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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 34  |  Issue : 3  |  Page : 173-179

An in vitro comparative evaluation of retreatability of a bioceramic and resin sealer using cone-beam computed tomography analysis


Department of Conservative Dentistry and Endodontics, Bangalore Institute of Dental Sciences and Hospital, Bengaluru, Karnataka, India

Date of Submission26-Mar-2022
Date of Decision07-May-2022
Date of Acceptance16-May-2022
Date of Web Publication30-Sep-2022

Correspondence Address:
Dr. Sumit Sharma
Bangalore Institute of Dental Sciences and Hospital, 5/3, Hosur Main Road, Adjacent to NIMHANS Convention Centre, Lakkasandra, Wilson Garden, Bengaluru - 560 027, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/endo.endo_84_22

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  Abstract 


Aims: The aim is to evaluate the retreatability of BioRoot RCS (BCS)/Gutta-percha (GP) as compared to AH Plus/GP with and without a solvent using cone-beam computed tomography (CBCT).
Materials and Methods: Mesio-buccal canals in 48 first mandibular molars were instrumented using iRace rotary files up to size 25.4% and obturated with GP using one of the following sealers, BCS and AH Plus. Post obturation, the teeth were scanned using a CBCT. All samples were divided into four groups (n = 12). Group 1: GP/BCS was removed using D-Race retreatment files and xylene as a solvent; Group 2: GP/BCS was removed using D-Race retreatment files without xylene; Group 3: GP/AH Plus was removed using D-Race retreatment files with xylene; Group 4: GP/AH Plus was removed using D-Race retreatment files without xylene. Time taken to reach the working length (WL) was recorded. Samples were again scanned using CBCT and the remaining filling material was calculated in the coronal, middle, and apical thirds. Data were tabulated and analyzed via Kruskal–Wallis and Mann–Whitney Post hoc test (P < 0.05).
Results: Group 3 exhibited significantly less time to reach WL as compared to Group 1. There was no significant difference between Group 2 and Group 4. In all groups, the apical third had the most remaining filling material (Group 1 – 13.75 ± 4.83, Group 2 – 18.33 ± 3.26, Group 3 – 10.42 ± 3.34, Group 4 – 15.42 ± 3.34). WL and patency were re-established in all the samples.
Conclusions: Irrespective of the retreatment technique employed complete removal of both the sealers could not be achieved. However, retreatability of AH Plus with xylene was superior to that of BioRoot RCS.

Keywords: AH Plus, BioRoot RCS, cone-beam computed tomography, D-Race, gutta-percha, retreatment


How to cite this article:
Sharma S, Raghu R, Shetty A, Rajasekhara S, Lakshmisetty H, Bharath G. An in vitro comparative evaluation of retreatability of a bioceramic and resin sealer using cone-beam computed tomography analysis. Endodontology 2022;34:173-9

How to cite this URL:
Sharma S, Raghu R, Shetty A, Rajasekhara S, Lakshmisetty H, Bharath G. An in vitro comparative evaluation of retreatability of a bioceramic and resin sealer using cone-beam computed tomography analysis. Endodontology [serial online] 2022 [cited 2022 Nov 30];34:173-9. Available from: https://www.endodontologyonweb.org/text.asp?2022/34/3/173/357705




  Introduction Top


A satisfactory outcome of primary endodontic therapy largely depends on a dense and homogeneous obturation extending up to 2 mm within the radiographic apex along with an adequate coronal restoration.[1] However, endodontic therapy does fail sometimes, and the percentage of cases that do not heal can range from 15% to 22%.[2] Treatment failures are considerably higher in teeth with pretreatment periradicular radiolucencies than in vital inflamed teeth, as reported by various studies.[3]

The first line of choice in case of failure of primary endodontic treatment is nonsurgical retreatment. According to the Glossary of Endodontics, “Retreatment is a procedure to remove root canal filling material from the tooth, followed by cleaning, shaping, and obturation of the canals.”[4]

Nonsurgical endodontic retreatment aims at relieving patient symptoms and re-establishing healthy periapical tissues. The goal is to remove all previous obturation materials from the root canal space, chemically disinfect the canals and address deficiencies of pathological or iatrogenic origin.[5]

