Comparative evaluation of the shaping performance of three NiTi rotary systems in distolingual canals of 3D-printed three-rooted mandibular first molars

Introduction: study compared the shaping ability of three nickel-titanium (NiTi) rotary systems in distolingual (DL) canals using 3D-printed three-rooted mandibular first molar (3RM1) replicas. Materials and methods: Two extracted 3RM1s with DL roots (curvatures: 21.9 ° and 37.5 °) were selected and replicated via 3D printing. Eighteen resin replicas per specimen were equally divided into three groups for instrumentation with OneShape (OS), WaveOne Gold (WOG), or ProTaper Universal (PTU), following manufacturers' protocols. Micro-computed tomography (micro-CT) scans were performed before and after DL canal instrumentation. Canal straightening, volume/surface area changes, maximum cutting thickness (MCT), and residual wall thickness (RWT) at cervical and furcation regions were analyzed. Results: PTU cause the most canal straightening (Specimen 1 replicas: 5.4 ± 0.4 °; Specimen 2 replicas: 11.0 ± 1.5 °), largest increases in canal volume (Specimen 1 replicas: 106.9 ± 41.0%; Specimen 2 replicas: 174.6 ± 26.8%) and surface area (Specimen 1 replicas: 40.3 ± 17.5%; Specimen 2 replicas: 60.0 ± 16.7%), thinnest RWT and highest MCT (Specimen 1 replicas: 0.28 ± 0.04 mm; Specimen 2 replicas: 0.39 ± 0.04 mm). Conversely, WOG showed minimal canal straightening (Specimen 1 replicas: 2.5 ± 0.40 °; Specimen 2 replicas: 4.8 ± 1.5 °), the least canal enlargement (Volume: 30.8 ± 13.1% and 78.6 ± 35.3%; Area: 10.1 ± 8.8% and 23.6 ± 15.3%), greatest RWT, and lowest MCT (Specimen 1 replicas: 0.20 ± 0.04 mm; Specimen 2 replicas: 0.30 ± 0.07 mm). OS performed intermediately. MCT consistently occurred at 2-3 mm below the furcation. Conclusion: Both single-file systems (WOG and OS) effectively shaped DL canals while maintaining proper geometry. However, OS requires caution in severe curvatures. PTU's aggressive cutting caused excessive resin removal, limiting its DL canal suitability.