{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,26]],"date-time":"2026-02-26T15:57:39Z","timestamp":1772121459286,"version":"3.50.1"},"reference-count":27,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2026,2,26]],"date-time":"2026-02-26T00:00:00Z","timestamp":1772064000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"2-Year Research Grant of Pusan National University"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>This study evaluated changes in the number of cycles to fracture (NCF) of Nickel\u2013Titanium (NiTi) files after repeated use in simulated canals and investigated the potential relationship with stress-induced martensite (SIM) transformation effect. A total of 225 ProTaper Ultimate (PTUL) files were divided into three groups: Group 1 consisted of new files, Group 2 comprised files used to shape two resin simulated canals, and Group 3 consisted of files used to shape four canals. The simulated resin canals with a 16 mm length of J-shaped with 35\u00b0 curvature were prepared using PTUL Slider, Shaper, F1, F2, and F3 files sequentially. After instrumentation, the cyclic fatigue resistance of each sequential file was assessed in a 35\u00b0 curved steel canal by rotating at 400 rpm using a custom-made device. Statistical analysis was performed using one-way ANOVA with Tukey\u2019s post hoc test or Kruskal\u2013Wallis with Dunn\u2019s test with Bonferroni correction for parametric and non-parametric data, respectively. Slider and Shaper maintained stable NCF across all groups (p &gt; 0.05). In contrast, F1 showed a transient increase (117.7%) after two uses but declined significantly (91.6%) after four uses (p &lt; 0.05). F2 and F3 demonstrated progressive NCF reductions (F2: 72.9%; F3: 71.5% after four uses), with F3 showing the most pronounced decline (p &lt; 0.05). Repeated use of NiTi files reduced their cyclic fatigue resistance in a file-specific manner, with larger finishing files most affected. The distinctive F1 pattern suggests potential preload-related or SIM transformation effects that warrant further metallurgical investigation.<\/jats:p>","DOI":"10.3390\/ma19050866","type":"journal-article","created":{"date-parts":[[2026,2,26]],"date-time":"2026-02-26T14:51:29Z","timestamp":1772117489000},"page":"866","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["File-Specific Cyclic Fatigue Resistance of NiTi Instruments After Repeated Use in Simulated Canals: Patterns Compatible with Potential Stress-Induced Martensite Transformation Effects"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0009-0001-2602-9317","authenticated-orcid":false,"given":"Hyeonu","family":"Jo","sequence":"first","affiliation":[{"name":"Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Dental and Life Science Institute, Pusan National University, Yangsan 50612, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7965-977X","authenticated-orcid":false,"given":"Sang Won","family":"Kwak","sequence":"additional","affiliation":[{"name":"Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Dental and Life Science Institute, Pusan National University, Yangsan 50612, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0469-4324","authenticated-orcid":false,"given":"Jung-Hong","family":"Ha","sequence":"additional","affiliation":[{"name":"Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu 41566, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Asgeir","family":"Sigurdsson","sequence":"additional","affiliation":[{"name":"Department of Endodontics, New York University College of Dentistry, New York, NY 10010, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8032-1194","authenticated-orcid":false,"given":"Hyeon-Cheol","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Dental and Life Science Institute, Pusan National University, Yangsan 50612, Republic of Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,2,26]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"346","DOI":"10.1016\/S0099-2399(88)80196-1","article-title":"An initial investigation of the bending and torsional properties of Nitinol root canal files","volume":"14","author":"Walia","year":"1988","journal-title":"J. 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