Evaluation of the root canal sealing properties and removability of four bioceramic sealers using micro–computed tomographic

Abstract

Background

Bioceramic sealers have been increasingly applied in endodontics due to their excellent sealing properties and biocompatibility. However, the sealing performance of different bioceramic sealers and their removability during re-treatment remain focal points of clinical concern. This study aimed to evaluate the root canal sealing performance and removability of four bioceramic sealers.

Methods

One hundred extracted human single-rooted premolars were randomly allocated into five experimental groups (n = 20) after standardized root canal preparation: SC1 (i-MTA SP), SC2 (C-root SP), SC3 (Neosealer Flo), SC4 (iRoot SP) using single-cone obturation, and warm vertical compaction (WVC) with AH-plus. Micro CT scans were performed at three distinct intervals (immediately, one-week, and one-month post-obturation) to quantify the percentage volume of voids (PVV). After one-year storage, sealer removal was performed using ProTaper Universal Retreatment system combined with ultrasonic agitation. Residual filling rate (RFR) was calculated via post-retreatment micro CT scan and reconstruction. Data were analyzed using the Kruskal-Wallis H-test and the Friedman test, with the significance level set at 5% (p < 0.05).

Results

The PVV at the same site exhibited no statistically significant differences between the groups at three distinct intervals. Immediately following the filling procedure, the PVV in the middle thirds of roots in the SC4 group was significantly less than that in the SC1 and WVC groups (p < 0.05). The PVV in the middle thirds was less than in the coronal thirds in the SC2 group, and the PVV in both the apical and middle thirds was less than in the coronal thirds in both the SC3 and SC4 groups (p < 0.05). One-week post-filling, the PVV in the middle thirds of roots in the SC2 group was less than that in the WVC group. The PVV in the middle thirds of roots in the SC3 group, apical and middle thirds of roots in both the SC2 and SC4 groups was less than coronal thirds (p < 0.05). One-month post-filling, the PVV in the apical thirds of roots in the SC1 group, middle thirds of roots in the SC3 group and apical and middle thirds of roots in both the SC2 and SC4 groups was less than coronal thirds of roots (p < 0.05). Post-retreatment analysis demonstrated significantly less RFR in SC1 apical thirds compared to SC4 (p < 0.05).

Conclusion

The choice among the bioceramic sealers tested had no significant effect on the sealing quality of single‑cone obturation. Among the four bioceramic sealers evaluated, i MTA SP was more readily removed than iRoot SP.

Background

In recent years, bioceramic sealers have gained increasing clinical acceptance owing to their favorable biocompatibility, antibacterial activity, and sealing efficacy [1]. The sealing ability of these materials constitutes a critical factor influencing the outcome of root canal treatment, as one of the essential objectives of root canal obturation is to achieve a tight seal of the canal system, thereby preventing bacterial microleakage and promoting periapical tissue healing [2]. Previous studies have indicated that bacterial presence is a primary cause of root canal treatment failure [3]. Voids within the filling material may allow bacteria to gain nutrients from both coronal and apical directions, while also providing space for bacterial proliferation and migration [4].Inadequate or incomplete obturation may lead to reinfection of the periapical region, necessitating nonsurgical endodontic retreatment [5].

When nonsurgical retreatment is required following root canal treatment failure, the removability of bioceramic sealers becomes another critical clinical consideration. Although favored for their excellent biocompatibility and stable chemical bonding in moist environments, these characteristics result in strong adhesion to the canal walls after setting [2, 6]. Compared to resin-based sealers, bioceramic materials are more difficult to remove mechanically and require extended operating time [7]. Multiple studies have shown that even with modern nickel‑titanium retreatment instrument systems, a significant amount of bioceramic material often remains within the root canal, which may compromise disinfection efficacy and subsequently affect the prognosis of retreatment [8, 9].

Micro-computed tomography is a technique that enables three-dimensional assessment of closed root canals and quantification of the volume of filling material within them. It not only permits non-invasive testing of samples but also offers a more intuitive visualization of root canal filling. Therefore, it serves as gold standard for three-dimensional evaluation of root canal filling quality in ex vivo studies [10, 11].

The objective of this research is to assess the sealing properties and removability of four root canal filling materials and compare their properties with that of warm vertical compaction with AH-plus by using micro-CT. The null hypotheses tested in this research were: (1) there is no significant difference in sealing properties among the four bioceramic sealers used with the single-cone technique compared to AH-plus sealer used with the warm vertical compaction; and (2) there is no significant difference in removability among the four bioceramic sealers.

