Influence of the filling technique on endodontic retreatment in curved mesial canals of mandibular molars – An in vitro study

doi:10.21203/rs.3.rs-5321675/v1

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Influence of the filling technique on endodontic retreatment in curved mesial canals of mandibular molars – An in vitro study

https://doi.org/10.21203/rs.3.rs-5321675/v1

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Objectives: To evaluate the influence of the filling technique associated with a bioceramic sealer on the remaining filling material and the impact on the remaining dentin after the filling removal in the retreatment of curved mesial canals of mandibular molars.

Materials and Methods:Eighteen curved mesial roots of mandibular molars with Vertucci type IV canals were prepared up to instrument 35/.05. Two groups were established according to the filling technique: single-cone (n=18) and continuous wave of condensation (n=18). Bio-C Sealer was used for both techniques. The filling was removed using the Reciproc Blue R25 instrument, and the repreparation was carried out using the Reciproc Blue R40 instrument. The samples were scanned by micro-CT before and after the filling removal. For statistical analysis, the data normality was checked, and parametric tests were used for normal distribution and non-parametric tests for non-normal distribution.

Results: The remaining filling material was observed in both groups during retreatment, with no differences. Analyses of transportation and centering ability also indicated similarities between the two groups.

Conclusions: Endodontic retreatment in curved mesial canals of mandibular molars filled with single-cone or continuous wave of condensation techniques and filled with bioceramic sealer was similar. The use of reciprocating instruments for filling removal and repreparation was efficient in curved mesial canals of mandibular molars, with no complications.

Clinical relevance: The filling technique did not influence the non-surgical endodontic retreatment in curved mesial canals. Regardless of the technique, it was not possible to remove all the filling material from the root canals.

Molar. Retreatment. Root Canal Obturation. Root Canal Sealer. X-Ray Microtomography

Non-surgical endodontic retreatment should be considered the first treatment option when endodontic therapy fails [1]. With the increasing use of bioceramic sealers, retreatment of teeth filled with these sealers is becoming more frequent. While some studies have shown that its removal during endodontic retreatment can be more difficult when compared to other sealers [2–4], other studies have found no differences [5, 6].

Comparing the single-cone and continuous wave of condensation techniques using a bioceramic sealer, Ma et al. (2012) [7] spent more time removing the filling with the second technique. When comparing the EndoSequence BC (Brasseler, Savannah, USA) and AH Plus (Dentsply DeTrey, Konstanz, Germany) sealers using the continuous wave of condensation technique, Kim et al. (2015) [8] observed that a longer time was spent removing the filling and a greater amount of remaining filling material was left for the bioceramic sealer. Comparing the same sealers, and including iRoot SP (Innovative BioCreamix Inc, Vancouver, Canada), Yang et al. (2021) [9] compared the single-cone and continuous wave of condensation techniques, and during filling removal, the authors spent more time when using the Endosequence BC and iRootSP sealers associated with the continuous wave of condensation technique; on the other hand, the bioceramic sealers showed less remaining material than the AH Plus sealer.

Based on the aforementioned complexity of endodontic retreatment, the difficulty of retreating roots with accentuated curvature, the growing use of bioceramic sealers, and the lack of studies evaluating the influence of the obturation technique in the retreatment of curved canals filled with bioceramic sealers, this study aimed to evaluate the influence of the filling technique associated with a bioceramic sealer on the remaining filling material after the filling removal and the impact on the remaining dentin after the repreparation of curved mesial canals of mandibular molars. The first null hypothesis was that the filling technique would not influence the filling removal. The second null hypothesis was that the filling technique would not influence the remaining dentin after the repreparation of the canals.

Sample size

The sample size was calculated using the G*Power v3.1 software for Mac (Heinrich Heine, Universität Düsseldorf, Germany), using the ANOVA test to determine the sample size

To determine the effect expected for this study, canal volume and dentin removal data from the studies by De-Deus et al. (2015)[10] and Gagliardi et al. (2015)[11], and volume of remaining filling material with bioceramic sealer data from the study by Romeiro et al. (2020) [6] were considered. The parameters set were an alpha error of 0.05, a beta power of 0.80, and an N2/N1 ratio of 1. A sample of 15 canals per group was stipulated (n = 15), but 18 canals were used considering the possibility of losing samples.

Sample selection

After approval by the local Research Ethics Committee (42870621.2.0000.0102), eighteen extracted mandibular first and second molars with a mesial root with a Vertucci type IV canal configuration and a curvature between 20° and 40° were selected. Micro-computed tomography scanner (SkyScan 1172, Bruker-microCT, Kontich, Belgium) was used to confirm the inclusion criteria with the following parameters: exposure time of 1750 ms, voltage of 80kV, the voxel size of10.89 μm, and filter of 0.5 mm aluminum.

