Comparative Evaluation of Obturation Techniques on the Retrievability of NeoSealer Flo Bioceramic Sealer: An Ex Vivo Study

Summary

This ex vivo study investigates the impact of single cone and cold lateral compaction obturation techniques on the retrievability of NeoSealer Flo bioceramic sealer during endodontic retreatment. Results demonstrate that the single cone technique allows for more effective retrieval than cold lateral compaction.

Abstract

The successful retreatment of root canal-treated teeth depends largely on the effective removal of existing filling materials. This study aimed to evaluate the influence of two obturation techniques, single cone (SC) and cold lateral compaction (CLC), on the retrievability of NeoSealer Flo bioceramic sealer during endodontic retreatment. Twenty-four extracted single-rooted mandibular premolars with standardized root canal morphology were mechanically prepared and randomly allocated into two equal groups according to the obturation technique employed (n = 12). Following obturation with NeoSealer Flo, specimens were stored for 14 days under controlled conditions to allow complete setting of the sealer. Retreatment procedures were then performed using rotary retreatment files according to manufacturers’ recommendations. The amount of residual filling material remaining after retreatment was assessed in the coronal, middle, and apical thirds of each root using stereomicroscopic examination and quantified through ImageJ software analysis. Additionally, the total time required to complete retreatment procedures was recorded. Statistical analysis was performed with a significance level set at p < 0.05. The results demonstrated that canals obturated using the CLC technique had significantly greater residual filling material in the middle and apical thirds compared to the SC technique. No statistically significant difference was observed between groups regarding retreatment time. Within the limitations of this in vitro study, the findings suggest that NeoSealer Flo is more readily removed when used with the single cone obturation technique, highlighting the importance of obturation method selection when bioceramic sealers are employed in clinical practice.

Introduction

A successful endodontic outcome depends on achieving and maintaining an effective three-dimensional seal of the root canal system, thereby preventing bacterial recontamination and supporting long-term periapical health¹. In recent years, the advent of bioceramic sealers has shifted the obturation paradigm from one focused primarily on mechanical filling to an approach that emphasizes bioactivity and chemical interaction with dentin². Resin-free bioceramic materials such as NeoSealer Flo are formulated to release calcium hydroxide during their setting reaction, promoting an alkaline environment with antimicrobial properties and facilitating the formation of a hydroxyapatite-like interfacial layer^3,4. This bioactive bond is intended to reduce interfacial gaps, enhance sealing ability, and potentially improve periapical healing.

Despite these advantages, the same physicochemical properties that enhance the clinical performance of bioceramic sealers may compromise their retrievability during orthograde retreatment. Unlike conventional epoxy resin-based sealers, bioceramic materials exhibit increased hardness after setting and a chemical affinity for dentin, which may hinder complete removal from the canal walls. Previous studies have reported that residual bioceramic sealer is frequently observed after retreatment, even when contemporary rotary or reciprocating systems are used^5,6,7. The obturation technique employed may further influence retreatment outcomes, as sealer distribution, thickness, and penetration into dentinal tubules differ among techniques.

The single cone (SC) technique, often advocated for use with bioceramic sealers, relies on sealer flow to achieve adaptation, resulting in a relatively uniform but potentially thinner sealer layer. In contrast, cold lateral compaction (CLC) introduces additional gutta-percha mass and may generate greater sealer penetration and compaction pressure, which could enhance initial sealing but complicate subsequent removal. Alternative obturation approaches, such as warm vertical compaction or carrier-based techniques, have also been associated with increased residual material during retreatment, underscoring the clinical importance of obturation method selection when long-term retreatability is a consideration.

From a practical standpoint, retreatment protocols must balance effective material removal with procedural efficiency and preservation of dentin. Understanding how obturation techniques affect the retrievability of bioceramic sealers can therefore inform clinical decision-making, particularly in cases with a higher likelihood of retreatment, such as those involving uncertain prognosis or complex anatomy. Accordingly, the aim of this ex vivo study was to evaluate and compare the effectiveness of NeoSealer Flo removal and the associated procedural time during retreatment of canals obturated using either the single cone or cold lateral compaction technique. The findings are intended to provide protocol-oriented guidance for clinicians regarding obturation strategy selection when using bioceramic sealers in routine endodontic practice.

Protocol

This study was conducted and reported in accordance with the PRILE guidelines (Supplementary File 1), and the overall experimental workflow is summarized in the PRILE flowchart (Supplementary File 2).

