Micro-Computed Tomographic Evaluation of the Shaping Ability of Vortex Blue and TruNatomyTM Ni-Ti Rotary Systems

doi:10.21203/rs.3.rs-3578917/v1

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Micro-Computed Tomographic Evaluation of the Shaping Ability of Vortex Blue and TruNatomyTM Ni-Ti Rotary Systems

https://doi.org/10.21203/rs.3.rs-3578917/v1

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Aim: To assess and evaluate the canal shaping ability of two different Ni-Ti rotary systems ex-vivo: Vortex Blue (VB) and TruNatomy (TN), using micro-computed tomography (micro-CT) in extracted premolar human teeth.

Materials and Methods: A total of 20 extracted bifurcated maxillary first premolars with two separate buccal and palatal canals wererandomly divided into two groups and prepared with either Vortex Blue or TruNatomy files. All teeth were scanned by micro-CT before and after root canal preparations. The micro-CT scans were analyzed to measure the following parameters: percentage of untouched canal surface area, changes in canal surface area, changes in canal volume, structural model index (SMI), changes in canal angulation and changes in dentin thickness. Statistical analysis was conducted to compare the means and standard deviations of the parameters between the two systems, with statistical significance level set at P-value < 0.05.

Results: Both VB and TN files exhibited a significant increase in the basic canal geometry parameters including canal surface area and canal volume after canal instrumentation with no statistical significant differences between both files and with no considerable shaping mishaps or errors. Both file systems showed no significant changes in the SMI and dentin thickness after canal instrumentation. TN files demonstrated less straightening of the canal curvature compared to VB files with no statistically significant difference. Furthermore, TN files showed less cervical dentin removal when compared to VB files with no significant difference. A significant difference was found in TN group regarding dentin removal between coronal and apical thirds.

Conclusion: Vortex Blue and TruNatomy files produced comparable root canal preparation with no considerable shaping mishaps or errors. Both files induced minimal canal straightening after preparation. TN files resulted in less removal of cervical dentin compared to apical dentin.

Shaping ability

Micro-CT

Vortex Blue

TruNatomy

Nickel–Titanium (NiTi) rotary systems are continuously evolving to achieve optimal root canal preparation with minimizing procedural errors and preventing instrument failure. Significant enhancements have been made in rotary files design to improve the fatigue resistance of NiTi rotary files. This has been achieved through alterations in the thermal and metallurgical properties of the NiTi wire or through modifications in the instrument design [1-4].

TruNatomy and Vortex Blue file systems are manufactured by a special thermomechanical treatment that resulted in super-elastic NiTi alloys with a shape-memory properties. Both file systems show symmetrical cross-sections, lack of radial land, asymmetrical blades and non-active tips, and have similar equi-atomic nickel–titanium ratios [5]. However, differences were found between both files in their cross-section design, number of blades, helical angles, taper, apical tip size and geometry [5].

Vortex Blue files are manufactured with 1mm maximum flute diameter and convex triangular cross-section. The files are available in two tapers (0.04 and 0.06) and multiple tip sizes (ISO 15-50).

TruNatomy files are manufactured with a slim NiTi wire design with a 0.8 mm maximum flute diameter and regressive taper. TruNatomy file set contains orifice modifier with tip size ISO 20 and fixed 0.08 taper and a glider with centered parallelogram cross-section with tip size ISO 17 and 0.02 taper. The active part is 14mm in length. In addition to three shaping files which are small with tip size of ISO 20 and 0.04 taper, prime with tip size of ISO 26 and 0.04 taper, and medium with tip size of ISO 36 and 0.03 taper. Shaping files have a cutting part of 16mm in length and an off-centered parallelogram cross-section.

Recently, micro-CT analysis became a reliable imaging and assessment tool in the endodontic field. This high-resolution, non-invasive, and non-destructive technology enables the recording and reviewing of three-dimensional views of the root canal system. Micro-CT imaging technology has been recognized as the most accurate research tool for the study of root canal anatomy and the morphological changes in the root canal system after chemo-mechanical instrumentation [6-8]. To our knowledge, only one study in the literature has conducted a comprehensive assessment of Vortex Blue with TruNatomy files [5].

