Sir, your informative and thought-provoking orthodontic themed issue (BDJ 2015; 218: issue 3) provided a timely insight into orthodontic treatment in the same month that NHS England produced the final draft of its 'Guide for commissioning dental specialities – orthodontics', which has some sensible guidance for commissioning, supported by the evidence and literature.

However, there is a requirement that anyone providing orthodontic treatment must conduct at least 50 case starts per year, which I understand from members of the working group is in the 'interests of patient safety'. What is the evidence base for this requirement? An electronic search of the literature produces none. A survey of the orthodontic workforce1 considered an orthodontic provider to be a specialist or a non-specialist who treated more than 30 cases per year. Why does NHS England now consider 50 to be the 'magic number'?

Two audit papers2,3 show that clinical assistant (CA) training produced good quality outcomes very similar to consultants and specialists in both hospital and general practice. The volume of cases treated was not found to be an indicator of the quality of outcome.

I underwent CA training 20 years ago with our local consultant and have worked part time in the department ever since. As a GDP I carry out 40 case starts per year in the general dental service. 'PAR' scores of my completed cases show 70+% are improved or greatly improved and I am sure that there are many other GDPs who are in a similar position. I have no objection to my work being judged on its merits using a recognised indicator but am now at risk of losing the orthodontic part of my contract based on an arbitrary number.

Since CA training was the only realistic way forwards for most of us it seems discriminatory that my generation now runs the risk of losing part of our livelihoods, and the NHS of losing our experience, based on a whim that will also variously disadvantage our patients. I would be very grateful if someone at NHS England would point me towards the evidence on which this requirement is based.