The access cavity was performed using 1012, 1015, and 3205 diamond tips (KG Sorensen, São Paulo, Brazil). The teeth were then sectioned by separating the mesial and distal roots. Only the mesial roots were used.

Root canal preparation

The canals were scouted with manual #08 and #10 C-pilot files (VDW, Munich, Germany) up to the working length (WL), which was defined considering 1 mm from the apical foramen. The canals were prepared using the 15/.03, 25/.01, 25/.04, and 35/.05 instruments (Prodesign Logic 2 System, Easy Equipamentos Odontológicos, Belo Horizonte, Brazil), and the canals were recapitulated with a manual #10 C-pilot file (VDW, Munich, Germany) after the use of each instrument. The root canals were irrigated with 2.5% sodium hypochlorite (NaOCl) (Asfer, São Caetano do Sul, Brazil) using a 5 ml disposable syringe (BD, Curitiba, Brazil) and a 30-gauge NaviTip needle (Ultradent Inc, South Jordan, USA). The root canals were then irrigated with 17% EDTA (Fórmula & Ação, São Paulo, Brazil). The irrigating substances were agitated with Easyclean instruments (Easy Equipamentos Odontológicos, Belo Horizonte, Brazil), and the canals were dried with intracanal suction tips (Ultradent, Indaiatuba, Brazil) and 35/.04 absorbent paper tips (VDW, Munich, Germany).

Root canal filling

The samples were filled using a 35/.05 gutta-percha cone (Easy Equipamentos Odontológicos, Belo Horizonte, Brazil) and the Bio-C Sealer (Angelus, Londrina, Brazil). A plastic needle was inserted 4 mm from the WL, and the sealer was inserted into the root canals with the syringe plunger gently pressed until it flowed back into the pulp chamber.

The buccal and lingual canals were randomly assigned (http://www.openepi.com/Menu/OE_Menu.htm) into 2 groups according to the filling technique:

- Single-cone (n=18): the gutta-percha cone coated with Bio-C Sealer was inserted into the canal up to the WL with brushing movements, spreading the sealer over the canal walls. Then, the gutta-percha cone was cut at the entrance of the canals using a heated hand plugger (Odous de Deus, Belo Horizonte, Brazil) and followed by cold vertical compaction.

- Continuous Wave of Condensation (n=18): the canals were filled using the BeeFill 2in1 system (VDW, Munich, Germany). The gutta-percha cone coated with the sealer was inserted into the canal, then the BeeFill 2in1 thermocompactor was introduced and activated into the root canal up to the root curvature, deactivated, maintained for 10 seconds, reactivated for 1 second, and then removed from the canal. Vertical compaction of the filling was performed with Buchanan hand pluggers (SybronEndo, Orange, USA) in the apical third. Next, using the BeeFill 2in1 thermoinjector, the back-fill was carried out with the gutta-percha heated to 160°C and inserted in the middle third followed by cold vertical compaction with hand pluggers, and then in the apical third following this same protocol.

Periapical radiographs were taken (Phosphor plate system, Durr, Porto Alegre, Brazil) to check the quality of the filling. The canals were then sealed with Coltosol (Coltene, Rio de Janeiro, Brazil), and the samples were kept in an oven at 37ºC and 100% relative humidity for 7 days for the complete setting of the sealer.

The samples were scanned again by micro-CT using the same parameters described before and the images were reconstructed using the NReconv1.6.4.8 software (Bruker, Kontich, Belgium). In the CTan software, the volume (mm³) of filling material was obtained at the 1-3 mm, 3-5 mm, and 5-7 mm segments from the apical foramen, and the dentin thickness (mm³) of the mesial, and distal walls at the 1 mm, 3 mm, 5 mm, and 7 mm segments.

Endodontic Retreatment

The filling material was removed using the Reciproc Blue R25 instrument (VDW, Munich, Germany) and the VDW Silver motor (VDW, Munich, Germany). The instrument was inserted into the mass of the filling material with pecking movements, advancing up to the WL. Every three movements, irrigation was carried out as in the preparation stage. When the WL was reached, movements were made against the canal walls until the filling material was detectably removed. Total removal was determined when no material remained on the instrument and the walls were clean when viewed under an operating microscope at 8x magnification (DFVasconcellos, Rio de Janeiro, Brazil).

The teeth were reprepared using a Reciproc Blue R40 instrument (VDW, Munich, Germany) with small in-and-out movements and gentle apical pressure until the WL was reached. Irrigation was carried out as in the canal preparation stage.

