title: The eternal tooth germ is formed at the apical end of continuously growing teeth.
abstract: Rodent incisors are known to be continuously growing teeth that are maintained by both the cell-proliferation at the apical end and the attrition of the incisal edge. This type of tooth had a special epithelial structure for the maintenance of stem cells, showing the bulbous epithelial protrusion at the apical end. The morphological transition of the epithelial-mesenchymal compartment by serial transverse sections of the apical end toward the incisal direction is likely to reflect the development of the tooth germ in the prenatal stage. Based on the present histological and previous molecular biological studies, the special structure at the apical end is obviously different from the cervical loop giving rise to Hertwig's epithelial root sheath (HERS), in human, mouse and rat molar tooth germs. Hence, we propose a new concept that the eternal tooth bud producing various dental progeny is formed at the apical end of continuously growing teeth, and a new term "apical bud" for indicating this specialized epithelial structure. Furthermore, BrdU labelling analysis suggested that the guinea-pig molars, which were continuously growing teeth, also possessed plural specific proliferative regions and "apical bud" at the apical end.
authors.affiliation: Department of Tissue Regeneration and Reconstruction, Niigata University Graduate School of Medical and Dental Sciences, 2-5274 Gakkocho-dori, Niigata 951-8514, Japan.
authors.forename: Hayato
authors.initials: H
authors.lastname: Ohshima
authors.forename: Naohiro
authors.initials: N
authors.lastname: Nakasone
authors.forename: Emi
authors.initials: E
authors.lastname: Hashimoto
authors.forename: Hideo
authors.initials: H
authors.lastname: Sakai
authors.forename: Kuniko
authors.initials: K
authors.lastname: Nakakura-Ohshima
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Harada
mesh_terms: D000818:Animals; D006168:Guinea Pigs; D007180:Incisor / Q000166:cytology / Q000254:growth & development; D051379:Mice; D008963:Molar / Q000166:cytology / Q000254:growth & development; D012038:Regeneration / Q000502:physiology*; D012377:Rodentia / Q000196:embryology*; D013234:Stem Cells / Q000166:cytology*; D019227:Tooth Apex / Q000166:cytology*; D014083:Tooth Germ / Q000502:physiology*