Alveolar bone Flashcards
What is alveolar bone?
It is a mineralised connective tissue that supports and protects the teeth
What percentage of alveolar bones net weight is inorganic material?
60%
What percentage of alveolar bones net weight is organic material?
25%
What percentage of alveolar bones net weight is water?
15%
What is the inorganic material of alveolar bone mainly made up of?
Hydroxyapatite crystal
What are hydroxyapatite crystals and what do they do?
They are crystals that impregnate and surround collagen fibres providing rigidity and resistance to compression
What is the organic component of alveolar bone made upon?
90% type I collagen
10% is a complex of non-collagenous proteins like glycoprotein (osteonectin and osteopontin), proteoglycans, osteocalcin, growth factors and serum proteins
Which cell produces all these proteins?
Osteoclasts
How much of the organic metric is made up of collagen?
90%
What is most of the collagen in the organic matrix regarded as?
intrinsic collagen secreted by osteoblasts
When is collagen considered extrinsic?
When it is inserted as Sharpey’s Fibres formed by adjacent fibroblasts
What is the major type of collagen found in the matrix?
Type I
But trace amounts of type III and V may also be present
What form does the mineral in alveolar bone take? And what is its relative width and thickness?
Mineral is found in the form of needle like crystallites
50 nm wide
8nm thick
Variable length
Where are the crystallites distributed in the bone?
Distributed within the space between and on the surface of the collagen fibrils
What are the 4 stages of bone remodelling?
Resorption
Reversal
Formation
Resting
(Basically bone removed then reformed)
What does bone remodelling allow the alveolar bone to do?
Allows the bone to remodel and adapt to changing functional demands placed upon it
Why is there no change in the overall shape of bone even though resorption is occurring?
As resorption is occurring at the same rate as bone formation so overall shape in bone is unchanged
How is the rate of formation and resorption co ordinated?
The actions of the various cell types is coordinated
Osteoblasts form bone
Osteoclasts resorb bone
And the combined action of osteoblasts and osteocytes have the ability to detect mechanical stresses the bone is subjected to
What happens to bone during the resorption stage?
Recruitment,migration and activation of osteoclasts causes resorption
What happens to bone during the reversal stage?
Resorption ends and osteoclasts disappear by apoptosis or migration
This stopping of resorption is characterised by a ‘reversal line’
What happens to bone during the formation stage?
Osteoblast recruitment, migration, differentiation and formation of new bone occurs in the resorption site
What happens to bone during the resting stage?
Formation of bone stops following mineralisation
Surface is lined by a flattened layer of cells (bone lining cells)
What are the 4 main cell types in bone?
Bone lining cells
Osteoclasts
Osteocytes
Osteoblasts
Describe the structure of bone lining cells and where they are found
Are seen as a layer of flattened cells when bone surfaces are in the resting stage
What is the role of osteoclasts and how does their structure help them do this?
Osteoclasts resorb bone
They lie in resorption concavities (called Howships’s lacunae) on the alveolar bone
What are Howship’s lacunae?
Resorption concavities where osteoclasts lie on the surface of alveolar bone
How many stages does resorption occur in and what are those stages?
Resorption occurs in two stages
- Mineral phase is removed
- Organic matrix is then removed
In what pH is the mineral phase dissolved (in resorption) and how is this pH achieved ?
Low pH (acidic conditions) is required for dissolving the mineral phase To provide this low pH the osteoclasts secrete protons across the ruffled borders
How is the organic matrix dissolved in resorption?
Organic matrix exposed in the resorbing lacuna is degraded by enzymes (mainly cathepsin K)