(1) Anatomy and Histology of the Periodontium - Alveolar bone Flashcards
What is the alveolar bone?
The part of the jaw that supports and protects the teeth.
forms the tooth socket
Is bone calcified?
YES
What is the composition of bone?
Bone is composed of 60% inorganic component,
25% organic component and
15% water by weight.
What is the main inorganic component of bone?
Calcium hydroxyapatite Ca10(PO4)6(OH)2
What is the main organic component of bone?
Collagen (mainly type I) forms 90% of the extracellular matrix
What is the most abundant type of collagen found in bone?
type I
What form does Calcium hydroxyapatite adopt in bone?
needle-like crystallites or thin plates.
What forms 90% of the ECM of bone?
collagen type I
What are other organic component of bone other than collagen?
serum proteins, acidic glycoproteins and small proteoglycans.
What substance is thought to be involved in mineralisation?
Osteonectin can bind to calcium and thus is thought to be involved in mineralisation.
What are examples of glycoproteins found in bone organic matrix?
osteonectin, osteopontin, thrombospondin,
osteocalcin and fibronectin are also present.
What is the role of proteoglycans in bone organic matrix?
Proteoglycans may regulate collagen fibril diameters and may
have a role in mineralisation.
What are examples of proteoglycans found in the bone organic matrix?
chondroitin sulphate and heparan sulphate glycosaminoglycans
What is the main form of chondroitin sulphate and heparan sulphate glycosaminoglycans (proteoglycans) in the bone organic matrix?
decorin and biglycan
Osteocalcin is only synthesised by what (organic matrix)?
osteoblasts and odontoblasts.
What is the role of locked in cytokines and growth factors in bone?
Exogenous proteins that circulate the blood and become locked in bone such as cytokines and growth factors have an important role in the life cycle of bone cells.
What does BMP stand for?
Bone morphogenetic proteins (BMP)s
How many proteins are in the BMP family?
16
What family are BMPs a part of?
They are part of the transforming growth factor beta (TGF-β) family.
What is the role of BMPs?
BMP(s) induce bone formation by influencing the movement, cell
division, and differentiation of stem and osteoproginator cells.
Name the 5 bone cells
osteoblasts
osteocytes
osteoclasts
bone lining cells
osteoprogenitor cells
What is the role of an osteoblast?
Osteoblasts secrete the organic extracellular matrix of new bone Osteoid which rapidly undergoes mineralisation to form bone.
What is an osteocyte?
Osteoblasts become trapped in bone in lacunae as osteocytes.
What is an osteoclast?
Osteoclasts are multinuclear cells involved in bone remodelling.
What are bone lining cells?
flat cells line bone during periods of inactivity.
What are osteoprogenitor cells?
Stem cells beneath the osteoblast layer.
What are the 2 main forms of bone?
woven bone
lamellar bone
Describe the woven form of bone
immature bone, with random organisation of its collagen.
Describe the lamellar bone?
Lamellar bone is composed of successive layers (lamellae). It may be formed as a solid mass (compact bone), or in an open sponge-like manner (cancellous bone).
What are the 2 types of lamellar bone?
compact
cencellous
What type of bone is shown?
compact bone
What is the structure of compact bone?
Compact bone is made of parallel bone columns which are disposed parallel to the long axis of long bones (in line of stress exerted on the bone).
What is a bone layer called?
lamellae
What is the structure of bone column in compact bone?
Columns are made of concentric bony layers (lamellae) arranged around a central channel with blood vessels, lymphatics and nerves (Haversian canals).
Name structures A-C
Columns are made of concentric bony layers (lamellae) arranged around a central channel with blood vessels, lymphatics and nerves (Haversian canals).
What do haversian canals with their lamalla form?
haversian systems (osteon).
What are Volkmann’s canals?
channels that assist with blood and nerve supply from the periosteum to the Haversian canal
How do neurovascular bundles interact with one another?
Volkmann’s canals
that pierce the columns at right angle or obliquely to haversian canals.
