Re: “Comprehensive comparison of canine retraction using NiTi closed coil springs vs elastomeric chains: A split-mouth randomized controlled trial” by Haya A. Barsoum, Hend S. ElSsayed, Fouad A. El Sharaby, Juan Martin Palomo, Yehya A. Mostafa et al. Angle Orthod 2021;91:441-448.

This was an interesting study, and we congratulate the authors for the publication. We wish to ask the authors to clarify a few points from the paper.

  1. Please provide more information about the baseline demographic data of the sample (age and sex) as this may have implications for the generalizability of the results.

  2. The authors have used the Independent T-test and Mann-Whitney Test to analyze the intergroup differences. As the observations were derived from a split-mouth design and inherently paired, why were paired t-tests not used?

  3. For the changes from baseline to 6 Months (Table 3), many variables in both the groups had standard deviation higher than the mean, implying a wide variation in the outcomes. Can you comment further on this?

  4. One of the study's conclusions was that ‘Significantly fewer days with pain were reported for the NiTi closed coil spring.' This appears to have been based on the significant inter-group difference of 1.47 % in the number of days with pain (Table 4). Considering that this was just over 21 hours (1.47% of 60 days) and that there are methodological issues in evaluating perceived pain with a split-mouth study design, what is the clinical significance of this conclusion?

Thank you for clarifying this information.