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This design is produced through an alternating offset machining process, resulting in a file whose center of mass is not aligned with its center of rotation. Such configuration is claimed to create increased space for debris removal during instrumentation while simultaneously reducing stress concentration on the instrument during cutting.<\/jats:p>\n                    <jats:p>Despite the manufacturer\u2019s claims regarding the novel geometry and expected advantages of ProTaper Ultimate files, independent clinical scientific evaluation of these features remains limited. Understanding whether the parallelogram cross-section and offset center of mass truly translate into improved clinical performance and enhanced debris elimination is essential for evidence-based endodontic practice. Therefore, this study aimed to objectively assess these claimed advantages, providing clinicians with reliable data regarding the bacterial reduction and postoperative pain of PTU. The findings will contribute to informed decision-making when selecting rotary systems and may clarify the clinical relevance of this new design concept.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Aim<\/jats:title>\n                    <jats:p>This prospective randomized double-blinded trial clinically compared postoperative pain and bacterial reduction after using two rotary systems; ProTaper Ultimate (PTU) versus ProTaper Gold (PTG) in necrotic maxillary premolars.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methodology<\/jats:title>\n                    <jats:p>Fifty-six patients with necrotic maxillary first premolars with normal periapical condition were randomly assigned to PTU (n=28) or PTG (n=28). Root canal preparation was performed using the allocated file system. The primary clinical outcome was postoperative pain and was recorded preoperatively and at 6, 12, 24, and 48 hours using a modified visual analogue scale (mVAS). The secondary outcome was intracanal bacterial load and bacterial reduction percentage, quantified as aerobic and anaerobic colony-forming units per milliliter (CFU\/ml). Samples were collected pre-instrumentation (S1), post-instrumentation (S2), and after final irrigation with 2.5% sodium hypochlorite (NaOCl) (S3). Incidence and number of analgesic intakes was also documented. Data were analyzed using Student\u2019s t-test, chi-square, Mann-Whitney U test, Friedman\u2019s test, frequencies (n), percentages (%), Fisher exact test, repeated measures ANOVA, and Spearman\u2019s correlation coefficient (\u03c1).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>Postoperative pain was significantly higher with PTU than PTG immediately (p=0.004) and at 12 hours (p=0.035), 24 hours (p=0.002), and 48 hours (p=0.005), with no significant difference at 6 hours (p=0.055). Analgesic intake was significantly greater in the PTU group, which was 3.45-fold more prone to require medication. PTU showed significantly lower bacterial reduction than PTG after instrumentation (S1\u2013S2: aerobic p=0.0014; anaerobic p=0.0326) and after final irrigation (S1\u2013S3: aerobic p=0.0183; anaerobic p=0.0276). Spearman\u2019s correlation analysis revealed no significant association between bacterial reduction and pain scores in either group (PTU: \u03c1 = 0.06, p = 0.760; PTG: \u03c1 = 0.03, p = 0.896).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>PTG, with its convex triangle cross-section and lower rotational speed and torque, resulted in lower postoperative pain intensity, less need for analgesics and statistically higher bacterial reduction compared to the parallelogram cross-section of PTU.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Trial registration<\/jats:title>\n                    <jats:p>\n                      The study protocol was listed on\n                      <jats:ext-link xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" xlink:href=\"http:\/\/www.clinicaltrials.gov\" ext-link-type=\"uri\">www.clinicaltrials.gov<\/jats:ext-link>\n                      (ClinicalTrials.gov identifier: NCT05305742)\n                      <jats:ext-link xmlns:xlink=\"http:\/\/www.w3.org\/1999\/xlink\" xlink:href=\"https:\/\/clinicaltrials.gov\/study\/NCT05305742?cond=Necrosis%26viewType=Table%26term=GOLD%26rank=5\" ext-link-type=\"uri\">https:\/\/clinicaltrials.gov\/study\/NCT05305742?cond=Necrosis&amp;viewType=Table&amp;term=GOLD&amp;rank=5<\/jats:ext-link>\n                      .\n                    <\/jats:p>\n                    <jats:p>ClinicalTrials.gov identifier NCT05305742 registration date (30\/03\/2022).<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1186\/s12903-026-07973-9","type":"journal-article","created":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T08:35:43Z","timestamp":1774427743000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Effect of different rotary instrument designs (protaper ultimate and protaper gold) on postoperative pain and bacterial reduction: a randomized clinical trial"],"prefix":"10.1186","volume":"26","author":[{"given":"Khaled Hassan","family":"Abed","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ahmed Abdel Rahman","family":"Hashem","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Reem Ahmed","family":"Lutfy","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Somaia Abdellatif","family":"Eissa","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dina Ahmed","family":"Morsy","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,3,25]]},"reference":[{"key":"7973_CR1","doi-asserted-by":"publisher","first-page":"921","DOI":"10.1111\/j.1365-2591.2006.01180.x","volume":"39","author":"European Society of Endodontology","year":"2006","unstructured":"European Society of Endodontology. 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Int Endod J. 2021;54:1026\u201336.","journal-title":"Int Endod J"}],"container-title":["BMC Oral Health"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/link.springer.com\/article\/10.1186\/s12903-026-07973-9","content-type":"text\/html","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/link.springer.com\/content\/pdf\/10.1186\/s12903-026-07973-9.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"text-mining"},{"URL":"https:\/\/link.springer.com\/content\/pdf\/10.1186\/s12903-026-07973-9.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,6,16]],"date-time":"2026-06-16T20:50:10Z","timestamp":1781643010000},"score":1,"resource":{"primary":{"URL":"https:\/\/link.springer.com\/10.1186\/s12903-026-07973-9"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,3,25]]},"references-count":50,"journal-issue":{"issue":"1","published-online":{"date-parts":[[2026,12]]}},"alternative-id":["7973"],"URL":"https:\/\/doi.org\/10.1186\/s12903-026-07973-9","relation":{},"ISSN":["1472-6831"],"issn-type":[{"value":"1472-6831","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,3,25]]},"assertion":[{"value":"21 November 2025","order":1,"name":"received","label":"Received","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"18 February 2026","order":2,"name":"accepted","label":"Accepted","group":{"name":"ArticleHistory","label":"Article History"}},{"value":"25 March 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 informed consent forms and the protocol were reviewed and approved by the applicable IRBs\/ECs [Institutional Review Boards\/Ethical Committees] at the Faculty of Dentistry, Cairo University, with respect to scientific content and compliance with applicable research and human subjects\u2019 regulations (reference number 23\/3\/22). The methods used in this study were in compliance with the 2013 revision of the World Medical Association\u2019s Declaration of Helsinki. Informed consent for trial participation was obtained from all patients 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":"698"}}