Retrievability of bioceramic-based sealers in comparison with epoxy resin-based sealer assessed using microcomputed tomography: A systematic review of laboratory-based studies

Abstract

Aim:

The objective was to evaluate the retrievability of bioceramic sealers in comparison with epoxy resin-based sealers assessed using microcomputed tomography.

Materials and Methods:

Four reviewers independently conducted a systematic literature search in four electronic databases. The risk of bias was assessed using modified Joanna Briggs Institute Critical Appraisal tools for Quasi-Experimental Studies.

Results:

Ten articles were included in this review and all had a moderate risk of bias. The results across the included articles were inconsistent with some indicating easier/difficult removal of bioceramic sealers, while others indicate no difference. The studies varied in terms of the type of bioceramic sealer used, root canal anatomy, and retreatment techniques followed. Due to heterogeneity, only a qualitative analysis was performed and no meta-analysis was conducted.

Conclusion:

The quality of evidence is low and no definitive conclusion could be derived regarding the retrievability of bioceramic sealer/AH plus sealer from the root canals during retreatment procedures.

INTRODUCTION

A recent systematic review and meta-analysis reported the incidence of apical periodontitis in root canal-treated teeth to be 41.3%.[1] Nonsurgical root canal treatment can fail due to various reasons such as the presence of intracanal and extracanal bacteria, inadequate shaping and cleaning of canals, lack of good coronal seal, untreated, unfilled or overfilled root canal spaces, and iatrogenic errors.[2,3] The overall pooled success rate of nonsurgical root canal retreatment is reported to be 80%,[4] making it the first line of treatment option for previously endodontically treated teeth with symptomatic apical periodontitis.[5]

Factors which influence the success of endodontic retreatment comprise of root canal morphology, periapical status, obturation material and technique, and endodontic sealers used.[6,7] The rationale of retreatment is to regain access to all parts of the root canal system followed by the removal of filling material which will facilitate a thorough disinfection of the root canals.[8] The residual filling material present after retreatment might harbor bacteria which are persistent and unaffected by antimicrobial substances and hence can become a source for reinfection leading to apical periodontitis.[8,9,10,11] Complete removal of the infected residual root canal filling material and secondary smear layer is essential as it allows for better disinfection of the root canal system, closer adaptation of the obturating material, and subsequent bonding of the resin posts to the root canal dentin.[8,9]

Root canal filling material can be removed by manual, rotary, or reciprocating stainless steel or nickel-titanium file systems during retreatment. At present, ultrasonic tips,[12] XP-endo finisher rotary files,[13] GentleWave system,[14] and photon-initiated photon acoustic streaming (PIPS)[15] are some of the supplementary techniques used to enhance the removal of previous root filling material. However, no retreatment technique till date facilitates complete removal of the filling material.[12,13,16]

Recently, bioceramic-based endodontic sealers have gained popularity due to their biocompatibility, stability, and minimal postoperative pain.[17,18,19] Bioceramic sealers are primarily calcium silicate-based sealers which have biomineralization capacity and thereby form strong chemical bonding with the root dentin.[20] It also has the ability to set in humid conditions, making it superior to other conventionally available sealers.[21,22] They have a high pH (>11) and release calcium ions in high quantities, making them antimicrobial.[22]

Due to the strong chemical bonds formed between the bioceramic sealer and dentine hydroxyapatite, removal of these sealers often poses challenges during retreatment. Some authors have reported difficulties such as increased operatory time,[23] inability in regaining working length and apical patency,[24] and incomplete removal of these type of sealers[25] when compared to resin sealer/AH plus sealer. Until now, AH plus sealer is one of the most commonly used epoxy resin-based sealers and hence is considered as a gold standard against which other sealers are most often compared. Previous literature pertaining to the retrievability of bioceramic-based sealers is mostly in comparison to AH plus sealer.[12,26,27]

The analysis of samples after retreatment procedures can be done by longitudinal sectioning,[28] clearing and sectioning,[29] cone-beam computed tomography (CBCT),[25] and microcomputed tomography (Micro-CT).[16]

Micro-CT is a nondestructive, high-resolution, three-dimensional imaging technology that allows the quantification of filling material present in the root canal wall before and after retreatment.[30] Although similar sequential analysis of the samples can be achieved using CBCT, it has lower resolution and sensitivity in comparison to micro-CT.[31]

Solomonov et al.[32] defined “effectively cleaned root canals” when only 0.5% of the root canal filling material remained. However, articles evaluating the removal of bioceramic sealers have reported remaining gutta-percha and sealer to vary from 3% to 22% and have defined the completion of retreatment procedure when the last retreatment file comes out of the root canal free of debris.[12,27] The results published in literature regarding the removal of bioceramics sealer and AH plus sealer are contradictory in nature.[15,24,25,26,27,33]

Hence, the aim and purpose of this systematic review were to evaluate the retrievability of bioceramic-based sealers in comparison with resin-based sealers assessed using micro-CT. The primary objective was to compare the retrievability between bioceramic sealer in comparison to resin-based sealer using micro-CT. The secondary objective was to evaluate other parameters such as time taken and apical patency established during retreatment.

MATERIALS AND METHODS

The current systematic review was reported according to the preferred reporting items for systematic reviews and meta-analyses statement,[34] and protocol of the review was registered in the Open Science Framework (OSF) registry (Centre for Open science, osf.io/chg2q/registrations) DOI 10.17605/OSF.IO/38J7M.

Article selection

A comprehensive search was performed in PubMed, Scopus, Web of Science, and EMBASE electronic databases until July 2021. The search strategy was developed and adapted for each electronic database [Supplemental Table S1]. In addition, International Endodontic Journal, Journal of Endodontics, Australian Endodontic Journal, and Clinical Oral Investigations were hand searched for similar articles. Furthermore, the corresponding authors of the included articles were contacted through E-mail to obtain additional information. Zotero software (Zotero 5.0 for Windows, Centre for History and New Media, George Mason University, Fairfax, Virginia, USA) was used to remove duplicates and organize the identified articles. Four independent reviewers (A. V, A. M, S. P, and S. E) performed title, abstract, and full-text assessment. Any disagreement was resolved by two senior reviewers (B. A and N. V).

