It is defined as the deposition of the mineral salts in and around the organic matrix to make it a calcified structure.

The mineralization process is based on 2 mechanisms:

1. Booster Mechanism
2. Seeding mechanism

And it is explained with the help of 3 Theories:

1. Booster Theory
2. Seeding Theory
3. Matrix Vesicle Theory

The theories explain the process of mineralization in different ways, so lets know about them:

Boosters Mechanism: According to this theory due to the concentration/action of the enzymes the concentration of the calcium and phosphate ions which are building stones of mineralization increases to such a level that would lead to their precipitation.

Seeding Mechanism: It refers to a presence of a seeding or nucleating substance which acts a mould (or) template on which the crystals are deposited, the seeding substance resemble apatite crystals.

Matrix Vesicle  theory: This theory states that, due to the presence of vesicles containing apatite crystals near each cartilage cell which aggregate and form a matrix which is mineralized. 

Now going into the details of each Mechanism:

Booster Mechanism: There are 2 theories which explain this mechanism of mineralization

Robinson’s Phosphatase theory: According to him the presence of alkaline phosphatase releases the ions which take part mineralization and increases their concentration to such a level that their precipitation is seen.

Objections: As alkaline phosphatase is present even in tissues which do not calcify.

Cartier’s theory: According to him there are 2 types of substances which inhibit and one which induce the process, so with proper control of their concentrations the mineralization takes place.

Inducer: Adenosine triphosphate

Inhibitor: Pyrophosphates

Seeding Theory : It was made on account of the shortcomings of the booster theory, and the experimental studies revealed collagen to act as a seed, with apetite crystals forming on the collagen fibers.

The possible seeding substances are:

1. Collagen
2. Chondroitin sulphate
3. Phosphoproteins

Matrix Vesicle Theory: According to this theory, due to the presence of vesicles containing apatite crystals near each cartilage cell which aggregate and form a matrix which is mineralized.

There are 2 types of vesicles:

Type I Vesicles: These are substances extruded from the cartilage cells.

                              Cause breakdown of proteoglycans and GAG.

Type II Vesicles: These are detached pieces of cartilage cells, are bounded by trilamellar   membrane.

                                Promote mineralization by a blend of booster and seeding mechanisms.