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Table of Contents   
ORIGINAL RESEARCH  
Year : 2021  |  Volume : 32  |  Issue : 1  |  Page : 79-86
Comparative evaluation of retreatability of calcium silicate-based root canal sealers and epoxy resin-based root canal sealers in curved canals-An In-Vitro micro-CT analysis


1 Post Graduate Student, SRM Kattankulathur Dental College & Hospital, Chennai, Tamil Nadu, India
2 Professor & Head of the Department, SRM Kattankulathur Dental College & Hospital, Chennai, Tamil Nadu, India

Click here for correspondence address and email

Date of Submission08-Apr-2020
Date of Decision29-Apr-2020
Date of Acceptance13-Jun-2020
Date of Web Publication09-Jan-2021
 

   Abstract 


Objective: To compare and evaluate the retreatability of calcium silicate-based root canal sealers and epoxy resin-based root canal sealers in curved canals using micro-CT scanning. Materials and Methods: Forty-five maxillary molars with curved roots were selected after confirming with the Schneiders test. Teeth were decoronated near the cemento-enamel junction and moderate to severely curved canals were selected for the study using cone-beam computed tomography. All the samples were subjected to pre-operative micro-CT scanning. Cleaning and shaping were done using step-back preparation, obturation was done using lateral compaction technique, and homogeneous obturation was achieved. All the specimens were kept in 10 mL of phosphate buffered-saline solution at a pH of 8.4 for 48 h and transferred to a plastic container containing moistened foam with 10 mL of phosphate- buffered saline solution, and stored at 37 °C with 100% relative humidity for 4 months. Retreatment was performed for all the samples using Protaper universal retreatment files. Micro-CT scanning was performed to compare and evaluate the remaining sealer volume and resultant cracks formed in the root canal after retreatment. Results: The volume of sealer remaining in the root canal and the length of a crack within the groups were analysed using kruskal–Wallis test and among the groups using post-hoc scheffe test showed that more sealer present in the Diaproseal sealer followed by MTA Fillapex and Bioroot RCS and more crack length was seen in Diaproseal sealer followed by MTA Fillapex and no visible cracks were seen in Bioroot RCS, which had statistically significant results with a P value of < 0.05. Conclusion: Within the limitations of the study it was concluded that in-terms of retrievability, Diaproseal sealer was the best among the tested groups followed by MTA Fillapex and Bioroot RCS.

Keywords: Bioroot RCS, Diaproseal sealer, Micro CT analysis, MTA fillapex, Retreatability

How to cite this article:
Mavishna M V, Venkatesh KV. Comparative evaluation of retreatability of calcium silicate-based root canal sealers and epoxy resin-based root canal sealers in curved canals-An In-Vitro micro-CT analysis. Indian J Dent Res 2021;32:79-86

How to cite this URL:
Mavishna M V, Venkatesh KV. Comparative evaluation of retreatability of calcium silicate-based root canal sealers and epoxy resin-based root canal sealers in curved canals-An In-Vitro micro-CT analysis. Indian J Dent Res [serial online] 2021 [cited 2021 Aug 3];32:79-86. Available from: https://www.ijdr.in/text.asp?2021/32/1/79/306618



   Introduction Top


Re-treatment of a root canal is a non-invasive and non-surgical treatment that involves the removal of entire obturating materials followed by cleaning, shaping and re-obturation of the canal.[1] Retreatment is achieved by complete retrieval of obturated material, which allows re-accessing of the root canal, disinfection and re-obturation in order to create a favourable peri-apical healing.[1],[2] However, all retreatment studies concluded that even after retreatment, some amount of obturated material remnants was present in the root canal.[3] A variety of complexities in the root canal anatomy such as webs, fins, isthumus, cul-de-sac, dumbbell, ribbon, S and C shaped canals may be frequently experienced, among them, the most challenging is treating a curved canal.[4],[5] A recent meta analysis study suggested that a success rate of 80% was observed in the non-surgical retreatment cases and 92% for the surgical retreatment cases.[6]

