cementum and root formation Flashcards
when does root formation take place?
between the apposition stage (late bell stage) and maturation stage of tooth development
what is Hertwigs epithelial root sheath?
double layer of epithelium formed by inner and outer enamel epithelium
important for root formation
root formation follows HERS extension
what happens to HERS
becomes epithelial rests of Malassez
which are epithelial remnants of HERS
how does root formation occur?
- occurs after crown formation
- apical extension of the inner and outer enamel epithelium to form HERS
- HERS induces differentiation of odontoblasts from radicular pulp
- forms pre dentine which will mineralise into root dentine
- root formation is almost complete when HERS is just a small tag of epithelium - becomes rim of the epical foramen
what is the composition of cementum?
- Approximately 50% organic, 50% inorganic
- 90% of the organic component of cementum is Type I collagen
- Remaining collagens consist essentially of
- Type III collagen
- (less cross linking, higher amounts in development, associated with repair)
- Not involved with tissue connection
- Type XII collagen
- (fibril associated, binds type I and non-collagen proteins)
- Binds to type I and non-collagen proteins such as:
- Growth factors
- Cementum
- Enzymes
- Type III collagen
- noncollagenous protiens such as
- Alkaline phosphatase, bone sialoprotein, osteopontin, osteonectin, fibronectin, vitronectin, proteoglycans, proteolipids, many growth factors.
- Cementum attachment protein (CAP) (unique)
- Cementum protein 1 (CMP-1) induced bone and cementum proteins
when does cementum formation take place?
immediately after root formation
what are the possible sources for cementoblasts
- Infiltrating dental sac or dental follicle cells
- cells infiltrate newly formed root dentine
- receive signals from predentine or HERS to differentiate into cementoblasts
- HERS cell transform into cementoblasts
- epithelial cells in rests of Malassez can proliferate and transdifferentiate into cementoblasts
- Stem cells from blood
- migrate from vascular region
- isolated from blood circulation
- differentiate into cementoblasts
what are the possible signals for cementum formation?
- loss of stellate reticulum
- may withdraw a signal to cause cementoblast differentiation
- HERS
- dental follicle cells migrate towards predentine and provide signal
- HERS cell apoptosis
- odontoblasts produce pre-dentine
- possible growth factors will signal
- unclear mechanism
what is the current evidence for cementogenesis and root formation?
Cells in dental follicle contribute to periodontal ligament cells and cementoblast precursor cells
PDL and cementoblast precursors reside within the dental follicle, and differentiation is under the control of factors in the local milieu.
HERS epithelial cells undergo epithelial-mesenchymal transdifferentiation into cementoblasts during development (immunocytochemical, structural data)
- HERS into cementoblasts
what factors regulate cementogenesis?
- Cementum protein 1 (CEMP-1)
- induced bone and cementum proteins in PDL cells
- BMP’s (BMP-2, BMP-4, BMP-7 (OP-1))
- promote cell differentiation during development and regeneration
- Into cementoblasts
- PDGF’s - +/- IGF’s
- promote cell proliferation, migration, and vasculogenesis.
- With or without IGFs
- FGF’s - as PDGF, but without cell cycle effects.
- Found in developing tooth
- Promote cell migration
- Adhesion Molecules - BSP, Osteopontin
- promote mineralisation of cell matrix and crystal growth.
- Collagens -
- I and III
- development and tissue regeneration.
- IV and XII
- may maintain PDL space avoiding continuous cementum formation.
- I and III
- Matrix Gla proteins -
- promote cell proliferation, migration, and vasculogenesis.
- Transcription factor’s - Cbfa-1 (Runx2) and Osterix
- master switch activators
- Cementoblast maturation
- Others - Alk Phos, MMP’s, RANKL-RANK-OPG, local cytokines and growth factors
- Other proteins - play a role in cementoblast differentiation and cementum formation
how are types of cementum classified?
Based on time of formation
- Primary cementum:
- formed before eruption
- Secondary cementum:
- formed after eruption
Based on presence or absence of cells in the matrix
- Acellular cementum
- Cellular cementum
Based on origin of collagen fibers in the matrix
- Intrinsic fiber cementum:
- fibers formed by cementoblasts
- Extrinsic fiber cementum:
- fibers resulting from incorporation of periodontal ligament fibers
- Also called sharpey fibre
what is Acellular cementum?
- aka primary cementum
- top part of root
- close to crown
- adjacent to unmineralised dentine
- which then becomes mineralised
- spreads into cementum
- strong union at cementodental junction
what is cellular cementum?
- aka secondary cementum
- rapidly formed
- less mineralised than acellular
- slow mineralisation
- deposited on dentine surface near advancing root edge
- Rapid cementum matrix deposition makes cementoblast trapped to become cementocytes
- Cementocytes occupy small space called ‘osteocytic lacunae’
what is cellular mix fibre cementum?
- fibres are derived from PDL and cementoblasts
- sharpey’s fibres are much thicker
- fibres run in different orientations
- intrinsic parallel to root, extrinsic perpendicular to root
what is acellular afibrillar cementum?
- Mineralised matrix but lacks collagen
- Plays no role in tooth attachment
- Deposited over enamel and dentine at the cementoenamel junction -
- cervical enamel surface
what is the association of cementum with enamel??
Overlap - 60%
Butt joint - 30%
Gap - 10%
