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The aim of this study was to identify factors affecting the unusual downward movement of the mandible 1-year after the surgery-first approach using IVRO, while focusing on cephalometric values.<\/jats:p>\n              <\/jats:sec><jats:sec>\n                <jats:title>Methods<\/jats:title>\n                <jats:p>This retrospective cohort study sample was divided into two groups based on the amount of vertical movement of the B-point 1-year post surgery (Group S, predictable upward movement; Group U, unpredictable downward movement greater than 2\u00a0mm). To evaluate cephalometric changes between the two groups, cephalograms were obtained before surgery, 1\u00a0day after surgery, 1\u00a0month after surgery, and 1\u00a0year after surgery. The data were analyzed using the independent <jats:italic>t-<\/jats:italic>test, Mann\u2013Whitney <jats:italic>U<\/jats:italic> test with Bonferroni correction, Pearson correlation analysis, and multiple regression analysis.<\/jats:p>\n              <\/jats:sec><jats:sec>\n                <jats:title>Results<\/jats:title>\n                <jats:p>At the initial examination, Group U showed a shallower anterior overbite. The vertical surgical change in the B-point was statistically different between the two groups (<jats:italic>p<\/jats:italic>\u2009&lt;\u20090.001), indicating that group U exhibited more upward movement of the mandible during surgery. Group U showed significant downward movement of the mandible 1\u00a0month after surgery, and this finding persisted until 1\u00a0year postoperatively. Clockwise rotation of the mandible was also observed. Surgical vertical movement of the B-point showed a strong correlation with postoperative vertical movement of mandible (<jats:italic>r<\/jats:italic>\u2009=\u2009-0.674; <jats:italic>p<\/jats:italic>\u2009&lt;\u20090.001) along a linear relationship, indicating that the amount of postoperative vertical downward movement of the mandible increased as the amount of surgical upward movement of the B-point increased (R<jats:sup>2<\/jats:sup>\u2009=\u20090.449; <jats:italic>p<\/jats:italic>\u2009&lt;\u20090.001).<\/jats:p>\n              <\/jats:sec><jats:sec>\n                <jats:title>Conclusions<\/jats:title>\n                <jats:p>This study revealed that unusual downward movement of the mandible after a surgery-first approach using IVRO is correlated with the amount of upward movement during the surgery. When planning surgery, in cases in which a significant upward movement of the mandible is anticipated, orthodontists should prepare for the possibility of subsequent unusual downward movement and a tendency for the anterior overjet to decrease during the postoperative orthodontic period.<\/jats:p>\n              <\/jats:sec>","DOI":"10.1186\/s12903-024-05021-y","type":"journal-article","created":{"date-parts":[[2024,10,10]],"date-time":"2024-10-10T09:02:19Z","timestamp":1728550939000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Factors affecting unusual postoperative vertical downward movement of mandible after surgery-first approach using intraoral vertical ramus osteotomy"],"prefix":"10.1186","volume":"24","author":[{"given":"Soo-Hyun","family":"Nam","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jung-Yul","family":"Cha","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kee-Joon","family":"Lee","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sang-Hwy","family":"Lee","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sung-Hwan","family":"Choi","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hyung-Seog","family":"Yu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2024,10,10]]},"reference":[{"key":"5021_CR1","doi-asserted-by":"crossref","unstructured":"Hardy DK, Cubas YP, Orellana MF. 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