Table S1.

Search strategy

Database	Search strategy	Results
PubMed	(removal OR retreatment OR retrieval OR retrievability OR ‘‘endodontic retreatment’)) AND (“bioceramic sealer” OR “bioceramic root canal” OR “calcium silicate sealer” OR “calcium silicate cement*” OR ”endodontic sealers” OR ” root canal sealing material” OR ”root canal sealers” OR ” tricalcium silicate sealer” OR sealer)	886
Scopus	(TITLE-ABS-KEY (removal OR retreatment OR retrieval OR retrievability OR “endodontic retreatment”) AND (TITLE-ABS-KEY (“bioceramic sealer” OR “bioceramic root canal” OR “calcium silicate sealer” OR “calcium silicate cement*” OR “endodontic sealers” OR “root canal sealing material” OR “root canal sealers” OR “tricalcium silicate sealer” OR sealer) AND (LIMIT-TO (SUBJAREA, “DENT”))	640
Web of science	(TS= (removal OR retreatment OR retrieval OR retrievability OR “endodontic retreatment”) AND (TS= (“bioceramic sealer” OR “bioceramic root canal” OR “calcium silicate sealer” OR “calcium silicate cement*” OR “endodontic sealers” OR “root canal sealing material” OR “root canal sealers” OR “tricalcium silicate sealer” OR sealer)	543
EMBASE	(Ti= (removal OR retreatment OR retrieval OR retrievability OR “endodontic retreatment”) AND (Ti= (“bioceramic sealer” OR “bioceramic root canal” OR “calcium silicate sealer” OR “calcium silicate cement*” OR “endodontic sealers” OR “root canal sealing material” OR “root canal sealers” OR “tricalcium silicate sealer” OR sealer)	2878

OR: Odds ratio, EMBASE: Excerpta Medica dataBASE, ABS: Abstract, KEY: Keyword, DENT: Dental, TS: Titles, TI: Title

Eligibility criteria

Research question: Retrievability of bioceramic-based sealers in comparison to epoxy resin-based sealers in human permanent teeth analyzed using micro-CT.

The review question was formulated as PICOS (P-Population, I-Intervention, C-Comparison, O-Outcome, S-Study design)

• P: Endodontic retreatment of human mature permanent teeth analyzed used micro-CT

• I: Bioceramic-based sealers

• C: Epoxy resin-based sealers

• O: Retrievability of sealers

• S: Laboratory-based micro-CT studies.

Inclusion criteria

Laboratory-based studies published in English that assessed the retrievability of bioceramic sealers in comparison with epoxy resin-based sealer in human mature permanent teeth using micro-CT were included in the study.

Exclusion criteria

Studies performed in animals, artificial teeth, endodontic training blocks, narrative reviews, book chapters, conference abstracts, and expert opinion were excluded from this review.

Article selection and data collection process

Titles and abstracts of the articles were screened according to the predefined inclusion/exclusion criteria and duplicates were removed (A. V, A. M, S. P, and S. E). After full-text reading, articles fulfilling the inclusion criteria were selected for final qualitative assessment. Data extraction sheet was done in a Microsoft Excel 2016 (Microsoft Corp., Redmond, WA, USA).

The following parameters were extracted from the articles: name of the first author, year, journal, teeth included, preoperative data (instruments used for initial preparation of the root canals and obturation technique), features evaluated (sealers used, waiting period, instruments used, method of removal, levels assessed), number of observers, method of assessment, statistical analysis, and results. Four reviewers (A. V, A. M, S. P, and S. E) extracted the data which were further verified by two senior endodontists (B. A and V. N) [Table 1].

Table 1.

