Original Article
Comparison of four different file systems in terms of transportation in S-shaped canals and apically extruded debris
2024 Volume 66 Issue 4 Pages 226-230
Details
2024 Volume 66 Issue 4 Pages 226-230
Purpose: This study evaluated transportation and extruded debris during preparation using different instruments.
Methods: Sixty resin blocks with S-shaped canals and 60 extracted teeth were separated into four groups (n = 15), which were instrumented with Reciproc Blue, XP-endo Shaper, WaveOne Gold, and Twisted File Adaptive. For evaluating transportation, pre- and post-preparation images were obtained under a stereomicroscope and superimposed with digital software. The distance between the inner and outer canal walls was measured. For the evaluation of debris extrusion, the samples were placed in Eppendorf tubes and instrumented using one of the four rotary files. The initial weight was subtracted from the post-instrumentation weight to determine the amount of extruded debris. The Kruskal-Wallis and Dunn multiple tests were performed.
Results: For transportation, no significant difference was found between the XP-endo Shaper-Twisted File Adaptive systems and between Reciproc Blue-WaveOne Gold groups (P > 0.05). The XP-endo Shaper and Twisted File Adaptive techniques led to significantly less transportation compared to the other systems (P < 0.05). Regarding debris extrusion, the XP-endo Shaper system extruded significantly less debris than the other groups (P < 0.05).
Conclusion: XP-endo Shaper extruded less debris compared to other groups, while XP-endo Shaper and Twisted File Adaptive caused less transportation than other files.
Preserving the original canal form during root canal shaping is a crucial stage in endodontic treatment [1]. However, in teeth with narrow and curved canals, some complications may arise during shaping, including apical transportation, zip (dilaceration or elbow formation), step formation, and perforations [2]. To avoid or overcome such complications, various techniques have been researched and developed, one of which involves making a mechanically and physically superior alloy for manufacturing endodontic nickel titanium files [3].
Other undesirable consequences of root canal shaping include postoperative pain, inflammation, and flare-ups, which occur as a result of apical extrusion of dentin particles, pulp remnants, and bacteria into periradicular tissues [4]. Notably, the amount of debris extrusion may vary depending on instrumentation methods and the file system design [5]. In endodontic practice, rotary instruments work on two basic principles: rotation and reciprocation. Reciproc Blue (RB; VDW, Munich, Germany) is a novel version of Reciproc files, which develops a unique blue color as a result of heat treatment. It has a non-cutting tip, two cutting edges, and an S-shaped cross-section, and works with a reciprocating action [6]. WaveOne Gold (WOG; Dentsply Maillefer, Ballaigues, Switzerland), which is a new generation reciprocal system, is produced using gold wire technology. This file has a parallelogram-shaped cross-section far from the center with a taper that decreases gradually. Only two points make contact with the canal walls during the cutting action [7].
Twisted File Adaptive (TFA; SybronEndo, Orange, CA, USA) is a rotary file system with a triangular cross-section that uses a combination of continuous rotation and reciprocation movements. It is produced by bending an R-phase wire under heat and further subjecting it to electrochemical polishing to improve its cutting efficiency. Due to its adaptive motion technology, the instrument can rotate under low pressure. If the file gets stuck in the canal, it adopts the reciprocation motion [8].
The XP-endo Shaper (XPS; FKG Dentaire SA, La Chaux-de-Fonds, Switzerland) is a spiral-shaped NiTi MaxWire rotary instrument that exhibits continuous rotation motion. The initial taper in the M phase is 0.01 when the instrument is cooled, and the molecular memory in phase A changes to 0.04 when exposed to body temperature (35°C). However, the instrument has a tip (Booster Type) with six cutting edges designed to adapt to the course of the canal. Machining starts at ISO size 15 and can have a diameter of ISO 30 [9].
