The supplementary use of XP-endo Finisher R after Reciproc enhances the removal of a bioceramic sealer in oval root canals
Abstract
This study compared the performance of Reciproc and Reciproc Blue endodontic files in retreatment time and re-establishment of apical patency, plus removal of a bioceramic sealer from the canal surface with the supplementary use of the XP-endo Finisher R. Following preparation, slightly curved oval root canals in mandibular incisors were filled using a corresponding gutta-percha point and a bioceramic sealer. Apical patency achievement was assessed and the time required to reach the original working length was recorded. The samples were split longitudinally and were photographed to assess the material remaining on the canal walls. No significant differences were observed regarding patency achievement or retreatment times when comparing Reciproc and Reciproc Blue. Significant less material remained on the canal walls when Reciproc was followed by XP-endo compared with Reciproc alone, and when the data for Reciproc and Reciproc Blue were pooled.
INTRODUCTION
Potential techniques for the removal of root canal fillings containing calcium silicate-based sealers have recently attracted attention [1-4], since the removal of existing root canal materials during the non-surgical revision of previously treated teeth is considered a crucial step [5]. It is required for access to the apical and peripheral root canal infection, overall decontamination, and provision of a well-condensed new root-filling material, all of which have been associated with improved outcomes for secondary root canal treatment [6]. Similarly, the likelihood of achieving the desired working length, followed by the re-establishment of patency, as well as the speed of removal of the intra-canal material, are considered of clinical and practical significance [1, 2, 5, 7]. Easy removal of the previous filling material reduces operator fatigue and facilitates the subsequent stages of root canal retreatment [1].
The efficacy of various engine-driven nickel–titanium instrumentation techniques for the removal of root-filling materials has been studied in the past, with inconsistent findings [5]. More recently, Reciproc (VDW, München, Germany), a reciprocating file produced using M-Wire technology and its version produced from a blue alloy by applying various heating processes to make the file more flexible and softer, Reciproc Blue (VDW), have been assessed for this purpose [7, 8]. Theoretically, the alloy that an instrument is made of may affect its ability to remove root filling material [7], and subsequently, the potential complications associated with this procedure, such as apical transportation, extrusion of root filling materials [9] as well as the formation of cracks and fractures [8]. Previous studies have found no significant differences for the purpose when comparing the use of Reciproc with Reciproc Blue in oval-shaped straight root canals [7], curved canals of different severity which were previously root-filled using a resin-based cement [8, 9], or in severely curved root canals root-filled using a bioceramic sealer [9]. It should be noted that the above studies consistently reported that no system can completely remove the previous root-filling material. In particular, the latter study found that after the use of Reciproc and Reciproc Blue, the mean remaining filling material ranged between 9% and 14% of the initial obturation volume [9].
Since conventional instrumentation techniques are unable to fully achieve the removal of root-filling materials, the use of hybrid and/or supplementary techniques should be considered [3, 5]. Nonetheless, irrigant agitation, including the use of ultrasonics and laser irradiation, also presents several limitations [5]. More recently, the use of XP-endo Finisher R (FKG Dentaire, La Chaux-de-Fonds, Switzerland; XP-endo), has been suggested [2]. The main feature of this instrument is the ability to change shape according to temperature [10], assuming a spoon shape when inside the root canal space in order to clean otherwise inaccessible areas whilst in rotation [3]. The XP-endo file acts mechanically by whipping, thus promoting superficial wear of the remaining root-filling material, which is subsequently removed by flushing with irrigant solutions [3].
The ability of engine-driven files to remove root canal filling and to reach the apical terminus may be influenced by the filling material and the different features of the root canal in question, as well as the instrument design and metallurgy. The role of usage of XP-endo after Reciproc files for the removal of root canal fillings containing bioceramic sealers requires further understanding. Therefore, the aims of the present study were to compare the performance of Reciproc and Reciproc Blue files for retreatment time and the re-establishment of apical patency, plus to assess the effect of the XP-endo on removal from the canal surface of a root canal obturation including gutta-percha and a bioceramic sealer. The first null hypothesis tested was that there is no difference in residual root-filling material on the canal wall, with or without the supplementary use of XP-endo following the use of Reciproc or Reciproc Blue. The second null hypothesis tested was that there is no difference in retreatment time and re-establishment of apical patency when Reciproc and Reciproc Blue were used.
MATERIAL AND METHODS
The present research was conducted in full accordance with ethical principles, including the World Medical Association Declaration of Helsinki (2008) and the additional requirements of Spanish law. The study was approved by the Ethics Committee of the European University of Madrid, Spain.