Methods

Tooth selection and grouping

An a priori sample size calculation was conducted using G*Power (version 3.1.9.7; Heinrich-Heine-Universität Düsseldorf, Germany). Assuming a one-way ANOVA design with an effect size of 0.5, an α of 0.05, and a power of 0.8, the minimum required sample size was 92. To account for potential attrition during specimen preparation and micro-CT scanning, a total of 100 extracted human teeth were included and randomly allocated into five experimental groups (n = 20 per group).

One hundred extracted human single-rooted mandibular premolars were collected in accordance with a protocol approved by the Ethics Committee of the School & Hospital of Stomatology, Wuhan University (certificate: WDKQ2024 B93). Written informed consent was obtained from all patients prior to tooth extraction. The inclusion criteria were single-rooted mandibular premolars with a single canal, root canal curvature less than 20° (measured by the Schneider method), no obvious calcification or previous root filling, completely formed roots with closed apices, and intact tooth structure without cracks. Teeth were excluded if they presented with multiple canals, root canal curvature exceeding 20°, anatomical anomalies of the root canal system, canal obliteration or a history of endodontic treatment, immature or open apices, or root fractures.

The specimens were randomly allocated into five experimental groups (n = 20 per group) using a computer-generated random number sequence (Microsoft Excel, version 2019). Prior to randomization, all teeth were numbered from 1 to 100 based on the order of collection. Subsequently, a random number between 0 and 1 was generated for each tooth using the Excel. The teeth were then sorted in ascending order according to these random numbers. The first 20 teeth were assigned to Group SC1, the next 20 teeth to Group SC2, the following 20 teeth to Group SC3, the subsequent 20 teeth to Group SC4, and the final 20 teeth to Group WVC. The 5 experimental groups were as follows:

• SC1: Single cone obturation with Gutta Percha Points (B&L Biotech, Seoul, Korea) and i-MTA SP (Longly Biotechnology, Wuhan, CHN)

• SC2: Single cone obturation with Gutta Percha Points (B&L Biotech, Seoul, Korea) and C-root SP (Sairute Dental Medical Devices, Beijing, CHN)

• SC3: Single cone obturation with Gutta Percha Points (B&L Biotech, Seoul, Korea) and Neosealer Flo (Avalon Biomed, Houston, Texas, USA. USA)

• SC4: Single cone obturation with Gutta Percha Points (B&L Biotech, Seoul, Korea) and iRoot SP (Innovative BioCreamix Inc, Vancouver, BC, Canada)

• WVC: Warm vertical compaction with Gutta Percha Points (B&L Biotech, Seoul, Korea) and AH-plus (Dentsply Sirona Endodontics, Tulsa, OK, USA)

Root canal instrumentation

All specimens were instrumented and obturated by the same operator, a specialist in endodontics. Following access to the pulp chamber, root canal patency was verified by inserting a size 10 K-file (Dentsply Sirona Maillefer, Ballaigues, Switzerland) into the apical foramen. The working length was determined with size 15 K-files (Dentsply Sirona Maillefer, Ballaigues, Switzerland) positioned 1 mm short of the apical foramen. Instrumentation was completed with X-smart plus (Dentsply Sirona Endodontics, Tulsa, OK, USA) and Waveone Gold (Dentsply Sirona Endodontics, Tulsa, OK, USA) by following the manufacturer's recommendations. The apical dimension established was size 25 with a 0.06 taper. Root canal was irrigated with 2 mL of 5.25% sodium hypochlorite (NaOCl) at each instrument change. After preparation, the canals were irrigated with 2 mL of 5.25% NaOCl and 17% EDTA and finally irrigated by using an ultrasonic tip (Woodpecker, Guilin, China) coupled to an ultrasound device (Woodpecker, Guilin, China) for 20 s. The instrumented canals were dried with paper points (Dentsply Sirona Maillefer, Ballaigues, Switzerland) and radiographs were taken to determine the preparation status. The instrumentation process was repeated until preparation was completed.

Root canal obturation

Single cone obturation

For the 4 single cone obturation experimental groups, injection needle was inserted into the middle of the root canal and respective sealers were injected into the canal while slowly withdrawing the needle until the middle and upper 2/3 are completely filled. Master gutta-percha cone, apical 4 mm coated with bioceramic sealer, was gently inserted into the working length. Then the master cone was seared off to the canal orifice by using heat source (B&L Biotech, Seoul, Korea) set at 180℃.

