Click on image to view larger version.
Figure 1. Scheme of the early development of the human upper jaw and dental arch. (A,B,C) Frontal view of the embryonic human face in the 5th (A) and 6th/7th (B,C) weeks of development. (A) The medial nasal (mn) and the maxillary (mx) processes before fusion. (B) Normal development; the mn and mx are fused. (C) Unilateral left-sided cleft; the mn and mx are fused on the right and not fused on the left side. ln, lateral nasal process. (D,E,F) Scheme of the development of the human upper jaw viewed from the oral cavity. (D) Normal development. The fusion of the dental epithelia is delayed compared with the facial processes. At the site of fusion of the dental epithelia, the germ of the lateral incisor (i2) emerges, containing material from both the mn and the mx. (E) The development of a unilateral left-sided cleft of the dental epithelium. The dental epithelia on the left side are clefted, giving rise to two i2. (F) The development of a unilateral left-sided alveolar cleft. Non-fusion of the mn and mx on the cleft side results in the jaw cleft and, consequently, in the non-fusion of the dental epithelia and the formation of two i2. Line pattern: dental epithelium of mn, reticulation-dental epithelium of mx.
