Development, growth and eruption of permanent incisor teeth in Romney sheep.
The development of permanent incisor teeth of sheep was followed from the age of six weeks to 116 weeks. The teeth were observed through the bud, cap and bell stages, and the development of enamel and dentine. At the same time that amelogenesis started, the papillary layer developed from the intermediate layer and the outer dental epithelium began to form the cell rests of Malassez. The ameloblasts went through secretory, transitional and maturational phases, and in due course disappeared, after which cementum was laid down over the enamel surface. Initially the connective tissue of the follicle surrounding the growing tooth was very loose, but was replaced from the crown end as the tooth developed, by more dense connective tissue. Around the time of eruption, melanocytes were found on the lingual surface of the coronal end of the follicle. The root was formed under the influence of Hertwig's epithelium, and the cell rests of Malassez appeared to continue to develop from the outer enamel epithelium. Odontoblasts, which arose from the pulp connective tissue, were initially cuboidal but became fusiform as the tooth matured. At the time of eruption, amelogenesis was almost complete and cementum covered the majority of the tooth surface. The cell rests and melanocytes of the tootth follicle appeared to migrate with the tooth as it erupted. The deciduous tooth was resorbed from the lingual surface. The junctional epithelium of the erupted permanent tooth may have arisen from the cell rests, remnants of the dental lamina or gingival epithelium, depending on the presence or absence of inflammation.
D000566:Amelogenesis; D000818:Animals; D003739:Dental Cementum / Q000502:physiology; D007180:Incisor / Q000166:cytology / Q000254:growth & development*; D008544:Melanocytes / Q000166:cytology; D012756:Sheep / Q000502:physiology*; D014078:Tooth Eruption; D014092:Tooth Root / Q000254:growth & development