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Isolating design variables by assessing the impact of cross-section geometry on the mechanical performance of nickel-titanium rotary instruments: a comparative in vitro study
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Anne Rafaella Tenório Vieira, Guilherme Ferreira da Silva, Emmanuel João Nogueira Leal da Silva, Rodrigo Ricci Vivan, João Vitor Oliveira de Amorim, Thaine Oliveira Lima, Raimundo Sales de Oliveira Neto, Marco Antonio Hungaro Duarte, Murilo Priori Alcalde
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Restor Dent Endod 2025;50(3):e28. Published online July 24, 2025
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DOI: https://doi.org/10.5395/rde.2025.50.e28
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 Abstract
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- Objectives
This study aimed to assess the effect of cross-section geometry on the mechanical properties of nickel-titanium (NiTi) instruments by comparing two instruments with identical tip size, taper, and thermal treatment but differing in cross-section design.
Methods
One hundred four NiTi rotary instruments, being S-shaped and triangular cross-section, manufactured with Blueish thermal treatment, were tested (n = 52 per group). Differential scanning calorimetry was employed, and the metal mass volume and cross-section area were assessed. The cyclic fatigue, torsional, and bending resistance tests were assessed. Data were analyzed using the Kolmogorov-Smirnov and Student t tests, and the level of significance was set at 5%.
Results
The instruments exhibited similar start and finish temperatures of phase transformation. The S-shaped instruments had significantly lower metal mass volume and cross-sectional area (p < 0.05). S-shaped instruments demonstrated superior cyclic fatigue resistance, greater angular deflection, and lower bending stiffness (p < 0.05).
Conclusions
Cross-section geometry significantly influences the mechanical properties of NiTi rotary instruments.
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