Characteristics of the included articles

General data		Preoperative data			Sealers used		Features
Number	Authors, Year, Journal	Teeth used (n)	Root canal preparation	Technique of obturation	Bioceramic sealer	Resin sealer	Waiting period	Instruments used for removal	Number of observers	Solvent	Microscope used (magnification)	Features evaluated
1	Salim et al. (2021), Braz. J. Oral Sci.	Teeth used: Me roots of mandibular molars (median length - 19.5 mm) and a root curvature angle of up to 25 n=40	File K3 files Canal size 30/0.04 Master cone TF group - #30/#35 GP AH plus group-Dentsply FM/M GP	CWC	Total fill BC sealer	AH plus	7 days	Primary technique Gates Glidden drills size 3, ProTaper Universal Retreatment files (D1,2,3) and ProTaper Next X4	NM	No	No	1. Volume of residual filling after retreatment procedure 2. Regaining apical patency
2	Liu et al. (2021) J. Dent.	Teeth used: Permanent mandibular molars with two Me canals and one oval-shaped D canal n=30	File Vortex Blue Canal Size 35/0.04 in Me canals and 40/0.04 in D canals Master cone NM	1. CWC 2. Single cone	EndoSequence BC	AH plus	54 months	Primary technique 1. D-Race DR1 (30/0.10) for C 3 mm 2. XPS Supplementary technique XPFR	NM	Yes (Chloroform in C for 1 min)	Yes (NM)	1. Percentage of filling material removed
3	Alsubait et al. (2020) Aust Endod J	Teeth used: Mandibular premolars with straight canal n=34	File ProTaper Next Canal Size: F3 file Master cone ProTaper F3 GP	Single cone	BioRoot RCS	AH plus	30 days	Primary technique ProTaper Universal Retreatment files (D1,2,3), F2 and F3 of ProTaper universal Supplementary technique PUI	1	No	Yes (NM)	1. Retreatment time 2. Volume of residual filling after retreatment procedure
4	Crozeta et al. (2020) Clinical oral investigations	Teeth used: D roots of mandibular molars with single and oval-shaped canals n=28	File R50 instrument Canal size 40/0.04 Master cone R40 GP	Single cone	EndoSequence BC	AH plus	14 days	Primary technique R50 (50.05) Supplementary technique PUI and XPFR	1	No	Yes (NM)	1. Volume of residual filling after retreatment procedure
5	Aksel et al. (2019) Int Endod J.	Teeth used: Mandibular molars with mesiobuccal root canal curvature (20-30° angle) n=30	File ProTaper Universal Canal size F2 file Master cone ProTaper F2 GP	Single cone	1. NeoMTA Plus 2. EndoSequence BC	AH plus	14 days	Primary technique ProTaper Universal Retreatment files (D1,2,3), F2 and F3 of ProTaper universal Supplementary technique None	1	NM	No	1. Volume of residual filling after retreatment procedure
6	Suk et al. (2019) Clinical oral investigations	Teeth used: D roots of mandibular molars with single and oval-shaped canals n=28	File R40 instrument Canal size 40/0.04 Master cone R40 GP	CLC	1. EndoSequence BC Sealer 2. MTA Fillapex	AH plus	14 days	Primary technique ProTaper Universal Retreatment files (D1,2,3), F2 and F3 of ProTaper universal Supplementary technique: PIPS	1	No	No	1. Volume of residual filling after retreatment procedure
7	Romeiro et al. (2019) Clinical oral investigations	Teeth used: Mandibular molars with severely curved mesial roots (20°-40°) n=60	File Reciproc R25 Canal size 25/0.08 Master cone R25 GP	Single cone	EndoSequence BC	AH plus	30 days	Primary technique 1. Reciproc 2. Reciproc Blue Supplementary technique None	1	No	No	1. Volume reduction of obturation material 2. Amount of dentin removed 3. Apical transportation 4. Apical extrusion of debris 5. Retreatment time
8	Kim et al. (2019) Restor Dent. Endod.	Teeth used: Single-rooted mandibular premolars (n=21), double-rooted maxillary premolars (n=21), mandibular second molars with Type 1 C-shaped (n=15) n=57	File: ProFile system Canal Size: 35/0.06 Master cone: R25 GP	1. CWC (AH plus) 2. Single Cone	1. EndoSequence BC 2. Endoseal MTA	AH Plus	10 days	Primary technique 1. Gates Glidden drills sizes 2, 3 and 4 2. ProFile (35/0.06) in single-rooted teeth and (30/0.06) in multirooted teeth Supplementary technique None	NM	No	No	1. Percentage of remaining root canal filling material
9	Athkuri et al. (2019) J Conserv Dent	Teeth used: Mandibular premolars with straight canals (<5°) n=90	File Mtwo Rotary Canal size 35/0.04 Master cone NM	1. CLC 2. WVC 3. TI	BioRoot RCS	AH plus	21 days	Primary technique MTwo R1 (15/.05) and MTwo R2 (25/.05), and MTwo up to (40/.04) Supplementary technique None	1	Yes (Endosolve E coronal third)	No	1. Retreatment time 2. Total percentage of residual root canal filling material and individually at different levels of root canal
10	Oltra et al. (2017) Restor Dent. Endod	Teeth used: Maxillary incisors n=56	File R40 instrument Canal size 40/0.04 Master cone R40 GP	1. CWC (AH plus) 2. Single cone (BC sealer)	EndoSequence BC	AH plus	30 days	Primary technique ProFile 45/0.04 taper + vortex blue size 45/0.04 Supplementary technique None	NM	Yes (Chloroform throughout the canal)	No	1. Volume of residual filling after retreatment procedure 2. Ability to regain patency
General data Number		Features			Results
		Statistical analysis	Micro-CT voltage, current, slice thickness, time	Levels of root canal assessed	Results			Reasoning			Conclusion
1		Normality analysis by Shapiro-Wilk test, Independent and paired t-test and ANOVA	70 kV, 114 mA, NM	Entire and all levels (C, M, A) of root canal	Remnants of residual filling material 1) AH=TF 2) AH group C < M C=A 3) TF group C=M = A Regaining apical patency 65% - AH group 75% - TF group			Similar physicochemical characteristics, such as high flow, biocompatibility and radiopacity between AH and TF Due to the presence of isthmus in middle third, in the AH group there was higher percentage of remaining filling material in the middle			Volume of remaining filling material AH group=TF group in the entire root canal and all levels In AH group, middle third highest remaining material
2		Shapiro-Wilk test and modified Levene test, One-way ANOVA and Tukey’s post hoc pairwise comparison, Kruskal-Wallis, Wilcoxon signed-rank tests and Mann-Whitney U test	90 kV, 200 µA, 30 µm, 500 ms	Entire and all levels (C, M, A) of root canal	XPS 1. BCS (Me: 96.1%; D: 89.0%)=AHS (Me: 94.8%; D: 83.8%) > AHW (Me: 85.7%; D: 77.8%) 2. Higher percentage of filling material removal in the Me canals than in the D canals XPFR 1. BCS (Me: 54.4%; D: 63.0%) > AHS (Me: 43.9%; D: 40.7%) and AHW (Me: 36.7%; D: 35.8%) 2. Removed more from C and M of the D canals > Me canals in BCS 3. AHS=AHW in Me and D canals Combined use of XPS and XPFR 1. Removed more from Me canals [BCS (98.2%) =AHS (97.3%)] > AHW (91.3%) 2. Removed from D canals in BCS (96.2%) > AHS (92.4%) > AHW (86.6%) Apical 3 mm 1) 23% complete removal of filling material with XPS and additional 30% after XPFR 2) Complete removal of filling material in the apical 3 mm in BCS (60%) > AHW (35%)			Filling material removal in AHS group>AHW group as warm vertical compaction technique compact root-filling material deeper into irregular root canal anatomies such as the isthmus, fin and oval-shaped canals Better performance in the mesial roots than in the distal roots due to oval-shaped canals in distal roots			XPS removes filling material more efficaciously from the Me roots. Supplementary instrumentation using the XPFR significantly enhances the removal
3		Kolmogorov-Smirnov test, Mann-Whitney and Wilcoxon tests	94 kV, 85 µA, 19 µm, NM	Entire root canal	Primary technique and supplementary technique BioRoot RCS < AH plus			Lower bond strength values of BC sealers and use of a chelating agent such as EDTA. The flow of BioRoot RCS is lower than AH plus sealer			Remnants of residual filling material BioRoot RCS < AH plus Time Taken BioRoot RCS > AH plus
4		ANOVA, Tukey’s tests	50 kV, 800 mA, 16.7 µm, NM	Entire and all levels (C, M, A) of root canal	Primary technique and supplementary technique EndoSequence < AH plus			Lower bond strength values of bioceramic sealers and use of a chelating agent such as EDTA			Primary technique and supplementary technique Remnants of residual filling material EndoSequence < AH plus
5		Kruskal-Wallis test, Friedman’s two-way ANOVA with Bonferroni correction	50 kV, 800 µA, 33 µm 2500 ms	Entire and all levels (C, M, A) of root canal	Remnants of residual filling material NeoMTA=AH plus EndoSequence BC=AH plus			Biomineralization ability and bond strength of NeoMTA plus			Remnants of residual filling material BC sealers=AH plus
6		Kruskal-Wallis test with additional post hoc Mann-Whitney U test	80 Kv, 60 µA, 1.2 µm, NM	Entire root canal	Primary technique and supplementary technique MTA Fillapex < AH plus EndoSequence BC=AH plus			Lower concentration of MTA (≈13%) in MTA fillapex resulting in lower biomineralization and lower bond strength to the root canal dentin			Primary technique and supplementary technique Remnants of residual filling material MTA Fillapex < AH plus EndoSequence BC=AH plus
7		ANOVA or Kruskal-Wallis, Student’s t-test and Mann-Whitney test	100 kV, 100 µA, 17.87 µm, 34-min	Entire and all levels (C, M, A) of root canal	Remnants of residual filling material EndoSequence BC=AH plus Time taken EndoSequence BC > AH plus			Similar adhesion and sealing ability of the AH Plus and EndoSequence BC			Remnants of residual filling material, amount of dentin, apical transportation, apical extrusion of debris, EndoSequence BC=AH plus Time Taken EndoSequence BC > AH plus
8		Shapiro-Wilk normality test, Kruskal-Wallis test, Mann-Whitney U test with the Bonferroni correction	100 kV 100 µA, 23.86µm NM	Entire and all levels (C, M, A) of root canal	Remnants of residual filling material EndoSequence BC=AH plus Endoseal MTA=AH plus (single- and double-rooted teeth) Remnants of residual filling material Endoseal MTA > AH plus (C-shaped roots)			Shorter setting time of Endoseal MTA and the mechanical bond formed between the C- shaped canal and MTA.			Remnants of residual filling material EndoSequence BC=AH plus Endoseal MTA=AH plus (single- and double-rooted teeth) Remnants of residual filling material Endoseal MTA > AH plus (C-shaped roots)
9		Two-way analysis of variance Tukey’s multiple post hoc test	micro-CT Specifics NM	Entire and all levels (C, M, A) of root canal	Remnants of residual filling material BioRoot RCS=AH plus Time Taken CLC < WVC=TI More remnants are seen in the apical third			Difficulty in engaging instruments in the apical root region			Remnants of residual filling material Bioceramic sealer=AH plus Time taken CLC < WVC=TI
10		ANOVA, Post hoc Tukey’s test, Fisher’s exact tests	65 kV, 154 µA, 35 µm, NM	Entire and all levels (C, M, A) of root canal	Remnants of residual filling material AH plus (with chloroform) < EndoSequence BC Patency could not be established in all samples			Ability of Bioceramic sealer to form calcium and phosphate tags in the intratubular dentin and hence better sealing and dentin bonding			Remnants of residual filling material AH plus (with chloroform) < EndoSequence BC

