Fig. 1From: A comparison of the shaping ability of three nickel-titanium rotary instruments: a micro-computed tomography study via a contrast radiopaque technique in vitroRepresentation drawing of tooth section showing how transportation and centring ratio were derived. Dark shaded area represents original canal space, and grey shaded area represents canal’s shape after instrumentation. X1 = shortest distance from the distal edge of the blocks to the distal periphery of the pre-instrumented canal; X2 = minimum distance between the distal of the blocks to the distal periphery of the instrumented canal; Y1 = shortest distance from the mesial edge of the blocks to the corresponding periphery of the pre-instrumented canal; and Y2 = the minimum distance between the mesial edge of the blocks to the mesial periphery of the instrumented canalBack to article page