alveolar bone and cementum Flashcards
what is intra-membranous ossification?
E.g. body of mandible & maxilla
Main mechanism of bone formation here
what occurs during intra-membranous ossification?
Bone formation directly within the mesenchyme
- Mesenchymal stem cells differentiation into osteoblasts.
- ECM synthesis / secretion (osteoid).
- From osteoblasts
- Matrix-mediated mineralisation.
- Remodelling
- Remodelling / turnover
what is endochondral ossification?
E.g. mandibular condyle & symphysis, long bone
Alternative mechanism
how is hyaline cartilage formed?
Chondrocytes undergo proliferation & hypertrophy.
& Enlarge
Cartilage ECM forms trabeculae & mineralises.
Chondrocytes die.
Bone marrow cells & blood vessels enter tissue
Lining osteoblasts form lamellae & ECM = bone.
Which become mineralised to form bone
Mineralised cartilage degraded.
Which types of bone are lamellar bone?
where are these bones found?
- found in post-natal tissues
- cortical / compact bone
- trabecular / cancellous / spongey bone
properties of cortical / compact bone
- Strongest in alveolar process
- Protection from external environment and trauma
- High density / low porosity (5-30%).
- High mineral content
- Osteons!
what are osteons?
Haversian canal system with concentric lamellae.
- Rings of type 1 collagen
- Blood & nerve supply to the bone
Cylindrical structures, consisting of concentric layers (lamellae), surrounding central Haversian canal.
- Osteons connected to each other & the periosteum by Volkmann’s canals.
- Some osteoblasts develop into osteocytes embedded in spaces (lacunae).
- Osteocytes make contact with the cytoplasmic processes of their counterparts, via network of small canals (canaliculi).
- Mature osteoblasts embedded
- Exchange nutrients / metabolic waste in different regions of bones
- Bone formation, Ca2+ homeostasis.
- Between adjoining osteons occupied by interstitial lamellae.
properties of cancellous bone?
other names for this bone?
tracbeular / cancellous / spongey bone
- Forms majority of the alveolar process
- Flexibility
- Low density / high porosity (30-90%).
- Vast bone marrow space
- Softer, weaker, more flexible.
- Reduced mineral content
- Flexible - allows withstand mechanical forces put on the teeth
- Trabeculae surrounded by bone marrow spaces.
- Blood & nerve supply.
- Collagen fibres run in parallel to bone marrow spaces .
properties of woven bone
- Not present in alveolar process
- Formed during bone development
- Only found in post-natal tissues during fracture repair
- Immature bone.
- Not well mineralised
- No mechanical strength
- Fewer collagen fibres, arranged in haphazard manner.
- Low density / mechanical strength.
- Produced when osteoblasts produce osteoid rapidly.
- e.g. foetal bone, adult bone fractures.
- Evident as fibrous matrix.
- Later replaced by lamellar (cortical or cancellous) bone in foetal tissues.
which types of bone make up alveolar bone
- cortical bone (lamellar)
- cancellous bone (lamellar)
- bundle bone (lamina dura)
properties of bundle bone
- Lining the tooth socket
- Immature bone (similar to woven bone).
- Inner alveolar plate / lamina dura.
- Rapid deposition with random collagen fibre orientation.
- Apparent at Sharpey’s fibres from the PDL, through the alveolar bone proper.
- High remodelling capacity.
- Formed the quickest
- Least mineralised - not well organised collagen fibres
how are osteoblasts formed
- Migration / proliferation of bone marrow-derived, MSCs (Osteoinduction)
- Migration to target - then proliferate
- Enhanced by TGF-bs, BMPs, PDGF, VEGF.
- MSC differentiation into mature osteoblasts (Osteoconduction).
- Induced by BMPs, TGF-b, VEGF.
- Inhibited by PDGF & bFGF.
- Osteoblast is formed
- Not until osteo progenitor cells express transcription factor called RUNX2
- (RUNX2 is required for osteoblast to be fully formed)
how is mineral deposited in alveolar bone
- framework of type I collagen
- mineral crystal initiation within the gap zone between collagen fibrils
- Collagen sulphate substitute decorin
- involved in formation of collagen fibres
- As core protein interacts with the collagen fibres
- Regulates the process
- GAG chains - chondroityn sulphate chains
- Extrude out and help attract calcium and phosphate to the regions for mineralisation to occur
- Get incorporated into hydroxyapatite crystals
- Bone glycoproteins - roles in mineralisation
- Regulate hydroxyapatite crystal growth
what are the properties of bone glycoproteins
how do they contribute to mineralisation?
Glycoproteins of mineralised tissues often very acidic in nature.
- High negative charge - allows them to bind to hydroxyapatite
- High acidic amino acid content - aspartate, glutamate, γ-carboxyglutamate.
Some glycoproteins carry sulphate groups.
Some glycoproteins are phosphorylated.
Correct arrangement of ionised groups in glycoproteins act as nucleators for HAP crystal growth
what is mineralised bone composed of?
Mineral content = 70%.
Hydroxyapatite - Ca10(PO4)6OH2.
Impurities = Mg2+, F-, CO32-.
Collagen = 90% of organic matrix.
- Mainly type I collagen,
- Also type III collagen.
Non-collagenous matrix = 30%.
Chondroitin sulphate-substituted, decorin & biglycan.
Bone sialoprotein, osteonectin, osteopontin, osteocalcin.
Mineral deposition, crystal size & morphology.
