Figure 1

FIGURE 1. Tooth attachment in actinopterygians. (A) Schematic representation of type 1 and type 2 tooth attachment modes according to Fink (1981). In type 1 (e.g., zebrafish), a cylindrical collar of tissue, hitherto called “bone of attachment” (“attachment bone” in the terminology of Fink, 1981), firmly ankyloses the tooth to the supporting bone, resulting in continuous mineralization between the tooth base and the supporting (dentigerous) bone. In type 2, the cylindrical collar of “bone of attachment” is connected to the tooth by a ligament. The collar is positioned either on top, or inserted into the supporting bone. Note that in the latter case, Berkovitz and Shellis (2016) label the “bone of attachment” as “pedicel”, reserving the term “bone of attachment” for the tissue serving to attach the pedicels. Note that the term “bone of attachment” is used between quotation marks, pending a more appropriate term based on the findings in this study. (B) and (C) Toluidine blue-stained semi-thin sections of a zebrafish initiator tooth at 6dph (B) and an adult tooth (C), both attached, as in type 1 attachment. Note multiple osteocytes in the adult supporting bone, a single one in the “bone of attachment” (encircled). Inset: enlargement of “bone of attachment” (dotted rectangle) with cell prolongations (open arrowhead). (D) Scanning electron micrograph of attached adult zebrafish teeth. (E) Overview transmission electron microscopy (TEM) picture of the base of a zebrafish first-generation tooth at the level of the cervical loop. The dentin, “bone of attachment” and supporting bone form a continuous mineralized tissue, covered along the pulpal side with scleroblasts that appear to be involved in the deposition of more than one matrix. cb, ceratobranchial cartilage; cl, cervical loop; d, dentin; dp, dental pulp; sb, supporting bone; asterisks, “bone of attachment”; arrows, scleroblasts forming “bone of attachment”; black arrowheads, odontoblasts. Scale bar (B)=10μm, (C)=50μm, (D)=100μm, and (E)=5μm.