Overview of registered studies in orthodontics: Evaluation of the ClinicalTrials.gov registry

•This is an overview of the orthodontic clinical studies in the ClinicalTrials.gov registry.•Most registered studies are single-center studies with sample sizes of 50 or fewer.•There are wide variations about treatment allocation approaches and randomization methods.•Publication bias should be assessed and kept in perspective when interpreting their results.•Our results indicate the need for multicenter clinical studies in orthodontics.

IntroductionThe Food and Drug Administration Modernization Act of 1997 made it mandatory for all phase II through IV trials regulated by this Act to be registered. After this, the National Institutes of Health created ClinicalTrials.gov, which is a registry of publicly and privately supported clinical studies of human participants. The objective of this study was to examine the characteristics of registered studies in orthodontics.MethodsThe ClinicalTrials.gov Web site was used to query all registered orthodontic studies. The search term used was “orthodontics.” No limitations were placed for the time period. All registered studies regardless of their recruitment status, study results, and study type were selected for analysis.ResultsA total of 64 orthodontic studies were registered as of January 1, 2014. Of these, 52 were interventional, and 12 were observational. Close to 60% of the interventional studies and 66.7% of the observational studies had sample sizes of 50 or fewer subjects. About 21.2% of the interventional studies and 16.7% of the observational studies had sample sizes greater than 100. Only 1 study was funded by the National Institutes of Health, and the rest were funded by “other” or “industry” sources. Close to 87.7% of the interventional studies were randomized. Interventional model assignments included factorial assignment (3.9%), parallel assignments (74.5%), crossover assignment (7.8%), and single-group assignment (13.7%). Most studies were treatment oriented (80.4%). The types of masking used by the interventional studies included open label (28.9%), single blind (44.2%), and double blind (26.9%). Outcome assessors were blinded in only 6 studies.ConclusionsOrthodontic studies registered in ClinicalTrials.gov are dominated by small single-center studies. There are wide variations with regard to treatment allocation approaches and randomization methods in the studies. These results also indicate the need for multicenter clinical studies in orthodontics.