Assessment of the inter-radicular alveolar bone volume of the maxillary right and left first molars. (A) Volumetric assessment of the inter-radicular bone was determined by first drawing a region of interest (ROI) around the maxillary left first molar (control side) extending from the mesial and distal extension of the CEJ to the apex of the mesial and distobuccal roots. This is extended buccally and palatally to encompass the complete buccopalatal width of the mesial root. Due to the root and alveolar resorption observed in the maxillary right side (experimental side), the root apices of the right molar could not be used as reliable reference points to establish the ROI. Instead, the 3-dimensional ROI (3-D ROI) created for the control side is transferred to the right molar using the CEJ as a reproducible reference plane to produce an ROI that is identical for both the left and right molars of each animal. (B) Inter-radicular bone was carefully contoured for every fifth slice with the intermediate slices initially interpolated by morphing. Each slice was subsequently visually inspected and the contour was modified where deemed necessary, ensuring that all root structure, and any cortical both, were excluded. (C) The region of the resultant 3-D ROI (red rectangle) with the maxillary first molar removed and is used to determine tissue volume (TV), bone volume (BV) and bone volume fraction (BV/TV) of the inter-radicular alveolar bone.