It is well to bear in mind that every tooth a man will ever have (except the false ones) is already formed or being formed in his jaws at birth. The teeth actually begin to be formed before any of their supporting structures in the bony alveolar process.
The anlage or germ appears as the dental ridge developing from the cells of the ectoderm, as early as the seventh week of fetal life. Out of this ridge the tooth-buds of the temporary teeth with the enamel organ's begin to be differentiated about the eighth week. These structures, invade the underlying mesoderm and together they form the "dental papilla" which becomes distinguishable during the ninth or tenth week.
The tooth-buds of all the deciduous teeth are definitely formed and the enamel organs of the permanent teeth have appeared by the fifteenth week. At about the twentieth week calcification sets in in the tip of the incisors to be followed by calcification in the canines and premolars in the twenty-fourth week.
The first permanent molars, in their origin and development, follow very closely the development of the temporary teeth. At about the fifteenth week their enamel organs first appear and this is followed two weeks later by the formation of their dental bulbs. The dental follicles of these teeth are complete and their calcification has begun by the ninth month. All of the other permanent teeth have also been laid down by this time and are calcified during early childhood.
Let us briefly review this: At birth all of the temporary teeth are definitely formed and calcification is in process; the six year molars are formed and calcification of their crowns is under way; all of the other permanent teeth have been laid down and await calcification during early childhood.
It is before birth, when these teeth are forming, that we must begin to save the teeth of child and adult. For, not only is it here that those defects are produced which are visible in so many teeth when they erupt, but here also are many of the defects initiated which are to appear later. A soft pre-tooth structure laid down in the jaws of the embryo, due to nutritional perversion of the mother, predisposes the teeth to cavities and decay. Finally calcification, due to nutritional perversions and deficiencies, injures both the temporary and the permanent teeth.