DEVELOPMENT OF TIGHT JUNCTIONS BETWEEN ODONTOBLASTS IN EARLY DENTINOGENESIS AS REVEALED BY FREEZE-FRACTURE

Background: Mature odontoblasts possess junctional structures constitu ted by adherens, gap, and tight junctions. Although adherens and gap j unctions appear early between odontoblasts, there is no information on the appearance and development of tight junctions between odontoblast s. In this study, we have examined freeze-fracture replicas of early d entinogenesis to study the development of tight junctions between odon toblasts and to determine whether these junctions are of zonular or ma cular type, Methods: Upper first molar tooth germs of Wistar rats betw een 1 and 3 days old were fixed in buffered 4% glutaraldehyde/4% forma ldehyde and subsequently cryoprotected with cacodylate-buffered glycer ol, Freeze-fracture replicas were obtained in a Balzers 301 apparatus, and early stages of dentinogenesis were examined in a Jeol 100 CX II electron microscope, Results: In the stage of early dentine matrix pri or to mineralization, odontoblasts exhibit only gap junctions, With th e progression of development, the distal plasma membranes of odontobla sts show numerous short tight junctions formed by fused particles and grooves. In the stage of advanced mineralization, branched and continu ous rows of fused particles or grooves constitute tight junctions of t he focal or macular type, Conclusions: The present study shows that ti ght junctions of focal or macular type appear on distal plasma membran e of early odontoblasts during differentiation. Formation of tight jun ctions indicates the establishment of a distal membrane domain and mat uration of odontoblasts. These events occur as mantle dentine formatio n ceases and circumpulpar dentine formation begins. (C) 1997 Wiley-Lis s, Inc.