Origin of the Deciduous Upper Lateral Incisor and its Clinical Aspects
M. Hovorakova1,2,*,
H. Lesot3,4,
R. Peterkova1, and
M. Peterka1,5
1 Department of Teratology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Videnska 1083, 142 20 Prague 4, Czech Republic;
2 Department of Anthropology and Human Genetics, Faculty of Science, Charles University, Prague, Vinicna 7, 128 00 Prague 2, Czech Republic;
3 INSERM U595, 11 rue Humann, 67085 Strasbourg Cedex, France;
4 Université Louis Pasteur, Faculté de Chirurgie Dentaire, 67085 Strasbourg, France; and
5 Clinic of Plastic Surgery, Faculty Hospital Kralovske Vinohrady, Srobarova 50, 100 34 Prague 10, Czech Republic
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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.
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Figure 2. Computer-aided 3D reconstructions of the epithelium on the oral surface of the right upper jaw quadrant in humans. (A,B) ED 40–42. The earlier fusion between the medial nasal (mn) and maxillary (mx) processes is clearly apparent (dotted line). A narrow groove (arrowhead) separates the two thickenings of dental epithelium (DE), originating separately from the mn and mx. (C,D) ED 42–44. The DE forms a continuous dental mound. The former fusion between the facial processes (dotted line), including the fusion site on the dental mound (arrowhead), can still be traced. (E) Prenatal week 8. One can see primordia of the deciduous central incisor (i1), lateral incisor (i2), canine (c), and first molar (m1). The mesial part of the i1 has been cut out on 3D to show the shape of the dental and vestibular (VE) epithelia on the section. A shallow furrow on the germ of i2 (arrowhead) suggests the fusion site between the dental epithelia of two origins. The location of the fusion of the mn and mx processes is also detectable in the VE (double arrowhead). An asterisk determines the mouth corner. The midline is shaded. (pc) primitive choana. (F) An insert shows a scheme of the 3D reconstruction of the oral epithelium (OE) and the dental epithelium (DE). It is possible to see the mesenchyme-facing surface of the epithelium (MSE), because the mesenchyme itself was not included in the 3D reconstruction. The shape of tissues on a frontal section is shown in grey. BM, basement membrane.
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Figure 3. Double lateral incisors in patients after surgical treatment of an orofacial cleft. (A) Double deciduous lateral incisors in a patient with a left-sided alveolar cleft. (B) Double deciduous lateral incisors in a patient with a left-sided cleft lip with an intact jaw (left central incisor is missing). (C) Double permanent lateral incisors in a patient with a left-sided cleft lip with an intact jaw. The midline is shaded. Arrow points to the double lateral incisors. Deciduous central incisor (i1), permanent central incisor (I1), deciduous canine (c), permanent canine (PC) (from the archive of the Clinic of Plastic Surgery, Prague).
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