A: Apical third of root canal, AH: AH plus sealer, AHS: AH plus sealer with single cone obturation technique, AHW: AH plus sealer with warm vertical condensation obturation technique, ANOVA: Analysis of variance, BC: Bioceramic, BCS: EndoSequence BC sealer with single cone obturation technique, C: Coronal third of root canal, CLC: Cold lateral compaction obturation technique, CWC: Continuous wave compaction technique, D: Distal, EDTA: Ethylenediaminetetraacetic acid, GP: Gutta-percha, M: Middle third of root canal, Me: Mesial, Micro-CT: Micro computed tomography, MTA: Mineral trioxide aggregate, NM: Not mentioned, PIPS: Photon induced photoacoustic streaming, PUI: Passive ultrasonic irrigation, TF: TotalFill BC sealer, TI: Thermoplasticised injectable, WVC: Warm vertical condensation obturation technique, XPFR: XP-endo finisher R file, XPS: XP-endoshaper file, RCS: RCS: Root canal sealer

Quality assessment

The quality assessment of the included articles was performed by four reviewers (A. V, A. M, S. P, and S. E) and any disagreements were resolved by consulting the two senior reviewers (B. A and V. N). Joanna Briggs Institute Critical Appraisal tools for Quasi-Experimental Studies (nonrandomized experimental studies) (https://joannabriggs.org/critical_appraisal_tools)[35] were used for quality assessment in this systematic review. The question pertaining to the follow-up was not related to this review and hence eliminated. Each of the questions was either answered as “yes,” “no,” “unclear,” and “not applicable.” The score of “1” was given if the question was answered as “yes” and score of “0” was given if answered as no, unclear, or not applicable. The included articles in systematic review were categorized into high (0%–33%), moderate (34%–75%), and low (76%–100%) risk of bias.

