Scanning electron microscopy evaluation of external surface defects in different nickel-titanium endodontic instruments
Authors
Gianluca Gambarini, Massimo Galli, Maya Feghali, Raffaella Castagnola, Nicola Maria Grande
Abstract
The aim of this study was to evaluate the presence and relevance of surface defects in each of five widely used NiTi systems: I-File ( Henry Schein Endodontics, which is also commercialized as Onyx , EdgeEndo, USA ), Mtwo ( Sweden Martina, Italy) , WaveOne Gold (Dentsply, USA) Reciproc Mwire, and Reciproc Blue (VDW, Germany). Each group uses a different type of alloy and manufacturing procedures, with differences in manufacturing and metallurgy that might yield observable differences in surface defect profiles. The null hypothesis tested was that there would be no significant difference in the prevalence or severity of external surface defects among the five brands, nor between heat-treated and non-heat-treated instruments. SEM imaging was performed using a scanning electron microscope (Quanta FEG 400, FEI, USA) at 100×, 500×, and 1000× magnification. Data were collected and statistically analyzed. Intergroup comparisons were performed using the Kruskal–Wallis test. Pairwise comparisons were adjusted with Bonferroni correction. Significance was set at α = 0.05. All instrument groups exhibited some degree of external surface irregularities, predominantly machining grooves and minor pits. Microcracks and protrusions were less frequent. No statistically significant differences were detected among the five brands for any defect category or total score. More precise statistical analysis revealed no significant differences among the five instrument systems in total surface defect scores (H(4) = 1.32, p = 0.86). Similarly, individual defect categories, including machining grooves, pits, microcracks, protrusions, and irregularities, did not differ significantly between brands (p > 0.05 for all comparisons). Across all systems, most defects were minor (score 1), with very few severe defects (score 3). No instrument exhibited severe microcrack scores >1. Within the limitations of this SEM analysis, the five NiTi instrument brands (I-File/Onyx, Mtwo, Reciproc Mwire, Reciproc Blue, and WaveOne Gold) demonstrated comparable external surface integrity, regardless of the grinding device or heat treatment.
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