ObjectivesAt the end of this chapter the student should be ableto understand the different phases of tooth eruptionand also the shedding of primary teeth.Sub topics1.Introduction2.Causes of shedding of teeth3.Events in shedding of teeth
Shedding of primary teethShedding is the exfoliation of primary teeth followed byphysiologic resorption of their rootsThe permanent anterior teeth develop lingually to thedeciduous teeth.When the deciduous anterior exfoliate the roots resorblingually and most of the pulp chamber remains intact.
The premolars develop between the divergent roots of thedeciduous molars.Resorption of interradicular dentin and cementum takesplace with some resorption of pulp chamber in exfoliatingdeciduous molarsShedding of deciduous teeth follow a fixed pattern.The pattern of shedding is the same as the pattern oferuption of permanent teeth.
There are three causes of shedding of teeth1.Loss of root2.Loss of bone3.Increased force
1.Loss of rootAs the permanent teeth grows it exerts pressure whichinduces the differentiation of osteoclasts and odontoclasts.Odontoclast cause the resorption of dental hard tissues ofthe root.They are similar to the osteoclasts in histology andfunction.
2. Loss of bone As root resorption continues the supporting structures of root are weakened and the modifications in alveolar bone follows. Loss of bone further loosens the root attachment. Osteoclasts are responsible for the bone resorption. During the process of resorption the pressure of the erupting tooth is first directed towards the bone. After this area is resorbed the force is directed towards the root of the primary tooth.
Osteoclasts are large multinucleated cells with a vacuolated cytoplasm and have a striated border (brush border) Acid phosphatase is the active enzyme released by the Osteoclasts. The brush border is adjacent to the resorbing front of the hard tissue. Osteoclasts appear in the cup shaped depressions called Howship’s lacunae towards the hard tissue being resorbed.
3. Increased force Increased muscular growth results in more force on the already weakened tooth and eventually the tooth falls.
Events in shedding of teeth The process of resorption involves the initial breakdown of small areas of hard tissue and then ingestion and complete dissolution of the breakdown products. When the hard tissue is attacked by enzymes, the collagen meshwork is disrupted and the crystals are released. The crystals are then taken up by the osteoclasts in their vacuoles and digested.
The disrupted collagen fibres are then destroyed by fibroblasts. Resorption like eruption is not a continuous process, periods of activity alternate with periods of rest.