Warm vertical compaction

Master gutta percha cone, apical 4 mm coated with AH-plus, was gently inserted into the working length and rotated to evenly coat the sealers on the root canal wall. The master cone was seared off to the canal orifice by using heat source (B&L Biotech, Seoul, Korea) set at 180℃ and was compacted with plugger (B&L Biotech, Seoul, Korea). Heat plugger was inserted into the root canal for 10s and then was activated for 1s. Approximately 3 mm of gutta percha was removed after extracting heat plugger while rest gutta-percha was compacted with plugger. This process was repeated until the plugger reached 3–4 mm short of the working length. Then, 3–5 mm warm gutta-percha was used to backfill root canal and was compacted with plugger each time until the rest of the space was obturated.

All root canal filling procedures were conducted under microscopic visualization (Zumax, Suzhou, China), and radiographic imaging was employed immediately following the completion of root canal obturation to ascertain the accuracy of the filling procedure. The evaluation was conducted by a doctor specialist in endodontics. Then flowable resin (SHOFU, Kyoto, Japan) was used to fill the access of obturated. The dental curing light (3M, Minnesota, USA) was positioned 1 mm away from the tooth and activated for 20 s. Following root canal obturation, all specimens were stored in 0.9% physiological saline at 37 °C and 100% relative humidity for one year.

Root canal retreatment

After one-year storage, root canal retreatment was performed using the ProTaper Universal Retreatment (PTUR) system. Retreatment procedures were standardized and performed by one experienced endodontist, with an assistant coordinating the operation and responsible for timing. To minimize potential bias, the five groups were randomized using a computer-generated random number table to determine processing sequence, with both the operator and the timing assistant remaining blinded to group allocation. Existing filling material was sequentially removed with PTUR-specific instruments D1, D2, and D3. No solvents were used during the retreatment procedure. Instruments were advanced apically at 500 rpm with a gentle pecking motion while irrigating continuously with 5.25% NaOCl to a working length of 12 mm. After each instrument change, the root canal was irrigated with 2 mL of 5.25% NaOCl. Following instrumentation, passive ultrasonic agitation was conducted for 60 s using an ultrasonic tip. The canal was then dried with paper points.

Micro CT scanning and software evaluation

Each specimen was subjected to micro-computed tomography imaging at three distinct intervals (immediately, one-week and one-month post-filling) and immediately post-retreatment with a micro-CT device (Bruker Corporation, Allentown, PA, USA). The following scanning conditions were employed: for both scans: 100 kV, 200µA, 7.03 μm voxel size and a 415-ms integration time. Following the completion of the scanning process, the data was reconstructed and imported into CT Analyser (V1.15.4.0), where a three-dimensional model of the root canals was created (Fig. 1). Each specimen was set with the apical stop at 0 mm, and the specimen was subsequently divided into three sections: apical (0–4 mm), middle (4–8 mm), and coronal (more than 8 mm). The volume of voids (Voidsvol), gutta-percha and sealer (Fillingvol) can be derived through thresholding and subsequent 3D analysis. The percentage volume of voids(PVV) was calculated as: PVV (%) = (Voidsvol / (Voidsvol + Fillingvol)) × 100%. Residual filling rate (RFR) was calculated as: RFR (%) = (Fillingvol post-retreatment / Fillingvol at 1 month) × 100%. Separate analyses were performed for overall, apical, middle, and coronal root thirds. All volumetric data were recorded and statistically analyzed.

Fig. 1.

3D reconstruction and data analysis in CTAn

Statistical analysis

The normal distribution and homogeneity of the data variance were determined using the Shapiro-Wilk test and the Levene test. For inter-group comparisons (among the five filling materials), the Kruskal-Wallis H test was performed for the apical, middle, coronal, and overall regions separately, followed by Dunn’s post-hoc test with Bonferroni correction for pairwise comparisons when significant differences were detected. For intra-group comparisons (among the three root regions within the same material), the Friedman test was used, followed by Nemenyi post-hoc test for pairwise comparisons. Data were analyzed using SPSS 20 software, and the level of significance was set at a P value < 0.05.

