The efficiency of calculus removal and the amount of lost tooth substance resulting from the use of hand curette, ultrasonic curette and rotating diamond and Roto-Pro points were examined by scanning electron microscopy (SEM). Root surfaces of mandibular incisors placed in a jaw model were cleaned of adhering deposits, photographed by SEM and evaluated at a standard magnification by three examiners. Scores were given for remaining calculus (RCI) and loss of tooth substance (LTSI) according to defined index criteria. The results revealed that calculus removal was most complete following diamond instrumentation, whereas the ultrasonic curette was least efficient in this respect. Hand curette, ultrasonic curette and Roto-Pro removed about the same amount of tooth substance whereas the diamond removed considerably more than the others. The diamond regularly removed all the cementum and left deep instrumental marks in the dentin; it seems advisable to avoid the use of such instruments in periodontal depuration.