Preparation of teeth
Sample size estimation was conducted a priori based on a comparable study [10] with an alpha value of 0.05, an 80% power difference ranging between 990 and 480 and a standard deviation value of 370. A sample size of 12 specimens was selected for each study group.
Recently extracted single-rooted mandibular incisors were assessed under 16× magnification using a dental operating microscope (A-Series, Global Surgical Corporation, St. Louis, MO, USA), to exclude those with bifurcations, open apices, resorptive defects, pulp canal calcification, and longitudinal fractures. The presence of a single and oval-shaped canal in the apical third (i.e., one dimension was at least twice that of a measurement made at right angles [11]), with curvature <10° and the absence of a previous root canal filling was assessed by exposing two films at 90° angles [12]. The teeth included were stored in a 0.5% thymol water solution at 6°C and used within 20 days of extraction. Seventy-two teeth were included.
Following the removal of calculus and periodontal tissue using ultrasonic tips, the lengths of the samples were standardised to 16 mm by decoronation with a double-sided cutting diamond disk (Kerr Dental, Barcelona, Spain) mounted on a low-speed straight handpiece. K-Files sizes 10 and 15 (Dentsply Maillefer, Ballaigues, Switzerland) were inserted in the root canals until they were visible through the apical foramen under 16× magnification. The root canals were prepared in a crown-down manner with Reciproc® R25 (VDW, München, Germany) 1 mm short of the apical foramen, in three steps. During the instrumentation, all the canals received 2 ml 4.25% sodium hypochlorite (NaOCl) (Dentaflux, Madrid, Spain) between steps, delivered using a syringe and a side-vented 27-gauge needle (Monoject, Tyco Healthcare, Mettawa, IL, USA) positioned 3 mm shorter than the working length or at the level of maximum needle penetration possible, associated with patency filing using K-Files size 15. A final rinse with 3 ml NaOCl +1 ml 17% EDTA (Dentaflux, Madrid, Spain) +3 ml NaOCl was completed. The latter step included agitation with an Endoactivator (Advanced Endodontics, Santa Barbara, CA, USA), with a size 25, 0.04 taper tip, 22 mm, set at 10000 cycles per minute, placed 2 mm shorter than the working length for 30 s. Finally, the canals were dried using a size 25 paper points (VDW).
Root canal filling
Following the random allocation using an online random number service (https://www.random.org/) 12 samples were not root-filled, thus becoming the negative controls. The root canals of the 60 remaining roots were filled using a corresponding Reciproc® gutta-percha point size/taper R25 point and BioRoot™ RCS (Septodont, Saint-Maur-des-Fossés, France). The sealer was mixed following manufacturer instructions and the amount used per canal was standardised to 0.01 ml using insulin syringes (Juvazquez, Leganes, Madrid). The point was coated with the sealer and firmly seated in the root canal. The excess coronal material was severed using the Alpha II Main Device (B&L Biotech, Fairfax, VA, USA), and the canal was sealed coronally with 3 mm of Cavit (3 M ESPE, Seefeld, Germany). A postoperative radiograph was exposed to confirm correct obturation in regard to density and evidence of material placement to the apical terminus.
Samples were allowed to set for 5 days at 37°C and 100% humidity to ensure the setting of the sealer.
Root canal retreatment
The 60 previously root-filled samples were randomly allocated to the positive control (no root canal filling removed) or the four experimental groups according to the retreatment protocol used (n = 12 per group) as follows: Reciproc (R25 followed by R40); Reciproc+XP-endo as the previous group, followed by XP-endo Finisher R file (FKG Dentaire, La Chaux-de-Fonds, Switzerland); Reciproc Blue (R25 followed by R40); (VDW); Reciproc Blue+XP-endo R25 followed by R40 and the XP-endo.
First, the temporary filling was removed, and Gates-Glidden drills No. 2 (Maillefer) were used to remove the coronal 4 mm of the root filling material. Mechanical retreatment using a crown-down sequence was carried out with light up–down pecking motions, up to the previously determined working length using the engine-driven file sequences described above. After 3 pecks, the files were wiped to remove the filling material. Rinsing with 1.5 ml NaOCl as described earlier was carried out, and apical patency was assessed using a size 10 K-file. The canal was considered patent if the file passed 1 mm beyond the WL without pressure being applied. A final rinse with 3 ml of NaOCl and EDTA (30 s each) was carried out as previously described.