The aim of this study was to evaluate and compare the shaping ability of TruNatomy versus Vortex Blue rotary systems by micro-CT in an ex-vivo model regarding the following parameters: untouched canal walls percentage, changes in surface area, changes in canal volume, changes in dentin thickness, changes in canal angulation and structure model index.

Ethical approval number (108-10-20) was obtained from the Research Ethics Committee, Faculty of Dentistry, King Abdulaziz University. A total of fourty canals were randomly divided into two groups: TruNatomy group TN (n=20) and Vortex Blue group VB (n=20).All teeth were extracted for orthodontic reasons and met specific criteria. Included teeth were sound maxillary first and second double rooted premolars with two distinct canals.Selected teeth had fully mature apices with canal curvature between 10 and 40 degrees according to the Schneider technique [9]. Teeth were cleaned and soaked in full concentration NaOCl for 5 minutes then autoclaved for 40 minutes at temperature of 121°C and pressure of 15 psi. Finally, teeth were stored in normal saline until further use [10]. Simple randomization was done to allocate both buccal and palatal canals into the TN and VB groups.

After access cavity preparation, the canals were located and negotiated to obtain apical patency. Working length was determined by inserting K-file size #10 until it was visually seen at theapical foramen, then the length was shortened by 0.5 mm. A glide path was established using K-file size #15. Instrumentation of both groups was carried out following the manufacturer’s instructions. Three pecking motions used to advance the file at a time while the canal was lubricated with 17% EDTA gel (Meta-Biomed Co. Ltd., South Korea). After each instrumentation cycle, copious irrigation with 3% NaOCl was done to flush out the debris. All procedures were done by the same operator under dental operating microscopy (DOM) and following the same chemo-mechanical protocols. In VB group, canals were instrumented using crown-down preparation technique up to file size 35 and 0.04 taper. In TN group, coronal third was enlarged with the Orifice Modifier. Then, glide path was refined with Glider. Root canal preparation continued using Medium file (size 36 and 0.03 taper).

Irrigation was delivered with a 30- gauge side-vented needle and activated with Ultra-X cordless ultrasonic activator (Eighteeth, China). Finally, prepared canals were flushed with a 3% NaOCl followed by 1ml of 17% EDTA solution. Canals then were irrigated with 2 ml of saline and dried with paper points.

Before instrumentation, clinical crowns of each sample were embedded in a polypropylene tube with PVS impression material (3M™, Minnesota, U.S.A.) leaving the anatomical root area visually exposed. An established reference point was identified while positioning the samples in the micro-stage during pre- and post- scanning inorder to produce a reproductible representation of the data sets. Scanning was acquired using the Bruker SkyScan 1172 high resolution micro-CT (Bruker SkyScan, Kontich, Belgium). Standardized scanner configuration for samples was used with the following parameters: 96kV voltage, 102 µA anode current, 316 ms exposure time, 19.70 µm image pixel size, 0.4 rotation step for 360° angle, frame averaging of 4 for improved signal to noise ratio, random movement of 8 to minimize ring artefacts and the use of Cu+Al filter to reduce beam hardening.After scanning, a reconstruction of the projected images was performed using N-Recon© program version 1.6.9.4 (Bruker Skyscan, Kontich, Belgium) to produce reconstructed cross-section images.

A co-registration data set was saved and loaded in the CTAn© version 1.20.8.0 software for imaging, analysis and quantification of root canal scans before and after instrumentation. The CTVol 2.3.2.0© (Bruker Skyscan, Kontich, Belgium) was used for 3D visualization and production of color-coded images of the samples used in the analysis. Images were then loaded in the IC Measure version 2.00286 software for angle measurement evaluation. Finally, CTVol 2.3.2.0© (Bruker Skyscan, Kontich, Belgium) was used for 3D visualization and production of color-coded images of the samples.

The following parameters were calculated and evaluated to compare the shaping ability of the two file systems: percentage of untouched canal walls, changes in surface area, changes in canal volume, changes in dentin thickness, changes in canal angulation, and SMI [11].

