Figure 1. Labeling in adult rat teeth. (A,B) Fluoro-Gold was placed in the sulcus (*) on the mesial side of the first molar. Three days later, it was found heavily labeling the odontoblasts (left arrow) near that site, and less intensely for cervical odontoblasts on other sides of the tooth (right arrow). There was no label of root pulp, but some intercuspal odontoblasts were labeled. (C) Similar Fluoro-Gold placement in rat incisor sulcus (*) did not produce any label of pulp (p) 3 days later. (D-G) Analysis of timing of Fluoro-Gold influx demonstrated labeled dentin plus a few odontoblasts (arrows) 1 hr after FG placement (D), many more odontoblasts at 4 hrs for cervical (E) and intercuspal (F) odontoblasts, with strong label of odontoblasts persisting at 13 days (G). Dentinal labeling was prominent at 1 and 4 hrs but weak or absent at 3-13 days, and was blocked by reparative dentin (RD, in Fig. 1E). (H) Intraperitoneal injection of Fluoro-Gold produced weak label of all odontoblasts (arrow) in all teeth. (I) At high magnification, Fluoro-Gold can be seen outlining acellular tubules of outer dentin (OD) and within odontoblast processes (arrows) of inner dentin (ID) 4 hrs after application. (J,K) Fluorescence microscopy of undecalcified teeth shows Fluoro-Gold in enamel (En) and staining inner dentin (den) and pulp (P) at 2 hrs after placement in the mesial sulcus next to first molars. The endogenous fluorescence of unlabeled teeth (K) was much less. Scales: A, 0.5 mm; B-H, 0.2 mm; I, 0.05 mm.