Gutta-percha (GP) is the most common root filling material used along with various sealers.[6] Many techniques such as the use of hand files, ultrasonic instruments, heated pluggers as well as various retreatment file systems, in conjunction with chemical solvents (chloroform, xylene, eucalyptol, orange oil) have been proposed for easy removal of root filling materials during retreatment.[7] Both the obturating material and sealer should be completely removed as they could potentially form a mechanical barrier that hinders canal cleaning and shaping during retreatment.[8]

Many nickel–titanium (NiTi) retreatment file systems such as Mtwo R, R-Endo, ProTaper Universal, and D-RaCe are in use now for the effective retrieval of root filling materials. They improve patient comfort and require less chair time. D-RaCe file system (FKG Dentaire, La Chaux-de-Fonds, Switzerland) was specifically created for simplifying the removal of filling material from the coronal (DR1), middle and apical thirds (DR2) of root canals.[9]

A variety of sealers are presently being employed for obturation. AH Plus sealer (epoxy-resin-based endodontic sealer) is considered gold standard due to its long history of use and research, and has been employed in many comparative studies. Nowadays, bioceramic sealers are gaining popularity. Bioceramic sealers are composed of tricalcium silicate, calcium phosphate monobasic, calcium hydroxide, and zirconium oxide. They demonstrate excellent sealability, extraordinary biocompatibility, and antibacterial activity along with the ability to stimulate the mineralization of periapical tissues. Recently, a new improved bioceramic sealer, BioRoot RCS (Septodont, SaintMaur-des-Fossés, France) has been introduced.[10]

Among the ideal properties of an endodontic sealer, sealing ability is very important. In situations where retreatment is necessary, easy retrieval from the canal space assumes greater significance. The literature has ample evidence regarding the retrievability of AH Plus sealers. On the other hand, since Bioroot RCS is a newly developed bioceramic sealer, enough data about its retrievability is lacking.

Retreatment efficacy can be assessed by sectioning the teeth, followed by evaluation under stereo microscope, dental operating microscopic, or scanning electron microscope, but these are invasive approaches. They also carry the risk of inaccuracy as splitting the teeth may result in the loss of some residual material.[11]

Recently, cone-beam computed tomography (CBCT) has been recommended as a noninvasive method to quantitatively evaluate retreatment procedures.[12] It allows an accurate evaluation of root filling removal without damaging the tooth. At present, there are not many studies using CBCT for evaluating the retreatability of bioceramic sealers.

Hence, the purpose of the present study was to comparatively evaluate the retreatability of BioRoot RCS and AH Plus sealer using CBCT. Whether the use of a solvent would improve the efficacy of retreatment of both sealers was also examined.

The null hypothesis is that there will be no difference between the two sealers regarding their retreatability and that the solvent will not influence the efficacy of retreatment.


  Materials and Methods Top


A power analysis was established by G*power, version 3.0.1(Franz Faul universitat, Kiel, Germany). A sample size of 48 participants (12 in each group) would yield 80% power to detect significant differences, with an effect size of 0.5 and a significance level at 0.05. A total of 48 extracted intact mandibular molars were chosen for this study after obtaining prior consent from the institutional ethical committee. Teeth with cracks, fracture, resorption, and restorations were excluded. The mesiobuccal canals with 10°–20° curvature were selected for the study. Preoperative CBCT (Carestream CS-9600) scans were done to standardize the canal dimensions.

Access preparation was done on each tooth using Endo access bur (Dentsply, Switzerland).

After checking canal patency, working length (WL) was established using a size #15 K-file (Mani Dental, Inc., Japan) by introducing the file into the canal until its tip was visible at the apical foramen. The WL was determined by reducing 1 mm from this length. The mesiobuccal canals were cleaned and shaped by hand files followed by iRace rotary files (FKG Dentaire, Switzerland) for canal preparation. The final apical preparations were done up to 25.4% at WL. During instrumentation, all canals were irrigated with saline and 5.25% NaOCl between each instrument. Finally, after chemomechanical preparation, the smear layer was removed using 17% EDTA followed by 5.25% sodium hypochlorite. The canals were dried with paper points and obturation was done using a single cone technique, GP and the tested sealers. Teeth were then stored in a humidor at 37°C for 2 weeks to allow the sealer to set completely.

