Guest editorial: what do prospective randomized clinical trials tell us about the treatment of class II malocclusions? A personal viewpoint.

The prospective randomized clinical trial (RCT) is seen by many to be the 'gold standard' for analysing treatment outcome and the only valid source of clinical data. In orthodontics, most RCTs have been designed to resolve the controversy surrounding the ability of functional appliances to significantly modify dentofacial growth. Given the variability in the timing, magnitude and duration of pubertal dentofacial growth, differing levels of motivation and patient compliance, the inherent inaccuracy of cephalometry and the questionable validity of the measurements themselves used to quantitate change, it is not surprising that the conclusions have not been as clear-cut as anticipated. Unlike a laboratory experiment, in which it is possible to limit the differences between experimental and control groups to the single factor being investigated, in a clinical trial an orthodontic appliance is just one of several variables affecting the outcome. Furthermore, RCTs are expensive and time-consuming; by the time the end-point of the study has been reached, the appliance may no longer be in widespread use, the fate of more than one recent well-publicized RCT. What RCTs have shown is that functional appliances such as the Herbst and twin block, based on the principle of 'jumping the bite', are more effective at modifying dentofacial growth and reducing overjets than headgear and more passive appliances such as the Andresen activator and its variants. However, if one asks whether RCTs have achieved their objective, or provided knowledge not previously available from retrospective studies or animal experimentation, then the answer would have to be no; it is also hard to justify the cost. What is particularly interesting is that knowledge based on years of clinical experience has been disregarded and then announced as if it was something completely new.