Sir, as co-ordinators of the eleven year-old PREP (Product Research and Evaluation in Practice) Panel, a UK -wide research group of currently 25 enthusiastic General Dental Practitioners (GDPs), we were interested to read the paper 'The advantages and disadvantages of running a clinical trial in general practices' (BDJ 2004, 197: 311–313) and the accompanying comments of the Editor (BDJ 2004, 197: 289).

We admire the ambitious original protocol and envy the understanding Ethics Committee. The experiences of the PREP Panels are well documented1,2,3, after over 40 clinical evaluations of materials and techniques, and also three, one- and two-year clinical trials of restorative materials. The clinical trials have all been reported in peer-reviewed journals. Our own experiences also contributed to the paper co-authored in 20024 on research in dental practice.

Some of the factors that we found useful were:

  1. 1

    The number of practitioners was kept small (around six) to aid monitoring and communication.

  2. 2

    The trial material was first used for a familiarisation period so both operator and dental nurse were fully conversant with the manufacturers' instructions.

  3. 3

    The clinicians were paid a realistic fee for the additional time involved per patient visit and a fee was also paid to the patient for their expenses in attending recall appointments (last trial – 88% recall rate at 2 years).

The GDPs seem to bear the brunt of the criticism in Dr Jones' paper (practitioners using clinical judgement as to what was in their patients' best interests!), some of which we feel is unwarranted. It would have been interesting to hear the GDPs' points of view e.g. organisation of the trial, ease of use of the material, adequacy of remuneration for their and their patients' time, support from the co-ordinators etc.

It is, however, worth recalling that in our first one-year trial we encountered an interesting diversion from the protocol (a compomer restorative material was incorrectly being placed in load-bearing situations) and these results were analysed separately, leading to the manufacturer's further development of the material to react to the use, now common, of the material in this way.

The majority of readers of the BDJ are GDPs and they want to know how materials perform in general practice.

We agree with the authors that, despite their less-than-rosy experiences in working with practitioners, there is a need for the profession to set up a way of conducting trials in general practices and also to avoid duplication of past negative experiences.

One of the authors of the paper, Dr C S Jones responds: We thank Dr R J Crisp and Professor Burke for their interest in our paper and for the information on the factors they found helpful in running the PREP panel.

We are aware of the success of this panel; indeed the test material in our study was evaluated by that panel. Furthermore, two of us were involved with the successful use of GDPs to evaluate materials by Peter Knibbs in the 1980s 5, 6, 7 . In consequence, the three factors they mention were at the fore-front of our mind in establishing the protocol.

  1. 1

    The number of practitioners was small. About six were involved at any one time although we replaced those from whom we received few or no results.

  2. 2

    The materials were provided for familiarisation before the start. In fact a session was devoted to meeting the GDPs and providing them with an opportunity to handle the material and additionally comment on the protocol. These comments were then included in the final study design. A pilot study had also been carried out with one GDP prior to the initial discussion.

  3. 3

    The amount of surgery time involved was discussed in respect of the level of remuneration and was agreed with the participants before the start.

However there is a difference between clinical evaluations as carried out by the prep panel and in Knibbs et al on single materials and a controlled clinical trial which was the objective here.

We did not intend to imply that practitioners should not exercise clinical judgement as to what was in their patients' best interests but the object of this clinical trial was to compare the use of a metal reinforced glass-ionomer cement as an alternative to amalgam in the permanent dentition. To get a valid assessment of the trial material it was necessary to place the restorations alternately accepting that the two materials might be used under the similar clinical conditions. Unfortunately other exclusion criteria appeared to have been adopted despite our attempts to circumvent this prior to the commencement of the trial. Apart from two practitioners, the restorations were not placed alternately. If the exercise of clinical judgement were based on finding that the performance of the test material was poor, this would be entirely proper. We would have expected this to be reported and participant(s) to withdraw. We received no such reports; nor did it come up in discussions with coordinators either initially or during the trial. In the light of this we feel that we were possibly trying to 'go a bridge too far'.