Retreatment time (i.e., reaching the previous working length) was measured using a digital chronometer. Only the mechanical retreatment time (i.e., nickel-titanium engine-driven file active in the canal) was taken into account.
For the XP-endo groups, the apical 4 mm was sealed using utility wax (Hygenic, Alstätten, Switzerland). In total, 3 ml of NaOCl and 1 ml of EDTA solution were delivered using a syringe and needle as previously described and agitated for 60 and 15 s, respectively, with the XP-endo at 800 RPM, with a slow up and down motion having a 7–8 mm amplitude (total time supplementary step 75 s).
All the root canal treatment procedures were carried out by an experienced endodontist in a 37°C water bath.
Assessment of remaining filling material
Two longitudinal grooves were created using a diamond cutting diamond disk not reaching the canal to prevent damage. The roots were split longitudinally using a Lecron #5 carver (Dentaltix, Madrid, Spain). The root canal walls were photographed using a digital camera (Canon EOS 750D; Canon Spain, Madrid, Spain) under 8× magnification linked to the operating microscope. Image-J analysis software (Image-J v1.44; US National Institutes of Health, Bethesda, MD, USA) was used to measure the residual root filling material on the canal wall and the total root canal area in mm2. Following calibration of the tooth length against a reference, the total area of the canal walls was delimited and measured and the area with remaining root canal filling material was delimited and calculated (Figure 1). The data acquired were used to calculate the percentage of filling remaining in the canal walls using Microsoft Excel (Microsoft, Seattle, CA, USA). The samples were evaluated by a trained and blinded assessor (VDJ). Intraobserver agreement was calculated using a randomly selected sample of 10% of included images, with a 30-day interval between observations. Figure 1 illustrates the methodology.
Statistical analysis
The quantitative variables were described as mean and standard deviation, whereas the qualitative variables were described in number and percentage. Normal distribution was tested by the Kolmogorov–Smirnov test. The two-way analysis of variance (ANOVA) was used for inferential analysis comparison between groups. The multiple comparisons were evaluated using the Bonferroni correction.
The Pearson's Chi-squared test was used to compare the achievement of apical patency and the Student's t-test was used to compare retreatment time.
The level of significance was set at p < 0.05. Statistical analyses were performed using the Stata 11.0 software (StataCorp LP, College Station, TX, USA).
RESULTS
Twenty samples were considered patent for Reciproc and 22 for Reciproc Blue, respectively, with no significant differences found (p = 0.383). The mean retreatment times (SD) were as follows: Reciproc 69.15 s (16.29); Reciproc Blue 70.20 s (25.41) without significant differences (p = 0.443).
None of the protocols completely removed the filling material from the root canal walls. The mean percentage (SD) of the remaining material was as follows: negative control 0 (0); Positive control 98 (1.41); Reciproc 32.58 (13.52); Reciproc + XP-endo 16.49 (8.92); Reciproc Blue 29.88 (13.34); Reciproc Blue + XP-endo 21.14 (8.76); both groups without XP-endo 31.23 (13.21); both groups with XP-endo 18.13 (9.58).
For all the experimental groups compared to the positive control (root canal filling not removed) significant differences were present (p = 0.000). Among the experimental groups, significant differences were found only when comparing Reciproc vs. Reciproc + XP-endo (p = 0.004). No further significant differences were found comparing the remaining experimental groups: Reciproc vs. Reciproc Blue (p = 1.000), Reciproc Blue vs. Reciproc Blue + XP-endo (p = 0.409), Reciproc + XP-endo vs. Reciproc Blue+XP-endo (p = 1.000). When the results of Reciproc and Reciproc Blue were pooled, the supplementary use of XP-endo resulted in a significantly reduced percentage of material remaining on the canal wall (p = 0.000).
Intraobserver agreement on the measurement of the remaining material on the canal walls was “almost perfect” [13] [intraclass correlation coefficient (ICC) = 0.998].
DISCUSSION
The present study established that, in our experimental set-up, the use of the XP-endo Finisher R after the use of Reciproc or Reciproc Blue enhances the removal of a filling material including a bioceramic sealer from the root of the canal walls, although significant differences were found only for Reciproc and no significant differences were found when comparing the Reciproc sequences tested per se. Therefore, the first null hypothesis was partially rejected. This may be explained by the differences in metallurgy between the files, with the Reciproc files being harder and more rigid, thus potentially being able to weaken the bond between the dentine and the BioRoot™ RCS, and subsequently facilitating the removal of the material with the supplementary use of the XP-endo Finisher R. No differences were found when comparing the systems' ability to reach the working length and/or obtain patency as well as retreatment times, thus the second null hypothesis was not rejected.
