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

Summary

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.

Abstract

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° 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 < 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.

Introduction

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 refilling^1,2.

Nickel-titanium (NiTi) instruments are of great importance in improving and facilitating endodontic procedures due to their flexibility and high cutting efficiency^3,4. The superelas....

Protocol

1. Sample procurement

1. Procure 80 acrylic blocks with an internal diameter of 1.5 mm, a radius of curvature of 5 mm, a 55° curvature, and a working length of 16 mm.

2. Cleaning and shaping procedure

1. Set the endomotor to a torque of 2.0 Ncm and a speed of 300 rpm.
   1. 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.
   2. Irrigate the canals with 5.25% NaOCl.
   3. Attach a 15/.04 tapered file to the motor and use it in a back-and-forth motion until th....

Results

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.......

Discussion

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.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acrylic block	ArdaDent Medical,Ankara,Turkey		for obturation
DiaRoot Biosealer	DiaDent, South Korea	BS23101161	for obturation
DualMove Endomotor	MicroMega, Coltene, France	52002023	for preparation
EndoArt  Smart Gold	EndoArt, Inci Dental, Turkey	SGK10114	for initial preparation
Gutta Percha	EndoArt, Inci Dental, Turkey	GD23080701	for obturation
Quattro ESEM	Thermo Fisher Scientific, USA		SEM analysis
Paper Points	Dentsply Maillefer, Ballaigues, Switzerland	1I0305	for dry to root canal
Remover File	MicroMega, Besançon, France	891144/873757/	for retreatment procedure
Sodium Hypochlorite	Saba Chemical&Medical, Turkey	3010225	for irrigation
SPSS v29	IBM SPSS Corp, Armonk, New York, USA		Statistical analysis