It means preparing a root canalwith instruments in decreasing sizes step-by-step toward the apex without using pressure. To begin with, it is necessary to determine the approximate canal length withan initial x-ray. The exact working length will be determined when reaching approx. 2/3 of the estimated canal length. Using one of the new electronic length determination devices, e.g. Raypex 6, ismore accurate and faster than x-rayimaging.
After this, the apex is enlarged with instruments in increasing sizes (each instrument tothe full working length).The crown-down method for rotary root canal preparation has been widely tried and tested.