root formation

Development of Teeth: Root Formation

Lesson - 2

Text and pictures in this presentation are taken

from Oral Histology text books: Ten Cates and

James Avery

ObjectivesAt the end of this chapter the student should be able to understand the process of root formation.,. including the role and function of the root sheath .

Sub topicsTopic 1. Root sheath developmentTopic 2. Formation of rootTopic 3. Fate of epithelial root sheathTopic 3. Fate of epithelial root sheath

1 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 structureThe rim of this disc like structure is called the epithelial diaphgramThe epithelial diaphgram encloses the primary apical foramen

2 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

Single roots and multiple rootsFor single-rooted teeth the root sheath grows like a cuff or tube around the newly forming pulpDevelopment 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 otherThis the divides the root into two or three

Root formation anomaliesIf 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 doesn’t form opposite the defect that occurred in the root sheathThe result will be a small lateral canal. This lateral canal is also called as supplemental canal or accessory canalAccessory canals connect the main root canal with the periodontal ligament

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

3 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 surfaceThey lie in the periodontal ligament and are called epithelial rests of MalassezThe epithelial rests of Malassez are found the in the periodontal ligament through out the lifeSometimes when there is chronic inflammation the epithelial cell rest of Malassez proliferate into cysts and tumours