Assessment of fracture behaviour in heat treated NiTi rotary endodontic files following multiple uses: An in-vitro study

• Author Details:   
• Parvathy Narayanan ^*
• Ravi SV
• Elsy P Simon
• Chandini Raveendran
• Sarin Koroth

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Aim and Objectives: Evaluate the fracture behaviour and warning signs (e.g., deformation) of two heat?treated nickel–titanium rotary files—EdgeEndo and TorqueEndo—during repeated simulated clinical use, and determine whether fracture risk differs between them.

Introduction: Nickel-titanium (NiTi) rotary endodontic files have revolutionized root canal therapy due to their superior flexibility and shape memory. However, despite advancements in heat treatment technologies that enhance their mechanical properties, these instruments remain susceptible to fracture, especially after repeated clinical use. Understanding the fracture behaviour of heat-treated NiTi files is essential for improving their safety and durability. This in-vitro study aims to assess how multiple uses influence the fracture resistance and failure modes of these instruments under simulated clinical conditions.

Materials and Methods: This in?vitro pilot study used 16 extracted maxillary first premolars with ~5° curvature (n?=?8 per file type). Each file was used up to 16 times or until fracture, following crown?down preparation, standard irrigation, and sterilization protocol. Files were inspected at 10× magnification after each use for permanent deformation or micro cracks. Fisher’s Exact Test was applied for statistical analysis due to the small sample size (??=?0.05).

Results: Edge Endo: 5 fractures; 4 preceded by bending, Torque Endo: 6 fractures; all preceded by deformation. No significant difference in fracture frequency was found (p?=?0.64). Warning signs typically appeared after approximately six uses.

Conclusion: Both file systems displayed visible warning signs—primarily bending—prior to fracture. No conclusive difference in fracture risk was observed, although this pilot study is limited by size, canal allocation bias, and its in?vitro setup. These findings support further large-scale, randomized studies with microstructural documentation.

Keywords: Cyclic fatigue resistance, File separation, Heat treatment, Microstructural analysis