S-shaped canals, also known as double-curved canals, are among the most difficult canal configurations to maintain the integrity of the original root canal shape [10]. These canals are found especially in the maxillary and mandibular molars [11]. The presence of double curvature in the root canal may pose a greater risk for instrument breakage, strip perforation, or transportation when compared to straight canals. Although the XPS system is widely used and has shown positive results in transportation in J-shaped canals [12,13,14], there is not sufficient information in the literature about its performance in S-shaped canals. Similarly, there are very few studies [9,15,16,17] on the use of the XPS technique when dealing with apical debris. There are no studies that compare XPS and TFA systems either. Four different NiTi systems were used in this study: RB, TFA, WOG, and XPS file systems. The objectives of the present in vitro study were both to evaluate and compare these four different systems with regard to canal transportation in artificial S-shaped canals and to assess the amount of debris extruded apically by these files. The null hypothesis was that all systems lead to a similar degree of transportation and debris extrusion.
The present study was approved by the Gaziantep University Ethics Committee (2019/38) and was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki. Informed consent was acquired from all research participants to use their teeth in the current research. The power analysis was performed using G*Power 3.1.9 software (Heinrich Heine University, Dusseldorf, Germany). In order to find significant differences between experimental groups (RB and XPS) according to the previous study [18], the minimum required sample size was estimated as 11 for each group for the canal transportation analysis (cohen d = 1.31, α = 0.05, 1-β = 0.80). The sample size calculation was performed by using data from another study by Keleş et al. [19], for debris extrusion analysis with α = 0.05 and 1-β = 0.80, and considering an effect size = 1.78, seven specimens per group were determined as the ideal size to detect significant differences between groups (RB and WOG). Because of the possibility of specimen loss during instrumentation procedure, it was decided to use 15 artificial canals and 15 extracted teeth for each test group.
Evaluation of extruded debris Sample selectionThe sample included 60 extracted human lower incisors with the following features: mature apices, single root and single canal, caries-free, endodontically untreated, and without root fracture or root resorption. Periapical digital radiographs of the teeth were taken to select only those with single and straight canals. The samples in which the file extruded from the apical foramen without any pressure application were excluded from the study. Incisors with a root length of approximately 14 ± 1 mm were selected, and shortening was performed on the incisal part with a bur so that the total tooth length was 20 mm, which was measured using a digital caliper (Insize Mini, Istanbul, Turkey). A size 15 K file was used to establish the width of the apical foramen. To detect the working length, a size 10 K-type hand file was inserted into the root canal until it was visible through the major foramen, and the working length was assessed to be 1 mm shorter than this length.
Coronal access cavities of the samples were performed under water using diamond burs.
Debris test apparatusThe extrusion model defined by Myers and Montgomery [20] was used to determine the amount of debris extruded apically (Fig. 1). A hot instrument was used to drill a hole in the plastic caps of the Eppendorf tubes, and the teeth were placed in these holes using slight pressure. The teeth were fixed to the plastic caps with the help of cyanoacrylate cement at the cemento-enamel junction. The Eppendorf tubes were placed in small glass bottles such that the apical part of the root would be in the tube in order for the extruded debris and irrigant to be collected. The teeth were isolated with a rubber dam to prevent the irrigating solution from leaking into the tube due to coronal extrusion and to blind the researcher to the apical portion of the root during root canal shaping. Air pressure between the inside and outside of the Eppendorf tube was balanced by placing a 27-G needle into the plastic caps of the tubes. Before the treatment, each tube (without a plastic cap) was weighed three times on a balance with a precision scale of 10-4 g (Shimadzu, Kyoto, Japan). The average of these weights was recorded as the initial weight of the tubes.
The files were examined preoperatively under a stereomicroscope to check for manufacturing defects (Leica MZ 12.5, Heerbrugg, Germany). The samples were randomly divided into four groups (n = 15):
All tooth preparations were performed by a single operator in a cabinet with a constant temperature of 37°C. During instrumentation, a side-vented 27-G irrigation needle (Endo-Eze, Ultradent, South Jordan, UT, USA) was placed in the root canal after each of three pecking movements. This was followed by irrigation using 2 mL of distilled water. Throughout each preparation, a total of 10 mL distilled water was used.
Data collectionThe Eppendorf tubes were kept in an incubator at 70°C for 5 days to ensure that the irrigation solutions evaporated. After this, the tubes along with the dry debris were weighed thrice. The average of these weights was recorded as the final weight. The weight of the extruded debris was assessed by subtracting the initial weight from the final weight.
