The permanent tooth is not formed after the loss of primary tooth. Normally there are tooth buds in the developing foetus itself. These tooth buds, sometimes called the tooth germs, are an aggregation of cells, which eventually form the tooth. A whole lot of processes happen inside the tooth bud to form a tooth. This phenomenon is generally referred to as calcification and this calcification of primary teeth takes place between 13 and 16 months of postnatal life. There are ten sets of primary tooth buds in both the jaws. After complete calcification the primary dentition takes two to three years to emerge into the oral cavity.
The transition from primary to permanent teeth begins at about 6 years of age. The permanent tooth buds stay beneath the primary teeth. The calcification process starts in the permanent tooth too. For the permanent teeth there are 16 sets of tooth buds, each forming at different years of age. The crown portion of the permanent teeth starts to form and this crown portion is formed by enamel. There are four centres for formation of each tooth. All these centres coalesce to form a lobe, which forms the crown of the tooth. After the crown is formed, root formation begins. At the cervix of the crown, cemetum accumulates for the root to be formed. Once root development takes place in the permanent teeth underneath the primary teeth, this initiates resorption or eroding of the roots of the primary teeth by cells called osteoclasts. This resorption of primary teeth roots causes exfoliation of the primary teeth, which is normally referred to as tooth shake. Once the primary tooth falls off, the permanent tooth starts to emerge through the gingival or the gums. The first permanent tooth that erupts is the lower first molar at the age of 6 years. Gradually all primary teeth begin to exfoliate and permanent teeth emerge into the oral cavity.
Source: The Hindu