An in vitro comparison of alterations in surface topographies of three different rotary files after root canal preparation with different irrigating solutions: Atomic force microscopic study

Abstract

Objectives:

The objective of the study was to evaluate and compare the surface topographies of WaveOne Gold (WOG), FlexiCON X1, and EdgeOne Fire (EOF) reciprocating files before and after root canal instrumentation using different irrigating solutions.

Materials and Methods:

Forty-eight extracted mandibular molars were selected and randomly assigned into three groups (n = 16) based on the file system used and each group was divided into two subgroups based on the irrigants used during root canal treatment. (Group-1: WOG; Group-2: FlexiCON X1; Group-3: EOF; Subgroup-A: 3% sodium hypochlorite [NaOCl] +17% ethylenediaminetetraacetic acid [EDTA]; Subgroup-B: Citra wash as irrigating solutions). The surface topography of the files was analyzed using atomic force microscope before and after instrumentation. Average roughness and root mean square roughness were calculated. Independent and paired t-tests and one-way analysis of variance with Tukey's post hoc were used for statistical analysis.

Results:

Atomic force microscopy results showed an increase in surface roughness after instrumentation, EOF showing the highest roughness. Citra wash showed more roughness compared to NaOCl and EDTA together. However, the surface roughness between the experimental groups WOG and EOF are statistically insignificant and this insignificance was also seen among subgroups (P>0.05).

Conclusion:

Instrumentation with various irrigating solutions affected the surface topography of EOF, WOG, and FlexiCON X1 reciprocating files.

INTRODUCTION

One of the most important steps that form the foundation of a successful root canal treatment is cleaning and shaping. Despite having superior properties, nickel–titanium (NiTi) files are also being separated in the root canals without any prior signs of permanent deformation, thereby reducing the success rate of root canal treatment.[1]

NiTi files with different heat treatments and cross-sectional designs have been introduced to increase the fracture resistance during clinical use. Several NiTi files have been introduced with reciprocating motion, as they show lesser amount of surface deformation or irregularities of the files, thereby increasing their fracture resistance and life span.[2]

WaveOne Gold (WOG) (Dentsply Maillefer, Baillagues, Switzerland) is a gold-treated single-file system with a parallelogram cross-section and an off-center design, manufactured using several heating–annealing cycles in the gold alloy after milling.[3] Available in four different sizes; as small - #20, primary - #25, medium - #35, and large - #45 with variable tapers. EdgeOne Fire (EOF) (EdgeEndo, Albuquerque, New Mexico, USA) files have a similar cross section to WOG and are manufactured using an annealed heat-treated NiTi alloy, brand named FireWire™, which offers high flexibility. These are available in four different sizes; as small - #20, primary - #25, medium - #35, and large - #45, with variable tapers.[4] FlexiCON X1 files (EdgeEndo, Albuquerque, New Mexico, USA) are now available as Edge files X1 files.[5] These files are also manufactured using FireWire™ NiTi alloy, with a parabolic cross section. According to the manufacturer, these files yield a better performance in terms of durability and incredible flexibility. These files are available in three sizes 20, 25, and 40.

Among the major concerns with the clinical use of NiTi rotary instruments is the potential for unexpected fracture during root canal preparation, even in the absence of any previously visible defects or deformations on the instrument surface. Several factors, such as manufacturing process, alloys used, fatigue of the files, root canal preparation with different irrigants, cause wear and deform the files, altering the surface topography of NiTi files, and leading to the decrease in fracture resistance.[6] Hence, it is essential to have knowledge of the surface topography of the endodontic files before and after their clinical use, as the defects and irregularities on the files surface caused during canal preparation may result in instrument failure on prolonged use.

Atomic force microscopy (AFM) has become a popular and documented technique for imaging three-dimensional surfaces and interfaces of a wide variety of materials.[7] Unlike scanning electron microscopy (SEM), AFM analyzes materials both qualitatively and quantitatively. AFM has several advantages over SEM, it works equally well on conducting and insulating surfaces and may be employed under ambient conditions in air, liquid, and in vacuum. In SEM, fragile samples are damaged by harsh sample preparation techniques such as sputtering, dehydration, and exposure to vacuum. Artifacts associated with such techniques can be avoided while using AFM.

