Theories of Mineralization
 MINERALIZATION is a process taking place in all
calcified structures in the body like the bone &
enamel.
 •Defined as the deposition of the mineral salts in
and around the organic matrix to make it a
calcified structure.
Mineralization
 Mineralization takes place by the deposition of inorganic
substance mainly calcium on the organic portion of a hard tissue
Hard tissues
Inorganic
Organic
Enamel
96%
4%
Dentin
70%
30%
Cementum
45%
55%
Bone
67%
33%
Components playing role in mineralization
 Cells: They produce the organic matrix of hard tissues
 Bone –> Osteoblasts
 Enamel –> Ameloblasts
 Dentin –> Odontoblasts
 Cementum –> Cementoblasts
 They
possess abundant Mitochondria,
endoplasmic reticulum & Golgi apparatus
Rough
It consists of type 1 collagen & other type of
macromolecules (Proteoglycans, Glycoprotein & Phospholipids)
 Organic component of enamel consists of enamel proteins
 Organic matrix:
 Minerals: They form the inorganic portion of hard tissues
 It generally consists of calcium in the form of calcium hydroxy
apatite crystals
MINERALIZATION IN 2 CIRCUMSTANCES
 HOMOGENOUS MINERALIZATION
 Local increase in concentration of mineral….allowing
formation of sufficient crystallites required for
mineralization.
 HETEROGENOUS MINERALIZATION
 Presence of nucleating substance that can act as a template
for crystal formation
 Nucleating substance can initiate mineralization even in the
absence of increase in ionic concentration
 THREE THEORIES
 •Booster theory
 •Seeding theory
 •Matrix vesicle theory
BOOSTER THEORY
 •Robinson’s ALKALINE PHOSPHATASE THEORY.
 •1923
 •Alk po4ase present in the organic matrix can hydrolyze
organic phosphates such as pyrophosphates or glucose 1-6
phosphate ….
 •Release inorganic orthophosphate resulting in local increase
in phosphate ion concentration.
 •Increase in local ion concentration has a boosting effect
which would proportionately increase the proportion of
phosphate ions to cause spontaneous precipitation.
 •Phosphate ions combine with the calcium ions available in
tissue fluid to form hydroxyapatite crystals.
 •UNSTABLE AMORPHOUS CALCIUM PHOSPHATE
IS CONVERTED TO CALCIUM HYDROXYAPATITE
 •THE BASIS OF ALKALINE PHOSPHATASE
 •Calcifying cartilage contains more alkaline phosphatase than
non calcifying cartilage.
 •Slices of cartilage + incubated with calcium & organic
phosphates= hydroxyapatite crystals were formed.
 •Alk phosphatase is capable of splitting inorganic phosphates.
Phosphates combine with calcium to produce apatite crystals
 Not widely accepted
 •abnormal tissue (Rachitic bone- affected by richets)
 •Alkaline phosphatase is observed in other tissues which do not calcify.
 •Inhibitors of certain enzymes which do not inhibit alkaline
phosphatase activity are found to be preventing mineralization.
 •Studies have shown that presence of inorganoic phosphate and
calcium is not sufficient to induce mineralization. This also requires
action of some other enzymes.
 •The organic phosphate presnt in tissue fluid of calcifying matrix is
insufficient to produce sufficient inorganic phosphate ions to induce
mineralization
The role of alkaline phosphatase in
mineralization
 •Group of enzymes that can cleave po4 ions from organic
phosphates at an alkaline pH.
 •Enzyme found in cell membrane of hard tissue forming cells
and in organic matrix of calcifying tissue.
 •May be involved in ion transport.
 •Neumann …….alkaline phosphatase may be playing an
important role in mineralization by hydrolyzing pyrophosphate
which is known as crystal poison which prevents mineralization
therefore helping in crysral growth
Collagen seeding theory /nucleation
theory /collagen template theory
 •SPATIAL ARRANGEMENT.
 •Can act as mould on template upon which
crystals can be laid down.
 •Nucleating substance can initiate mineralization
even when the ionic concentration is less and also
reduce energy required for mineralization.
 •Collagen =seed
 •Amino acid present in collagen with charged side chains
provide a specific spatial arrangement that can constitute a
template matching hydroxyapatite.
 •Calcium and phosphate ions present in the extracellular
fluid binds to these sites to form hydroxyapatite crystals
which further grow by addition of ions.
 Collagen was added to a solution containing
calcium and phosphate, crystal formation was
found even when the concentration of ions were
lower than what is required for spontaneous
mineralization…….. Seeding capacity of collagen
 •The gaps between collagen molecules are filled with
proteoglycans which bind to calcium,
 •Calcium is released by enzymatic degradation of proteoglycans.
 •After the removal of proteoglycans phosphoproteins are attached
to collagen which is broken down by alkaline phosphatase to give
rise to phosphate ion.
 •Ions combine to form apatite crystals in the gap zone of collagen
 Theory is unable to explain mineralization in all
tissues.
 •Enamel is highly mineralised but does not contain
collgaen.
 •Mineralization of cartilage begins in ground
substance and not in association with collagen,.
 OTHER NUCLEATING MATERIALS
 •Lipids
 Phospholipids to amorphous calcium phosphate.
 Phospholipids are also found in matrix vesicle
 •Protein polysaccharides act as seed for
mineralization.
 •Proteoglycans and glycosaminoglycans have the
capability of binding to calcium ions.
 • protein polysaccharides regulate
mineralization rather than initiation
Matrix Vesicle theory
 •MEMBRANE BOUND VESICLES ISOLATED FROM
AREAS OF CALCIFICATION.
 •Structures bud off from synthetic cells and are
released into organic matrix.
 •Matrix vesicles induces precipitation
 •Matrix vesicles have the capacity to initiate
mineralization.
Two types
 •Type i: round or ovoid …..Containing lysosomes …
 •Enzymes such as acid phosphatase and aryl
phosphatase.
 •Enzymes breakdown proteoglycans and
glycosaminoglycans…….Which are inhibitors of
mineralization
 •Type ii: matrix vesicles are irregular membrane
bound structures having enzymes such as ATPase,
alkaline phosphatase,pyrophosphatase,
proteoglycans, metalloproteinases but relatively
less acid phosphatase.
 •Phospholipids ….great affiinity for calcium.
Role of matrix vesicle in mineralization
 •Provides local environment for initial crystal
formation.
 •All the characteristics needed for induction of
calcification.
 •Freshly isolated vesicles contain relatively high
calcium content bound to phospholipids which act
as a nucleating site within the vesicle
 •Rich in alkaline phosphatase activity, the vesicles
have the capacity to hydrolyze a variety of organic
phosphate .substrates…….increases substantially
the local availability of free phosphate ions to
initiate apatite crystallization
 •Removal of inhibitors of mineralization.
 •ANNEXIN V…..membrane associated protein
mediating influx of calcium into matrix vesicles,
enabling crystal growth.
 •Type ii and type x collagen. The first crystal
formed is the matrix vesicle.
 •The crystal growth continues in vesicle by further
addition of ions which is followed by rupture of
vesicle membrane.
 •The crystals are released into the organic
matrix…..growing using ions in the tissue fluid and
mineralization surrounding the matrix.
All three mechanisms(theories) involved in
mineralisation
 •Collagen acts as a seed and helps in intrafibrillar
calcification.
 •Similarly matrix vesicles help in extra fibrillar
calcification.
 •Alkaline phosphatase helps in providing more
phosphate ions and also remove crystal poison.