Investigation of transportation Canal preparationA transparent resin block (Endo Training Block-S; Dentsply Maillefer, Ballaigues, Switzerland) with a total of 60 S-shaped canals was used. The blocks had an apical diameter of 0.15 mm, a length of 16 mm, and a taper angle of 0.02. The first curvature of the S-shaped blocks had an angle of 30° and the second curvature had an angle of 20°.
The blocks were randomly divided into four groups, with 15 blocks in each group: Group RB, Group TFA, Group WOG, and Group XPS. The abovementioned preparation procedure was followed to shape the canals.
Pre- and post-instrumentation imagesThe treated (Fig. 2b) and untreated (Fig. 2a) blocks were placed in a special apparatus and imaged under a stereomicroscope . The images were then transferred to the computer in the same size with ×10 magnification in both TIFF and JPEG file formats. Computer software Adobe Photoshop CS5 Extended (Adobe Sytems, San Jose, CA, USA) was used to superimpose the images taken before and after the shaping process. An image analysis software called ImageJ 1.48v (National Institutes of Health, Bethesda, MD, USA) was used to make measurements on the superimposed images. Following this, ten consecutive guide circles with a center distance of 1 mm intervals between the ends of the artificial canal and a linear distance between them were drawn on the superimposed images (Fig. 2c). From the apical to the coronal part, the points where each circle line intersected the canal trace were numbered from 1 to 10. These numbers were counted as measuring points. Next, the surface distance between the outer boundary images of the canal before and after shaping was taken to be perpendicular to the canal surface at each measurement point and was measured linearly. A total of 20 distances were measured for each canal, 10 from the inside of the artificial canal and 10 from the outside. After the measurement data on 10 measurement points were recorded, the first three measurement points (1st, 2nd, and 3rd measurement points) were evaluated as the apical region, the next four measurement points (4th, 5th, 6th, and 7th measurement points) were evaluated as the middle region, and the last three measurement points (8th, 9th, and 10th measurement points) were evaluated as the coronal region measurements.
The amount of transportation (T) after preparation at either the outer or inner part of the canal curvature was calculated by subtracting the distance at the outer surface from the distance at the inner surface (T = O-I). If the T value was zero, there was no transportation in the canal. If it was positive, the direction of transportation was toward the outside of the canal, and if it was a negative value, the direction of transportation was toward the inside of the canal.
The Shapiro Wilk test was used to determine whether the data’s distribution was normally distributed. Multiple comparison tests (Kruskal Wallis and Dunn) were employed for comparing the non-normally distributed features in more than two independent groups. Descriptive statistics are provided for the numerical variables using the median, 25th percentile (Q1) and 75th percentile (Q3) values. The statistical analysis was conducted using the IBM SPSS for Windows version 22.0 (IBM Corp., New York, NY, USA) package application, and a significance level of P < 0.05 was applied to the data.
The amount of debris that extruded from the apical foramen is shown in Table 1. The amount of debris extrusion was significantly lower in the XPS group compared to the other three groups (P < 0.05). There was no statistically significant difference between the other groups (P > 0.05) (Fig. 3).
| RB (n = 15) | TFA (n = 15) | WOG (n = 15) | XPS (n = 15) | P | |
|---|---|---|---|---|---|
| Median (Q1-Q3) |
0.005 (0.003-0.007)a |
0.003 (0.003-0.005)a |
0.004 (0.003-0.005)a |
0.003 (0.001-0.003)b |
0.001* |
*Different superscripts mean statistically significant difference. Significant at the 0.05 level; Kruskal Wallis test
A comparison of the amount of transportation between groups is shown in Table 2. When comparing the amount of transportation regardless of the region, there was no significant difference between XPS and TFA (P > 0.05), while these groups had significantly lower transportation values than other groups (P < 0.05) (Fig. 4).