RESULTS

The initial search yielded 4947 articles from four electronic databases, namely PubMed, Scopus, Web of Science, and EMBASE. Among these, 437 articles were eliminated as duplicates. After reading the titles and abstracts, only ten articles[12,13,15,26,27,33,37,38,39,40] were found eligible and hence were included in this systematic review Figure 1. The general characteristics of the included articles are given in Table 1.

Figure 1.

Preferred reporting items for systematic reviews and meta-analyses flowchart

Quality assessment

All the articles were assessed to have moderate risk of bias. The graphs of summary of quality assessment of the articles performed were generated using RevMan Software (2014)[36] [Figures 2 and S1 ^{(788KB, tif)} ].

Figure 2.

Risk of bias graph assessed using Joanna Briggs Institute Critical Appraisal tools for Quasi-Experimental Studies (nonrandomized experimental studies) presented as percentages across all included studies

Types of teeth

The included articles have used different types of teeth/roots for the experimental analysis. The sample size in the included articles ranged from 28 to 90 (teeth/roots). Two articles had used single-rooted anterior teeth.[15,26] One article[39] used all the three roots (two mesial canals and one oval shaped distal canal) of a mandibular molar, whereas three articles used only the mesial roots of mandibular molars (both mesiobuccal and mesiolingual roots canals).[13,37,40] Four articles[12,15,33,38] used single-rooted mandibular premolars and one article[27] used distal roots of first and second mandibular molars. One article[33] used both double-rooted maxillary premolars (both buccal and palatal root canals) and mandibular second molars with C-shaped canals classified as Fan et al. Class I.[41] The curvature of mesial roots of mandibular molars ranged from 20° to 40° and was mentioned in only three of the included articles.[13,37,40]

Types of bioceramic sealers used in the included articles

Six different types of bioceramic sealers, namely EndoSequence BC sealer, Endoseal MTA, BioRoot RCS, NeoMTA plus, MTA fillapex, and TotalFill BC sealer were used in the included articles. EndoSequence BC sealer was used in seven articles[13,15,26,27,33,37,39] while BioRoot RCS was used in two articles.[12,38] Endoseal MTA,[32] NeoMTA plus,[13] MTA fillapex,[15] and TotalFill BC sealer[40] were used in one article each, respectively [Figure S2 ^{(178.9KB, tif)} ]. All the included articles compared the retrievability of the bioceramic-based sealers with AH plus sealer. Composition and properties of the sealers used in the included articles are given in Supplemental Table S2.

Table S2.

Properties and composition of sealers used in the included articles

Sealer	Composition	Setting time	Working time	Radiopacity (mmAl)	Flow (mm)
EndoSequence BC Sealer	Zirconium oxide calcium silicates, calcium phosphate, calcium hydroxide, filler and thickening agents	4 h	>4 h at room temperature	6.68	18.45
MTA fillapex	Paste A: Salicylate resin Bismuth trioxide Fumed Silica Paste B: Fumed Silica Titanium Dioxide MTA (40%) Base resin	130 min	35 min	3.01	34.13
NeoMTA plus	Powder: Tricalcium silicate, dicalcium silicate, tantalum oxide, tricalcium aluminate calcium sulfate and gypsum Liquid: Water-based gel with thickening agents and water soluble polymers	315 min	20 min	3.76	25-29
BioRoot RCS	Powder: Tricalcium silicate, zirconium dioxide, povidone Liquid: Water, calcium chloride and polycarboxylate	4 h	10 min	5.2	16
Endoseal MTA	Calcium silicates, calcium aluminates, calcium aluminoferrite, calcium sulfates, radio-opacifier, thickening agents.	12 min	12 min	9.50	20.21
AH plus	Paste A: 25%-50% bisphenol A 10%-25% zirconium dioxide NS calcium tungstate NS iron oxideleftPaste B: 2.5%-10% N, n-dibenzyl-5-oxanonandiamin-1,9 2.5%-10% amantadine	8 h	4 h	10.00	21.87
TotalFill BC sealer	Zirconium oxide Calcium silicate Calcium phosphate Calcium hydroxide Fillers and thickening agents	4 h	Greater 4 h	4±0.15	24.63

BC: Bioceramic, MTA: Mineral trioxide aggregate, AH: AH plus sealer, RCS: Root canal sealer

Obturation techniques used in the included articles

Various obturation techniques employed within the included articles were single-cone obturation,[12,13,27,33,37,39] continuous-wave compaction,[26,33,39,40] and cold lateral compaction techniques.[15,38] Gutta-percha was used as the core obturating material in all the included articles. Athkuri et al.[38] compared the retrievability using three different obturation techniques, namely cold lateral compaction, warm vertical compaction, and thermoplasticized injectable technique and reported no significant difference in the retreatment time among the tested sealers. However, according to the authors, the time taken to retrieve the remaining filling materials obturated with cold lateral compaction technique was the least and highest for warm vertical compaction. There was no significant difference between warm vertical compaction technique and thermoplasticized injectable obturation technique.

Retreatment technique

Use of solvents

Three articles[26,38,39] stated the use of solvents such as Chloroform and Endosolv E. Athkuri et al.[38] and Liu et al.[39] used Endosolv E and Chloroform, respectively only during the initial phase of retreatment technique in the coronal third of the teeth. Oltra et al.[26] used chloroform throughout the root canal and reported that it effectively aided in the removal of remaining filling material.

Role of instrumentation, magnification, and irrigation

Retreatment rotary/reciprocating files, namely ProTaper Universal retreatment files,[12,13,15,40] ProTaper Next,[40] D-Race,[39] XP-Endoshaper,[39] Mtwo retreatment files,[38] and Reciproc and Reciproc Blue,[27,37] were used in the included articles. A few of the included articles also utilized regular rotary files such as Profile rotary file[26,33] and Vortex blue files[26] in the retreatment procedures. In all the included 10 articles that used various file systems, the root canal was enlarged one or two sizes larger in comparison to the initial size of preparation.

