We would like to express our sincere gratitude to Bogazici University for providing the laboratory facilities and technical support necessary for this research. We also thank Dr. Demet Sezgin Mansuroglu, Dr. Eda Karadogan, and Dr. Mustafa Enes Ozden for their valuable assistance in data collection and analysis. The research was funded by the authors. No external financial support was obtained.

1. Sample procurement
<ol>
	<li>Procure 80 acrylic blocks with an internal diameter of 1.5 mm, a radius of curvature of 5 mm, a 55&#176; curvature, and a working length of 16 mm.</li>
</ol>
2. Cleaning and shaping procedure
<ol>
	<li>Set the endomotor to a torque of 2.0 Ncm and a speed of 300 rpm.
	<ol>
		<li>Attach a 10/.04 taper file to the motor and use it in a back-and-forth motion until the working length (16 mm) is reached, ensuring that it does not bind...

Surface Defects in NiTi Files After Single and Multiple Uses in Endodontic Retreatment

This study evaluated the presence and types of microscopic defects on the external surfaces of Remover files after single, triple, and six-times use in acrylic blocks simulating curved canals. Ideally, human teeth are recommended for use in studies evaluating the fracture resistance of files to better simulate clinical use28. In their study, Peters and Barbakow29 found an increase in fracture initiation and propagation rates in instruments used in blocks compared to extract...

Endodontic retreatment is a procedure performed when a previously treated tooth fails to heal or develops new pathologies, such as persistent infection, reinfection, or missed anatomy. The procedure involves the removal of the existing root canal filling material, thorough cleaning and disinfection of the canal system and subsequent refilling1,2.
Nickel-titanium (NiTi) instruments are of great importance in improving and facilitating endodontic procedures due to their flexibility and high cutting efficiency3,4. The superelasticity of NiTi instruments permits them to better adapt to canal curvature, exhibit less wear, and have a higher resistance to fracture5,6. However, one of the major concerns with NiTi files is that they can fracture without visible deformation3.
The most common cause of fracture in NiTi rotary instruments is cyclic fatigue7. Cyclic fatigue occurs due to alternating tensile and compressive stresses on opposing surfaces of the instrument as it rotates continuously in a curved root canal without binding8,9. Fracture due to cyclic fatigue results from metal exhaustion10. Several factors influence the occurrence of fracture due to cyclic fatigue, including the physical properties of the instrument11,12, the root canal morphology13, repeated clinical use, and the sterilization process14,15. Therefore, to improve the fatigue resistance of NiTi rotary files, various modifications in the manufacturing method and core diameter, as well as changes in the cutting-edge and cross-sectional designs, have been attempted16. The Remover file is a new generation file produced by thermal treatment and a special electropolishing process called C-wire. Its design features are claimed to increase fatigue resistance. The file has a 30/100 mm non-cutting (inactive) tip and a minimally invasive core diameter. It is manufactured with a variable triple helix cross section that is symmetrical for the first 3 mm and then becomes asymmetrical towards the shaft. In addition, it is designed to preserve periradicular dentin by having a 7% taper in the first 10 mm, followed by a 0% taper towards the shaft17.
Cyclic fatigue fractures in NiTi rotary files typically occur without any visible plastic deformation18,19,20. As a result, these fractures cannot be evaluated clinically, and structural changes must be examined under high magnification using tools such as a stereomicroscope or scanning electron microscope (SEM)21. Due to the impracticality of performing such examinations on a routine basis, manufacturers recommend that files be used only once22,23. However, due to the high cost of NiTi files, many clinicians choose to reuse them24. Therefore, it is important to investigate the effects of clinical reuse on these files. One clinical study showed that rotary instruments can be safely reused up to 4x25. However, other studies have evaluated much higher reuse rates and there is no consensus on how many times a file can be safely reused24,26.
In previous studies that have evaluated the reuse of NiTi files, the primary focus has been on the effects of root canal widening and shaping on the fracture resistance of the files. A review of the literature, therefore, reveals that there is only one study that specifically evaluates the repeated use of retreatment file systems27. The aim of this study is to evaluate the impact of repeated use on the surface characteristics of the Remover file using scanning electron microscopy (SEM). It is hypothesized that increased clinical use will result in an increase in surface defects, thereby elevating the risk of fatigue fractures. The specific objective is to analyze the changes in surface defects of the Remover file after single and multiple uses, and to discuss the implications of these changes for clinical practice.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Acrylic block</td>
			<td>ArdaDent Medical,Ankara,Turkey</td>
			<td></td>
			<td>for obturation</td>
		</tr>
		<tr>
			<td>DiaRoot Biosealer</td>
			<td>DiaDent, South Korea</td>
			<td>BS23101161</td>
			<td>for obturation</td>
		</tr>
		<tr>
			<td>DualMove Endomotor</td>
			<td>MicroMega, Coltene, France</td>
			<td>52002023</td>
			<td>for preparation</td>
		</tr>
		<tr>
			<td>&#160;EndoArt&#160; Smart Gold&#160;</td>
			<td>EndoArt, Inci Dental, Turkey</td>
			<td>SGK10114</td>
			<td>&#160;for initial preparation</td>
		</tr>
		<tr>
			<td>&#160;Gutta Percha</td>
			<td>EndoArt, Inci Dental, Turkey</td>
			<td>GD23080701</td>
			<td>for obturation</td>
		</tr>
		<tr>
			<td>Quattro ESEM&#160;</td>
			<td>Thermo Fisher Scientific, USA</td>
			<td></td>
			<td>SEM analysis</td>
		</tr>
		<tr>
			<td>Paper Points</td>
			<td>Dentsply Maillefer, Ballaigues, Switzerland&#160;</td>
			<td>1I0305</td>
			<td>for dry to root canal</td>
		</tr>
		<tr>
			<td>Remover File</td>
			<td>MicroMega, Besan&#231;on, France</td>
			<td>891144/873757/</td>
			<td>for retreatment procedure</td>
		</tr>
		<tr>
			<td>Sodium Hypochlorite&#160;</td>
			<td>Saba Chemical&#38;Medical, Turkey</td>
			<td>3010225</td>
			<td>for irrigation</td>
		</tr>
		<tr>
			<td>SPSS v29&#160;</td>
			<td>IBM SPSS Corp, Armonk, New York, USA</td>
			<td></td>
			<td>Statistical analysis</td>
		</tr>
	</tbody>
</table>

