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Figure 4: Remodeling of the PDL of incisors is defective in mice. H&E-stained PDL section from 12week (a) and (b) mice. Arrows indicate the shear zone, which is the boundary between the TR (tooth-related) and AR (alveolus-related) regions. The shear zone is clearly visible in 12 week old mouse (a) and absent in mouse (b). TEM of the incisor PDL shows evidence of digestion of collagen fibers in (c) but undigested and abundant collagen bundles in mice (d). De, dentin; Al, alveolar bone. (Reprinted from Kii et al., 2006 [102], with permission, Elsevier 2006, and thanks to Dr. A. Kudo for his generous approval.)