Figure 4

X-ray radiography analyses. (a–d) The plain X-ray radiographic analyses of the mandibles from the 7-day-old (P7), 14-day-old (P14), 28-day-old (P28) and 42-day-old (P42) mice. (e–h) μCT analyses of mandibular first molars from 28-day-old (P28) and 42-day-old (P42) mice. (a) At P7, the mineralized walls of pulp chambers in the mandibular first molars of the cKO mice appeared thinner than in control mice; the first molar in the cKO mice was covered by a large amount of overtopping bone (arrow) on the oral cavity side, whereas no obvious bone tissue was observed on the oral cavity side of the first molar in the normal mice. (b) At P14, the pulp chamber walls in cKO mice were thinner compared with control mice, and a significant amount of bone (arrow) was still present between the mandibular first molar and the oral cavity in the cKO mice. (c, d) In the P28 and P42 cKO mice, the pulp chamber walls were much thinner, and the crowns were shorter than in the control mice. These X-ray observations indicated that the eruption of the mandibular first and second molars in the cKO mice was dramatically delayed. M1, mandibular first molar; M2, mandibular second molar; arrows indicate the bone tissues overlying the oral cavity side of the mandibular first molars. (e, f) Compared with the control mice, the occlusal surface of the mandibular first molar in the P28 cKO mice was rougher. (e1, f1) On section views, an enamel layer (arrow) was clearly visible in the molars of the normal mice, whereas no enamel or enamel-like structures could be identified in the molars of the cKO mice. (g, h) At P42, the occlusal surface of the first molar in the cKO mice was nearly flat, and the tooth crown was much shorter than in the control mice. (g1, h1) An enamel layer (arrow) was clearly visible in the control mice but not in the cKO mice. e, f, g and h: full views; e1, f1, g1 and h1: longitudinal-section views. cKO, conditional knock out; Ctrl, control; μCT, micro-computed tomography.