bone and cartilage Flashcards
2 types of bone
- cortical, compact bone
- cancellous, spongy bone
cortical, compact bone is
- dense outer plate
- 80-85% of skeleton
cancellous, spongy bone is
- internal trabecular scaffolding
- 15-20% of skeleton
in alveolar bone what type of bone lines tooth sockets?
cortical
it is penetrated by bundles of collagen fibres of PDL (Sharpey’s fibres)
what is in the cortical alveolar bone?
nutirent canals (contains BVs)
composition of bone by weight
60% inorganic (HA)
15% water
25% organic
what makes up the 25% organic portion of bone?
gylcoproteins
- Osteocalcin
- Osteonectin
- Osteopontin
- Sialoproteins
proteoglycans
- Chondroitin SO4
- Heparan SO4
compare dentine and bone constituents
dentine has a lower inorganic and higher water and organic component
what are the types of bone resorption you can get in the oral cavity
vertical and horizontal
Vertical resorption of bone can maybe grow bone to have more attachment between bone and tooth
- Trying to regenerate periodontal tissue
Osteocalcin and Osteonectincan be added to regions to help regenerate
what is the characteristics of the extracellular matrix?
“Ground substance” and fibres
- Semi-fluid gel
- Long polysaccharide molecules
what makes up the extracellular matrix?
Glycos-amino-glycans (GAGs)
- Hyaluronic acid
- Proteoglycans
(Chondroitin sulphat; Dermatan sulphate; Heparan sulphate; Keratan sulphate)
Fibres (reinforce extracellular ground substance):
- Collagen
- Elastin
- Other non-collagenous proteins
2 microscopic types of bone
woven
lamellar
woven bone properties
- rapidly laid down
- Irregular deposition of collagen
- present in fetus,
- fracture repair (callus)
- contains many osteocytes
important for forensics for recognising fractures
lamellar bone properties
- laid down more slowly (Well organised_
- Collagen fibres laid down in parallel
- normal form in adult
- contains fewer osteocytes
compact bone histology
- Laid down in concentric lamellae (lamellar bone)
- Form longitudinal columns
- Organised in Haversian systems around central (Haversian) canal
- Lateral (Volkman’s) canals linking 2 Haversian systems
- Canals contain blood vessels
what are lacunae?
= small canals
- Radiating osteocytes
- Some canaliculi link adjacent Haversian systems
- Nutrition and communication
cancellous bone properties
- Network of thin trabeculae
- Trabeculae consist of lamellae
- Osteocytes present
- No obvious Haversian systems
- The bone is thin, and nutrients can diffuse in
- Bone marrow present in the spaces between trabeculae
osteoblasts lie….
on surface of bone
what did osteoblasts derive from?
mesenchymal stem cells
what do osteoblasts do?
Synthesise and secrete collagen fibres forming a matrix
The matrix is mineralised by calcium salts
- When not mineralised it is an osteon
osteocytes are
become trapped in mineralised bone
where do osteocytes lie?
lie within lacunae (spaces)
how to osteocytes contact each other?
via cytoplasmic processes that run in canaliculi
- Allows communication between
Osteocytes also appear to communicate with osteoblasts
how do differentiate histologically between dark spaces in cementum and osteocytes in bone?
Most of the time don’t see canaliculi in cementum
- If you do then will only radiate unidirectionally towards periodontal ligament (vascularised, nutrient source)
what are osetoclasts?
Large, multinucleate cells, derived from haemopoietic stem cells
what cell type are osteoclasts related to?
macrophages
what do macrophages do?
aggregate for defence function of engulfing and removing material from tissue
what do osetoclasts do?
resorb bone (acid phosphatases)
where do osteoclasts lie?
lie in concavities in bone
- Howship’s lacunae
what is the logic of bone remodelling (turnover)?
Removal and replacement of bone tissue, without change in overall shape
Resorption balanced by deposition (apposition).
how much cortical bone is replaced each year?
2%
how much cancellous bone is replaced each year?
25%
what controls bone remodelling?
osteoblasts
what regulates bone remodelling?
- hormones (e.g. parathyroid hormone, calcitonin)
- Paracrines (various cytokines)
what are the advantages of bone remodelling?