Five articles[13,15,26,33,37] mentioned the use of root canal irrigants, sodium hypochlorite (NaOCl) (2.5%–6%), and ethylenediaminetetraacetic acid (EDTA) (15%–17%) during the retreatment procedure. Four articles[12,27,39,40] only used 2.5%–6% NaOCl during the retreatment procedures. Athkuri et al.,[38] however, failed to mention the irrigants used during treatment and retreatment procedures

It is also interesting to note that only three of the included articles[14,38,39] mentioned the use of dental operating microscope for the retreatment procedure.

Supplementary techniques for retreatment

In addition to using a primary technique (retreatment files) for the removal of root canal filling material, supplementary techniques were used in five of the included articles.[12,13,15,27,39] The supplementary techniques used were passive ultrasonic irrigation,[12,27] PIPS,[15] and XP-endo finisher.[13,27,39] Supplementary techniques were seen to enhance the retrievability of root canal filling material in comparison to the primary technique.

Analysis of remaining root canal filling materials

Volumetric analysis of the retrievability of the sealers before and after retreatment procedures was done using micro-CT analysis with a slice thickness ranging from 1.2 μm to 33 μm. Retreatment of the specimens was done after a waiting period ranging from 7 days to 54 months.

To evaluate the retrievability of the bioceramic sealers, the included articles considered various primary and secondary outcomes. The primary outcomes were volume of remaining root canal filling material[13,15,26,27,33,38,40] and volume of root canal filling material reduced.[12,37,39] Secondary outcomes assessed were the ability to regain working length[26] and apical patency,[26,40] time taken for retreatment procedure,[12,37,38] amount of root dentin removed, apical transportation, and apical debris extrusion.[37]

Retrievability of bioceramic sealer versus resin-based sealers

All the ten included articles showed varying results in relation to retrievability and remaining filling material on comparing bioceramic-based sealers to AH plus sealer [Figure S3 ^{(197.8KB, tif)} ]. None of the included articles could completely remove the gutta-percha and both sealer types from the root canals.

Three articles assessed the retrievability of two bioceramic sealers in comparison to AH plus sealer.[13,15,33] Aksel et al.[13] found no significant difference in the remaining filling material after retreatment between AH plus group, EndoSequence BC and NeoMTA plus. Kim et al.[33] assessed the retrievability of Endoseal MTA, EndoSequence BC, and AH plus sealer in single, double, and C-shaped canals. They found no significant difference in ease of retrieval of sealers in single and double-rooted canals whereas there were significant remaining remnants in the C-shaped root canals obturated with Endoseal MTA followed by AH plus and EndoSequence BC sealer. Suk et al.[15] reported that there was significantly reduced remaining material in the MTA Fillapex group in comparison with AH plus and EndoSequence BC sealer groups. However, there was no significant difference between AH plus and EndoSequence BC sealer groups.

The remaining seven articles assessed the retrieval of a single bioceramic sealer in comparison to AH plus. Three articles reported retrieval of bioceramic sealer to be easier,[12,27,39] three articles found no difference in the retrievability of AH plus and bioceramic sealer,[37,38,40] and one article reported that bioceramic sealers were more difficult to retrieve.[26]

It is interesting to note that seven articles compared the retrievability of EndoSequence BC in comparison to AH plus sealer. Four articles[13,15,33,37] found no difference between the retrievability of the sealers whereas Romeiro et al.[37] and Liu et al.[39] reported easier removal of EndoSequence BC[37] and Oltra et al.[26] reported easier retrieval of AH plus sealer.[26] Similarly, two articles compared the retrieval of BioRoot RCS against AH plus,[12,38] while one article reported easier removal of BioRoot RCS,[12] the other reported no difference between the sealers.[38] Although the respective articles have provided justifications for their findings, the cumulative disparity in the results can be attributed to the inherent procedural heterogeneity.

Assessment of remnants of root canal filling material based on different levels of root canal

Oltra et al.[26] reported that the remnants of EndoSequence BC sealer were seen most commonly in the coronal third, Romeiro et al.[37] reported significant reduction of EndoSequence BC sealer retrieved using Reciproc file in the apical third of the root, whereas Liu et al.[39] reported significant reduction of EndoSequence BC sealer from the coronal and middle thirds of the distal canals using XP-endo finisher R files. Three other articles[27,33,38] reported more remnants in the apical third. Salim et al.[40] found no significant difference in reduction of filling materials using AH plus and TotalFill BC sealer in all the levels. However, these articles assessed different bioceramic sealers with different retreatment techniques.

Secondary outcome assessment

Two articles[26,40] assessed regaining apical patency and one article[26] assessed working length re-establishment. Oltra et al.[26] reported that the apical patency and working length was re-established in all the samples in the AH plus sealer groups with and without chloroform. For the EndoSequence BC sealer groups retrieved with chloroform, working length and apical patency were re-established in 93% of the samples. Whereas, when retrieved without chloroform, working length was re-established in 93% of the samples and apical patency was regained in only 14% of the samples. Salim et al.[40] reported that the apical patency was regained in 65% of the AH plus group and 75% of the TotalFill BC group.

Time taken for retreatment was assessed by Romeiro et al.[37] and Alsubait et al.[12] Both the articles reported that the retreatment time was longer for removal of bioceramic sealers (EndoSequence BC and BioRoot RCS) in comparison to AH plus. Romeiro et al.[37] additionally assessed the amount of dentin removal, apical transportation, and apical extrusion of debris during retreatment and reported no significant difference between the sealers.

