3. Mineralized and have firm intercellular
substances.
Includes bone, cementum, dentin and enamel
Except enamel , they are all -Specialised
connective tissue & Collagen (principally Type
1) plays a role in determining their structure.
HARD TISSUE FORMATION: Cells-
production of organic matrix-capable of
accepting mineral + activity of alkaline
phosphatase + a good blood supply
prerequisites
4. Ability to synthesize and secret organic matrices of
hard tissues :-
Fibroblast
Odontoblast
Ameloblast
Cementoblast
Osteoblast
They all possess :
Abundant mitochondria
Golgi apparatus
Rough endoplasmic reticulum
Transport vesicles and secretory vesicles
5. Collagenous proteins:
Type I collagen : It acts as scaffold that accumulate
the minerals in holes and pores of fibrils.
Non - collagenous proteins:
Proteoglycans
Phospholipids
Phosphoprotein
Non collagenous protiens are involved in mineralization
of enamel whereas in other hard tissues collagen play
an important role.
6. consist of a distinctive family of enamel proteins:
90% amelogenins :-
Proline, Histidine, Glutamine
- helps to maintain space between crystals.
10% non- amelogenins :-
Tuftelin, enamelin, amelin
-helps in nucleation and growth of crystals.
Nevertheless, all hard tissues regardless of their
composition are capable of accepting minerals in form of
hydroxyapatite crystals.
7. Inorganic component of mineralized tissue
Consist of mainly: calcium hydroxyapatite i.e. a
biological apatite. Ca10(PO4)6(OH)2
Unit cell - least no. of Ca, phosphate and hydroxyl
ions able to establish a stable ionic relationship.
Shape-stubby rhombic prism
Unit cells stacked together - lattice of crystal
Various size – number of repetition of this
arrangement
HA crystal in mesenchymal hard
tissue:100*200*50*50A
HA crystal in enamel: length – 1400A ; width –
800A
8. Deposition of mineral salts in and around the organic
matrix to make it a calcified structure.
Although , tissue fluid is supersaturated with Ca & P
ions, spontaneous precipitation of calcium phosphate
does not take place.
BECAUSE :-
Inhibitory macromolecules-inhibit crystal
formation.
Unstable-initial cluster of ions needed to form a
lattice structure.
Furthermore, the formation of clusters of ions
requires the expenditure of energy and an energy
barrier must be overcome for crystallization.
9. Alkaline phosphatase, Pyrophosphatase, Ca ATPase,
Metalloproteinase, Proteoglycans & anionic
Phospholipids bind Ca & P ions
Calcium-inorganic phosphate-phospholipids complex
Initiate mineralization.
Crystallites grows rapidly & rupture from vesicle
Fuses with adjacent clusters-form mineralized matrix
10.
11. Mineralization process is based on two
mechanisms:
1. Booster mechanism: According to this, due to
concentration/action of enzymes, the
concentration of Ca and Phosphate ions
increases to such a level that would to lead their
precipitation.
2. Seeding mechanism: It refers to a presence of
seeding or nucleating substance which acts as a
template on which crystals are deposited.
13. Alkaline phosphatase is the enzyme which
participates in the process of calcification.
It resides in matrix vesicle.
This enzyme hydrolyses the organic phosphate
containing substrate and increases the local
inorganic phosphate concentration.
This enzyme hydrolyses inhibitor of HA &
provide Pi for the formation of HA crystals.
14. 1. Alkaline phosphatases seen in other tissues
which do not calcify.
2. Organic phosphate is not sufficient to produce
inorganic phosphate to initiate calcification
process.
15. Neumann and Neumann (1953)
According to this theory, a nucleus is formed
probably in relation to collagen, effective in
aggregating Ca and Phosphate ions. Then, HA
crystals grow spontaneously.
16. Nucleation sites and their nucleating
agents:
1. Ground substance : Sulfated glycosaminoglycans,
Proteoglycans
2. Collagen : Collagen fibrils, Phosphoproteins
including Osteonectin
3. Mitochondria : the earliest storage sites of Ca
and Phosphate in the form of amorphous CaPo4.
This stored mineral is made available
extracellularly which causes growth of crystals
forming extracellularly in association with matrix
vesicles.
17. HOMOGENOUS NUCLEATION :
Any local increase in concentration of
inorganic ions permits a sufficient no. of ionic
clusters & crystallite to form.
HETEROGENOUS NUCLEATION:
The presence of nucleating substance allows
crystal formation to occur, in absence of a
locally increased ionic concentration.
18. Fails to explain mineralization in enamel and
cartilage.
Fails to explain mineralization in soft tissues
though it contains collagens because collagens
in soft tissues are densely packed which
impede phosphate ion access to nucleation
sites.
19. The mineralization requires the presence of
extracellular matrix vesicles.
Matrix vesicle are small membrane bound
structures, 25-250 nm in diameter, lying free in
the matrix, where calcification occurs.
The vesicles are rich in Phospholipids; esp.
Phosphotidyl serine, a lipid with high affinity
for Ca ion.
The vesicles also contain Annexins, which
forms Ca channel thus incorporating the ion
within the matrix vesicle.
20. Matrix vesicle accumulate Ca and their membrane
furnish binding site for the nucleation of HA
crystals.
They serve as site for Ca and inorganic P
accumulation where deposition of initial
amorphous mineral complexes(nucleation) occurs
and where HA is produced.
HA crystals are released into the extracellular
matrix after reaching certain thickness which is
triggered by phospholipases, thus leading to tissue
calcification.
Most acceptable theory.
21. Pyrophosphate, Diphosphonates or Adenosine
triphosphate:- can delay or prevent the
transformation of amorphous calcium
phosphate to HA.
Citrate, Magnesium and proteins like Albumin.
Components of bone matrix- eg; Proteoglycans
22. ENAMEL DENTIN
Formative cell is
Ameloblast.
Organic matrix are
Amelogenin & Non-
Amelogenin.
Has HA>90%
Non-amelogenin
proteins helps in
nucleation.
Formative cell is
Odontoblast.
Organic matrix are
Collagen & Non-
Collagenous proteins.
Has HA>67%
Nucleation takes place
in Matrix vesicles.