The roots were scanned by micro-CT using the same parameters as the previous scans and reconstructions. With the CT Analyzer software, the volume (mm³) of filling material was measured at the 1-3 mm, 3-5 mm, and 5-7 mm segments from the apical foramen, and the values were converted into the percentage of filling material.

The dentin thickness (mm) of the mesial, and distal walls were measured at the 1 mm, 3 mm, 5 mm, and 7 mm segments to assess the transportation and centering ability of the endodontic repreparation.

The canal transportation (mm) was calculated in each third of the root canal and considered the extent and direction of transportation by measuring the distances between the canal and the root edges in the mesiodistal direction, following the equation (X1-X2) - (Y1- Y2), where X1 is the shortest distance between the mesial edge of the root and the canal before instrumentation, and X2 is the shortest distance between the mesial edge of the root and the instrumented canal. Y1 is the shortest distance between the distal root edge and the canal before instrumentation, while Y2 is the shortest distance between the distal root edge and the instrumented canal (Figure 1). A zero result indicates that there is no root canal transportation. A positive result indicates transportation in the mesial direction, while a negative result indicates transportation in the distal direction.

The centering ability was calculated in each third of the root canal using the equation (X1-X2)/(Y1-Y2). A score of "1" indicates perfect centering, while a score of "0" indicates no centering.

Statistical Analysis

After checking the data normality, the t-test (parametric) or Mann-Whitney test (non-parametric) was applied to the intergroup data, and the ANOVA test (parametric) or Kruskal-Wallis test (non-parametric) was applied to the intragroup data. A significance level of 5% (p < 0.05) was considered for all tests. Statistical analysis was carried out using the GraphPad Prism 9 software (La Jolla, CA, United States).

The greatest amount of remaining filling material was found in the apical third (Figure 2). In the intragroup comparison, the two groups only showed differences between the cervical and apical segments. In the intergroup analysis, the single-cone and continuous wave of condensation groups had similar amounts of remaining material (Table 1).

Table 1. Median (minimum and maximum), in percentage, of remaining filling material among the root canals thirds.

	Single-cone⁺⁺	Continuous wave of condensation⁺⁺
1 – 3 mm*	21.16 (0–44.65)^aB	17.41 (0–48.06)^aB
3 – 5 mm**	3.18 (0–42.69)^aAB	2.25 (0–38.76)^aB
5 – 7 mm**	0.85 (0–19.74)^aA	0.76 (0–17.04)^aA

*T-test was used for intergroup comparison.

** Mann-Whitney was used for intergroup comparison.

++Kruskal-Wallis and Dunn’s multiple comparison tests were used for intragroup comparison.

Different superscript lowercase letters in the rows indicate intergroup differences, while different superscript uppercase letters in the columns indicate intragroup differences.

Both groups were similar in all the segments evaluated regarding the centering ability. No intragroup differences were found either. Regarding transportation, no significant differences were found between the groups or in the intragroup evaluation (Table 2).

Table 2. Median (minimum and maximum) values for transportation and centering ability.

	Single-cone⁺	Continuous wave of condensation⁺⁺
Transportation
1 mm**	0.05 (-0.37–1.28)^aA	0.05 (-0.20–0.67)^aA
3 mm**	-0.012 (-0.25–0.23)^aA	0.078 (-0.55–0.30)^aA
5 mm*	-0.09 (-0.55–0.40)^aA	0.04 (-0.30–0.34)^aA
7 mm*	-0.07 (-0.52–0.65)^aA	-0.03 (-0.31–0.46)^aA
Centering ability
1 mm*	0.553 (0.03–0.93)^aA	0.406 (0–0.87)^aA
3 mm*	0.620 (0.21–0.98)^aA	0.290 (0–0.99)^aA
5 mm**	0.409 (0.01–0.99)^aA	0.372 (0.02–0.82)^aA
7 mm**	0.314 (0–0.93)^aA	0.459 (0–0.97)^aA

*T-test was used for intergroup comparison.

** Mann-Whitney was used for intergroup comparison.

+ ANOVA was used for intragroup comparison.

++Kruskal-Wallis was used for intragroup comparison.

Different superscript lowercase letters in the rows indicate intergroup differences, while different superscript uppercase letters in the columns indicate intragroup differences.

To guarantee the similarity between the groups, the filling volume was measured to pair-match the sample and then randomly distribute the root canals (p > 0.05). Our results showed similar amounts of remaining filling material for the single-cone and continuous wave of condensation techniques, so the first null hypothesis was accepted.

