Figure 2. Comparison of immature and very old rat molars. (A,B) The Fluoro-Gold label of odontoblasts (arrows) was widespread and intense for first (M1) and second (M2) molars 3 days after placement on the mesial side of M1 in juvenile rats. The third molar (B) was not yet erupted and was unlabeled. (C) Year-old molars have much less odontoblast labeling (arrow) compared with immature teeth (AB), and Fluoro-Gold did not reach the posterior side of either the first or the second molar. (D,E) Differences in odontoblast height and labeling for young and old molars are shown in these higher-magnification views from Figs. 2A and 2C. Scale bars: A, C, 0.5 mm; B, D, E, 0.2 mm.