Prepared By : Murtada A. Sa’afin 20510541 & Ibtehal Nazzal 205

The Hertwig's epithelial root sheath Frequently abbreviated as "HERS“. It is a proliferation of epithelial cells located at the cervical loop of the enamel organ in a developing tooth. Hertwig's epithelial root sheath initiates the formation of dentin in the root of a tooth by causing the differentiation of odontoblasts from the dental papilla. The root sheath eventually disintegrates, but residual pieces that do not completely disappear are seen as epithelial cell rests of Malassez “ERM”.

(1) The HERS. (2) ERM. (3) Dental follicle. (4) cementoblasts. (5) periodontal ligament. (6) alveolar cells. (7) bone. (8) odontoblasts.

Germ Tube A mass of tissue, including the enamel organ and dentinal papilla, that has the potential of developing into a tooth and tooth bud. Or we can say that the germ tube is a primitive cell in the embryo that is the precursor of a tooth.

dental papilla The dental papilla is a condensation of ectomesenchymal cells called odontoblasts, seen in histologic sections of a developing tooth. It lies below a cellular aggregation known as the enamel organ. The dental papilla appears after 8-10 weeks intra uteral life. The dental papilla gives rise to the dentin and pulp of a tooth. The enamel organ, dental papilla, and dental follicle together forms one unit, called the tooth germ. This is of importance because all the tissues of a tooth and its supporting structures form from these distinct cellular aggregations

A: enamel organ B: dental papilla Histologic slide showing a tooth bud A: enamel organ B: dental papilla C: dental follicle

inner enamel epithelium The inner enamel epithelium, also known as the internal enamel epithelium, is a layer of cells located on the rim nearest the dental papilla of the enamel organ in a developing tooth. This layer is first seen during the bell stage. The location of the enamel organ where the outer and inner enamel epithelium join is called the cervical loop.

Bell Stage the developmental stage of tooth development during which the cup-shaped enamel organ is transformed into a bell-shaped structure. Fourth stage of odontogenesis, in which differentiation occurs to the period when the cap of enamel organ on the developing tooth is converted to a bell shape in cross section its furthest extent. At the bell stage, the final shape of the tooth crown begins to become apparent – this is known as morpho-differentiation.

This slide shows the early bell stage of tooth development This slide shows the early bell stage of tooth development. It is called the bell stage because (with imagination at this early stage) the enamel organ is bell-shaped.

The neonatal line The neonatal line is a particular band of incremental growth lines seen in histologic sections of a deciduous tooth. It belongs to a series of a growth lines in tooth enamel known as the Striae of Retzius. The neonatal line is darker and larger than the rest of the striae of Retzius. It is caused by the different physiologic changes birth and is used to identify enamel formation before and after birth. In forensic dentistry, the neonatal line can be used to distinguish matters such as if a child died before or after birth and approximately how long a child lived after birth.

Incremental Lines Transverse line's sometimes seen in dentin, due to improper calcification. Counting incremental lines in dental cementum is an accepted method for estimating age in many wild mammals., In human teeth such countings, have given variable results, and the aim of the present investigation was to find out if one incremental line is formed per year in human teeth as well.

The Tooth Fairy is a mythical character depicted as a fairy that gives a child money in exchange for a baby tooth that has fallen out. ... ( so the child Believe that this Fairy took their primary teeth and give them the permanent teeth as A GIFT )

Thank You