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Root formation

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From Ten Cate's Oral Histology …

From Ten Cate's Oral Histology
For BDS students


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  • 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
  • 4. 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
  • 5. 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
  • 6. 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
  • 7. 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
  • 8. 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