Results

As illustrated in Table 1. and Fig. 2., immediately following the filling procedure, the PVV in the middle thirds of roots in the SC4 group was less than that in the SC1 and WVC groups. Kruskal-Wallis H test results indicated significant differences in the PVV among the five groups in the apical thirds; however, post-hoc pairwise comparisons with Bonferroni correction revealed that all pairwise comparisons yielded p values greater than 0.05. The PVV in the middle thirds was less than in the coronal thirds in the SC2 group, and the PVV in both apical and middle thirds was less than in the coronal thirds in both the SC3 and SC4 groups (p < 0.05).

Table 1.

Comparison of immediate PVV (x ®±s, %)

	Apical	Middle	Coronal	Overall	P value
i-MTA SP	0.81 ± 1.75Aa	0.68 ± 1.00Ab	1.92 ± 2.90Aa	1.64 ± 2.12a	0.20
CRoot SP	0.70 ± 1.52ABa	0.64 ± 1.13Bab	0.91 ± 1.29Aa	0.85 ± 1.10a	0.019
Neosealer Flo	0.09 ± 0.22Aa	0.06 ± 0.13Aab	0.72 ± 1.12Ba	0.36 ± 0.36a	0.000
iRoot SP	0.13 ± 0.39Aa	0.10 ± 0.29Aa	1.31 ± 1.68Ba	0.94 ± 1.26a	0.000
AH-plus	0.92 ± 1.66Aa	0.64 ± 1.20Ab	0.26 ± 0.35Aa	0.40 ± 0.57a	0.819
P value	0.031	0.002	0.340	0.343

Capital letters read horizontally indicate statistical differences in the PVV at different sites within the same group. Lowercase letters read vertically indicate statistical differences in the PVV at same site between groups

Fig. 2.

The PVV in the SC1, SC2, SC3, SC4 and WVC groups at immediately post-filling

As illustrated in Table 2. and Fig. 3., one-week post-filling, the PVV in the middle thirds of roots in the SC2 group was less than that in the WVC groups. The PVV in the middle thirds of roots in the SC3 group, apical and middle thirds of roots in both the SC2 and SC4 groups was less than coronal thirds (p < 0.05).

Table 2.

Comparison of the PVV in one-week post-filling (x ®±s, %)

	Apical	Middle	Coronal	Overall	P value
i-MTA SP	0.77 ± 2.04A	0.77 ± 1.29Aab	1.50 ± 2.42Aa	1.38 ± 1.91a	0.069
CRoot SP	0.20 ± 0.35A	0.20 ± 0.55Aa	0.35 ± 0.57Ba	0.32 ± 0.50a	0.002
Neosealer Flo	0.42 ± 0.89AB	0.08 ± 0.16Aab	0.95 ± 1.17Ba	0.60 ± 0.66a	0.001
iRoot SP	0.16 ± 0.44A	0.79 ± 2.91Aab	1.43 ± 1.71Ba	1.22 ± 1.53a	0.000
AH-plus	0.98 ± 1.60A	0.74 ± 1.24Ab	0.32 ± 0.40Aa	0.47 ± 0.53a	0.626
P value	0.182	0.009	0.204	0.241

Fig. 3.

The PVV in the SC1, SC2, SC3, SC4 and WVC groups at one-week post-filling

As illustrated in Table 3. and Fig. 4., one-month post-filling, the PVV in the apical thirds of roots in the SC1 group, middle thirds of roots in the SC3 group and apical and middle thirds of roots in both the SC2 and SC4 groups was less than coronal thirds of roots (p < 0.05). Kruskal-Wallis H test results indicated significant differences in the PVV among the five groups in the middle thirds; however, post-hoc pairwise comparisons with Bonferroni correction revealed that all pairwise comparisons yielded p values greater than 0.05.

Table 3.

Comparison of the PVV in one-month post-filling (x ®±s, %)

	Apical	Middle	Coronal	Overall	P value
i-MTA SP	0.66 ± 1.78A	1.00 ± 1.33AB	1.75 ± 2.25B	1.56 ± 1.77	0.006
CRoot SP	0.31 ± 0.46A	0.30 ± 0.58A	1.02 ± 2.21B	0.84 ± 1.56	0.001
Neosealer Flo	0.34 ± 0.67AB	0.08 ± 0.18A	0.88 ± 1.05B	0.58 ± 0.61	0.001
iRoot SP	0.19 ± 0.45A	0.62 ± 2.37A	1.57 ± 1.88B	1.26 ± 1.46	0.000
AH-plus	1.06 ± 1.72A	0.63 ± 1.28A	0.32 ± 0.33A	0.44 ± 0.52	0.951
P value	0.243	0.009	0.284	0.301

Fig. 4.