5. Statistical analysis:

Mean and standard deviation (SD) were used to express the data. Shapiro-Wilk test was conducted to test for normality distribution. Independent-Samples T test or Mann–Whitney U test were used to compare parameters between the two systems. Paired-Samples T test or Wilcoxon Signed Rank test were used to evaluate pre- and post-instrumentation differences. One-way ANOVA, then post hoc Tukey’s test were used to compare between the different levels of the root canals in each instrumentation system. All statistical analyses were conducted using the Statistical Package for the Social Sciences (SPSS), Version 20. Significance level was set at P < 0.05.

The qualitative analysis showed that there were no procedural errors after instrumentation in either group, such as instrument separation, perforations, zipping, canal blockage or ledges.

The percentage of untouched surface area, changes in canal surface area and canal volume, changes in SMI and canal angulation are represented in Table 1. The mean untouched surface area showed no statistically significant difference between both groups. The changes in the canal surface area and canal volume produced by the studied files showed no statistically significant differences between both groups Also, no statistically significant difference was found in the changes of SMI between the VB and TN groups.

Changes in canal angulation showed that VB file tends to straighten the root canal curvature while TN file preserves the original canal curvature with almost no changes. However, no statistically significant difference was found in the changes in canal angulation between both groups.

Representative images of the pre- and post-instrumentation 3D reconstructed canals, that were prepared with either VB or TN files, are shown in (Figure 1). Figure 2 shows 3D reconstructed image of the tooth in which the root canal space is represented by grey color, while the untouched canal walls are represented by orange color. Also, it shows the cross-section view of the prepared canals in different root levels (Figure 2).

Table.1. Comparison between the evaluation parameters of both two instrumentation systems.

Parameter	VB Mean ± SD	TN Mean ± SD	P-value
Untouched surface area (%)	27.81 ± 17.46	22.74 ± 16.28	0.2^†
Changes in surface area (mm²)	3.68 ± 2.63	3.27± 1.87	0.6^‡
Changes in canal volume (mm³)	0.97± 0.64	0.76± 0.46	0.2^†
Changes in SMI	0.11± 0.36	0.0008±0.15	0.3^‡
Changes in canal angulation (degree)	1.68 ± 6.81	0.22 ± 3.24	0.4^‡

^†Mann-Whitney U test, ^‡Independent samples t-test.

Changes in dentin thickness measurements are represented in Table.2. The overall changes in dentin thickness were 0.07± 0.012mm in VB group and 0.06± 0.016mm in TN group with no statistically significant difference between both groups in each tested root level. TN group showed significantly less dentin wear in the coronal 7 mm compared to the apical 3mm, while no statistically significant difference was found between the different root canal levels in VB group.

Table 2. Comparison of the dentin thickness changes after preparation by the two instrumentation systems.

This study aimed to assess and compare the shaping and centering ability of two NiTi rotary systems, Vortex Blue versus TruNatomy, using micro-CT analysis in an ex-vivo model.

Mechanical instrumentation of the root canal aims to remove the inner infected layer of dentin, facilitating irrigation delivery and disrupting microbial biofilm [12, 13]. All previous studies showed that, even with the great improvement in the endodontic NiTi rotary files, no file was able to touch all the inner walls of the canal where the untouched surface area ranged between 5 to 80%[14-18].

In the literature, TruNatomy files showed 50-52% of untouched canal surface area which had insignificant difference when compared to Vortex Blue files [5], but significantly higher percentage compared to EdgeFile X3, XP-Shaper, WaveOne Gold, Reciproc Blue, TRUShape and iRace [8, 19, 20]. On the other hand, Vortex Blue files resulted in 55-58% of untouched canal surface area with a significant higher percentage when compared to XP-Shaper and TRUShape [21-23]. The previous studies showed higher percentage of untreated canal walls [19, 20].

