Assessment of total root volume and mesial root volume. (A) Root structure is carefully highlighted, ending at the CEJ, for every fifth sagittal slice containing the maxillary first molar roots. Intermediate slices were initially interpolated by morphing and then visually inspected, with the contours modified where necessary, to ensure that all root structure was included. (B) Reconstruction of the sagittal slices produced a 3-D representation of the entire root structure to allow assessment of root volume (RV). (C) The mesial root was then digitally resected from this rendering and its volume is analysed individually.