilcox LR, Krell KV, Madison S, Rittman B. Endodontic retreatment: Evaluation of gutta-percha and sealer removal and canal reinstrumentation. J Endod 1987;13:453-7.  Back to cited text no. 8
    
9.
Tasdemir T, Er K, Yildirim T, Celik D. Efficacy of three rotary NiTi instruments in removing gutta-percha from root canals. Int Endod J 2008;41:191-6.  Back to cited text no. 9
    
10.
Madani ZS, Simdar N, Moudi E, Bijani A. CBCT evaluation of the root canal filling removal using D-RaCe, ProTaper retreatment kit and hand files in curved canals. Iran Endod J 2015;10:69-74.  Back to cited text no. 10
    
11.
Hülsmann M, Stotz S. Efficacy, cleaning ability and safety of different devices for gutta-percha removal in root canal retreatment. Int Endod J 1997;30:227-33.  Back to cited text no. 11
    
12.
Brackett MG, Martin R, Sword J, Oxford C, Rueggeberg FA, Tay FR, et al. Comparison of seal after obturation techniques using a polydimethylsiloxane-based root canal sealer. J Endod 2006;32:1188-90.  Back to cited text no. 12
    
13.
Piskin B, Aydin B, Sarikanat M. The effect of spreader size on fracture resistance of maxillary incisor roots. Int Endod J 2008;41:54-9.  Back to cited text no. 13
    
14.
Zmener O, Pameijer CH, Banegas G. Retreatment efficacy of hand versus automated instrumentation in oval-shaped root canals: An ex vivo study. Int Endod J 2006;39:521-6.  Back to cited text no. 14
    
15.
Highgate DJ, Frankland JD. Patent number. Vol. 4. United States Patent Office; 1986. Deformable polymeric compositions; p. 565,722.  Back to cited text no. 15
    
16.
Tay FR, Pashley DH. Monoblocks in root canals: A hypothetical or a tangible goal. J Endod 2007;33:391-8.  Back to cited text no. 16
    
17.
Baig AR, Ali SN, Saoji H. Smart seal: Unique obturation system in dentistry. IJADS 2016;2:1-2.  Back to cited text no. 17
    
18.
Best SM, Porter AE, Thian ES, Huang J. Bioceramics: Past, present and for the future. J Eur Ceram Soc 2008;28:1319-27.  Back to cited text no. 18
    
19.
Hess D, Solomon E, Spears R, He J. Retreatability of a bioceramic root canal sealing material. J Endod 2011;37:1547-9.  Back to cited text no. 19
    
20.
De-Deus G, Brandão MC, Fidel RA, Fidel SR. The sealing ability of GuttaFlow in oval-shaped canals: An ex vivo study using a polymicrobial leakage model. Int Endod J 2007;40:794-9.  Back to cited text no. 20
    
21.
Vasiliadis L, Kodonas K, Economides N, Gogos C, Stavrianos C. Short- and long-term sealing ability of Gutta-flow and AH-Plus using an ex vivo fluid transport model. Int Endod J 2010;43:377-81.  Back to cited text no. 21
    
22.
Hammad M, Qualtrough A, Silikas N. Three-dimensional evaluation of effectiveness of hand and rotary instrumentation for retreatment of canals filled with different materials. J Endod 2008;34:1370-3.  Back to cited text no. 22
    
23.
Nakashima K, Terata R. Effect of pH modified EDTA solution to the properties of dentin. J Endod 2005;31:47-9.  Back to cited text no. 23
    
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Stewart AD, Boyde A. Ion etching of dental tissues in a scanning electron microscope. Nature 1962;196:81-2.  Back to cited text no. 24
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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