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Standardized access cavities were prepared, followed by uniform root canal instrumentation, while irrigation protocols were conducted as assigned. Root canals were filled, and access cavities were sealed with resin composite. Specimens underwent compressive fracture testing using a universal testing machine to determine the maximum load to fracture after thermo-mechanical fatigue, and failure modes were assessed. Data were statistically analyzed, with the significance threshold set at\n                      <jats:italic>p<\/jats:italic>\n                      \u2009&lt;\u20090.05 and a 95% confidence interval (CI).\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      All experimental groups, along with the negative control group, exhibited significantly reduced fracture resistance and notable irreparable failure patterns in comparison to intact teeth (563.92\u2009\u00b1\u200928.52\u00a0N; CI: 548.13\u2013579.71) (\n                      <jats:italic>p<\/jats:italic>\n                      \u2009&lt;\u20090.001). No statistically significant differences in the maximum load to fracture were observed among the CSI (473.90\u2009\u00b1\u200913.94\u00a0N; CI: 466.18\u2013481.62), CUI (470.94\u2009\u00b1\u200912.5\u00a0N; CI: 464.02\u2013477.87), SIA (468.15\u2009\u00b1\u20099.68\u00a0N; CI: 462.79\u2013473.51), SIA\u2009+\u2009CUI (467.61\u2009\u00b1\u20096.74\u00a0N; CI: 463.88\u2013471.35), and the negative control group (474.45\u2009\u00b1\u20095.62\u00a0N; CI: 471.34\u2013477.56), despite increased volumes and longer exposure to NaOCl in activation groups (\n                      <jats:italic>p<\/jats:italic>\n                      \u2009&gt;\u20090.05). The majority of failure modes were catastrophic across the tested and NC groups, though distribution did not vary significantly (\n                      <jats:italic>p<\/jats:italic>\n                      \u2009=\u20090.06).\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>The repeated activation of full-strength NaOCl via SIA, CUI, or their combination did not compromise fracture resistance compared to CSI. Root canal treatment itself reduced structural integrity relative to intact teeth, with a noted increase in the likelihood of unfavorable fracture types, underscoring the necessity for meticulous preservation of tooth structure during root canal procedures.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1186\/s12903-026-08082-3","type":"journal-article","created":{"date-parts":[[2026,4,1]],"date-time":"2026-04-01T01:44:56Z","timestamp":1775007896000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Influence of repeated cycles of full-strength sodium hypochlorite activation on the mechanical behavior of root canal-treated teeth: a laboratory study"],"prefix":"10.1186","volume":"26","author":[{"given":"Mohammed Hammad Abdu","family":"Ismail","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ahmed Mohamed","family":"Bakry","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4250-9951","authenticated-orcid":false,"given":"Mohammed","family":"Turky","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,4,1]]},"reference":[{"key":"8082_CR1","doi-asserted-by":"publisher","unstructured":"Dutner J, Mines P, Anderson A. 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J Oral Rehabil. 2009;36(4):299\u2013312. https:\/\/doi.org\/10.1111\/j.1365-2842.2009.01940.x.","DOI":"10.1111\/j.1365-2842.2009.01940.x"}],"container-title":["BMC Oral Health"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/link.springer.com\/article\/10.1186\/s12903-026-08082-3","content-type":"text\/html","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/link.springer.com\/content\/pdf\/10.1186\/s12903-026-08082-3.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/link.springer.com\/content\/pdf\/10.1186\/s12903-026-08082-3.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,6,16]],"date-time":"2026-06-16T21:16:53Z","timestamp":1781644613000},"score":1,"resource":{"primary":{"URL":"https:\/\/link.springer.com\/10.1186\/s12903-026-08082-3"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,4,1]]},"references-count":48,"journal-issue":{"issue":"1","published-online":{"date-parts":[[2026,12]]}},"alternative-id":["8082"],"URL":"https:\/\/doi.org\/10.1186\/s12903-026-08082-3","relation":{},"ISSN":["1472-6831"],"issn-type":[{"value":"1472-6831","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,4,1]]},"assertion":[{"value":"19 October 2025","order":1,"name":"received","label":"Received","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"9 March 2026","order":2,"name":"accepted","label":"Accepted","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"1 April 2026","order":3,"name":"first_online","label":"First Online","group":{"name":"ArticleHistory","label":"Article History"}},{"order":1,"name":"Ethics","group":{"name":"EthicsHeading","label":"Declarations"}},{"value":"The present study was conducted in accordance with the principles outlined in the Declaration of Helsinki. Approval was obtained from the Research Ethics Committee at the Faculty of Dentistry, Minia University, Egypt (Registration No. 1136). All methods were implemented in line with the relevant guidelines and regulations. Written informed consent was secured from all participants involved in the study.","order":2,"name":"Ethics","group":{"name":"EthicsHeading","label":"Ethics approval and consent to participate"}},{"value":"Not applicable.","order":3,"name":"Ethics","group":{"name":"EthicsHeading","label":"Consent for publication"}},{"value":"The authors declare no competing interests.","order":4,"name":"Ethics","group":{"name":"EthicsHeading","label":"Competing interests"}}],"article-number":"635"}}