Tooth development is divided into 4 stages based on physiological process of tooth growth:
Initiation: It is a part of Bud Stage. For Initiation Epithelial Ectomesenchymal interactions are essential. Initiation is the first step in the development of tooth. Each tooth has its own initiation time and it is not know how this time is determined. Even in case of teeth located in abnormal positions initiation is started on time.
Proliferation: As the name says Proliferation in tooth development is increase in Size and Shape of the developing tooth germ and the cells. Which have the ability to differentiate into various structures based on stimulation in the later stages of tooth development.
Histodifferentiation: Seen in the early Bell Stage of tooth developement. The formative cells of the tooth germ undergoes many functional and morphologic changes to transform into functional cells. Which gives the cells an ability to multiply. the peripheral cells of the dental papilla differentiate into odontoblasts which produces dentin. And as we know that presence of Dentin stimulates the presence of Enamel. In the absence of Dentin, Enamel formation does not occur.
Morphodifferentiation: The dentinoenamel junction and the cementoenamel junction are developed by the continuous deposition of enamel, dentin and cementum from ameloblasts, odontoblasts and cementoblasts. Which results in the complete formation of Morphologic outline, pattern, size and shape of the tooth.
Apposition: Apposition is the addition of new layers on teh existing ones and after the morphologic part of tooth development is completed, a rhythmic, layer like deposition of an extra cellular matrix of enamel and dentin takes place. It is charecterized by a regular, rhythmic deposition of extracellular matrix. In this stage periods of Activity and Periods of Rest are seen.
Abnormalities in each physiologic stages of tooth development leads to the following anomalies of tooth:
Abnormality in Initiation:
- Missing Tooth
- Supernumerary tooth
- Amelogenesis imperfecta
- Dentinogenesis Imperfecta
- Peg Lateral
- Dens in Dente
- Absence of Cusp or root
Abnormality in Apposition: