Root Development
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When does root development begin?
Once the crown has formed
What does the onset of root development coincide with?
Axial phase of tooth eruption
What is the axial phase of tooth eruption?
When the tooth breaks through the gum
What 3 components are involved in root development?
• Dental follicle • Root sheath of Hertwig • Dental papilla
What forms the root sheath of Hertwig?
Internal and external enamel epithelium at the cervical loop
How does the root sheath proliferate?
Apically
Why does the root sheath proliferate apically?
Map out the shape of the future root
How does a primary apical foramen subdivide to create multiple root patterns?
Ingrowth of shelves
How is root dentin formed?
Cells of internal enamel epithelium induce mesenchymal cells of papilla to differentiate into odontoblasts and produce root dentin
What 3 things occur once root dentinogenesis has begun?
• Root sheath loses continuity and separates from developing root dentin • Epithelial cells of sheath disperse into small clusters - Epithelial cell rests of Malessez • Mesenchymal cells differentiate into cementoblasts and produce cementum
What happens to any remaining cells in dental follicle once cemetogenesis has begun?
Differentiate into fibroblasts and produce collagen of periodontal ligament
Describe the vascularity and innervation of cementum
Avascular with no innervation
What are 3 functions of cementum?
• Provide attachment of collagen fibres of periodontal ligament • Cover root surface • Provide seal for open dentinal tubules
Name 3 ways that cementum can form a relationship with enamel
• Overlap • Meet • Gap
What is a potential problem with a gap between the enamel and cementum?
Due to gingival recession, dentinal tubules could become exposed
Describe the chemical properties of cementum
45% inorganic 33% organic 22% water
Describe the inorganic component of cementum
Calcium hydroxyapatite
Describe 2 things found in the organic component of cementum
• Collagen Type I 2. GAGs
What are 2 contributing factors to whether cementum is calcified?
• Presence / absence of cells 2. Nature and origin the organic matrix
What is the primary difference between primary and secondary cementum?
Secondary cementum contains cells - cementoblasts / cementocytes
Where does acellular cementum tend to be found?
Covering root adjacent to dentin
Where 2 areas is cellular cementum likely to be found?
• Apical area overlying acellular cementum 2. Interradicular areas
What is an interradicular area of a tooth?
The area between roots
What 2 sources is the organic matter of cementum derived from?
• Sharpey’s fibres from PDL (extrinsic fibres) 2. Cementoblasts (intrinsic fibres)