{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,1]],"date-time":"2025-12-01T15:41:45Z","timestamp":1764603705470,"version":"build-2065373602"},"reference-count":31,"publisher":"MDPI AG","issue":"22","license":[{"start":{"date-parts":[[2020,11,20]],"date-time":"2020-11-20T00:00:00Z","timestamp":1605830400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Pusan National University Dental Hospital","award":["2019 Clinical Research Grant"],"award-info":[{"award-number":["2019 Clinical Research Grant"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Nickel-titanium (NiTi) endodontic rotary instruments are used extensively in root canal procedures by both general dentists and specialists. However, their vulnerability to fracture is the major reason for clinicians\u2019 concern regarding their use. The objective of this study was to investigate the potential effects of spring machining of the file shaft on the fatigue and torsional resistances of NiTi rotary instruments. Three types of NiTi rotary systems with (S) and without (NS) spring machining were used in this study (n = 15 each): a spring file (SPR; #25\/.06, SPR-S, SPR-NS), a ProTaper Next X2 (PTN; #25\/variable taper, PTN-S, PTN-NS), and a ProTaper Gold F2 (PTG; #25\/variable taper, PTG-S, PTG-NS). Spring machining was adjusted on the 6 mm of each file system\u2019s shaft via a laser cutting process. The number of rotation cycles until fracture (i.e., cyclic fatigue resistance), ultimate torsional strength, the distortion angle, and the toughness of each subgroup were estimated with specially designed devices. The results were analyzed using a paired t-test at a significance level of 95%. NiTi rotary instruments with spring machining exhibited a higher cyclic fatigue resistance than instruments without spring machining. The groups with spring machining exhibited a higher toughness and larger distortion angle than the groups without it (p &lt; 0.05). In conclusion, spring machining on the shank of NiTi instruments may provide a stress-bearing area and attenuate the torsional and cyclic fatigue of NiTi rotary instruments.<\/jats:p>","DOI":"10.3390\/ma13225246","type":"journal-article","created":{"date-parts":[[2020,11,20]],"date-time":"2020-11-20T09:46:18Z","timestamp":1605865578000},"page":"5246","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":4,"title":["Advancement of Mechanical Properties of Nickel-Titanium Rotary Endodontic Instruments by Spring Machining on the File Shaft"],"prefix":"10.3390","volume":"13","author":[{"given":"Sangmi","family":"Ahn","sequence":"first","affiliation":[{"name":"Department of Conservative Dentistry, School of Dentistry, Dental Research Institute, Dental and Life Science Institute, Pusan National University, Yangsan 50612, 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 41940, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"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, Korea"}],"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, Korea"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2020,11,20]]},"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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