The aim of this study was to identify outcome-related discrepancies between registry trial entries and final published reports in orthodontic randomized controlled trials (RCTs). The percentage of registered orthodontic RCTs was also recorded.Five trial registries, ClinicalTrials.gov (https://clinicaltrials.gov/), International Standard Randomised Controlled Trial Number registry (http://www.isrctn.com/), European Union Clinical Trials Register (https://www.clinicaltrialsregister.eu/), Australia New Zealand Clinical Trials Registry (http://www.anzctr.org.au/) and Clinical Trials Registry of India (www.ctri.nic.in/) were searched up to April 2018 in order to identify completed orthodontic RCTs. The unique trial identifier, the title and authors name were used to search for publications based on entries within Google (https://www.google.com), Google Scholar (https://scholar.google.gr/) and MEDLINE via PubMed (https://www.ncbi.nlm.nih.gov/pubmed/). Outcome reporting discrepancies and a number of other entry/publication characteristics were recorded including timing of registration, type of journal/publication, significance of the primary outcome in the final report. The number of trials registered among the total number of published RCTs in orthodontics was recorded within the time span assessed.One hundred and twenty-four entries were identified for completed orthodontic RCTs, whereas 53 of those were related to published final reports. Outcome reporting discrepancies were ascertained for 47 per cent of publications (n = 2 5); discrepancies were more prevalent for non-primary outcomes (n = 21, 40 per cent). Only 16 per cent of the published orthodontic RCTs had been registered.Only a subset of trial entries were assessed as these were related to publication records.Registration of clinical trials in orthodontics remains far from universal. A significant level of outcome reporting discrepancy was observed within this subset of registered trials.