Tooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans. For human teeth to have a healthy oral environment, enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development. Primary (baby) teeth start to form between the sixth and eighth weeks, 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.
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 branchial arch that is necessary for the development of teeth. In vertebrates several specializations of epithelial tissue ('phanères') generate after thickening specific structures: keratinized structure (hair, nails) or exoskeletons structure (scales, teeth). Placoids scales and teeth of sharks are considered homologous organs.
One of the earliest steps in the formation of a tooth that can be seen microscopically is the distinction between the vestibular lamina and the dental lamina. The dental lamina connects the developing tooth bud to the epithelial layer of the mouth for a significant time.
Tooth development is commonly divided into the following stages: the bud stage, the cap, the bell, and finally maturation. The staging of tooth development is an attempt to categorize changes that take place along a continuum; frequently it is difficult to decide what stage should be assigned to a particular developing tooth. This determination is further complicated by the varying appearance of different histologic sections of the same developing tooth, which can appear to be different stages.
Research published by the University of Helsinki, Finland, indicates that cytostatic and radiation therapies administered before stem cell transplantation often damage children's permanent teeth.
Detrimental effects of cytostatic and radiation therapies on dental development have been known for a long time, but knowledge about the dental consequences of high-dose anticancer therapy preceding stem cell transplantation has so far been scarce. Licentiate in Dentistry, from the Institute of Dentistry, University of Helsinki, has studied the effects of high-dose anticancer chemotherapy and total body irradiation on the development of permanent teeth.
The children examined in the current study, treated for cancer or aplastic anemia, had received stem cell transplantation at the age from 1 to 9.4 years, preceded with a high-dose anticancer chemotherapy and, in most cases, with total body irradiation. In her research, she studied how many of the treated children lacked permanent teeth or had unusually small teeth, and how often dental roots were poorly developed.
The results indicated that 31% of the treated children lacked permanent teeth (as opposed to 8% of the Finnish population), when wisdom teeth were excluded. Lack of permanent teeth was most frequent (77%) among children who had been less than three years old at stem cell transplantation. The highest number of missing teeth was 12. Those who had been over five years of age at stem cell transplantation lacked only wisdom teeth. A significant finding was that a high-dose anticancer chemotherapy alone caused a lack of permanent teeth nearly as often as when combined with total body irradiation, which, however, slightly increased the number of missing teeth.