Sample selection

CAUTION: Extracted human teeth represent a potential biohazard. Handle all samples using appropriate personal protective equipment (PPE), including gloves, masks, and protective eyewear. Dispose of all biological waste in designated biohazard containers according to institutional and local regulations.

The study protocol received approval from the local institutional review board (MIU-IRB-2122). A power analysis using G*Power (v3.1.9.7) based on Baranwal et al ⁽⁸⁾ determined that a sample size of 12 per group would provide 80% power to detect significant differences based on an effect size of 0.586. Twenty-four freshly extracted, single-rooted permanent mandibular premolars (Vertucci Class I) with straight, mature roots were collected from the Oral and Maxillofacial Surgery Department at Misr International University. The teeth were extracted for orthodontic or periodontal reasons unrelated to this study. Immediately following extraction, any adherent soft tissue or calculus was removed using periodontal scalers, and the teeth were washed under running water. To ensure disinfection and maintain hydration, the samples were stored in a 0.1% thymol solution at 4 °C until use. Teeth were examined under 8X magnification; those with fractures, previous endodontic treatment, calcifications, or resorptive lesions were excluded from the study.

Sample preparation

CAUTION: Use appropriate sharps containers for the disposal of all endodontic files, needles, and diamond discs.

Crowns were removed at the cemento-enamel junction using a high-speed diamond disc under water cooling to standardize root length. Working length (WL) was established by inserting a size 10 K-file until visible at the apical foramen and subtracting 1 mm. Canals were pre-flared with HyFlex EDM Glide Path files (10/.05) at 400 × g. Instrumentation was completed using a HyFlex EDM OneFile (25/variable taper) to the full WL.

The final irrigation protocol was performed using 17% EDTA followed by 2.6% NaOCl.

NOTE: Dispose of chemical irrigant waste in appropriately labeled chemical waste receptacles in accordance with laboratory safety standards. Each solution was activated ultrasonically for 30 seconds using an ultrasonic unit equipped with a size 20, .02 taper silver-nickel activator tip. The tip was placed 2 mm short of the WL and operated at a medium power setting (approximately 45 kHz) in a passive ultrasonic irrigation (PUI) mode, ensuring the tip vibrated freely without binding against the canal walls.

Obturation protocol

Samples were randomly allocated into two groups (n = 12) using a computer-generated sequence using Microsoft Excel to ensure an unbiased distribution.

• SC Group: The canal was dried with paper points. NeoSealer Flo was injected into the coronal third of the canal using the manufacturer's intra-canal tip, and a size 25 HyFlex EDM master cone was coated with a thin layer of sealer and slowly seated to WL.
• CLC Group: A .02 taper master cone was dipped in sealer and seated to WL. A size 25 finger spreader was inserted to within 1 mm of the WL to create space laterally. Auxiliary cones (size fine-fine) were coated with sealer and compacted laterally using the same spreader until the canal was full.

Accesses were sealed with Cavit. The quality of the obturation and the absence of voids were verified radiographically using a digital intraoral sensor and an X-ray unit operating at 65 kV and 7 mA. Radiographs were taken from two orthogonal angulations (bucco-lingual and mesio-distal) to ensure a three-dimensional assessment of the filling density. The images were analyzed under 2X magnification. Samples were stored at 37 °C and 100% humidity for 14 days to ensure the sealer set completely.

Retreatment

Retreatment was initiated using ProTaper Universal retreatment files (D1, D2, and D3; Dentsply Sirona, Ballaigues, Switzerland). Following the removal of the bulk of the filling material, further enlargement was completed using ProTaper Next files X2 (size 25, .06 taper) and X3 (size 30, .07 taper) at 500 × g and 2.0 Ncm torque. Irrigation with 5.25% NaOCl was performed between each file using a 30-gauge side-vented needle.

The clinical endpoint for retreatment was defined as the moment the X3 file reached the full working length and the file flutes appeared free of visible filling material remnants when inspected under 8X magnification. This criterion represents a standardized clinical "stop-point" for the procedure. However, this does not imply the total elimination of all of the filling material from the canal, as microscopic remnants often persist within dentinal irregularities and were subsequently quantified during the stereomicroscopic evaluation phase.

The procedural retreatment time was recorded in minutes and seconds using a digital stopwatch. The timing interval commenced the moment the first retreatment file (D1) touched the coronal gutta-percha and was paused during irrigation, file changes, and flute cleaning to ensure only active instrumentation time was captured. The timing ended when the final apical file (X3) reached the established working length.