The purpose of a sealer is to fill the gaps between the root canal wall and core material to reduce leakage from coronal as well as apical restoration. Excellent sealing ability, insolubility, dimensional stability and biocompatibility are the ideal features of endodontic sealer according to Grossman.[7] Based on chemical components the endodontic sealers are divided into resin-based, glass ionomer-based, zinc oxide eugenol, silicone-based, calcium hydroxide containing and newer bio-ceramic-based sealers.[8],[9],[10]

Bio ceramics have shown superior properties in terms of biocompatibility, bioactivity, antimicrobial and are capable of promoting mineralization of periapical tissues.[11],[12],[13] Endodontic therapies have gained great benefits from tri-calcium silicates technology.[14] Several forms of tri-calcium silicate sealers were developed.[15] Bioroot sealer is a tricalcium-based material, available as a powder and liquid form, which has been marketed since 2015.[16] It has excellent clinical results due to its bioactivity, capacity to form carbonated deposits of apatite, ability to release calcium ions, its strong alkalizing activity and radio-opacity.[17]

MTA Fillapex sealer marketed commercially in 2010,[15] is composed of tri-calcium containing silicate particles i.e., forty percentage of mineral trioxide aggregate, bismuth oxide, silicon dioxide, natural and salicylate resin. It showed excellent biocompatibility, bioactivity, osteoconductivity and has suitable physical properties to be used for endodontic therapy.

Schroeder introduced the epoxy resin-based sealers, now its modified original formulae are also used to achieve better properties. Dia-proseal sealer is a two-component epoxy resin- based root canal sealer available since 2014. Its physicochemical properties, biocompatibility and sealing abilities are acceptable.[16]

Literature is replete with proof of chemical performance to support the superiority of both resin-based and calcium silicate sealers.[18] Data concerning the removal of sealers such as Bioroot RCS, MTA Fillapex sealer and Dia-proseal sealer in curved canals is limited.[18] Three-dimensional imaging in endodontics is a high-precision tool to evaluate the remaining root canal filling material.[19],[20],[21] Most of the retreatment studies analysed the remaining volume of sealers by sectioning the teeth by viewing under a different optical light microscope, scanning electron microscope, stereomicroscope, micro-raman spectroscope and different digital radiographic methods.[19],[20],[21] However, the use of nano-CT and micro- CT provide three-dimensional quantitative analysis of the volume of sealers left in the root canal.[22],[23],[24]

The present study was designed

  1. To evaluate the remaining volume of Bioroot RCS, MTA Fillapex and Diapro-seal sealers after retreatment.
  2. To assess the evidence of crack formation in the root canal wall after retreatment.
  3. To compare the remaining sealer volume and resultant cracks formed in the root canal after retreatment among the groups using micro-CT scanning.



   Materials and Methods Top


Forty-five extracted human maxillary first molars with curved mesio-buccal roots were collected. They were cleaned of calculus and debris by hand scaling (Hand scalers, GDC, India). The samples were analysed using radiovisiography and subjected for further curvature analysis test.

Ethical Clearence date for study: approval from the ethics committee is obtained IEC No. 1252, Date of approval : 27.10.2017.

Schneiders test

The roentgenographed printed images were drawn in a tracing sheet, drawn two lines on the mesio buccal roots, first one to the long axis of the canal and second one from apical foramen towards the long axis of the canal, till it intersects the first line. It results in the formation of 3 points, which were represented as A, B and C. First line drawn was labelled as A, the point where the flare started to deviate was labelled as B, and the third point was labelled at the apical foramen as C. The angle of 15–30 degree, which is formed due to the intersection of these lines was taken for this study, others discarded.

All the selected samples were decoronated at the level of cemento-enamel junction using diamond disk (NTI Flex D 345-190, Kerr dental, USA) in a slow-speed micro-motor handpiece (Marathon, saeyang company, korea), 16 mm of root length was taken up as a standardised procedure.

Cone-beam computed tomography (CBCT) images were taken to confirm the 15–30-degree curvature of the root at a small field of view setting of 70 kVP, 92 mAs and viewed under CS 3D imaging software.

