Shaping Performance of XP4 versus ProTaper Next in C-Shaped Canals: A Micro-CT Study of 3D-Printed Mandibular Second Molar Replicas.

Abstract

Introduction: This micro-computed tomography (micro-CT) study aimed to evaluate the shaping ability of two nickel-titanium (NiTi) rotary systems-XP4 and ProTaper Next (PTN)-in 3D-printed replicas of C-shaped canals.

Methods: Two extracted mandibular second molars with C-shaped root canals-one continuous (Melton's Category I) and one discontinuous (Melton's Category II/III)-were selected and replicated via 3D printing. Replica accuracy was validated by best‑fit alignment. Sixteen resin replicas per specimen were randomly assigned to PTN or XP4 instrumentation (n = 8 per group) following the manufacturers' protocols. Pre- and post-instrumentation micro-CT scans were performed. Three-dimensional registration and reconstruction enabled quantitative analysis of (1) volume/surface area changes and (2) unprepared canal surfaces.

Results: The replicas demonstrated high fabrication fidelity. In continuous C-shaped canals, PTN removed significantly less resin (2.7 mm³, 7.4% of initial volume) than XP4 (4.3 mm³, 11.6%; p < 0.01). Conversely, in discontinuous C-shaped configurations, PTN exhibited greater removal (13.0 mm³, 23.1%) versus XP4 (8.9 mm³, 15.8%; p < 0.01). Unprepared canal surface in continuous C replicas was higher with PTN (42.0%) than XP4 (25.5%; p < 0.01), whereas no significant difference was observed in discontinuous C replicas (PTN: 32.0%, XP4: 31.6%; p > 0.05). Procedural complications were observed exclusively in discontinuous C-shaped canals, with PTN causing two cases of critical wall thinning and XP4 exhibiting two instrument separations.

Conclusion: In continuous C-shaped canal replicas, XP4 showed superior shaping capability with significantly lower percentages of unprepared surface compared to PTN. In discontinuous C-shaped configurations, both systems achieved comparable unprepared surface areas, although they differed markedly in resin removal patterns and iatrogenic risks. These results indicate that the relative performance and safety profiles of NiTi systems may vary depending on specific C-shaped canal anatomy. Clinicians should consider canal configuration, curvature severity, and dentin thickness when selecting instruments for C-shaped canal instrumentation.