The PVV in the SC1, SC2, SC3, SC4 and WVC groups at one-month post-filling

The PVV at the same site exhibited no statistically significant differences among the three distinct intervals for each sealer.

As illustrated in Table 4. and Fig. 5., post-retreatment analysis revealed that the RFR in the apical thirds of the SC1 group was significantly less than that in the SC4 group (p < 0.05). Within-group comparisons demonstrated: In the SC1 and WVC groups, RFR in the coronal thirds was less than that in the apical thirds. In the SC2, SC3 and SC4 groups, RFR in the coronal and middle thirds was less than that in the apical thirds (p < 0.05).

Table 4.

Comparison of the RFR post-retreatment (x ®±s, %)

	Apical	Middle	Coronal	Overall	P value
i-MTA SP	22.35 ± 24.79Aa	9.48 ± 14.99ABa	3.72 ± 5.69Ba	7.48 ± 9.23a	0.002
CRoot SP	24.14 ± 26.33Aab	7.34 ± 10.14Ba	5.31 ± 9.90Ba	7.68 ± 8.14a	0.006
Neosealer Flo	32.91 ± 27.68Aab	10.78 ± 16.19Ba	9.00 ± 16.69Ba	12.82 ± 15.12a	0.005
iRoot SP	29.96 ± 30.41Ab	11.95 ± 18.39Ba	10.35 ± 13.55Ba	12.70 ± 12.73a	0.000
AH-plus	30.38 ± 35.77Aab	22.55 ± 30.64ABa	6.73 ± 13.40Ba	11.89 ± 16.36a	0.002
P value	0.387	0.016	0.362	0.091

Fig. 5.

The RFR in the SC1, SC2, SC3, SC4 and WVC groups post-retreatment

And representative 3D reconstructions of micro-computed tomography images of roots and cross-sections images of the apical (3 mm), middle(6 mm), and coronal (9 mm) thirds of roots in the SC1, SC2, SC3, SC4 and WVC groups at immediately, one-month post-filling and post-retreatment were shown in Fig. 6.

Fig. 6.

Representative 3D reconstructions of micro-computed tomography images of roots and cross-sections images of the apical (3 mm), middle(6 mm), and coronal (9 mm) thirds of roots in the SC1, SC2, SC3, SC4 and WVC groups at immediately, one-month post-filling and post-retreatment

Discussion

Bioceramic sealers establish a stable sealing barrier within the canal space owing to their distinct physicochemical properties [1]. Previous studies have confirmed their superior sealing properties, which is closely associated with their favorable flowability and ability to penetrate into fine anatomical structures [7, 12]. This excellent sealing capacity effectively reduces bacterial microleakage and decreases the risk of periapical inflammation recurrence, representing a core clinical advantage of these materials. However, in terms of removability during retreatment, bioceramic sealers exhibit relatively high residual filling rate, with residual material prone to retention in complex anatomical areas of the root canal [13]. Such residual filling material may serve as a niche for bacterial colonization, thereby potentially compromising the success of retreatment. This constitutes a critical concern that necessitates attention in the clinical application of these materials.

The comparison of the PVV in the apical, middle and coronal thirds of roots within each group revealed the following: Immediately following the filling procedure, the PVV in the middle thirds was less than in the coronal thirds in the SC2 group, and the PVV in both apical and middle thirds was less than in the coronal thirds in both the SC3 and SC4 groups. One-week post-filling, the PVV in the middle thirds of roots in the SC3 group, apical and middle thirds of roots in both the SC2 and SC4 groups was less than coronal thirds. One-month post-filling, the PVV in the apical thirds of roots in the SC1 group, middle thirds of roots in the SC3 group and apical and middle thirds of roots in both the SC2 and SC4 groups was less than coronal thirds of roots. The results from three intervals indicate that the single cone obturation exhibits superior sealing properties in the apical and middle segments when compared to the coronal segments. In contrast, warm vertical compaction did not produce a statistical difference, but the data showed that the PVV was less in the coronal segments than in the apical and middle segments in all three intervals, which is also in line with the existing studies. In a retrospective study, Krug et al. observed that in the single cone obturation, the inhomogeneity shifted to the middle and coronal segments, while apical thirds of roots exhibited radiologically acceptable filling [14]. These differences may be attributed to the combined effects of material flowability, tubular permeability, and void entrapment, warranting future mechanistic studies [15, 16].

