This study sought to assess the effect of miniscrew insertion angle (vertical and oblique) on its clinical survival under shearing forces in orthodontic patients undergoing canine retraction. In this split-mouth randomized controlled clinical trial, 50 miniscrews were placed bilaterally in 25 patients with 45° and 90° insertion angles relative to a line perpendicular to the occlusal plane distal to the maxillary first premolar extraction site. Allocation of insertion angles to the right/left side was random using the Random Allocation Software. The patients, clinician, and statistician were blinded to the allocation of miniscrews to the side of jaw. The patients were followed-up monthly for 6 months. The primary outcome was the clinical survival of miniscrews, which was evaluated at each follow-up session. The secondary outcomes were the miniscrew stability based on the Periotest value (PTV) and the level of pain experienced by patients at 1, 12, and 24 h, and 7 days after miniscrew placement using a visual analog scale (VAS). Data were analyzed using paired t-test, repeated measures ANOVA, and McNemar’s test. The clinical survival rate of miniscrews placed at 90° and 45° angles was 76% and 88%, respectively. This difference was not statistically significant (P = 0.375). No significant difference was noted between the two groups regarding the PTV or the pain score either (P > 0.05). Clinically, the insertion angle of miniscrews (90° versus 45° relative to a line perpendicular to the occlusal plane) has no significant effect on the miniscrew survival rate or stability during orthodontic treatment. This trial was registered at www.irct.ir ( IRCT20190901044659N1 ). The protocol was published after trial commencement.

中文翻译：

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上颌颊板微螺钉插入角度对其临床生存率的影响：一项随机临床试验

本研究旨在评估微螺钉插入角度（垂直和倾斜）在剪力作用下对进行犬齿回缩的正畸患者的临床生存率的影响。在这项分口随机对照临床试验中，25 名患者在双侧放置了 50 颗微型螺钉，相对于上颌第一前磨牙拔除部位远端咬合平面的垂直线呈 45° 和 90° 插入角。使用随机分配软件随机分配右侧/左侧的插入角度。患者、临床医生和统计学家不知道微螺钉在颌侧的分配。对患者进行每月随访，为期 6 个月。主要结果是微型螺钉的临床存活率，在每次随访时进行评估。次要结果是基于 Periotest 值 (PTV) 的微型螺钉稳定性以及使用视觉模拟量表 (VAS) 的微型螺钉放置后 1、12、24 小时和 7 天患者所经历的疼痛程度。使用配对 t 检验、重复测量方差分析和 McNemar 检验分析数据。以 90° 和 45° 角放置的微型螺钉的临床存活率分别为 76% 和 88%。这种差异没有统计学意义（P = 0.375）。两组在 PTV 或疼痛评分方面均无显着差异（P > 0.05）。临床上，微螺钉的插入角度（相对于垂直于咬合平面的直线为 90° 与 45°）对正畸治疗过程中微螺钉的成活率或稳定性没有显着影响。该试验在 www.irct 注册。红外（IRCT20190901044659N1）。该方案在试验开始后公布。