To date, no studies have compared the surface topographies of WOG, FlexiCON X1, and EOF files. Therefore, the objective of this study was to evaluate and compare the effect of sodium hypochlorite (NaOCl) with ethylenediaminetetraacetic acid (EDTA) and Citra wash (20% citric acid) irrigating solutions on the surface topographies of three different reciprocating file systems using AFM. In particular, average roughness (Ra) and root mean square (RMS) values of instrument surfaces were analyzed.

MATERIALS AND METHODS

All the sample size was calculated based on the formula given below:

n = r + 1/r (standard deviation [SD])² (Z beta + Z alpha/2)²/(mean difference)².

Forty-eight freshly extracted mandibular molars with mesial canals having an apical curvature of 0°–20° by the Schneider method were included in this study and stored in 0.9% saline until further use.[8] Conventional access cavities were prepared, and working length was determined using 15-size K-files. All samples were embedded in self-cure acrylic resin and randomly assigned into three groups (n = 16) based on the reciprocating file system used. Each group was divided into two subgroups based on the irrigants used during root canal preparation.

• Group 1: WOG files

• Group 2: FlexiCON X1 files

• Group 3: EOF file.

• Subgroup A: 3% NaOCl and 17% EDTA as irrigating solutions

• Subgroup B: Citra wash (20% citric acid) as irrigating solution.

Samples in each group (n = 16) were prepared using four primary-sized (size #25) files of the respective file system assigned to each group (1 file = 4 mesiobuccal canals). Samples were prepared according to the manufacturer's instructions using X-SMART plus endo motor (Dentsply Maillefer, Switzerland). In half of the samples from each group, canals were irrigated with 3% NaOCl and 17% EDTA using a 30 gauge side-vented irrigation needle (RC-Twents; Prime) and in the remaining samples, canals were irrigated with 20% citric acid (Citra wash; Prime). All samples were finally irrigated using 5 ml of 0.9% saline.

Before and after the root canal instrumentation, files were ultrasonically cleaned for 3 min. Surface topography of four primary size files from each file system was analyzed, at 3 mm from the tip of the file, using an Atomic force microscope (A–100, A. P. E. Research, Italy). Ra and RMS values of the files were recorded before and after the instrumentation and the obtained data was processed using Gwyddion software version 2.61 [Figures 1 and 2].

Figure 1.

AFM images of three reciprocating files before instrumentation in 10 μm × 10 μm. (a) WaveOne Gold, (b) FlexiCON X1, (c) EdgeOne Fire (μm = micrometers)

Figure 2.

AFM images after instrumentation using different irrigants. (a) WaveOne Gold with NaOCl and EDTA, (b) WaveOne Gold with Citrawash, (c) FlexiCON X1 with NaOCl and EDTA, (d) FlexiCON X1 with Citrawash, (e) EdgeOne Fire with NaOCl and EDTA (f) EdgeOne Fire with Citrawash

Statistical analysis

Data were analyzed using IBM SPSS version 20 software (IBM SPSS, IBM Corp., Armonk, NY, USA) at a significance level of 5%. Independent t-tests, one-way analysis of variance (ANOVA) with Tukey's post hoc, and paired t-tests were done to analyze the data.

RESULTS

The means and SD of Ra and RMS values were shown in Tables 1 and 2 and depicted in Graphs 1 and 2, respectively.

Table 1.

