From Ten Cate's Oral Histology For BDS students

1. Development of Tooth:
Root Formation

2. Sub topics
Root sheath development
Formation of root
Fate of epithelial root sheathFate of epithelial root sheath

3. Root sheath development
The root starts to develop after the crown is completed
 Epithelial cells of the inner and outer enamel epithelium proliferate from the
cervical loop to form two layers of epithelium called Hertwigs root sheath
 The first formed part of the root sheath bends to form a disc like structure
The rim of this disc like structure is called the epithelial diaphragm
The epithelial diaphragm encloses the primary apical foramen

10. Formation of Root
After the formation of epithelial root sheath and the epithelial diaphragm
the root grows in length
The diaphragm maintains a constant size while the root sheath grows in
length at the angle of the diaphragm and not at its tip
 The cells of the lengthening root sheath induce the adjacent dental
papilla cells to differentiate into odontoblasts
 The newly formed odontoblasts then form the root dentine
 As the root lengthens the crown moves occlusally

11. Single roots and multiple roots
For single-rooted teeth the root sheath grows like a cuff or
tube around the newly forming pulp
Development of multi-rooted teeth takes place in a same
manner until the furcation area.
 When the furcation area is reached the epithelial diaphragm
develops tongue like extensions that grow until they contact
each other
This divides the root into two or three

14. Root formation anomalies
If the continuity of the root sheath is broken before the
dentine is formed it results in missing or abnormal epithelial
cells
 When the epithelial cells are missing the Odontoblasts do
not differentiate, and dentine does not form opposite to the
defect that occurred in the root sheath
The result will be a small lateral canal. This lateral canal is
also called as supplemental canal or accessory canal
Accessory canals connect the main root canal with the
periodontal ligament

16. If the epithelial root sheath does not degenerate at the
proper time and remain stuck to the surface of the root
dentine, then that area becomes devoid of cementum
 Areas of root without cementum can be a cause of
sensitivity if the there is gingival recession

17. Fate of epithelial root sheath
After dentine formation in root takes place, the epithelial
root sheath breaks down and its remnants migrate away
from the dentinal surface
They lie in the periodontal ligament and are called
epithelial rests of Malassez
The epithelial rests of Malassez are found the in the
periodontal ligament through out the life
Sometimes when there is chronic inflammation the
epithelial cell rest of Malassez proliferate into cysts and
tumours