Design Systematic review

Study population Orthodontic patients undergoing treatment with removable thermoplastic retainers compared with conventional fixed orthodontic appliances. The mean age of patients was between 15 and 33 years.

Data sources Six electronic databases including: Scopus, Web-of-Science, PubMed, Cochrane, Clinical Trials and Grey Literature were searched in addition to a search of references in eligible studies with no restriction of language. Out of 559 studies, 55 were eligible. Only four articles were included; three non-randomised and one randomised controlled trial (RCT) involving 96-182 patients. The studies included were completed within 2005-2016.

Study selection Clinical trials involving orthodontic patients undergoing treatment using thermoplastic removeable aligners, namely Invisalign, in comparison to conventional fixed orthodontic appliances of either self-ligating or tip-edge bracket systems were included.

Data extraction and synthesis Two members of the research team independently selected articles which fulfilled the inclusion criteria and compared results prior to data collection. A third party examiner was available to resolve disagreements.

The study quality was analysed for presence of bias; three non-randomised studies were evaluated and scored using the Methodological Index for Non-Randomised Studies (MINORS), one study was considered high methodological quality, two were considered moderate. The RCT was assessed using the Cochrane Collaboration Common Scheme for Bias and was deemed to be low risk of bias.

Results The results suggest that Invisalign can provide successful alignment, however, it poses difficulties in achieving occlusal contacts, buccolingual inclination and vertical movement of teeth. One study found that Invisalign cases are more susceptible to relapse, which can be explained through the tipping mechanism compared to bodily movement, of conventional fixed appliances. Furthermore some studies show that although using aligners can result in overall shorter treatment time the final occlusion was not favourable. The outcome of the RCT, showed that aligners can be successful in treating class I malocclusions in extraction cases.

Conclusions This systematic review found that the use of clear aligners made no significant difference to treatment time compared with conventional appliances. Additionally, removable aligners were effective in crowding cases but had limitations in achieving favourable outcomes in the anterior-posterior position and final occlusion, as well as being more likely to relapse post treatment.

设计系统评价

与传统的固定式正畸矫治器相比，研究人群正接受可移动热塑性固定器治疗的正畸患者。患者的平均年龄在15至33岁之间。

数据源除了在没有语言限制的合格研究中搜索参考文献外，还搜索了六个电子数据库，包括：Scopus，科学网络，PubMed，Cochrane，临床试验和灰色文献。在559项研究中，有55项符合条件。仅包括四篇文章；三项非随机和一项随机对照试验（RCT），涉及96-182名患者。纳入的研究已于2005-2016年完成。

研究选择与使用自结扎系统或尖端支架系统的常规固定式正畸矫治器相比，涉及使用正畸治疗的正畸患者进行治疗的临床试验，该矫正器使用热塑性可拆卸对准器（即Invisalign）。

数据提取和合成研究团队的两名成员独立选择了符合纳入标准的文章，并在收集数据之前比较了结果。第三方审查员可以解决分歧。

分析研究质量是否存在偏倚；使用非随机研究方法索引（MINORS）对3项非随机研究进行了评估和评分，其中一项研究被认为具有较高的方法学质量，另外两项被视为中等。使用Cochrane偏爱协作共同计划对RCT进行了评估，并认为偏倚风险较低。

结果结果表明，Invisalign可以提供成功的对齐，但是，它难以实现咬合接触，颊舌倾斜和牙齿垂直运动。一项研究发现，与传统的固定器具相比，Invisalign病例更容易复发，这可以通过倾斜机制与身体移动相比来解释。此外，一些研究表明，尽管使用矫正器可以缩短总体治疗时间，但最终的咬合并不理想。RCT的结果表明，在拔牙病例中，对准器可以成功治疗I类错牙合。

结论该系统评价发现，与常规矫治器相比，使用透明矫正器对治疗时间没有显着影响。另外，可移动对准器在拥挤病例中是有效的，但是在前后位置和最终闭塞方面取得令人满意的结果方面存在局限性，并且在治疗后更可能复发。