Comparison of pre- and postinstrumentation average roughness within each group based on the irrigant used

Group	Irrigant	Pre/post	Mean	SD	SE	P
WOG	3% NaOCl +17% EDTA	Pre	173.00	15.556	11.000	0.548
		Post	210.00	52.326	37.000
	Citra wash	Pre	154.50	103.945	73.500	0.832
		Post	194.00	89.095	63.000
FlexiCon X1	3% NaOCl +17% EDTA	Pre	18.00	0.000	0.000	0.277
		Post	44.50	17.678	12.500
	Citra wash	Pre	34.50	13.435	9.500	0.174
		Post	75.50	7.778	5.500
EOF	3% NaOCl +17% EDTA	Pre	179.00	35.355	25.000	0.449
		Post	211.00	8.485	6.000
	Citra wash	Pre	200.50	16.263	11.500	0.283
		Post	235.00	16.971	12.000

Paired t-test; P≤0.05 considered statistically significant. SD: Standard deviation, SE: Standard error, WOG: WaveOne Gold, EOF: EdgeOne Fire, EDTA: Ethylenediaminetetraacetic acid, NaOCl: Sodium hypochlorite

Table 2.

Comparison of pre- and postinstrumentation root mean square roughness within each group based on the irrigant used paired t-test; P≤0.05 considered statistically significant

Group	Irrigant	Pre/Post	Mean	SD	SE	P
WOG	3% NaOCl +17%EDTA	Pre	206.00	0.000	0.000	0.431
		Post	279.50	84.146	59.500
	Citra wash	Pre	219.50	125.158	88.500	0.826
		Post	283.50	176.070	124.500
FlexiCon X1	3% NaOCl +17% EDTA	Pre	24.50	0.707	0.500	0.315
		Post	56.00	24.042	17.000
	Citra wash	Pre	45.00	18.385	13.000	0.2
		Post	88.00	9.899	7.000
EOF	3% NaOCl +17% EDTA	Pre	215.50	47.376	33.500	0.42
		Post	261.00	9.899	7.000
	Citra wash	Pre	239.00	15.556	11.000	0.277
		Post	268.50	12.021	8.500

SD: Standard deviation, SE: Standard error, WOG: WaveOne Gold, EOF: EdgeOne Fire, EDTA: Ethylenediaminetetraacetic acid, NaOCl: Sodium hypochlorite

Graph 1.

Comparison of preinstrumentation and postinstrumentation average roughness within each group based on the irrigant used

Graph 2.

Comparison of preinstrumentation and postinstrumentation root mean square roughness within each group based on the irrigant used

• All the three file systems showed an increase in the surface roughness after instrumentation. EOF showed the highest, FlexiCON X1 files showed the least amount of surface roughness among all experimental groups both before and after the instrumentation. Citra wash showed more roughness compared to NaOCl and EDTA together. However, the surface roughness between the experimental groups WOG and EOF are statistically insignificant and this insignificance was also seen among subgroups (P>0.05).

• Before and after root canal treatment, one-way ANOVA with post hoc analysis for multiple pairwise comparisons, there were significant differences between all possible pairs except between WaveOne Gold and EdgeOne Fire

• Independent Student's t-test was used for comparison of preinstrumentation and post instrumentation study parameters, respectively, within each group based on the irrigant used and no significant differences were observed.

DISCUSSION

The visual inspection of NiTi files is not considered a reliable method for assessing used files since NiTi rotary files may fracture during clinic use, within the elastic limits, without any prior sign of permanent deformation. During cleaning and shaping, NiTi files give up their surface contents and wear upon usage due to mechanical friction between file and dentin and due to irrigants used during preparation cause surface defects such as scratches and microcracks, leading to file separation.[9] Various defects seen are pitting, metal flash, and grinding marks which act as stress concentration points, reducing the fracture resistance.[10] Assessing the change in the surface topography of files during instrumentation is important and tells a lot about the instrument safety during the clinical use of the files.

In the present study, extracted mandibular molars, with mild-to-moderate apical curvatures, were selected to better represent common clinical conditions. Previous studies had used artificial canals made of acrylic, which minimizes the variations among samples, but they do not match the hardness values of natural teeth.[11,12] It has also been reported that the heat generated during canal preparation melts the acrylic and gets accumulated in the flutes of the files.[13]

The manufacturer recommends the files to be used only once. Using only once does not mean that usage of file for a single canal; a single use file can be used in a molar tooth with 3-4 canals.[14] In the present study, four mesiobuccal canals of four different mandibular molars were instrumented using each test file. A single operator prepared all the canals to eliminate the interoperator variable.