Stereomicroscopic evaluation

Each root was prepared for longitudinal splitting by creating two superficial grooves (approximately 0.5 mm deep) on the buccal and lingual surfaces using a diamond disc under water cooling. The roots were then cleaved by placing the blade of a sterile chisel into the grooves and applying a light tap with a mallet. Each half was photographed at 8X magnification. Images were imported into ImageJ. To ensure standardized measurements, the software's measurement scale was first calibrated. This was done by selecting the "Straight Line" tool to draw a line across the photographed physical ruler, then opening the "Set Scale" dialog box to input the known distance (1 mm) to convert pixels into millimeters (mm²). Next, the "Polygon Selections" tool was used to manually trace the exact perimeter of the total root canal space to calculate the total canal area. Subsequently, the same tool was used to trace the perimeters of all visible islands of residual sealer and gutta-percha to calculate their total combined area. The percentage of residual filling material was then calculated by dividing the total area of the remnants by the total area of the canal space and multiplying by 100.

The remnants at the three root levels, coronal, middle, and apical were evaluated by the following scoring system according to Sherif et al.⁹. Consistent with the limitations of stereomicroscopic analysis, no attempt was made to distinguish between gutta-percha and sealer; therefore, all residual debris is referred to collectively as "residual filling material”.

Statistical analysis:

All analyses were performed using the complete raw dataset generated in this study (Supplementary File 3). Ordinal data were presented as frequency and percentage values. Numerical data are presented as mean and standard deviation values. Data were checked for normality using Shapiro-Wilk's test and were found to be not normally distributed. For inter-group comparisons between the SC and CLC groups at each root third, the Mann-Whitney U test was employed. For intra-group comparisons across the three root levels (coronal, middle, and apical), the Kruskal-Wallis test was used, followed by Dunn’s post-hoc test for pairwise comparisons where significant differences were detected. To account for multiple sectional comparisons and reduce the risk of Type I errors, a Bonferroni correction was applied, adjusting the significance level accordingly. The level of significance was set at P < 0.05. Statistical analysis was performed with R statistical analysis software version 4.3.1 for Windows (Table of Materials).

Results

Following the rotary retreatment protocol using ProTaper Universal and Next files, full working length and apical patency were successfully regained in 100% of the samples across both the SC and CLC groups. No procedural complications, such as file separation, canal transportations, or perforations, were observed during the retreatment process.

Percentage of Residual Filling Material (Derived from ImageJ Area Measurements):
Based on the quantitative area measurements performed using ImageJ...

Discussion

Bioceramic sealers are favored for their ability to penetrate complex canal anatomy, yet this study demonstrates that no technique ensures their total removal^10,3.

Complete removal of filling materials from the root canal system is essential to expose microbial biofilms sequestered within the dentinal tubules. This debridement allows for direct contact with irrigants and intracanal medicaments, which is critical for the eradication of ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Bioceramic Sealer	Avalon Biomed, Houston, TX, USA	NeoSealer Flo
Glide Path File	Coltene/Whaledent AG, Altstätten, Switzerland	HyFlex EDM Glide Path (10/.05)
Shaping File	Coltene/Whaledent AG, Altstätten, Switzerland	HyFlex EDM OneFile (25/0.08)
Master Cone	Coltene/Whaledent AG, Altstätten, Switzerland	HyFlex EDM Gutta-Percha Cone
Ultrasonic Unit	Guilin Woodpecker Medical Instrument Co., China	Woodpecker Ultra X
Temporary Restorative Material	3M ESPE, Seefeld, Germany	Cavit
Digital Intraoral Sensor	DEXIS, Hatfield, PA, USA	Dexis Platinum
X-ray Unit	Planmeca, Helsinki, Finland	Planmeca ProX
Retreatment Files	Dentsply Sirona, Ballaigues, Switzerland	ProTaper Universal Retreatment (D1-D3)
Retreatment Finishing Files	Dentsply Sirona, Ballaigues, Switzerland	ProTaper Next (X2, X3)
Randomization Software	Microsoft Corp., Redmond, WA, USA	Microsoft Excel
Imaging Software	DEXIS, Hatfield, PA, USA	DEXIS Software
Image Analysis Software	National Institutes of Health, Bethesda, MD, USA	ImageJ
Statistical Analysis Software	R Foundation for Statistical Computing, Vienna, Austria	R version 4.3.1
Power Analysis Software	Heinrich-Heine-Universität, Düsseldorf, Germany	G*Power (v3.1.9.7)