| RB (n = 15) | TFA (n = 15) | WOG (n = 15) | XPS (n = 15) | P | |
|---|---|---|---|---|---|
| Median (Q1-Q3) |
0.120 (0.070-0.210)a |
0.080 (0.050-0.150)b |
0.130 (0.050-0.220)a |
0.085 (0.030-0.140)b |
0.001* |
Different superscripts mean statistically significant difference. * Significant at the 0.05 level; Kruskal Wallis test
The mean values of transportation by region are shown in Table 3. While there was a statistically significant difference between the groups in the apical and middle regions in terms of the amount of transportation (P < 0.05), there was no significant difference in the coronal region (P > 0.05). The results for the amount of transportation in the apical region were consistent with the overall assessment. There was no significant difference between the TFA and XPS groups, or RB and WOG groups in terms of transportation. The TFA and XPS groups showed significantly lower transportation values than the RB and WOG groups.
Regarding the amounts of transportation in the middle region, the XPS group showed significantly lower transportation values than the other groups. While no significant difference was observed between the TFA group and the RB group, there was a significant difference between the TFA and the WOG group. There was no significant difference between the RB and WOG groups (Fig. 5).
| RB (n = 15) | TFA (n = 15) | WOG (n = 15) | XPS (n = 15) | P | |
|---|---|---|---|---|---|
| Apical | 0.090 (0.030-0.170)a |
0.050 (0.020-0.080)b |
0.110 (0.040-0.170)a |
0.060 (0.020-0.110)b |
0.001* |
| Middle | 0.200 (0.085-0.270)ab |
0.140 (0.080-0.185)b |
0.230 (0.110-0.315)a |
0.090 (0.040-0.140)c |
0.001* |
| Coronal | 0.100 (0.060-0.160)a |
0.070 (0.040-0.120)a |
0.060 (0.040-0.130)a |
0.100 (0.040-0.160)a |
0.078 |
Different superscripts mean statistically significant difference. * Significant at the 0.05 level; Kruskal Wallis test
The first stage of this study evaluated the amount of debris extruded from the apex during treatment processes using the RB, TFA, WOG, and XPS file systems, each of which has a unique design and operating system. In order to exclude potential issues such as the loss of WL or improper instrumentation and irrigation in curved root canals, extracted teeth with straight single-root were employed in this investigation. To prevent any potential sodium hypochlorite crystallization, distilled water was employed as an irrigation solution. The Myers and Montgomery technique was preferred to collect the apically extruded remnant [20]. Notably, one drawback of this method is that there is no material (agar, foam, etc.) that simulates the apical pressure of the periodontal ligament against the extrusion of debris. Although the 1.5% agar gel model is known to show density similar to that of periapical tissues and provides similar resistance to apically extruded debris [21], it does not represent all periapical conditions [22].
Several other studies [15,16] have shown that XPS extruded significantly less debris from the apex than RB and WOG, which is in agreement with the present work. This may be attributed to the design of the XPS file, as it makes contact with the canal walls at limited points and causes less debris accumulation and packing. Wang et al. also noted that when multiple pecking motions are performed, XPS extrudes much less volume of debris compared to the WOG and RB systems [17].
Previous studies did not find any statistical difference between the WOG and TFA systems with regard to the amount of debris extruded apically [23,24]. Elashiry et al. compared the extruded debris of the WOG, RB, and HyFLex systems and found no significant difference between WOG and RB [25]. These findings are in agreement with the findings of this study.
Furthermore, the results of the present study support the notion that constant rotation, which functions like a screw conveyor, may carry the debris coronally [26]. Similarly, previous studies have reported that the taper angle can affect the amount of debris extruded apically [16,27]. In this study, the amount of apically extruded debris was very low in the XPS group which had the lowest taper angle.
The S-shaped root canal structure, which is mostly observed in maxillary and mandibular mesiobuccal canals [10,11], makes preparations while preserving the canal anatomy, quite difficult. In the second part of the current study, four different rotary file systems were compared with each other with regard to transportation. Artificial canals were preferred due to the difficulty of collecting root canals with an S shape at the same root angle in extracted human teeth. To this end, standard models were created for all the groups, and a fair comparison was achieved. According to Wu et al., apical transportation of less than 0.3 mm would not adversely affect root-filling leakage [28]. No observation of transportation after shaping above this value was observed in any of the samples.