Groups

The teeth were then divided into four groups of 12 teeth each: Group 1 – Obturated with single GP cone and BC sealer and retreatment with D-Race retreatment file system in conjuction with xylene as solvent. Group 2 – Obturated with single GP cone and BC sealer and retreatment with D-Race retreatment file system without xylene. Group 3 – Obturated with single GP cone and AH-Plus sealer and retreatment with D-Race retreatment file system in conjunction with xylene as solvent. Group 4 – Obturated with single GP cone and AH-Plus sealer and retreatment with D-Race retreatment file system without xylene.

The mesiobuccal canal in Groups 1 and 2 was obturated with Diadent GP (Dentsply, Switzerland) of size 25.4% taper coated with BCS and sealed using a heated instrument at the level of the orifice of the canal. The canal in Groups 3 and 4 was obturated with Diadent GP of size 25.4% taper coated with AH Plus sealer and sealed using a heated instrument at the level of orifice of the canal.

Retreatment procedure

D-Race retreatment files DR1 and DR2 (FKG Dentaire SA, Switzerland) were used for the removal of obturation material. The retreatment file was progressed until it reached the WL. The time taken to reach the WL was recorded in seconds and minutes using a stop watch.

Cone-beam computed tomography analysis

CBCT scans were taken before and after the retreatment for the evaluation of the remnants [Figure 1] and [Figure 2].
Figure 1: (a) CBCT image of BCS group before retreatment, (b) CBCT image of AH Plus group before retreatment. CBCT: Cone-beam computed tomography

Click here to view
Figure 2: CBCT images of Mesio-buccal canal of groups divided into coronal, middle and apical thirds after retreatment. CBCT: Cone-beam computed tomography

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Grading system (Somma et al.)[13] was used to score the amount of filling material residues at the coronal, middle, and apical portions of the canal as follows:

  • Score 1 – No or slight presence (0%–25%) of debris on the dentin surface
  • Score 2 – Presence of debris (25%–50%) on the dentin surface
  • Score 3 – Presence of moderate amount debris (50%–75%) on the dentin surface
  • Score 4 – Heavy presence (>75%) of debris on dentin surface.



  Results Top


Time taken to reach working length

The mean time taken (in secs) to reach WL between all four groups is presented in [Graph 1]. The difference was statistically significant at P < 0.001. Group 3 exhibited significantly less time to reach WL as compared to other groups.



Remnant scores

Comparison of mean scores of residual filling material in coronal 3rd, middle 3rd, and apical 3rd between all four groups are shown in [Table 1]. The mean difference of remnant scores in between the four groups was statistically significant.
Table 1: Comparison of mean scores of residual filling material in different regions between four groups using Kruskal-Wallis test

Click here to view


The percentage of residual filling material remaining in different regions between four groups was assessed using Kruskal–Wallis Test is shown in [Graph 2].




  Discussion Top


The success of the nonsurgical retreatment depends on the complete removal of the root canal filling material, followed by improved debridement and three-dimensional obturation.[14] Most studies evaluating the removal of various root filling materials confirm that complete removal of these materials is not possible. However, WL and apical patency must be re-established as a prerequisite for effective retreatment.[15]

The use of rotary NiTi instruments for the removal of root filling materials during retreatment has been found to be safer and quicker, reducing clinical time and operator fatigue.[16] They have been shown to be more efficient than manual methods in preparing a tapered root canal with minimum risk of irregularities and canal transportation. In this study, a recently developed NiTi rotary retreatment files, namely the D-Race system, was used. There have been few studies evaluating the efficacy of the D-Race system, particularly in the retreatment of curved canals.[9] D-RaCe files are reported to be highly efficient in removing GP and sealer during retreatment. This finding may be attributed to the superior sharpness of these instruments due to their alternating cutting edges and smooth surface produced by electropolishing treatment. It is also likely that the GP is adherent to the flutes, allowing the file to cut more efficiently.[17] According to Rödig et al., D-RaCe was significantly more effective than ProTaper retreatment files and hand files in removing filling material from curved canals.[9] The space for dentin removal on the back of the blades is deep, allowing for the escape of dentinal debris, resulting in better removal of the obturating material. Hence, this file system was employed in the present study.