DISCUSSION

There has been a paradigm shift towards the increasing use of bioceramic-based sealers when compared to other type of sealers in recent years.[42] The hydroxyapatite formed with the root dentin by the bioceramic-based sealers could make the removal of these sealers difficult during retreatment procedures.[20] Although our inclusion criteria comprised of retrievability of bioceramic sealer with epoxy resin-based sealers, incidentally all the included articles had used AH plus sealer as the comparative group.

During nonsurgical endodontic retreatment, various techniques have been employed to retrieve the root canal filling material. Gates Glidden drills and hand instruments were commonly used earlier by the clinicians, but with the advent of rotary and reciprocating nickel titanium retreatment files, their use has become less popular in recent times.[43,44,45]

Ideally, complete removal of residual filling material is desired but it is rarely achieved by any retreatment technique employed till date.[12,13,16] This has been attributed to the increased dentinal tubule penetration of the sealers making it difficult to retrieve it thoroughly[46] and also due to the inability of the instruments to engage all parts of the root canal system.[47] Retreatment also results in the formation smear layer which is composed of debris and remnants of plasticized gutta-percha and sealer.[48]

Micro-CT allows accurate three-dimensional analysis and quantification of the remaining root canal filling material at different stages of the experiment allowing a sequential analysis in the same sample.[30] It is a nondestructive methodology that allows longitudinal evaluation of the same specimen which is not possible with other sectioning methods used earlier.[49,50]

The overall risk of bias of the included articles in this systematic review was assessed using modified Joanna Briggs Institute Critical Appraisal tools for Quasi-Experimental Studies and was found to be moderate. The question on the reliability of outcome measured was modified and assessed based on three parameters in this review as follows, multiple observers, calibration of the evaluators and whether the inter and intra-rater reliability scores were mentioned. As none of the included articles mentioned the use of multiple operators for performing the assessment, this could have led to investigator bias, and hence, all the articles were assessed to have a moderate risk of bias. By employing multiple blinded calibrated operators, this bias could have been eliminated.

The root canal shapes are usually categorized as round, oval, or ribbon shaped.[51] Majority of the articles used single straight root canals and did not clearly state the shape of the root canal. Although Suk et al.,[15] Oltra et al.,[26] and Liu et al.[39] mentioned the inclusion of oval-shaped root canals in their samples, they failed to confirm the canals to be oval based on the buccolingual and mesiodistal dimensions.[52] Crozeta et al.[27] have selected only oval distal canals after an initial micro-CT assessment. The use of matched samples was only done in two articles[12,40] which could possibly eliminate the influence of root canal anatomy on the results of the study. Apart from the shape of the root canal, retreatment efficacy in the intracanal communications was not considered in any of the included articles, excepting Kim et al.[33] who used C-shaped root canals. They reported more remnants left behind with both types of sealers due to the presence of thin fin, slit, and webs. Accumulated debris formed during the retreatment procedure could limit the action of the chemical irrigants in these areas. Root canal anatomy is a major factor in influencing the removal of filling materials, and further studies are required using complex canal morphologies.

None of the articles included in the review, except Athkuri et al.[38] assessed the influence of obturation technique on the retrievability of the sealers. Athkuri et al.[38] reportedthat warm vertical compaction and thermoplasticised injectable technique left more remnants in comparison to cold lateral compaction technique. They concluded that type of obturation technique had an impact on the residual filling materials as well as the time taken for retreatment procedures. Unfortunately, there is no consensus regarding the ideal method of obturation technique to be followed while using bioceramic sealers. It has been suggested that the use of heat during obturation can influence the physical properties of bioceramic sealer such as the flow, viscosity, and weight of the sealer.[53] Bioceramic sealers are calcium silicate-based sealers which are hydraulic cements that require the presence of water or tissue fluid to set.[54] Warm vertical compaction which employs heat can lead to loss of moisture, thereby altering their physical and chemical properties.[55] Hence, single-cone obturation technique has been suggested by few authors while using bioceramic-based sealers.[54,56,57]

It is important to ensure a complete set and maturation of the sealer by allowing a “waiting period” after obturation, before retreatment is attempted in laboratory-based studies to avoid a disparity and bias in the results. The setting time for the sealers used in the included articles ranged from 4 to 8 h and all included articles had a waiting period of minimum of 7 days, which would have ensured a complete set. In clinical scenarios, patients could report for retreatment procedures after few months/years. Pedullà et al.[58] and Liu et al.[39] in their laboratory-based studies aged the samples for a period of 4–54 months before subsequently assessing the retrievability of bioceramic sealers.

Oltra et al.[26] reported that chloroform effectively aided in the removal of remaining filling material whereas, Athkuri et al.[38] and Liu et al.[39] used the solvent only in the coronal third to soften and aid in easier penetration of the rotary files through the root canal filling materials. Rossi-Fedele and Ahmed[16] reported that even though the use of a solvent may reduce the procedural time at initial stages of retreatment, it may interfere with the complete removal of filling material.[20] Nonetheless, clinicians should be cautious with the use of solvents such as chloroform due to its toxicity and carcinogenic potential.[59,60,61,62] Furthermore, the use of solvents would create a thin layer of plasticized gutta-percha adhering to the root canal wall and its irregularities making the operatory time longer and retreatment procedure challenging.[63,64] Garrib and Camilleri[65] reported that a chemical adjunct (10% formic acid) along with mechanical instrumentation is efficient to retreat teeth obturated with gutta-percha and bioceramic sealer as it eliminated over 95% of root canal filling material as well as re-established apical patency and working length.

