In search of the sample: recent experiences of a trial team in orthodontics.

Randomised clinical trials are commonly undertaken in medical and dental research. However, few authors discuss the difficulties associated with such studies, including costs, ethical issues and recruitment of an adequate number of patients. There is little information available on the number of studies which are terminated early as a result of these issues, but it seems likely that at least 10% of clinical studies never reach completion. This paper reviews two nationally funded clinical studies which were terminated early. It highlights the problems associated with patient recruitment and also some issues which may benefit researchers undertaking similar studies in the future.