The complete debridement of the residues of resin-based sealers that strongly attach to the dentin is a difficult process. As a result, literature suggests the use of solvents as adjuncts to retreatment instruments. Solvents are expected to reduce the resistance of obturating materials inside the canal, making their removal easier in conjunction with instruments. In a recent review on retreatment techniques for removal of GP/BCS, the use of rotary instruments along with solvent was recommended.[18] Another study observed that the use of solvents reduced the amount of debris extruded apically as well as time taken to retreat.[19] Chloroform is the most effective and extensively used endodontic solvent for GP removal in clinical practice. It has a quick action and rapidly evaporates, but its carcinogenic potential and tissue toxicity raise concerns about its future usage. Some investigators have recommended xylene as an effective substitute for chloroform. Xylene (dimethyl benzene) is an aromatic organic compound with efficient solvent action against GP, resins, and sealers. Its toxicity is much lesser than that of chloroform. It softens rather than dissolves the obturating material and when used along with retreatment files, provides a safe and effective way of removing them.[20],[21] Hence, it was used in this study.

Mandibular molars are the most common teeth requiring retreatment. They have a complex morphology[22] as compared to premolars and anterior teeth. The mesial roots of mandibular molars have conventionally been employed to examine the efficiency of retreatment procedures due to the presence of curvatures. The present study was performed on mesiobuccal canals of mandibular molars for the same reason. Before retreatment, the teeth were stored in humidifier in 100% humidity for 2 weeks to allow complete setting of the sealer.

In vitro studies analyzing the efficacy of retreatment procedures have employed various methodologies, such as two-dimensional radiographs or root sectioning and examination under a microscope. However, two-dimensional radiography does not reliably evaluate the amount of residual root filling materials and sectioning involves the risk of damaging the sample or material being examined.

In the field of endodontics, CBCT has already proven to be quite useful for diagnosis and treatment planning in various special situations such as developmental anomalies, resorption, and traumatic injuries.[23] It provides a detailed three-dimensional evaluation of the teeth and offers valuable information for the clinician in the volumetric evaluation of the amount of residual filling material in root canals. The data provided by CBCT is reproducible and can be used for comparison of root canals before and after retreatment. The use of CBCT in endodontics employs a small field of view which results in less artifacts. In the present study, artifact-reducing filters were also utilized for better image clarity.

Presently, calcium silicate sealers are increasingly in use for root canal obturation. BioRoot RCS (Septodont, Saint Maur des Fossés, France) is a tricalcium silicate-based material that has been available since 2015. It consists of a fine powder of tricalcium silicate and zirconium oxide, and a liquid containing polycarboxylate polymer and calcium chloride.[24],[25]

Calcium silicate sealers are known to be hard upon setting. Their distinct setting activity and hardness may increase their adherence and resistance to dislocation from dentin, obstructing their removal during retreatment.[26] Hence, evaluating retreatability of BioRoot RCS is clinically relevant.

Our study evaluated various parameters to assess the retreatability of BioRoot RCS and AH Plus sealers. These included: time taken to reach WL, role of the solvent and the amount of residual remnants in the coronal, middle, and apical third of the root canal. In addition, the risk of instrument fracture during retreatment was also assessed.

The null hypothesis of this study was partially rejected as some differences were observed in filling remnants in root canals obturated with GP/Bioroot RCS and with GP/AH Plus sealer. The present study reported minimal filling remnants when xylene was used for retreatment of AH Plus group than for BCS group. More time was taken for removing both sealers in the absence of solvent. In addition, regardless of the retreatment technique used, more filling remnants remained in the apical thirds of the canal.