Pre-Operative Micro CT scanning

The specimens were scanned using a micro-CT scanner for volumetric analysis. The samples were numbered and wrapped in cardboard tubes and placed into the sample holder. Scanning parameters for all samples were kept constant. Scanning was performed with an X-ray voltage of 50 kV and a current beam of 500 μA using aluminium filter 0.5 mm to capture the X-ray projections, which were digitised with a pixel of 1000 × 668 to 8000 × 2672 and brightness gradations of 4096 (12 bit). The X-ray projections were recorded at a rotation interval of 0.6° to 360°.

Root canal preparation

In accordance with the degree of curvature seen, a 10 size k-file was pre-curved, and working length was measured. The filing was done in a sequential order till its working length until 25 size k-file. Apical enlargement of 30 size, and step back preparation of 50 size NiTi k-files was done. Root canals were irrigated using 3% sodium hypochlorite and 5 mL of 17% ethylene diamine tetra aceticacid with a 25-gauge open-ended needle. Finally, canals were dried using paper points.

Root canal filling

The samples were randomly assigned as 3 groups (n = 15) based on the sealers used for filling the root canal. Group 1, Bioroot RCs (Septodont, Siant-Maur-des Fosses, France) Group 2, MTA Fillapex sealers (MTA Fillapex, Angelus, Londrina, Parana) and Group 3, Diaproseal sealer (Dia proseal, Diadent, Cheongju, Korea). Each canal was trial fitted with a 30, 0.02 taper Gutta percha with tug-back at the working length and confirmed with a radiograph. The sealer was mixed according to the manufacturer instructions and coated on the root canal wall using Lentulo spirals.

Mixing of Bioroot RC sealer

Root canal sealers were mixed by progressively adding the powder to liquid. Mixing was done for about 60 seconds until a smooth creamy paste was obtained. It had a minimum working time of 10 min and a maximum setting time of 4 hours.

Mixing of MTA Fillapex sealer

An equal volume of base and catalyst paste was dispensed on the paper pad by pressing the plunger. The mix was immediately mixed for about 30 seconds to get a homogeneous consistency. It had a working time of 23 minutes.

Mixing of Diaproseal sealer

The safety cap of the dual syringe was removed and squeezed out base and catalyst material in a ratio of 1:1 onto the mixing pad. Mixing was done using a mixing spatula for about 10–20 seconds until it was mixed completely and turned into an ivory colour. The setting time of this material was 6.5–7.5 h.

All the sealers were mixed to obtain a 'string-like consistency' and were coated on the walls of root canals using a 25-size Lentulo Spiral under 600 RPM speed. All the canals were obturated with the lateral compaction technique. The Gutta-Percha was compacted and excess was removed using a heated plugger, and with a temporary filling material the orifices were sealed. The sample was then radiographed to confirm homogeneous obturation. Each sample was then placed in a gauze package soaked with phosphate-buffered saline solution contained a pH of 8.4 kept for 48 h. This buffered solution helps to provide a constant pH. Later transferred to a plastic container containing moistened foam with 10 mL of PBS and are stored at 37 °C with 100% humidity for 4 months. The replenishment of foam was done with 5 mL of PBS every consecutive week. The retreatment was performed after this period time. [Figure 1]: overall procedures (Curvature analysis, non surgical root canal treatment with different types of sealers with Gutta-percha).
Figure 1: Curvature analysis, non surgical root canal treatment with different types of sealers with Gutta-percha

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All the samples were subjected for micro-CT analysis to confirming the homogeneous obturation in the root canal.

Retreatment procedures

For retreatment, Protaper universal retreatment files were used in all the groups in accordance with the manufacturer's recommended protocol. One set of instruments (D1, D2 and D3) were used with a brushing action in a crown-down method to remove the obturated material until the working length was achieved with a recommended speed of 300 RPM and 3 N cm torque being followed [25] Irrigation was done using 3%of sodium hypochlorite (NaOCl) irrigant and 17% ethylenediamine tetraacetic acid EDTA while removing the obturating material from the root canal. The irrigation protocol followed was for each sample, 5 mL of NaOCl and EDTA for 2 min, followed by 2 mL of sterile saline for 1 min, and the canals were dried using paper points.