What do osteocytes in their lacunae interact with?
Osteocytes in their lacunae interact with each other and with the central canal via cytoplasmic extensions in canals called canaliculi.
How do osteocytes interact with the central channel?
cytoplasmic extensions in canals called canaliculi.
What is the outermost layer of compact bone called?
dense cortical bone.
What does compact bone act as? What is the role of compact bone?
weight bearing pillars
Compact bone is able to withstand high levels of mechanical stress.
What is the innermost aspect of compact bone?
lamellae
What does lamellae merge with ?
lamellae
merge with trabeculae of cancellous (spongy bone).
What is cancellous bone?
spongey bone
Name structures 1 and 2 of spongy bone
Cancellous (spongy) bone is made of a network of bone trabeculae (2)
separated by interconnected spaces containing bone marrow (1).
What are the 2 components of spongy bone?
network of bone trabeculae
separated by interconnected spaces containing bone marrow
What is trabiculae?
Trabiculae are thin and composed of irregular bone lamellae.
Does cancellous bone have haversian canals?
NO
Where do osteocytes get their nutrition?
via canaliculi connecting them to blood sinusoids in the marrow.
What is the role of spongy bone?
Spongy bone gives bone its flexibility due to the presence of marrow spaces.
Where is trabeculae found?
Trabiculae are aligned along lines of stress so as to withstand forces applied to the bone while adding minimally to the mass.
What separates sockets of alveolar bone?
interdental septa.
What separates roots of alveolar bone?
interradicular septa.
What is the fundus?
socket floor
What are examples of exogenous proteins?
cytokines + growth factors
What is a single unit of bone?
osteon
What are the 2 forms of electron microscopy?
transmission
scanning - surface (3D image of the surface)
What do the small holes show in this image?
Where sharpeys’s fibres into the bone
inserted at right angles
not fully mineralised bone
What do the large holes in this image show?
lacunae where osteocytes can get trapped
What is the difference between the above and below image?
above = fully anorganic electron microscopy (scanning)
below = partially anorganic electron microscopy
What does the bottom image show?
collagen fibrils parallel to the bone surface
How would you describe Sharpey’s collagen fibres?
extrinsic collagen fibres coming at right angles
whereas intrinsic run parallel to the surface of bone
What do A and B show in this electron microscopy image?
A = bone resorption ; howships lacunae
B = longer snail track resorption lacunae
What is bone called when there is no bone formation or resorption?
resting bone
Name structures A-E
A = Alveolar bone
B = Labial cortical plate
C = body mandible
D = lingual cortical plate
E = cribriform plate
the base of the tooth is the fundus
In childhood, what is more predominant bone deposition or resorption?
deposition
What is bone remodelling like in adult life?
equilibrium between bone deposition and resorption
In old age, what is the bone remodelling like?
bone resorption exceeds deposition
What does the bone on the right show?
osteoporosis
bone mass is lost
How are osteoblasts involved in bine remodelling?
Osteoblasts could stimulate the production of osteoclasts by the release of cytokines and growth factors, activate osteoclasts
Osteoblasts could produce enzymes that degrade osteoid thus exposing bone for osteoclasts to work on.
What is a reversal line?
Reversal lines (arrowed) marks the change in bone activity.
between the newly formed bone and the old bone, represents the change in activity form bone resorption to bone formation.
What do the black arrows show?
reversal lines
could be evidence of a fracture
Are bones constantly remodelled?
YES to adapt to pressure
How often does spongy bone and compact bone remodel?
Spongy bone remodels 25% of its mass every year.
Compact bone remodels 3% of its mass per year
What is the bone called between 2 roots?
interseptal bone
What are trans-septal sharpey’s fibres? (or transseptal alveolar fibres)
enter the interseptal bone and exit through the other side and are continuous with the periodontal ligament on the other side of the interseptal bone
Name A-C
Transalveolar fibres (A).
B Periodontal Ligament
C Dentine
decalcified section