- Calcium in low concentration in cell (used in number of essential events)
- Main store in bones
- Way organism maintains 2.4mmolar Ca for essential functions
- Always changing
process of bone remodelling
PTH acting on cell to promote collagenase production
Cells will join together to form osteoclasts,
PTH stimulates aggregation
Osteoblasts become active to form osteoid matrix
how can bone remodelling be used to dentist advantage?
Used to our advantage
- Speed up resorption
- Speed up rebuilding of Ca at another site
Could move teeth (apoptosis in front and rebuild behind)
- Orthodontic treatment (osteoclasts in a targeted region; osteoblasts in a targeted region)
- Drifting of teeth
what is the reversal line?
Scalloped edge shows where bone resorption changes to bone deposition.
what does tooth movement require?
require remodelling of adjacent soft and hard tissues
when does remodelling of adjacent soft and hard tissues occur?
- during eruption (Resorption of crypt where tooth was, resorption for root formation, deposition to cover root)
- post-eruptive (e.g. mesial drift)
- orthodontic forces
describe cartilage
Semi-rigid, unmineralised connective tissue
several different types of cartilage
cartilage matrix
similar to bone
- Ground substance
- Fibres (see earlier)
- No mineral content
several different types of cartilage
hyaline cartilage locations
Widespread
- Larynx, nasal septum, trachea, ends of ribs (costal cartilages), articular surfaces, embryonic skeleton (precursor to bone)
flexible
fibrocartilage locations
Intervertebral discs, pubic symphysis
- Allows pubic to detach and reattach when giving birth
Need remodelling but need certain level of flexibility
elastic cartilage locations
External ear, epiglottis, Eustacian tube
what forms cartilage cells?
Formed by chondroblasts
- These get trapped the matrix and become chondrocytes
is cartilage vascularised?
no, it is avascular
if cutting tissue and have no bleeding = cartilage
how does cartilage get nutrients?
Nutrient diffuses in
Some channels are present in thick areas of cartilage
Chondrocytes contain energy stores of lipid, glycogen
what are 2 key bone growth processes?
- endochondral ossification
- intramembranous ossification
what does endochondral ossification require?
presence of cartilage
- Long’ bones
- Cartilage precursor
- Cartilage proliferation
- Cartilage replaced with bone
where does intramembranous ossification requrie?
- ‘Flat’ bones
- Bone formed de novo in C.T. (connective tissue)
- No cartilage precursor
- Skull and Face growth
growth of bone onto membranous tissue without cartilage
process of bone growth in the skull
Skull has high Ca in some areas and some less
- Concentrated in specific areas
Spaces in between parts of skull allow Intramembranous – foramina
- vault of skull
process of endochondral ossification
Initially, a cartilage skeleton is laid down.
The cartilage is replaced with bone.
- There are several centres of ossification.
- Starts to ossify at the centre
Cartilage proliferation (and growth) occurs at the epiphyses - Ossification centre going out from diaphysis to epiphysis when bone is finalised
Dynamic process
what occurs at spheno-occipital synchondrosis?
Skull can have intramembranous as of spaces (foramina)
Base of skull needs elongation
- Needs endochondral ossification (sphenoid (needs lateral and longitudinal growth))
what is achondroplasia?
- Genetic defect of cartilage growth
- Endochondral bone growth is impaired. Intramembranous bone growth is unaffected.
e.g. Eleanor (Ellie) Simmonds
how does the bone develop at the TMJ?
Endochondral calcification at condylar cartilage
- Condyle lies inside articular eminence
Allows cartilage to grow, remodel and reshape if necessary
- Change shape as we are born
- Rearrangement when we grow and lose teeth
3 key parts of the mandible
- Alveolar process - can be removed or disappears
- Angular process
- Coronoid
Important in remodelling throughout life due to Insertion of muscles (angular and coronoid) and teeth presence (alveolar)
what happens to edentulous jaws?
alveolar process has been resorbed after tooth loss
Minimised coronoid process, angular and alveolar all changed shape
- Reduction of areas
- Not fully closed appearance
what are the characteristics and functions of the angular and coronoid processes?
- associated with muscles
- weaker and less force
what must happen if the alveolar bone resorbs?
resorbs if edentulous
- Need to put denture
Dentures held simply through suction
- Need to keep a sealed surface near the borders
Minimise lateral forces - denture cusps are not as prevalent as in real teeth - so less movement. Keep close to lining mucosa
- Maxilla easier as palate there
- Tongue can force denture out of mandible
- Difficult arrangement if no seal
