The odontogenesis of the primary dentition begins in the embryonic period, between the sixth and the seventh week of prenatal development. The first stage of tooth development is initiation, where ectoderm induces the mesenchymal tissue in order to initiate the process. There are 4 main stages of development of the tooth: The first stage begins in the fetus at about 6 weeks of age. This is when the basic substance of the tooth forms. Next, the hard tissue that surrounds the teeth is formed, around 3 to 4 months of gestation.