The present study did not evaluate different sealers, but a previous study found that the Bio-C Sealer left less material than the AH Plus, an epoxy-resin-based sealer. This is probably due to the bioceramic sealer's higher solubility and the epoxy-resin-based sealer's high bond strength [12]. However, when comparing the difficulty of removing calcium silicate-based and epoxy-resin-based sealers, the former is harder and more time-consuming to remove during the endodontic treatment. Still, they are not impossible to penetrate and recover patency [6], as observed in our study.

The warm obturation techniques were developed to better adapt the filling material to the canal walls and promote a more homogeneous filling mass, thus achieving a better three-dimensional filling of the root canal [13]. However, when the primary endodontic treatment fails, the non-surgical retreatment may be influenced by the technique used for the primary filling. A study that evaluated the endodontic retreatment of oval root canals filled with bioceramic sealer and the single-cone and continuous wave of condensation technique showed no differences between these two techniques regarding the remaining filling material, but the latter took more time [14]. There was a need for studies on curved root canals, as the curvature also represents a challenge during the endodontic treatment and retreatment and it may favor transportation and compromise the success of the treatment [15].

A higher amount of remaining material was present in the apical third when compared to the cervical third, probably because of the aid of an operating microscope, as it was possible to see the remaining filling material before the root curvature. This result is in line with previous studies [15–17] and corroborates the findings of Siqueira et al. (2013) [18], who stated that the anatomy of the root canal has a greater influence than the cleaning methods used, and Fruchi et al. (2024) [19], who showed that Vertucci type II root canals presented more filling material than Vertucci type IV in the apical third.

The major apical diameter of the mesial canals of the mandibular molar has a median of approximately 0.37 mm [20], so the use of an instrument with a tip size of 0.25 such as Reciproc R25 would probably be inefficient to clean the apical area [19], requiring the use of instruments with a bigger tip, but that keeps the preparation centered, without causing transportation.

However, considering the root curvature, the Reciproc Blue R25 instrument was used before the Reciproc Blue R40 instrument to create a path during the removal of the filling material. It was efficient in penetrating the filling mass with no instrument fractures and had good results in transportation and centering ability, even in canals with pronounced curvature. The blue oxide layer on the surface of the instrument is a result of specific heating and cooling processes that improve the resistance to rotary fatigue and the flexibility of these instruments [21]. Compared to the M-Wire Reciproc, the Reciproc Blue instruments showed to be similar in the amount of remaining filling material of curved canals, with the M-Wire Reciproc instruments causing more apical transportation than the Reciproc Blue instruments [22].

The Reciproc Blue R40 instrument used for repreparation maintained a similar centralization of the preparation with little transportation for both filling techniques, so the second null hypothesis was also accepted. Romeiro et al. (2020) [6] have already demonstrated the efficiency and safety of these instruments in a study on the retreatment of teeth filled with bioceramic sealer using the single cone technique. Previous studies that evaluated the retreatment of curved mesial canals of mandibular molars filled with a bioceramic [15] or epoxy-resin-based sealer [23] using the continuous wave condensation technique showed that the repreparation with a 50/0.01 instrument decreased the percentage of remaining filling material in the apical third while maintaining the dentin in the cervical and middle thirds. However, even when increasing the apical diameter, it was not possible to remove all the filling material.

The complete removal of the filling material was also not possible in our study. The permanence of filling material after retreatment can have major clinical implications, as it can be a reason for maintaining the infectious process and consequent therapy failure [26]. So, further studies assessing new supplementary methods, beyond apical enlargement, are needed to retreat curved root canals.

The single-cone or continuous wave of condensation techniques associated with the bioceramic sealer did not influence the filling removal in curved mesial canals of mandibular molars. The use of Reciproc Blue instruments for filling removal and repreparation proved to be efficient without causing complications. However, it was not possible to remove all the filling material from the canals.

Ethics Approval and Consent to Participate

Not Applicable.

Conflict of Interests

The authors deny any financial and non-financial conflict of interest.

Funding

No funding was obtained for this study.

Author Contribution

All authors contributed to the study's conception and design. Material preparation, data collection, and analysis were performed by F.A.C., L.Y.O., and B.C.C. The first draft of the manuscript was written by F.A.C. and L.Y.O. The manuscript was reviewed by R.M.S.L., C.T.R., and M.A.H.D. All authors read and approved the final manuscript.

Acknowledgement

Our best thanks to LAMIR/UFPR laboratory for the support with the micro-CT acquisitions.

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No competing interests reported.

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Influence of the filling technique on endodontic retreatment in curved mesial canals of mandibular molars – An in vitro study

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Abstract

Figures

INTRODUCTION

MATERIAL AND METHODS

RESULTS

DISCUSSION

CONCLUSION

Declarations

Ethics Approval and Consent to Participate

Conflict of Interests

Funding

Author Contribution

Acknowledgement

References

Additional Declarations

Status:

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