scanning electron microscopic evaluation of surface defects of remover retreatment file after single and multiple uses

This study aimed to evaluate surface defects of Remover rotary Nickel-Titanium (NiTi) files after single and multiple uses in conventional endodontic retreatment procedures using scanning electron microscopy (SEM). Eighty acrylic blocks, simulating root canals with a 1.5 mm internal diameter, a 5 mm radius of curvature, and a 55&#176; curvature, were utilized. After chemomechanical preparation and obturation, 24 new Remover files (N30, 7%, L23) were randomly assigned to three groups: single use, triple use, and six uses. The files were operated at 600 rpm with a torque of 2.5 Ncm, cleaned, and sterilized after each use.
SEM analysis at magnifications of 100x, 250x, and 500x revealed surface defects, including tip deformation, microcracks, fracture, unwinding, surface pitting, and blade disruption. Deformation was observed in 75% of the files after a single use and in 100% of the files after three and six uses. Microcracks were absent after single use but appeared in 25% and 87.5% of files after three and six uses, respectively, showing a statistically significant increase (p &#60; 0.001). Surface pitting also significantly increased among groups (p = 0.004).
No fractures were observed in any group. The most common defects were tip deformation (91.7%) and surface pitting (70.8%). The findings suggest that repeated use of NiTi files significantly increases surface defects, elevating the risk of fatigue fractures. Thus, the results recommend limiting the reuse of Remover files to a maximum of 3x. Further research is needed to correlate defect types with anatomical factors and to assess file effectiveness in retreatment scenarios.

Author Spotlight: Evaluation of Surface Integrity and Safe Usage Limits of the Remover Retreatment File

Scanning Electron Microscopic Evaluation of Surface Defects of Remover Retreatment File After Single and Multiple Uses

Deformation was observed in 75% of files after single use and in 100% of files after three and six uses, but the differences between the groups were not statistically significant (Table 1). The evaluation of deformation types among groups is shown in Table 2. When the types of deformation were evaluated separately, no microcracks were observed after a single use, while microcracks were observed in 25% of the files after three uses and in 87.5% of the files after six uses; this difference...

Here, we present a protocol for evaluating the surface characteristics of endodontic retreatment files after repeated use in retreatment procedures, utilizing scanning electron microscopy to identify and analyze potential surface defects.

This study aimed to evaluate surface defects of Remover rotary Nickel-Titanium (NiTi) files after single and multiple uses in conventional endodontic ...

scanning-electron-microscopic-evaluation-surface-defects-remover

Scanning Electron Microscopic Evaluation of Surface Defects of Remover Retreatment File After Single and Multiple Uses

Abstract