Post-operative Micro CT scanning

The samples were subjected to micro CT scanning with the same parameters applied by a technician who was blinded to the experimental groups. The volume of remnants of filling material was calculated by comparing the pre- and post-operative micro CT scanned reports. The samples were numbered and wrapped in cardboard tubes and placed into the sample holder and were stabilized with clip attachment apparatus present in the micro-CT machine. For calculation, rendering settings were applied to both scan data sets (teeth after obturation and after retreatment procedure), and the volume of sealer was determined by the use of reconstructed raw data scans sliced into multiplanar images with the computer program (NRecon) software in all the three planes of the tooth (trans-axial, coronal and sagittal) and viewed under Data viewer software.

[Table 1] shows the values of pre- and post-operative volumes, overall remaining sealer volume and volume of dentin removed in the Bioroot RCS group. [Table 2] shows the values of pre-and post-operative volumes, overall remaining sealer volume and volume of dentin removed in the MTA Fillapex group. [Table 3] shows the values of pre and post-operative volumes, overall remaining sealer volume and volume of dentin removed in the Diaproseal sealer group. [Table 4] shows the values of remaining sealer volume at each level (coronal, middle, apical third) of root canal in Bioroot RCS, MTA Fillapex and Diaproseal sealer group. [Table 5] shows the values of crack length observed in Bioroot RCS, MTA Fillapex and Diaproseal sealer group.
Table 1: Remaining sealer mean volumes of Bioroot RCS, MTA Fillapex, Diaproseal sealer groups

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Click here to view
{Table 3}
Table 3: Intra and inter group comparison of volume of dentin removed in Bioroot RCS, MTA Fillapex, Diaproseal sealer groups Post hoc scheffe analysis

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Table 5: Intra and inter group comparison of crack length in Bioroot RCS, MTA Fillapex, Diaproseal sealer groups Post hoc scheffe analysis

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All statistical values were evaluated with IBM.SPSS 10.0 version software. Intra-group comparative analysis was performed using Kruskal–Wallis test and inter-group comparative analysis was performed using the post hoc Scheffe test. The P value (P < 0.05) was considered statistically significant.

This implies that more remaining sealer volume present at the apical third level of root canal in the Bioroot RCS group followed by the MTA Fillapex and Diaproseal sealer group. Intra- group comparative results were statistically significant. This shows that the volume of sealer varies within the groups.

The inter-group comparative results showed that in all the groups, more sealer volume was present at the apical third part of the root canal as compared to the middle third and coronal third. Bioroot RCS group showed more sealer volume as compared to MTA Fillapex followed by Diaproseal sealer. All inter-group comparative values showed statistically significant differences.

More amount of dentin has been removed from BioRoot RCS and MTA Fillapex compared to the Diaproseal sealer group. The inter-group comparative results were statistically not significant. This shows that not much difference were observed in the volume of dentin removed among the groups.

No cracks were seen in BioRoot RCS, more cracks were seen in Diaproseal sealer followed by the MTA Fillapex group.

[Figure 2] shows Micro CT images showing pre-operative, obturation, retreatment, cracks in Bioroot RCS group, [Figure 3] shows Micro CT images showing pre-operative, obturation, retreatment, cracks in MTA Fillapx sealer group, [Figure 4] shows Micro CT images showing pre-operative, obturation, retreatment, cracks in Diaproseal sealer group.
Figure 2: Micro CT images showing pre-operative, obturation, retreatment, cracks in Bioroot RCS group

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Figure 3: Micro CT images showing pre-operative, obturation, retreatment, cracks in MTA Fillapx sealer group

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Figure 4: Micro CT images showing pre-operative, obturation, retreatment, cracks in Diaproseal sealer group

