The ONE File: Design Concept and Finite Element Analysis of a Novel Sixth-Generation 3D-Printed Thermoplastic Polyurethane Hollow Lattice Endodontic Instrument with Combined Rotational-Vibrational Motion.

OBJECTIVES: Endodontic instrumentation has evolved through five technological generations, each addressing shortcomings of its predecessor. This study proposes the theoretical construct of a sixth generation - the ONE File - a 3D-printed thermoplastic polyurethane (TPU) hollow diamond-lattice endodontic instrument designed for combined rotational-vibrational motion. We aimed to evaluate, through finite element analysis (FEA), the stress distribution, deformation behaviour, and biomechanical safety of the ONE File compared with a ProTaper Gold F2 instrument (PTG-F2; Dentsply Sirona, Ballaigues, Switzerland; D00.25 mm, taper 0.08, Gold-wire heat-treated NiTi). METHODS: A parametric CAD model of the ONE File (diamond-cell hollow lattice, D0= 0.25 mm, ISO 25/.04 taper, 16 mm active length) was analysed in Ansys Workbench 2023 R2. TPU was modelled with a hyperelastic Mooney-Rivlin constitutive model (C1= 0.822 MPa, C2= 0.206 MPa) and NiTi with the Auricchio superelastic model. A 35° curved canal model (5 mm radius, micro-CT derived) was used. Combined loading - rotation at 300 RPM and axial vibration at 30 Hz (0.5 mm amplitude) - was applied to the ONE File; standard rotation at 300 RPM was applied to the NiTi Control Group (PTG-F2). Outcome variables included maximum von Mises stress, total deformation, predicted geometric contact coverage, and safety factor. RESULTS: The ONE File demonstrated maximum von Mises stress of 4.2 MPa (6.8-13.5% of TPU tensile strength; safety factor 7.4-14.8) compared with 487 MPa for the NiTi Control Group (PTG-F2) (87% of yield strength; safety factor 1.15-1.6). Predicted geometric contact coverage was 94.3% versus 61.8%. Total tip deformation was 0.38 mm (fully elastic) for the ONE File versus 0.12 mm with 0.02 mm residual plastic strain for NiTi. The stress concentration factor was 1.18 for the ONE File versus 3.42 for NiTi. SIGNIFICANCE: Within the limitations of FEA, the ONE File demonstrates superior biomechanical safety, elastic adaptability, and theoretical canal wall coverage compared with conventional NiTi. As a Phase 0 translational concept, it requires in vitro fabrication and tribological validation before any clinical inference is drawn.