The important of oral mucosal epithelium (gingival epithlium) in the early stage of the development of the tooth germ is well known. The epithelial cells along the margin of the gingiva that occupy the space of future development of the tooth proliferate into the deeper regions of the jaw to form the tooth germ after dividing into 3 layers. Each of these dental laminae branch halfway to proliferate and grow. This outbranchings are referred to as successional tooth laminae or tooth germs for the permanent teeth, and this sequence of events has been generally accepted without argument. In general, however, the dental laminae proliferate and invade the deeper regions of the jaw in an arch-shaped dam-like configuration over the entire structure of the upper and lower jaws. According to accepted theory, the dental laminae branching from this configuration forms each of the tooth germs.
The purpose of this investigation was to determine whether or not the early dental lamina proliferates and grows over the entire range of the jaw in an archshaped dam-like configuration, and to further determine whether or not the dental lamina of th permanent first molar is an extension of the dental lamina of the primary second molar.
The upper and lower jaws of human fetuses of 3,6,8 and 10 months of age were prepared in serial sections in both the sagittal and frontal plaes. The dental laminae between the deciduous central incisors and the deciduous canine teeth are formed each by one dental lamina. The dental lamina of the primary first molar forms the tooth germ of the primary first molar, and the dental lamina separated halfway extends posteriorly through the connective tissue beneath the epithelium, forming the tooth germ of the primary second molar from the dental lamina separated from the first deciduous molar. The original dental lamina of the primary second molar further extends posteriorly. The dental lamina from the epithelial tissue corresponding to the upper aspect of the first molar also extends into the deeper region of the jaw, uniting halfway with the posteriorly extends into the deeper region of the jaw to form the tooth germ of the first molar, whereas the other end forms the second molar after proceeding further posteriorly (centrifugally) through the connective tissue.