Comparative In Vitro Assessment of Original Reciproc® Blue Instruments vs. Two Replicas: Mechanical Characteristics, Safety, and Efficacy Analysis

Background/Objectives: To compare mechanical behavior, shaping performance, and safety of an original reciprocating endodontic instrument (Reciproc® Blue) with two visually similar replicas obtained from an online marketplace. Methods: The original Reciproc® Blue and two replica (designated Replica 1 and Replica 2) instruments purchased from AliExpress were tested. Evaluations included torque resistance, bending resistance, cyclic fatigue resistance (all according to ISO 3630-1 standards, n = 10 per group per test), and an in vitro shaping procedure using artificial root canals in plastic blocks (5 canals per instrument, n = 10 instruments per group) were carried out. Preparation time, number of pecks, procedural errors (blockages, ledges, deformations), and instrument fractures were recorded. Surface characteristics of unused (n = 2) and used instruments (n = 2) were examined using scanning electron microscopy (SEM). Statistical analysis used one-way ANOVA, Welch ANOVA, or Kruskal–Wallis tests according to the distribution and variance pattern of each endpoint, followed by the corresponding post hoc test. Repeated use was analyzed with a linear mixed effects model and checked with a robust generalized estimating equation sensitivity analysis. Deformation-free and fracture-free event curves were compared with exploratory log rank tests. Results: The original instrument showed the highest Mf/D3 and Mt/D3 values. Overall group differences were significant for Mf/D3 (Welch p < 0.001) and Mt/D3 (Welch p = 0.001), with significant Games Howell contrasts between the original and Replica 2. Replicas showed longer cyclic fatigue life (Original 407.1 s, Replica 1 490.2 s, Replica 2 607.8 s; ANOVA p < 0.001). The original instrument had a lower average preparation time for each canal than both replicas (72.8 s vs. 95.8 s and 92.3 s; Kruskal–Wallis p < 0.001) and a lower average number of pecks (8.64 vs. 9.71 and 10.00; p = 0.008). Exploratory log rank comparisons also showed group differences in the deformation-free and fracture-free event curves (Holm adjusted p = 0.005 and p = 0.024, respectively). Both replicas failed to reach working length in 4 out of 10 cases each, with high rates of blockages (Replica 1: 7/10; Replica 2: 2/10), ledges (Replica 1 only), and deformations. The limited SEM subsample revealed severe wear of cutting edges in Replica 1. Conclusions: Both tested replicas exhibited significant deviations in mechanical behavior and markedly inferior shaping safety compared to the original Reciproc® Blue instrument, despite superficial visual similarity. Therefore, dental practitioners should be aware that low-cost imitations may compromise clinical safety.