The findings of the present study are in agreement with previous similar studies assessing retreatment procedures. When comparing the removal of a bioceramic cement by Reciproc (made using a conventional alloy) versus Reciproc Blue, no differences were found in the curved canals [8, 9], and, in oval canals previously filled using a resin-based cement, no differences were found in the removal of root filling, the time required to perform retreatment or the ability to regain apical patency [7]. Thus, overall, the metallurgical properties of the engine-driven files tested do not influence the removal of intracanal root-filling material. Finally, the addition of a supplementary step using the XP-endo Finisher R enhances the removal of bioceramic or resin-based cement from single-oval canals [3, 10] and canals with moderate curvature [14], but this was not the case in the present study for Reciproc Blue.
Preparation sizes influence root canal filling removal [5, 7]. In the present study, the final instrument used was the R40, which is compatible with previously reported canal diameters for mandibular incisor teeth [11]. Excessive enlargement of the root canal should be avoided as this may predispose the root to fracture [7]. Furthermore, assuming that the circular pattern of the engine-driven files produces a minimum circular size [15], eccentric parts present in oval roots canals would likely retain root filling material, therefore, apart from the canal size, its shape as well as its curvature should be expected to affect the outcomes. In the presence of curved canals restoring forces may affect the contact between retreatment files and root canal walls [15].
The achievement of patency and the ability to reach the predetermined working length was assessed, which are considered important outcome predictors in root-canal retreatment [5, 6]. Based on our results, the re-establishment of working length and apical patency are achievable with bioceramic cements and were comparable for the files tested, however, the literature is discordant [1, 3, 14, 16, 17]. The time required to achieve apical patency in root canals can be influenced by the root type [1], therefore, the results of the present study may not be directly transferable to canals with other morphology.
Various methodologies have been used to assess the removal of materials during root canal retreatment. In the present study, the removal of root canal filling was assessed using a simple and well-established method [2, 10, 18, 19]. This aims to assess not only the elimination of likely contaminated obturation materials [5], but also the subsequent access to possibly contaminated root canal surface for recleaning, which is important from the clinical standpoint [5]. The consistency of the quantitative measurements made by the observer (i.e., remaining filler material in the canal walls) was confirmed using ICC.
A limitation of the study is that the methodology requires longitudinally splitting the roots making assessment at different time points not possible, thus lacking a longitudinal observational character [20]. Conversely, this is possible when micro-computed tomography imaging is used [5]. The use of photography is not associated with artefacts, magnification or distortion that may occur when other imaging techniques are used for this purpose [21, 22].
Two-dimensional imaging was used to standardise the samples, and the anatomy of the root canal systems under investigation has been listed as a potential confounding factor [23]. However, it should be noted that the procedure described in a seminal study for oval canals was used [11]. Oval-shaped canals were selected as these are considered challenging for the removal of previous root-filling materials [7]. The use of calcium-silicate-based sealers with a single-cone technique has been purported to provide homogeneous root fillings [12], although, the results of the present study may not be transferrable to other canal morphologies, obturation techniques, and/or bioceramic materials.
The results of the present study confirm the limitations of currently available techniques for the complete removal of the root canal filling materials tested. Resin-based and bioceramic cements can be removed with a similar effort, based on the best available evidence [1-4, 15, 16, 24], although the process may require more time and be associated with iatrogenic errors more often when compared to resin-based sealers based on previous studies [1, 9]. It should be reiterated achieving patency and the absence of procedural errors are considered significant predictors for retreatment outcomes, therefore are significant intra-operative factors in endodontics [6].
To summarise, within the limitation of the present laboratory study Reciproc and Reciproc Blue were shown to have similar ability to remove a bioceramic cement-containing root canal filling from the walls of slightly curved oval canals, and should be considered predictable in their ability to reach the apical terminus in the presence of this sealant. The supplemental use of XP-endo significantly improved root canal filling removal from the canal walls only with Reciproc files.
AUTHOR'S CONTRIBUTION
VDS, GL, and OVP performed the research. VDS, GL, OVP, RE, and AC designed the research study. RE, AC, GRF, and RC analysed the data. RE, GRF, and RC wrote the article.
ACKNOWLEDGEMENT
Open access publishing facilitated by The University of Adelaide, as part of the Wiley - The University of Adelaide agreement via the Council of Australian University Librarians.
