The reporting of blinding in orthodontic randomized controlled trials: where do we stand?

To analyse in 10 orthodontic journals how many randomized controlled trials (RCTs) performed 'single-', 'double-', 'triple-', or 'outcome assessors blinding' and to evaluate, from the number of RCTs that did not conduct blinding, how many could actually have achieved it.

Randomized controlled trials published in 10 orthodontic journals between 1 September 2012 and 28 February 2018 were included. A search was performed in PubMed and conducted for publication type 'randomized controlled trial' for each journal. Two reviewers independently analysed each RCT and registered that blinding was performed and included which specific type. It was also evaluated whether misclassifications of blinding items occurred and whether it was possible to achieve blinding among the RCTs that did not perform blinding.

After applying the inclusion criteria, 203 RCTs were assessed, and 61.6 per cent of them had used blinding, with the main type being 'outcome assessors blinding' (40.4%) followed by 'single-blinding' (15.3%), 'double-blinding' (2.5%), and 'triple-blinding' (3.4%). In 38.4 per cent of the trials, no blinding was performed; however, 79.4 per cent of them could have achieved blinding. Fifteen RCTs (7.3%) misclassified the blinding in relation to single-, double-, or triple-blinding. Journals followed the CONSORT (AJODO, EJO, JO, OCR) published together significantly more RCTs that performed blinding than journals not following the CONSORT.

Blinding of outcome assessors was the most frequent type, as orthodontic trials are often of intervention design and thereby difficult to mask for patients and trial staff. The misclassifications of blinding items may indicate suboptimal knowledge among researchers and peer-reviewers regarding the definitions for diverse blinding types.