<Table> <Tr> <Td> </Td> <Td> This article may be too technical for most readers to understand . Please help improve it to make it understandable to non-experts, without removing the technical details . (September 2010) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article may be too technical for most readers to understand . Please help improve it to make it understandable to non-experts, without removing the technical details . (September 2010) (Learn how and when to remove this template message) </Td> </Tr> <P> Tooth development or odontogenesis is the complex process by which tooth form from embryonic cells, grow, and erupt into the mouth . For human teeth to have a healthy oral environment, all parts of the tooth must develop during appropriate stages of fetal development . Primary (baby) teeth start to form between the sixth and eighth week of prenatal development, and permanent teeth begin to form in the twentieth week . If teeth do not start to develop at or near these times, they will not develop at all, resulting in Hypodontia or Anodontia . </P> <P> A significant amount of research has focused on determining the processes that initiate tooth development . It is widely accepted that there is a factor within the tissues of the first pharyngeal arch that is necessary for the development of teeth . </P>

When do the first signs of tooth development begin