17 - Histogenesis of periodontium Flashcards
Periodontal ligaments
Fibrous CT between alveolar bone + cementum covering root
This ligament covers the root + connects w/the gingiva
PDLs occupy periodontal space + is composed of:
- Fibres
- Cells
- Intercellular substance
Cells of PDL
dental follicle cells differentiate into ⇢ collagen-forming cells of ligament + cementoblasts
- Some cells of ligament invade tooth root sheath + break it apart
- Other cells of ligament form delicate fibres ⇢ these appear along the forming roots near cervical region of the crown
The thickness of PDL varies in each tooth
- PDL is thickest near middle part of the root
- As age ⇡, width of PDL ⇣
Genesis of PDL
Dental follicle is responsible for development of PDL
- Mesenchymal cells differentiate into fibroblasts, cementoblasts + osteoblasts
- Fibroblasts ⇢ form PDL
- Factors secreted by fibroblasts⇢ inhibit mineralisation + prevent tooth ankylosis
- Fibroblasts get embedded in developing cementum + alveolar bone
- Initially developing fibres of PDL run obliquely in coronal direction from tooth-bone
- This changes as the tooth erupts
- PDL fibres in cementum + alveolar bone = Sharpey’s fibres
Formation of periodontal space
- Under influence of HRS ⇢ mesenchymal cells group arranged under cementoblasts
- They produce thick fibres - arranged parallel to root in at the beginning
Inner cell’s package of fibroblasts
- Fibroblasts produce fine fibrils oriented around regions of cementogenesis
- They are inserted between cementoblasts + epithelial cells of root sheath
- They anchor onto uncovered cementum areas
- First formed fibres ⇢ parallel to root
- Cementum matrix ⇢ uses specific receptors to attract fibres
- Adhesins + specific receptors responsible for attachment of fibres
- Fibres inserted into cementum matrix perpendicular to dentin
- After attachment ⇢ fibres coated w/cementum matrix + remain as sharpey’s fibres
- Their ends freely hang in periodontal space
External package of fibroblasts
- Fibres inserted into osteoblasts that form alveolar bone matrix
- With its mineralisation ⇢ fibres remain embedded in the bone
- They are continuously modelled + remodelled + remain hanged in periodontal space
- Hanging ends thicken + point to central part of periodontal space
Intermediate group of fibres
- Formed from fibroblasts in periodontal space between alveolar bone + cementum
- These fibres form a network in periodontal space
- THEY DO NOT PARTICIPATE IN THE LIGAMENTS
1st stage of ligament formation
- Short + numerous bundles coming out of cement
- They branch out as a bush
- From alveolar bone ⇢ leaving as smaller but thicker bundles
- Among them are axial fibres
- Loose fibres occupy majority of periodontal space
2nd stage
- Anchored fibrils grow in length
- They are branching
- ¾ of periodontal space remains engaged w/free fibrils
3rd stage
- Both groups of anchored fibrils are growing
- They are approaching central zone of periodontal space
- They are pushing the free fibrils
4th stage
- Fibres are overlapping
- They continue to ⇡ thickness
- They appear continuous, although they are overlapped
- They carry out constant remodelling of fibres resulting from masticatory forces
Intermediate plexus
A zone that allows mechanical slippage between cemental + osseous fibres during rapid eruption
Histology of PDL
Composed of:
- Cells ⇢ fibroblasts, cementoblasts, osteoblasts, osteoclasts, undifferentiated mesenchyme cells
- Extracellular components ⇢ collagenous fibres, elastic fibres, ground substance, nerves, vessels
Principal fibres - collagen type I
- bundles that exit alveolar bone + cementum from PD
According to location they are classified as:
- Dentoalveolar fibres ⇢ alveolar crest, horizontal, oblique, apical + interradicular fibres
- Gingival fibres ⇢ dentinogingival group, alveogingival group, circular + trans-septal fibres
