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Patterns of Fluoro-Gold Entry into Rat Molar Enamel, Dentin, and Pulp

¹ Dept. of Anesthesiology, Box 356540 , and
² Dept. of Endodontics, Univ. of Washington, Seattle, WA 98195-6540;

View larger version (115K): [in a new window]   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.

View larger version (136K): [in a new window]   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.

View larger version (160K): [in a new window]   Figure 3. FG patterns for different dental injuries. (A) A flap procedure (f) on the mesial side of the first molar without tooth injury gave patterns similar to those in normal teeth. (B) Scraping of exposed crown and root after a gingival flap procedure (f/s) gave strong labeling of coronal and root dentin, weak label of odontoblasts beneath the labeled dentin, and diffuse label throughout the mesial pulp. (C) Odontoblasts, dentin, and adjacent pulp on the distal side of the molar in panel B were labeled at the normal intensity. (D) Higher magnification of the injury site in Fig. 3B, showing variable intensities in the odontoblast layer. (E) Prior induction of reparative dentin (RD) blocked entry of most of the FG, which persisted in the dentinal tubules that were blocked by the reparative matrix. (F,G) When Fluoro-Gold was placed into molar pulps (*) through small cavities, it spread throughout the pulp and into dentin, where the odontoblast layer was broken, but was kept out of dentin by intact odontoblast layers (Od). Scale bars: A,B,C,E,F = 0.2 mm. D,G = 0.1 mm.

View larger version (111K): [in a new window]   Appendix Fig. Fluoro-Gold stained the enamel yellow within a few minutes after being placed into the sulcus on the mesial aspect of the first maxillary molars of this young adult rat. It also dissolved in sulcular fluid, moved around the first molar sulcus to reach the second molar, and spread into intercuspal grooves. The most intensely yellow regions corresponded to the areas with greatest influx of Fluoro-Gold into the pulp, shown in the text in Figs. 1-3.