According to the results obtained, no statistical difference was found in the surface porosity between unused WOG and EOF files. The difference in Ra and RMS values of unused files is due to their different manufacturing and finishing processes.

WOG files are manufactured using thermomechanically heat-treated NiTi gold wire which is subjected to the proprietary postmachining heat processes after being ground by machine.[15] FlexiCON X1 and EOF files are manufactured using an annealed, heat-treated, cryogenically tempered NiTi alloy known as FireWire™.[16] In this study, FlexiCON X1 group had showed the least amount of surface roughness, because of the electropolishing process done additionally during manufacturing of FlexiCON X1 files. FireWire™ alloy also povides more torsional resistance to the instruments than the Gold Wire alloy (Bhandi S et al.). [17,18]

After the preparation, used files showed increase in surface roughness. The results of the current study are in line with the findings of AlRahabi and Atta and Zafar as both studies reported an increase in the surface roughness values following endodontic instrumentation.[14,19]

The increase in surface porosity observed in all the three groups of files after use suggests that the files deteriorate with clinical use. Files with higher surface roughness are more prone to surface deterioration and initiate crack formation, which can lead to file breakage.[20] Pereira et al. observed similar findings in different new NiTi files and found the presence of marks left by the machining process during manufacturing and the propagation of transverse cracks 3 mm from the tip after clinical use.[21]

Increase in surface roughness of WOG files after instrumentation was in line with a previous study done by Bhatia et al.[22] This may be due to the formation of a less passive surface layer on the WOG as compared to Twisted File Adaptive (TFA) and XP EndoShaper (XPS) systems.

The higher amount of surface roughness of EOF and WOG files, when compared to FlexiCON X1, might be due to their use as a single file system in the canal and their greater taper in the apical region. In contrast, FlexiCON X1 file system is not a single file system requiring the usage of multi[le files with a constant taper of 6%. This features reduces the friction between files and radicular dentin, thereby reducing the surface roughness.

The cross section of an instrument also plays an important role in the deterioration of surface characteristics and other features of the file. In the present study, higher amount of surface roughness in EOF and WOG files might be due to their parallelogram cross section, which contributes to the bulk of the instrument when compared to parabolic cross section of FlexiCON X1 files.

Based on AFM results, files instrumented using Citra wash as an irrigant showed higher surface roughness values, compared to those instrumented with NaOCl + EDTA as irrigating solutions.

Ametrano et al. evaluated the surface topographic changes of ProTaper instruments immersed in 5.25% NaOCl and 17% EDTA solution for 5 min and 10 min using AFM and concluded that the samples immersed for a longer duration of time showed greater increase in roughness.[23] They also showed that EDTA caused more amount of roughness than NaOCl. The results of the present study are in accordance with other studies, which reported that NaOCl and EDTA were associated with deterioration of the file surface, as a result of a chemical reaction creating surface roughness.[24]

Increased surface roughness in the Citra wash subgroup, might be due to its low pH of 2.80. Eldeniz et al. evaluated the effect of EDTA and citric acid solutions on root dentin roughness.[25] When compared with EDTA, citric acid showed the increased surface roughness of root dentin because of the low pH of citric acid. This might be the reason for the increased surface roughness of files in the present study. Insignificant difference in results between the two irrigant subgroups was because of the short-term action of the irrigant on the NiTi files, which is not sufficient to trigger cracks and cause superficial changes.

This is the first and foremost study to be conducted on the Citra wash and to evaluate the surface roughness of FlexiCON X1 and EOF files using AFM. Additional studies are required to test the effect of Citra wash on the surface roughness, corrosion, and other physical properties of NiTi files and also to determine its effectiveness as an irrigating solution. Further, evaluation of surface topographies of investigated files in different clinical conditions, with a larger sample size, is required.

CONCLUSION

Within the limitations of the present study:

• All the three file systems showed an increase in the surface roughness after instrumentation

• After the root canal instrumentation, EOF files have shown the highest amount of surface roughness, followed by WOG and the least in FlexiCON X1 files

• Citra wash irrigant has been shown to induce more amount of surface roughness compared to NaOCl and EDTA, although no significant differences were found among them.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.