The results of three different studies using J-shaped resin blocks [13] and curved mandibular molar mesial roots [12,14] showed that XPS files cause less transportation compared to the WOG system, which is consistent with the findings of the present study. Another study showed that the XPS rotary file system created less transportation compared to the RB system [18]. Emina et al. used mesiobuccal canals with 25-40° curvatures of molar teeth in their study and determined the measurement points from the apex as 3 mm apical, 5 mm middle, and 7 mm coronal. While there was no statistical difference in the apical part, RB caused considerably more transportation in the middle and coronal regions than XPS did [29]. However, the samples in this study consisted of resin blocks, meaning the results in the apical region may have differed because the previous study used extracted teeth. Another reason may be the canal configuration, which was J for the previous study and S for the present study. The enhanced mechanical behavior and higher performance of XPS may be partially explained by MaxWire alloy’s flexibility and better ability to adapt to the double-curved intracanal morphology.
Keskin et al. found that the RB file caused statistically more transportation than the WOG file in three of the five points determined on the artificial tooth [30]. The results of the above study are inconsistent with those of a previous study [25] and the present study. It can be assumed that this may be due to operator skill. This inconsistency may also be attributed to the difference in the canal configurations between the present study and the other.
Previous studies on the transportation performance of the TFA system, in which rotation and reciprocation motion are used together, focused on Reciproc and Wave One systems [8,31,32]. This study is the first to compare TFA with both blue and gold technology and XPS systems. In particular, TFA deviated much less from the canal shape in the apical region compared to the WOG and RB systems and only the WOG system in the middle region. It can be supposed that this is because, through adaptive motion, the force placed on the files during the formation of the curved regions of S-shaped artificial canals was reduced and the files remained in a more central position.
One of the limitations of this in vitro study is that root canal shaping was evaluated using two-dimensional images. Surface and volumetric measurements of teeth can be made by micro-CT instead. In this way, the teeth can be examined in three dimensions. However, micro-CT was not used owing to time and cost constraints. On the other hand, with two-dimensional imaging, changes in artificial teeth can be easily monitored. Another limitation is the usage of resin blocks, as they do not fully reflect the clinical situation because the physical properties of dentin and resin are not the same. However, resin blocks were preferred because they allowed for standardization of canal width, curvature degree, and location.
Considering the effects of the preparation techniques used in the current in vitro study on debris extrusion and transportation, the null hypothesis was rejected. It is difficult to compare the various sample selection criteria, irrigation programs, and test procedures, as well as results from the studies using different teeth. Therefore, there is a need for more studies investigating file systems with different alloys and movement principles using similar methodologies.
This in vitro study shows that XPS has the best performance in terms of both canal transportation and debris extrusion. It also shows that TFA leads to less transportation in both apical and general transportation. Although RB and WOG exhibited similar findings with respect to debris extrusion and transportation, XPS seems to be an advantageous system for the preparation of canals with double curvature.
CT: computed tomography; JPEG: Joint Photographic Experts Group; NiTi: nickel titanium; RB: Reciproc Blue; TFA: Twited File Adaptive; TIFF: Tagged Image File Format; WOG: WaveOne Gold; XPS: XP-endo Shaper
Ethical approval for the use of human teeth was obtained from the institutional review board of Gaziantep University Ethics Committee (No. 2019/38).
The authors declare no competing interests.
This research was funded by Gaziantep University Scientific Research Projects (Project no: DHF.DT.19.07).
FT: conceptualization, investigation, formal analysis, writing and supervision; MA: conceptualization, investigation, methodology, data curation, software, visualization; All authors read and approved the final version of the manuscript.
MA: shr2007a7a@gmail.com, https://orcid.org/0000-0002-0986-0619
FT*: ftmguller@hotmail.com, https://orcid.org/0000-0003-0568-4248
The authors would like to thank Prof. Dr. Seval Kul, who provided assistance with biostatistics.
Data generated during the current study are available from the corresponding author on reasonable request.
