Ultrastructure of Hertwig's epithelial root sheath during early root development in premolar teeth in dogs

Ultrastructural and histochemical study on the morphogenesis of epithelial rests of Malassez.

“…Similar findings have been reported by another worker (LESTER, 1969b). It has been generally accepted that such epitheliomesenchymal relationships are essential in the induction of odontoblasts and cementoblasts from mesenchymal cells in tooth formation (LESTER, 1969b;SLAVKIN, 1974;OWENS, 1978). In other organs such as the doudenum, interactions with underlying connective tissue cells are thought to play an important role in the cytodifferentiation of epithelial cells (MATHAN et al, 1972).…”

“…Attention has thus been focused on the role of the sheath cells in the sequence of events occurring during root formation. Although the ultrastructural profile of migrating sheath cells as well as epithelial cells in the rests of Malassez in teeth after eruption has been reported by several authors (VAL-DERHAUG and NYLEN, 1966;LESTER, 1969a;OWENS, 1978), no precise ultrastructural study has been available describing the morphogenesis of epithelial rests of Malassez.…”

“…The importance of epithelial mesenchymal interactions between cells of Hertwig's epithelial root sheath and cells of the dental papilla in the induction of odontoblasts and dentine production has been recognized (SLAVKIN, 1974;OWENS, 1974). According to LESTER (1969a), some of the epithelial cells derived from Hertwig's root sheath are incorporated in the cementum, whereas others migrate into the periodontal ligament.…”

Role of Hertwig's epithelial root sheath cells in tooth root development

“…However, our experiments indicate that HERS cells in vitro express osteocalcin, thus leaving the possibility that the basement membrane disruption is caused by HERS cells when they start depositing the acellular cementum. Furthermore, it has been suggested that the basement membrane contains chemotactic proteins, deposited by the HERS cells, which serve to direct the migration of precementoblast cells (Owens, 1978;Slavkin et al, 1989;Thomas and Kollar, 1989;MacNeil and Thomas, 1993) or induce cementoblast differentiation (Paynter and Pudy, 1958;Slavkin et al, 1988). Recent studies suggest that the collagenous-like protein CAP isolated from cementum, and as demonstrated in this study is present in HERS cells both as a membrane-associated protein and as a secreted protein, possesses chemotactic activity and is capable of recruiting putative cementoblast precursors (McAllister et al, 1990;Pitaru et al, 1995;Metzger et al, 1998;Barkana et al, 2000).…”

“…Amongst the different functions attributed to these cells are that of inducers and regulators of root formation, including the size, shape, and number of roots (Ten Cate, 1996). It has also been suggested that HERS cells deposit chemotactic proteins into the basement membrane to direct the migration of precementoblast cells (Owens, 1978;Thomas and Kollar, 1989;MacNeil and Thomas, 1993). Another role attributed to HERS cells is that of inducers of differentiation of odontoblast cells to form root dentine (Selvig, 1963, Ten Cate, 1978 or dental sac cells to differentiate into cementoblasts (Paynter and Pudy, 1958).…”