Early development of the lower deciduous dentition and oral vestibule in human embryos.

The aim of this work was to investigate the early development of the deciduous dentition and oral vestibule in the human embryonic lower jaw. Histological sections and three-dimensional reconstructions from prenatal weeks 6-9 were used. A continuous anlage for the oral vestibule did not exist in the mandible. In contrast to the upper jaw, where we previously observed that the dental and vestibular epithelia developed separately, two dento-vestibular bulges differentiated in the incisor region of the mandible. The lingual parts of each bulge were found to give rise to the respective central and lateral incisors, whereas the labial parts differentiated into the vestibular epithelium. In the canine and molar areas, the dental and vestibular epithelia originated separately. Later, the segments of the vestibular epithelium fused into the labial vestibular ridge, giving rise to the lower oral vestibule in the lip region. In the cheek region, the oral vestibule was found to originate in the mucosal inflection between the developing jaw and the cheek. A similar heterogeneous developmental base for the oral vestibule was also observed in the upper jaw. There is thus no general scheme for the early development of the dental and vestibular epithelia that applies to both the upper and lower jaws, and to both their anterior and posterior regions.