Except for initiation, there is overlap of all the stages, but each tends to predominate in certain period.
The dental lamina and tooth buds are the representatives of this stage. Different teeth are initiated at definite times by unknown factors. The lack of initiation may result in absence of one or more tooth. The initiation may be abnormally high leading to formation of single or multiple supernumerary teeth.
Proliferative growth causes regular changes in the size and proportions of the growing tooth germ and results in the bud, cap and bell stages.
The formative cells of the tooth germ undergo definite morphologic as well as functional changes acquire their functional potencies. This phase reaches its highest development in the bell stage just preceding the beginning of matrix formation. So differentiation of ameloblasts and odontoblasts is essential before enamel and dentin formation.
The morphologic pattern is determined by differential growth (which starts from the early bell stage). At the late bell stage, morphodifferentiation is established by outlining the future dentinoenamel and amelocemental junctions. Disturbances in morphodifferentiation may affect the form and size of the teeth.
It is the deposition of the newly synthesized matrix of the hard tissues and their mineralization. It is confined to the late bell stage. Periods of activity and rest alternate at definite intervals resulting in the formation of incremental lines in all hard tissue.