Fig. 2

Manual X-ray bone loss measurement method and PCA measurement method based on tooth semantic segmentation results. (a) Two manual methods for RBL measurement are described as max (L1/L2, R1/R2) ×100 and max (L3/L4, R3/R4) ×100. The red lines indicate the length of the CEL to the ABC, and the green lines indicate the length of the CEJ to the AP. The yellow lines indicate the distance from the CEL to the ABC, and the blue lines indicate the distance from the CEJ to the AP. L and R represent proximal and distal, respectively. (b) The external ellipse of the tooth body and its principal axis were obtained via PCA. The red line indicates the tooth’s smallest enclosing ellipse, and the dark blue line represents the tooth’s longitudinal axis. The green dot represents the center of the red ellipse. (c) Length A of the principal axis of the ellipse passed through the convex hull of the suprabony portion of the root. (d) Length B of the principal axis of the ellipse passed through the convex hull of both the suprabony and intrabony portions of the root. PCA, principal component analysis; CEJ, cemento-enamel junction; ABC, alveolar bone crest; AP, apical point