Iglecias and colleagues found that single cone obturation can produce comparable sealing properties to continuous wave filling, except for the coronal thirds of roots [10]. In light of the findings from experimental studies and clinical experience, it is proposed that a modified single cone obturation may be a viable option for root canal filling. The initial filling of root canals is conducted using the single cone obturation with bioceramic sealers. Subsequently, the coronal segment of the canal is obturated using a heat plugger to remove the gutta-percha, followed by continuous wave filling technique with gutta-percha. This proposed filling method addresses the issue of the high percentage volume of voids in coronal thirds of roots of the single cone obturation.

The comparison of the PVV in same segment between the groups revealed the following: Immediately following the filling procedure, the PVV in the middle thirds of roots in the SC4 group was less than that in the SC1 and WVC groups. One-week post-filling, the PVV in the middle thirds of roots in the SC2 group was less than that in the WVC groups. The discrepancies were all observed in the middle thirds of roots, which may be attributed to the fact that when employing single cone obturation, the bioceramic sealers were predominantly injected into the root canal via a needle that can only reach the middle segment. The volume of apical thirds of roots were limited, and the sealers were conveyed by gutta-percha while the middle and coronal thirds of roots were more susceptible to the formation of bubbles when injecting the sealers. It may be attributed to the properties of sealers that no statistical difference was observed in the PVV between the groups. A comparison of the data from the three-time intervals revealed that the single cone obturation with four bioceramic sealers yielded results that were comparable to those of warm vertical compaction.

It is noteworthy that the Kruskal-Wallis H test for PVV in the apical thirds immediately post-filling and middle thirds one-month post-filling demonstrated a statistically significant difference among groups; however, post-hoc pairwise comparisons with Bonferroni correction revealed that all pairwise comparisons yielded P values greater than 0.05. This seemingly paradoxical result can be statistically explained as follows: the Kruskal-Wallis test, as an omnibus test, evaluates whether any difference exists among all groups with a significance level (α = 0.05) applied to a single test; conversely, the Bonferroni correction divides the significance level by the number of comparisons, thereby substantially elevating the threshold for rejection. When the overall effect is marginal, genuine inter-group variation may fail to reach significance in specific pairwise comparisons due to insufficient power after correction. From a clinical perspective, this finding suggests that the four bioceramic sealers exhibit generally comparable sealing performance, with subtle numerical fluctuations not reaching clinically meaningful differences. This aligns with the primary conclusion of this study that different bioceramic sealers have no significant impact on the sealing efficacy of single-cone obturation.

The comparison of the PVV within each group at three intervals revealed the following: The PVV of four groups of the single cone obturation with bioceramic sealers and the warm vertical compaction with AH-plus exhibited no statistically significant differences in the three intervals either overall or in the apical, middle, and coronal thirds of roots. This finding contrasts with the results of some previous studies. Liu et al. conducted micro-CT scans of teeth obturated by single cone obturation and warm vertical compaction at 1 day versus 54 months post-filling and found that the PVV for all subgroups were smaller and statistically different at 54 months than the PVV at 1 day [17]. Gandolfi et al. observed a reduction in the PVV of teeth in the presence of simulated body fluid [18]. This may be attributed to the volumetric expansion of the sealers and the formation of apatite deposits. According to the literature, calcium silicate-based sealers achieve initial setting within 24 h, reach relative dimensional stability within one week, and demonstrate sustained ion release up to four weeks [19].Ivana et al. observed a diminished, though not statistically significant, discrepancy in the overall percentage volume of voids between AH-Plus and EndoSequence BC at the six-month relative to the one-week post-filling [20]. The discrepancy can be attributed primarily to the fact that the selected scanning intervals for this experiment were immediate, one-week, and one-month post-filling, which are shorter than the 6 or 54 months of the other experiments while the change of the PVV is a gradual process that may require a longer observation period. This represents a significant finding of the experiment, which addresses a gap in the previous research on the impact of short- and medium-term sealers on the change of the PVV. The subsequent phase of the experiment will entail an extension of the storage period, with the objective of evaluating the variation in the PVV over time. Furthermore, in both Liu’s and Ivana et al.‘s studies, the root canal orifices were sealed with glass ionomer cement, a material capable of permeating water from the external environment [17, 20]. In this experiment, flowable resin was utilized to seal the root canals in order to align with the clinical treatment scenario. It is plausible that the distinction in sealing materials may have an impact on the outcomes of the experiment. It is important to note that the isolated tooth experiment differs from the oral cavity. Therefore, the experimental data must be viewed with caution.

