Development of Teeth: Root Formation Lesson - 2
Text and pictures in this presentation are takenfrom Oral Histology text books: Ten Cates and James Avery
ObjectivesAt the end of this chapter the student should be ableto 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 sheath
1 Root sheath developmentThe root starts to develop after the crown is completed Epithelial cells of the inner and outer enamel epitheliumproliferate from the cervical loop to form two layers ofepithelium called Hertwigs root sheath The first formed part of the root sheath bends to form adisc like structureThe rim of this disc like structure is called the epithelialdiaphgramThe epithelial diaphgram encloses the primary apicalforamen
2 Formation of RootAfter the formation of epithelial root sheath and theepithelial diaphragm the root grows in lengthThe diaphragm maintains a constant size while the rootsheath grows in length at the angle of the diaphragm andnot at its tip The cells of the lengthening root sheath induce theadjacent dental papilla cells to differentiate intoodontoblasts The newly formed odontoblasts then form the rootdentine As the root lengthens the crown moves occlusally
Single roots and multiple rootsFor single-rooted teeth the root sheath grows like a cuffor tube around the newly forming pulpDevelopment of multi-rooted teeth takes place in a samemanner until the furcation area. When the furcation area is reached the epithelialdiaphragm develops tongue like extensions that grow untilthey contact each otherThis the divides the root into two or three
Root formation anomaliesIf the continuity of the root sheath is broken before thedentine is formed it results in missing or abnormalepithelial cells When the epithelial cells are missing the Odontoblastsdo not differentiate and dentine doesn’t form opposite thedefect that occurred in the root sheathThe result will be a small lateral canal. This lateral canalis also called as supplemental canal or accessory canalAccessory canals connect the main root canal with theperiodontal ligament
If the epithelial root sheath does not degenerate at theproper time and remain stuck to the surface of the rootdentine, then that area becomes devoid of cementum Areas of root without cementum can be a cause ofsensitivity if the there is gingival recession
3 Fate of epithelial root sheathAfter dentine formation in root takes place, the epithelialroot sheath breaks down and its remnants migrate awayfrom the dentinal surfaceThey lie in the periodontal ligament and are calledepithelial rests of MalassezThe epithelial rests of Malassez are found the in theperiodontal ligament through out the lifeSometimes when there is chronic inflammation theepithelial cell rest of Malassez proliferate into cysts andtumours
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