Found it !
Royal Navy Sick Berth Attendant (Dental Attendant) 1949
Also Dental Nurse : Dental Nurse. Royal Navy. Cloth. Embroidered. Blue on white. Circle. Letters 'DN' in centre.
Regarding variations : White printed or Embroidered.Gold on blue.
Rank : Chief Petty Officer Crown above. Small.
..........Petty Officer Crown above. Large.
P.S While searching I found the Navy equivalent of my own qualification !
Royal Navy Sick Berth Attendant/Technician (Operation Room Attendant) 1949-65
> Army title O.T.T (Operating Theatre Technician)
> Old civilian title O.D.A (Operating Department Assistant)
> Current civilian title O.D.P (Operating Department Practitioner)