Human tooth development focused on determining the processes that initiate tooth development. It is widely accepted that there is a factor within the tissues of the first pharyngeal arch that is necessary for the development of teeth. The tooth germ is an aggregation of cells that eventually forms a tooth. These cells are derived from the ectoderm of the first pharyngeal arch and the ectomesenchyme of the neural crest. The tooth germ is organized into three parts: the enamel organ, the dental papilla and the dental sac or follicle. The "enamel organ " is composed of the outer enamel epithelium, inner enamel epithelium,
Smear layer Smear layer The smear layer is a layer of microcrystalline and organic particle debris that is found spread on root canal walls after root canal instrumentation. It was first described in 1975 and much research has been performed since then to evaluate its importance in assisting or preventing the penetration of bacteria into the dentinal tubules. More broadly, it is the organic layer found over all hard tooth surfaces. Early studies of dentinal walls after cavity preparation performed by Brännström and Johnson (1974) showed the presence of a thin layer of debris that was 2 to 5 micrometres thick. In