Teeth

At S18, an epithelial thickening forms in each of the upper and lower jaws, parallel to the edge of the lips (vestibular band, labiogingival lamina). A furrow (labiogingival sulcus) develops from this plate, which later gives rise to the vestibule of the mouth. The development of the teeth begins with a ridge-like thickening of ectoderm, which arises at the labiogingival lamina and branches towards the oral cavity. It forms a U-shaped band, called the dental lamina. The dental lamina later gives rise to 10 round or oval tooth buds in each of the upper and lower jaws, facing the lips. The tooth buds grow into the neighbouring mesenchyme and represent the primordia of the milk teeth (deciduous teeth). Around week 10, the first buds of the permanent teeth develop on the lingual side of the dental lamina. The primordia of the 2nd permanent molars form only 4 months after birth and the primordia of the 3rd permanent molar when the child is 5 years old.