Tooth Development IV - Root Development Flashcards
When does root development occur?
- Proceeds some time after the crown has formed
What’s the initial stage of root formation?
- When enamel and dentine formation are well advanced, the INTERNAL & EXTERNAL ENAMEL EPITHELIA at the CERVICAL LOOP FORM a DOUBLE LAYERED ROOT SHEATH
= HERTWIG’S ROOT SHEATH
How does the Hertwig’s Root Sheath proliferate?
- Apically, to map out the shape of the future root
Epithelial shelves grow to demarcate the location of multiple roots
What does the Dental Follicle form?
- Lies external to the root sheath
Forms:
- Cementum
- Periodontal Ligament
- Alveolar Bone
Cementogenesis: What’s the process of Primary (acellular) cementum formation?
- Starts at the cervical margin and extends apically
1. Hertwigs root sheath induces dental papilla cell differentiation into Odontoblasts (root pre-dentine)
2. Due to the their being no Odontoblastic processes in the initial few microns of the tissue; its responsible for the HYALINE LAYER
3. Hertwig’s Root Sheath deterioration allows the adjacent fibroblast-like cells of the Dental Follicle o lie closer to the surface of the Hyaline layer
4. These cells represent the cementoblasts associated with the formation of the primary cementum; they then secrete collagen fibrils - Strong union with the Dentinal collagen
5. Cementoblasts produce non-collagenous proteins which might be involved with Chemoattraction/mineralisation/cell attachment
6. Slow increase in Cementum thickness and the secretion of ground substance
What initiates the mineralisation in cementum?
- Presence of Hydroxyapatite crystals in the dentine
- Periodontal fibroblasts may play a role due to them being rich in Alkaline Phosphatase
(no calcosperes have been observed)
Does Acellular Cementum possess incremental lines?
- Yes
- Closes together than cellular cementum
Acellular Afibrillar Cementum: What is it and what’s its function?
- Thin layer of cementum overlying enamel
- Reduced enamel epithelium over that enamel is damaged or lost
- Cells in the follicle then come in contact with enamel and differentiate into cementoblasts
- Produce an afibrillar matrix that calcifies
Cellular Cementum: Where is this variation of cementum typically found?
- Apical root 1/3 & furcation area
- Associated with an increase in the rate of formation of the tissue
Cellular Cementum: What’s the process of formation?
- Following the loss of continuity of the epithelial root sheath, large basophilic cells are seen to differentiate from the adjacent cells of the dental follicle against the surface of the root dentine
- Form a distinct layer of cementoblasts
- Possess more more cytoplasm and more cytoplasmic processes than the cells associated with Acellular cementum - Cementoblasts secrete the collagen fibres (& ground substance) that form the intrinsic fibres of the secondary, cellular cementum
- Fibres are orientated parallel to the root surface - Linear mineralisation of the cementum occurs but it is less mineralised than the acellular cementum
What’s special about the way Cementoblasts secrete collagen and ground substance?
- Multipolar mode of matrix secretion
- Results in cell becoming incorporated into the forming matrix and theses are converted into cementocytes
What structure can the Cementocytes be found in?
- Lacunae
What’s the significance of cementocytes being in lacunae?
- It necessitates the generation of new cementoblasts from stem cells within the periodontal ligament
Are incemental lines and sharpey’s fibres present?
- Yes
- No - no role in tooth attachment
What’s an Enamel Pearl?
- Small droplet of enamel on the root, near the furcation
- Budding of Hertwig’s root sheath - differentiation of ameloblasts
- Problem for RDT
