| Study | Reason for exclusion |
|---|---|
| Abdelrahman 2015 | Did not meet age range specified for review |
| Agarwal 2021 | Did not meet age range specified for review |
| Akyalcin 2007 | Not RCT |
| Alcan 2006 | Did not report on crowding |
| Almeida 2015 | Did not meet age range specified for review |
| Altug 2005 | Did not report on crowding |
| Angelieri 2008 | Not RCT |
| Atik 2018 | Did not report on crowding; retrospective |
| Atik 2019 | Does not meet age range specified for review |
| Bansal 2019 | Did not meet age range specified for review |
| Battagel 1998 | Not RCT |
| Baumrind 1996 | Not RCT |
| Bennett 1999 | Did not report on crowding |
| Bhasin 2017 | Did not report on crowding |
| Bhavra 2002 | Did not report on crowding |
| Bondemark 2005 | Did not report on crowding |
| Bondemark 2007 | Not RCT |
| Caprioglio 2014 | Not RCT |
| Celebi 2019 | Unclear if meets age range specified for review; study authors contacted, but no response |
| Cerruto 2017 | Did not report on crowding |
| CTRI/2018/05/014070 | 25% of participants > 16 years old |
| CTRI/2018/10/016038 | Did not meet age range specified for review |
| Dmitrenko 2016 | Not RCT |
| Fan 2009 | Did not meet age range specified for review |
| Feldmann 2008 | Did not report on crowding |
| Fleming 2009a | Did not meet age range specified for review |
| Fleming 2009b | Did not meet age range specified for review |
| Fleming 2010 | Did not report on crowding |
| Germec 2008 | Not RCT and did not meet age range specified for review |
| Germec‐Cakan 2010 | Did not meet age range specified for review |
| Gibreal 2019 | Did not meet age range specified for review |
| IRCT2016042427577N1 | Did not meet age range specified for review |
| Kaklamanos 2017 | Did not report on crowding |
| Keski‐Nisula 2008a | Not RCT |
| Keski‐Nisula 2008b | Not RCT |
| Krishna 2016 | Not RCT |
| Lombardo 2018 | Did not meet age range specified for review |
| Mahmoudzadeh 2018 | Did not meet age range specified for review |
| Mateu 2018 | Did not report on crowding |
| Miles 2018 (AJO‐DO) | Did not report on crowding |
| Mittal 2020 | Did not meet age range specified for review. Surgical procedure |
| Murakami 2016 | Not RCT |
| Nabbat 2020 | Does not meet age range specified for review |
| NCT03645356 | Did not report on crowding |
| NCT03652454 | Does not meet age range specified for review |
| NCT04106141 | Did not meet age range specified for review |
| Nordstrom 2018 | Did not meet age range specified for review |
| Pandis 2007 | Not RCT |
| Pandis 2010b | Not RCT |
| Scott 2008 | Did not meet age range specified for review |
| Silva 2012 | Did not report on crowding |
| Silvola 2009 | Did not report on crowding |
| Soldanova 2012 | Did not meet age range specified for review |
| Taner 2003 | Did not report on crowding |
| Virkkula 2009 | Did not report on crowding |
| Wasserman 2009 | No contact from study author to gain further study information |
| West 1995 | Data not available; results were pooled |
| Xu 2010 | > 60% of participants had < 3 mm crowding |
| Yavuz 2018 | Did not meet age range specified for review |
| Yildirim 2018 | Unclear if age range matches that specified by review ‐ unsuccessful contact with study authors |
| Yu 2008 | Not RCT |
RCT: randomised controlled trial