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   Discussion Top


The primary role of a sealer is to fill irregularities between a root canal and core material. When there is a failure of root canal therapy, retreatment is an option.[26] The main objective of retreatment is the eradication of all microorganisms and its by-products that leads to peri-apical pathosis.[27] The remaining obturating material resides in areas that are difficult to reach such as lateral canals, isthumus and dentinal tubules, which act as mechanical barriers.[27] Hence all the filling remnants should be removed to provide access for irrigation and placement of medicaments in every part of the root canal system.[28],[29] One of the most frequently encountered anatomical difficulties is the curved canal. In the maxillary first molars, the mesio-buccal root is broad in the bucco-palatal plane and narrow in the mesio-distal plane. It often curves disto-palatally in the apical third of the root.[23],[30],[31] Radiographically, the root may appear straight, but curvatures at the apical third are common. The inability to remove filling material can lead to failure.[24],[32],[33] To fulfill the criteria of ideal requirements for this purpose, obturated material must be easily removable when retreatment is indicated. The canal curvatures are generally categorized as straight (5° or less), moderately curved (10 to 20°), or severely curved (>20°).[25],[26],[27],[34] In this study, moderate to severely curved canals with a curvature of 15–30 degrees were taken. These canals have an incidence of ledge formation of about 49.5% for the moderately curved canal and 52.3% for the severely curved canal.[29] This is the reason to choose moderate to severely curved canals for this study.

The selected samples after the Schnieders test are subjected to cone-beam computerized tomography (CBCT) analysis to reduce false- negative results and get a more accurate three-dimensional determination of moderately curved root canal.

Many newer root canal sealers are available in the market; recently introduced Bioroot RCS is a tri-calcium silicate-based two-component system.[30] The powder consist of povidone, zirconium dioxide, tricalcium silicate and the liquid contains water, polycarboxylate and calcium chloride.[30] The sealing effectiveness of Bioroot RCS is comparable with the AH Plus sealers, micro CT studies have been shown that it might be due to the reduced flow and working time than AH Plus.[16] Energy-dispersive X-ray spectroscopy analysis showed that Bioroot RCS contains carbon, calcium, oxygen, zirconium, chlorine, silicon and no added toxic elements or heavy metals.[35] The elements detected in this study were biologically compatible and the same results observed by an experimental study done by Camilleri et al.[31],[32] MTA Fillapex is a two-component catalyst-paste system. The base consists of silica, bismuth oxide and salicylate resin components such as butylene glycol, colophony and methyl salicylate.[16],[36] The catalyst consists of titanium dioxide, silicon dioxide and base resin components such as toluene sulphonamide, rosinate, penta erythritol, and set MTA component of 13.2% as filler. Reszka et al. analysed the components of MTA Fillapex and AH Plus by energy-dispersive X-ray spectroscopy in which the MTA Fillapex showed a surface rich in titanium, silicon, oxygen, bismuth, calcium and AH Plus mainly contains carbon. The cementation phase of MTA Fillapex showed a high peak of titanium, bismuth, oxides and AH Plus exhibited tungsten, zirconium and oxide.[32] Neelakantan et al. demonstrated the retreatability of MTA plus and MTA Fillapex sealer using CBCT and showed that MTA plus has more sealer remnants compared to MTA Fillapex. Diaproseal sealer is an epoxy resin-based sealer. It has various properties such as good sealing of complex root canal system, fast-setting time, volume stability, dual syringe system and long-term storage ability allowing easy mixture.[33],[36] Song YS et al., demonstrated various properties of Diaproseal sealer such as sealing ability, biocompatibility were compared with the AH plus and AD seal, concluded that Diaproseal has a high pH range about 6.7–7.2, dimensional changes about 0.5%, less solubility of about 0.5 × 10[−4], adequate flow with acceptable physicochemical properties, biocompatibility and sealing ability. There is no data present about the retrievability of diaproseal sealers.[33]

Phosphate buffer solution (PBS) was used in this study, to preserve the micro-elastic properties of dentinal and cemental tissues. It is a hydrated salt solution containing sodium chloride, potassium dihydrogen phosphate, disodium hydrogen phosphate and potassium chloride.

