Structural components of Expandable Micro-motor Bur. A) Bur components in position, Bur Head (female member) (a), Spacers (b), Bur Base (male member) (c) clutched together for mounting to micro-motor through Main shank, expanded Bur Head (d) and cross-section view (e). B) Bur Base (male member) consists of Spiral grooved shaft (a), Spacers (b) and Main shank (c); the tip portion is round (d) and grooveless (e), spacers removed from male member (f) and cross-section view (g). C) Bur Head (female member), tip view of Bur Head spinning in root canal. Different degrees of expansion occurs in the canal as shown while Spiral grooved shaft bears three (a), two (b), one (c), no spacers (d) and cross-section view (e).