Limitations and generalisability
incisors
This single-centre RCT has limited generalisability compared to a multi-centre RCT since the latter usually has more involved staff members and operators, which can decrease the risk of bias. Furthermore, it is reported that single-centre trials tend to report higher treatment effects than multi-centre studies (This study presented some dropouts. A per-protocol analysis would consequently suffer from attrition bias. Thus, we applied the ITT principle and replaced the missing values with the group’s mean. This imputation may impact the results, and no golden rule for the imputation exists. Instead, the choice of imputation method must be evaluated for every trial. It can be discussed whether other methods of imputation or per-protocol analysis would have been preferable. However, as Nich and Carroll (Finally, a long-term evaluation of the stability of the maxillary incisors is necessary. Nonetheless, the present short-term evaluation provides essential information for a long-term follow-up. Also, it supports the results of a previous retrospective 10-year follow-up, which shows that the most considerable changes occur in the first and second year after retention (