Enlargement of the root canal up to two sizes more than the initial instrument file during retreatment enhances the efficacy of removal of the filling material by ten to twenty times.[66] This creates abundant space for effective shaping and cleaning, thereby reducing the residual filling material and intracanal bacteria and aiding in better apical healing.[66,67,68,69] There is a formation of a layer comprising of debris and remnants of plasticized gutta-percha and sealer during retreatment which is similar to the secondary smear layer formed during post space preparation.[48] None of the articles mentioned about the secondary smear layer. Removal of endodontic smear layer can be achieved by using irrigating solutions such as 17% EDTA and 3%–5% NaOCl and activation techniques.[70]

Retreatment outcomes have been shown to improve in teeth with apical periodontitis when larger apical preparations were performed.[71] NaOCl concentrations ranging from 2.5% to 6% alone or in combination with EDTA (15%–17%) were used as irrigants during retreatment procedure in the included articles. In clinical studies, the use of 0.5% or 1% NaOCl and 2% chlorhexidine as irrigants have shown the success rate of retreatment in teeth with persistent infections to be ranging from 58% to 84%.[72,73]

The retrieval procedures were performed using specially designed retreatment files such as ProTaper Universal retreatment files[12,13,15,40] and Mtwo retreatment files.[38] A few of the included articles utilized regular rotary files for enlarging root canals, namely Profile rotary file,[26,33] Vortex blue files,[26] Reciproc and Reciproc Blue,[27,37] ProTaper Next,[40] D-Race,[39] XP-Endoshaper[39] which have been proven to be efficient during retreatment procedures. Rossi-Fedele and Ahmed[16] reported no difference between the reciprocating and rotary kinematics in the retrievability of root canal filling material in their systematic review and that irrespective of the file system utilized, complete removal of root canal filling material was not possible.

None of the articles excepting three[12,38,39] reported the use of magnification during retreatment. Carr and Murgel[74] and Chauhan et al.[75] reported that the dental operating microscope is a valuable tool in the identification and visualization of residual root canal filling material thereby increasing the ability of the operator to remove obturating material and sealer from the root canal walls effectively. A recent article by Volponi et al.[52] assessing the retrieval of bioceramic sealers utilized a dental microscope under 13X magnification for all procedures, including clinical confirmation of retreatment procedure completion.

The additional usage of supplemental techniques reported an increase of 1.15–2.1 times in the removal of root canal filling material. Among the supplementary techniques analyzed, Crozeta et al.[27] was the only article to employ both ultrasonic and XP-endo finisher files. They reported ultrasonic to be significantly better in comparison to XP-endo finisher files. The vibration,[29,76,77,78] increase in temperature,[79,80] enhanced acoustic transmission and cavitation bubbles, and hydrodynamic shear stresses produced[81] could aid in the displacement and breakage of the structure of residual material from the root canal walls.[82]

The results were not consistent across the articles included in this review, with some reporting easier retrievability of bioceramic-based sealers or others reported easier removal of AH plus and few even reporting that there is no difference in the remnants left behind. The similarity in adhesion and sealing ability was quoted as the reasons for the finding no significance difference in retrieval among the sealers.[15,37,40] Articles reporting more remnants for bioceramic sealers indicated higher bond strength values, biomineralization ability, and shorter setting time to be the reasons for difficulty in removal of bioceramic sealers.[26,33] On the other hand, few articles suggest that the better bond strength and flow properties of AH plus sealer could make it difficult to retrieve.[83,84,85,86,87,88] A recent meta-analysis assessing the push out bond strength of bioceramic and epoxy-based sealers reported an increase in dislodgment resistance of the epoxy-based sealers in comparison to the bioceramic sealers.[89] This can be attributed to the covalent bonds formed between the epoxide ring and amine groups in the dentin collagen.[90] Interestingly, EndoSequence BC was the most commonly tested bioceramic sealer in the included articles, but even among those articles, the results were not consistent.

Due to the vast heterogeneity among the included articles, a meta-analysis was not performed. The variations in results and their respective justifications of the included articles could be attributed to the difference in sample size, type of roots/teeth and curvature of the canal, type of bioceramic sealers used, technique of obturation, and subsequent retreatment techniques used.

Clinical relevance

Irrespective of the sealers used, remnants were present in the root canals of all the included articles. Mechanical enlargement of the root canal up to two sizes more than the initial instrument file along with the use of supplementary retreatment techniques and irrigation activation systems and use of magnification could aid in better removal of previous root filling materials.

Strength

The present review followed strict eligibility criteria and only included the articles that were evaluated by micro-CT which facilitates sequential pre and postoperative evaluation to assess the amount of remaining filling material. Moreover, the quality of all the included articles was assessed with a modified Joanna Briggs Institute Critical Appraisal tool tailor made for this review.

Limitations

The evidence available in this systematic review is based on laboratory-based studies which are considered to be low.[91] The heterogeneity within the included articles prevented a quantitative assessment of the systematic review.

Future perspectives

A standardized retreatment protocol is necessary to be established. The use of pair-matched samples and standardized retreatment procedures will allow for a more homogenous assessment. Future micro-CT studies assessing the retrievability should incorporate fluorescence images also to differentiate between sealer and gutta-percha.[92]

CONCLUSION

Within the limitations of this systematic review, the available quality of evidence is low due to the inclusion of laboratory-based studies, and no definite conclusion could be derived regarding the retrievability of bioceramic sealer/AH plus sealer from the root canals during retreatment procedures. Future studies are required under standardized conditions to arrive at a definite conclusion.

Key points

1. Complete retrievability of bioceramic sealer and AH plus sealer is not possible.

2. Supplementary techniques such as passive ultrasonic irrigation, XP endo finisher rotary files, photon initiated photon acoustic streaming, and enlargement of the root canal to two sizes larger could aid in better removal of the sealers.

3. Quality of evidence is low and no definite conclusion could be derived regarding the retrievability of bioceramic sealer/AH plus sealer from the root canals during retreatment procedures.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Figure S1

Risk of bias graph assessed using Joanna Briggs Institute Critical Appraisal tools for Quasi-Experimental Studies (nonrandomized experimental studies) for each included study

Figure S2

Distribution of included articles based on the type of bioceramic sealer used

Figure S3

Distribution of included articles showing no difference, favoring easier bioceramic sealer removal and favoring easier AH plus sealer removal