Following retreatment with ProTaper Universal Retreatment instruments and ultrasonic agitation, all groups exhibited residual gutta-percha and sealer remnants. Analysis revealed that residual rates and spatial distribution were influenced by sealer type and root canal region. The critical finding was that the SC1 group demonstrated significantly less residual filling rate RFR in apical thirds compared to the SC4 group (p < 0.05). Considering root canal retreatment, i-MTA SP’s favorable removal characteristics support its application in single-cone obturation. This discrepancy likely stems from inherent differences in physicochemical properties among bioceramic sealers. While bioceramic sealers are renowned for superior flowability and biocompatibility, these attributes—including nanoscale particle size and chemical adhesion to moist dentinal walls—may paradoxically promote dense apical sealing, rendering mechanical instrumentation and irrigation less effective during retreatment [13]. No significant intergroup differences were observed in middle or coronal thirds, suggesting that sealer type has diminished impact in anatomically accessible regions where conventional retreatment techniques achieve adequate clearance. Although no statistical significance was detected, Neosealer Flo and iRoot SP—sealers with less void volume in primary obturation—exhibited higher residual rates compared to i-MTA SP and C-root SP. This indicates that bioceramic sealers with optimal sealing properties, while beneficial for initial obturation, may compromise retreatment efficiency. Clinicians should therefore balance sealing performance and removability when selecting bioceramic sealers for single-cone obturation.

All groups (SC1, SC2, SC3, WVC) exhibited significantly higher RFR in apical thirds compared to middle and coronal thirds, which aligns closely with findings from prior studies. The apical thirds presented critical anatomical challenges: minimal root canal diameter and maximal curvature, limiting the accessibility and maneuverability of retreatment instruments. This anatomical constraint led to incomplete material removal, with debris retention predominantly observed in apical regions. Concomitantly, middle and coronal thirds—being more accessible to instrumentation and irrigation—demonstrated less RFR values [21]. He et al. highlighted that while larger filling volumes might exist in coronal thirds, residual material predominantly accumulates in apical thirds due to heightened technical difficulty in clearing these confined spaces [22]. Collectively, bioceramic sealer retreatment remains feasible in most scenarios but necessitates supplementary active irrigation and mechanical removal strategies to mitigate apical residue [23].

This study was limited to the evaluation of sealing efficacy and retreatability of bioceramic sealers, without addressing biocompatibility, antibacterial properties, or other clinically relevant characteristics. Furthermore, the ex vivo environment of extracted teeth differs substantially from the dynamic and complex conditions of the oral cavity, which may influence the long-term performance of root canal fillings. Future research should validate these findings through clinical trials.

Conclusions

In this study, the four bioceramic sealers combined with single-cone obturation achieved comparable sealing outcomes to warm vertical compaction. In light of the limitations of the relative coronal obturation observed with the single cone obturation, modified single-cone obturation is recommended for enhanced obturation. The removability varies among four bioceramic sealers, leading to differences in removal difficulty during retreatment. Clinicians should therefore consider not only their sealing properties and bioactivity but also their removability in potential future retreatment scenarios when selecting permanent root canal sealers.

Abbreviations

micro-CT

Micro-computed tomography

PVV

Percentage volume of voids

RFR

Residual filling rate

PTUR

ProTaper Universal Retreatment

Authors’ contributions

JZ contributed to the investigation, data curation, formal analysis, and was a major contributor in writing and revising the manuscript. YD and WQ performed the investigation and contributed to data visualization. ML assisted in data visualization. LW conceived and supervised the study, acquired resources and funding, administered the project, and participated in manuscript review. All authors read and approved the final manuscript.

Funding

This research received no external funding.

Data availability

The datasets generated and analyzed during the current study are not publicly available due to patient privacy and ethical restrictions but are available from the corresponding author on rea-sonable request.

Declarations

Ethics approval and consent to participate

This study adhered to the Declaration of Helsinki (https://www.wma.net/policies-post/wma-declaration-of-helsinki/). And this study was approved by the Ethics Committee of School & Hospital of Stomatology, Wuhan University (WDKQ2024 B93). Written informed consent was obtained from all patients prior to tooth extraction.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.