A study by Kim et al. demonstrated the penetrability of bioroot RCs into dentinal tubules and compared with conventional root canal sealers using confocal microscopy, found that a high intensive level of sealer penetration was observed in the middle third part of the root canal.[36]

The present study evaluated the retreatability of different epoxy resin-based and calcium silicate-based endodontic sealers. The micro-CT analysis revealed that bioroot RCs showed more volume of sealer remnants at the apical third part of root canal than MTA Fillapex sealer and followed by Diaproseal sealers. This reveals that the apical curvature of a root canal minimizing the contact of retreatment instruments in all the walls of the root canal.[37] The difficulties encountered while removing Bioroot RCS was 'its rock-like consistency' compare to MTA Fillapex and Diaproseal sealer. The additional finding observed in the study was the retreatment with protaper universal retreatment files produced a certain amount of cracks on the root dentin in all the groups except the Bioroot RCs group, whereas the Diaproseal sealer did not prevent any cracks. In Bioroot RCS, more volume of sealer remnants in the root canal and prevention of cracks after retreatment might be due to increased biomineralization activity of this material. Each component of Bioroot RCs plays an important role in its biomineralization activity.[30],[38] Interaction of calcium-silicate sealer with dentin causes the formation of intra-tubular tags in conjunction with an interfacial mineral interaction layer referred to as mineral infiltration zone.[34],[35],[39],[40] For the setting of bioceramic sealer, it utilizes inherent moisture within the dentinal tubules. As the reaction proceeds, the water combines with the calcium silicates and forms additional calcium silicate hydrate gel-like form. The resultant apatite, deposits on collagen fibrils, that triggers the formation of the interfacial layer with tag-like structures at the interface.[41],[42],[43],[44] On the other hand, the diaproseal sealer showed better retreavability and no such crack-preventing properties. Because it is a resin based-sealer and it does not have any attributive capabilities for biomineralization. MTA Fillapex group showed crack formation not as much as that of Diaproseal sealer group. Since the tubular penetration ability of Bioroot RCs is greater as compared to MTA Fillapex sealer, it showed fewer sealer remnants in the root canal and prevented less formation of cracks after retreatment as compared to Bioroot RCS.

No other studies mentioned the crack resisting property of Bioroot RCs root canal sealers. The crack formation during retreatment is due to dilation and increasing compliance of regions surrounding the crack. As the crack opens, the collagen filaments extend across it and distribute the energy by their deformation or friction.[25],[37],[45] The increased zone of mineral infiltration and mineral plug formation of bioroot root canal sealers may be the reason for the resistance of crack growth.

This study used statistical software IBS.SPSS 19.0 Version, Kruskal–Wallis test was used to determine the intra-group comparative analysis and Post hoc Scheffe test for inter-group comparative analysis. The overall mean of sealer volume remained in the canal for bioroot RCs is greater than MTA Fillapex and Diaproseal sealers and at the apical third of root canal, Bioroot RCs are greater than the middle third and apical third. The mean crack length of Diaproseal sealer was greater than MTA Fillapex, and no visible cracks were seen in Bioroot RCS. Both Kruskal–Wallis test and the post hoc Scheffe test show statistically significant results.

The presence of bio-mineralizing capacity for a root canal sealer exhibits a lack of retrievability during retreatment procedures. In questionable cases like craze lines or cracks in the root canal wall and thin root dentin can lead to crack propagation during instrumentation procedures. In such clinical situations, Bioroot RCs can be recommended as a treatment of choice. The clinical implications of this study show that using Bioroot sealers can resist the crack formation on retreatment procedures. In clinical situations, post-retreatment failure occurs because of crack formation with the use of aggressive instruments. No other studies found the importance of crack resisting property of Bioroot sealer.

The short coming of this study was the depth of penetration of sealer into the dentinal tubules has not been evaluated, only one type of rotary file system was used for the removal of sealer, and this study did not use any type of solvents for the removal of obturated material.


   Conclusion Top


Within the limitations of this in vitro study, it can be concluded that

  • Among all the three groups, none of the groups showed complete removal of obturated material from the root canal.
  • More volume of sealers was present in the Bioroot RCS group followed by MTA Fillapex and Diaproseal sealer.
  • No visible crack was seen in the Bioroot RCS group. More crack length was observed in Diaproseal sealer followed by the MTA Fillapex sealer group.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Dr. M V Mavishna
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DOI: 10.4103/ijdr.IJDR_328_20

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