One of the prerequisites of an ideal root-filling material is its ease of removal. The simplest way to determine the ease of removal is by measuring the time taken to complete the procedure.[27] In the present study, BioRoot RCS with solvent took a longer time (207.00 ± 42.97), for removal than AH Plus sealer (169.17 ± 46.32). This finding concurs with the results of other studies, suggesting that BioRoot RCS, like other bioceramic sealers, is a little more difficult to remove than AH Plus due to its increased hardness.[8] It has been reported that the dentinal adhesion of AH Plus and BioRoot RCS is similar. However, in the case of BioRoot RCS, there is a mineral infiltration zone (up to 2000 μm) due to the precipitation of the apatite and cement plugs within the dentinal tubules. This brings about a combined chemical and micro-mechanical adhesion resisting dislocation of the sealer from dentin.[28]

This zone is absent in the case of AH Plus although it does exhibit penetration into the dentinal tubules.

The role of the solvent in speeding up the retreatment process was significant. In the absence of solvent, removal of both sealers took a longer time (BioRoot RCS-269.58 ± 32.19, AH Plus-264.67 ± 55.74). Along with the retreatment files, the use of solvent resulted in faster removal of GP and sealer in both BioRoot RCS and AH Plus groups. It must be noted that so far there are only a few reports of xylene being used as a solvent for bioceramic sealer. However, previous research has shown that the use of solvents may either speed up or delay the retreatment process.[29]

For both sealers, removal from the coronal third was more efficient than the apical third of the canal. The taper of DR1 and the anatomy of the canal in this region are responsible for this. Although there is a higher percentage of filling material in the coronal third, the rise in temperature due to the rotational speed of the NiTi instrument readily plasticizes the GP and facilitates its removal. This is supported by other studies.[11]

CBCT analysis revealed that Bioroot RCS showed more volume of residues than AH Plus, especially in apical one-third of the canal. This has also been observed in other studies. In contrast, a few studies have reported a similar amount of remaining filling material during retreatment of canals obturated with Bioroot RCS and AH Plus.[8],[30] However, because the retreatment procedures and techniques employed in these researches were varied, it is impossible to draw definite conclusions.

There are various reasons to justify the presence of more residues in the apical third. One possibility is that during retreatment, the coronal and the middle thirds of the root canal are more accessible than the apical third. It is also likely that the filling material may get packed in the apical third during removal.[31] In a previous study, this was also attributed to differences between the tip size and taper of the instruments used for primary preparation and retreatment. However, in the present study, both the canal preparation and the retreatment were done using instruments with similar tip size and diameter. (R2-25.4%, DR2-25.4%). It has been suggested in a previous research[32] that since DR2 is thinner and has an inactive tip, it may be difficult to penetrate the GP effectively in the apical third. Another probable reason for more residues in the apical third could be greater anatomical variations such as accessory canals and apical delta seen in this region.

The present study did not report any iatrogenic errors such as instrument separation or ledge formation. A probable reason could be that the D-Race instruments exhibit increased resistance to torsion and metal fatigue due to electropolishing. The presence of alternate cutting edges in the instrument design also prevents screwing-in effect, limiting the risk of instrument separation.

In our study, WL was re-established in all samples (100%), irrespective of whether AH Plus or BioRoot RCS was employed as the sealer. This is similar to the findings of Hess et al.[30] who also reported regaining WL 100% during retreatment with AH Plus or a bioceramic sealer when WL was maintained up to apical constriction.

The achievement of apical patency during retreatment has been shown to enhance periradicular healing. In the present study, patency was attained in all the samples. On the other hand, Hess et al.[30] reported that apical patency could be gained only in 80% of the samples obturated with a bioceramic sealer when WL was established 2 mm short of apical constriction. This difference may be expected because no solvent was employed in their study.

The present study evaluated retreatment of AH Plus and BioRoot RCS when the obturation was done using single cone technique. Further studies are required to evaluate the retrieval of bioceramic sealers when different obturation techniques are employed, particularly thermoplasticized obturation.

The development of newer solvents, techniques, and instruments for retreatment of bioceramic sealers needs to be explored further, particularly in more complex situations like oval and irregular canals. Finally, randomized controlled clinical trials are necessary to validate the findings of the present study.


  Conclusions Top


None of the tested sealers could be completely removed from the root canals. Retreatability of AH Plus sealer was better than BioRoot RCS as there were less remnants and retreatment time was shorter. The use of xylene as solvent helped further to reduce the working time.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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