The changes in root canal surface area and canal volume after preparation with both VB and TN groups were similar with no significant differences. TruNatomy showed no significant differences in the changes in canal area after instrumentation when compared to Vortex Blue, ProTaper Next, XP-Shaper [5, 19, 24]. Although significantly less changes in canal surface area were observed when TruNatomy was compared to WaveOne Gold, Reciproc Blue, TRUShape and iRace [19]. Vortex Blue files showed no significant difference in canal area after instrumentation when compared to TRUShape, but significantly less changes when compared to XP-Shaper [16, 19]. Also, TruNatomy produced less volume changes when compared to XP-Shaper, WaveOne Gold, Reciproc Blue, TRUShape and iRace [19, 20]. Although, similar volume changes were observed when TruNatomy was compared to Vortex Blue, Edgefile X3 and ProTaper Next [5, 20, 24]. Vortex Blue was found to have the same canal volume changes when compared to TRUShape, ProTaper Next and ProTaper Universal, but less volume changes when compared to XP-Shaper in oval canals [21, 22, 25].

SMI is a morphometric evaluation parameter that is used to assess if the root canal tends to be a plate-like or a cylinder-like shape. In this study, both files tend to preserve the original SMI of the canals with no statistically significant difference after canal instrumentation.

Canal angulation changes after instrumentation were insignificant in both groups. This could be explained by the flexibility of the heat-treated files that makes them suitable for preparing curved canals [26].

Less dentin removal was noticed in the coronal third in both files which support the minimally invasive endodontics concept in preserving the cervical dentin. However, TN group showed significantly less dentin removal in coronal third compared to apical third, while VB group had no significant differences in dentin removal for all root levels. That can be explained by the difference in the files’ taper since TruNatomy had less taper than Vortex Blue files. In the literature, TruNatomy was found to produce similar dentin removal with no significant difference when compared to XP-Shaper and Edgefile X3[20].[14] Vortex Blue showed significantly less dentin removal compared to XP-Shaper, WaveOne Gold, ProTaper Next and ProDesign Logic file system [21, 27].

According to the discussed results, TruNatomy files demonstrated significantly less dentin removal in cervical third compared to the apical third. In contrast, Vortex Blue showed insignificant differences in dentin removal across the different root levels. However, all other evaluation parameters including: the untouched canal surface area percentage, the changes in canal area, the changes in canal volume, SMI, the changes in canal angulation and the overall changes in dentin thickness showed no significant differences between both file systems at of 0.05 P- value level of significant criterion.

The limitations of the present study were primarily related to its ex-vivo study design, which may not fully replicate the real clinical scenario. The experiment was conducted in natural teeth, standardization of the samples could not be done due to minor morphological differences. Also, standardization of the preparation size was done regardless of the initial apical size of each canal. Furthermore, heat-treated files’ behavior can be affected by the body temperature; the presented study was done at room temperature which was around 20-25 C^o.

Future studies could be carried out on a special 3D printed tooth to standardize the evaluated canal geometry and angulation. Also, canal instrumentation could be carried out on body temperature rather than room temperature by using a water bath with a temperature of 30-37C^o.

Within the limitations of this ex-vivo study, it can be concluded that both Vortex Blue and TruNatomy files produced comparable root canal preparation with no considerable shaping mishaps and errors. Both files showed minimum canal straightening after preparation. TruNatomy files removed less cervical dentin than apical dentin. Both files support the concept of minimally invasive endodontics by removing minimum dentin and maintaining the original shape of the treated canals.

Availability of Data and Materials

The datasets generated and/or analysed during the current study are not publicly available due intellectual reasons, but are available from the corresponding author on reasonable request.

Conflict of Interest

The authors declare that there are no conﬂicts of interest.

Authors’ contributions

B.A.: manuscript preparation, writing, reviewing, and editing. MA.H.: manuscript reviewing, and editing. Li.B.: statistical analysis, methodology, and result interpretation. A.A.: laboratory experiment. Le.B.: laboratory experiment, resources supplementation, and data analysis. L.A.: project administration and validation, manuscript reviewing and editing. All authors read and approved the final manuscript.

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No competing interests reported.

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Micro-Computed Tomographic Evaluation of the Shaping Ability of Vortex Blue and TruNatomyTM Ni-Ti Rotary Systems

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