Commentary

This very interesting study is the first RCT in dentistry where the post-randomised single-consent design described by Zelen in 19791 has been used. The rationale for introducing a study design where the participants are randomised before acquiring consent was that it might enhance patient recruitment to clinical trials. Interestingly, not many trials in biomedicine have applied this design, and the majority of those that have suggest that the reason is to avoid bias due to a Hawthorne effect a distortion of the results caused by the response the participants to the special attention they receive from researchers rather than to improve recruitment.2

Many, if not most, interventions in restorative dentistry and prosthodontics can be considered as elective. For many potential patients, the most relevant treatment outcomes are previous patients' satisfaction with the treatment and how it may affect their quality of life. In this context it is important to present to the patient unbiased evidence from appropriately designed clinical studies, to enable him or her to consent to a particular treatment strategy. Unfortunately, however, there is a paucity of research data available. It is also questionable whether such data, arising from participants in stringently controlled clinical studies, are applicable to all. The reason for this is that voluntary participation in clinical trials is influenced by patients' prior expectations and general attitudes towards dental care and research.3 Thus, people who volunteer to participate, for example, in RCT, which are inherently associated with an element of risk, may not be representative of others who may have strong treatment preferences, for right or wrong reasons of their own. It is unfortunate therefore that there are so few trials in the dental literature that have used those alternative designs that take into account participants' preferences. Notable exceptions are the trials and publications by Feine and colleagues in Montreal, Canada.4

One of the intriguing findings in this trial is the relatively high proportion of individuals (12 out of 45; 25%) who did not accept receiving an “expensive, high quality intervention”, ie, the implant-supported overdenture instead of simple denture. Risking a high proportion of refusals is in fact one of the main criticisms of the Zelen design, because statistical power is lost. This adds to the already controversial ethical dilemmas associated with this study design.2

Could this high dropout have been predicted? Perhaps not, as a similar occurrence also puzzled the authors of another recent implant trial.5 In the latter, approximately one-third of the participants refused implants. It appears that the fairly high proportions of individuals who say that they would never consider receiving dental implants, as reported in different cross-sectional studies (eg, Kronstrom et al., 2002),6 cannot be disregarded simply because of inadequate patient education. It also underscores the value of appraising cross-sectional studies for addressing questions about patient values and preferences.

Future clinical trials in prosthodontics should focus on patient-centred outcomes and use study designs that take into account patient and clinician treatment preferences.7 Moreover, when calculating study power, it is necessary to allow for the not-insignificant proportion of patients who will refuse to be allocated to one or other arms of a trial.