An appreciation of the fundamental principles associated with the development of the craniofacial structures is essential for attaining competency within the fields of facial surgery, dentistry and pediatrics. The objective of this literature review was to highlight the main stages and precise time ranges of human upper lip development, as well as to elucidate the fundamental mechanisms of normal morphogenesis and possible congenital malformations. The structures of the head and neck arise from the lateral portion of the neural tube, which forms five pairs of branchial arches. Recent studies have identified various molecular pathways (including Bmp, Fgf and Shh signaling) and genetic mechanisms in human face development. Primordial structures of the upper lip begin to appear early within the 6th week of ontogenesis; their development involves a number of highly coordinated, genetically programmed ontogenetic mechanisms that include growth and expansion of the facial prominences, programmed cell death, active fusion and breakdown of the epithelial seam between the initially freely maxillary, medial nasal, and lateral nasal processes. Defects of epithelial and mesenchymal fusion during upper lip formation result in orofacial cleft. Further research should be directed to studying normal ontogenesis at the molecular and topographical levels with the determination of critical periods, time ranges and developmental stages that are sensitive to teratogens.
The aim: To investigate morphology and developmental features of anatomical structures in the infrahyoid triangles of human neck during prefetal and fetal periods of human ontogenesis.
Materials and methods: We have studied 30 specimens of human prefetuses from 7th till 12th week (16,0-82,0 mm of parieto-coccygeal length (PCL)) and 30 human fetuses aged from 4th till 10th month (84,0-360,0 mm PCL) of intrauterine development by the means of macro-, microscopy, morphometry, three-dimensional remodeling and statistical analyses.
Results: We can observe anterior triangle in human fetuses after the time when common precursor muscular mass splits into two: the anterior and posterior portions which will give rise to the sternocleidomastoid and trapezoid muscles accordingly. The area index of the central triangle in human fetuses 4th – 10th month of intrauterine development shows the increasing tendency with the highest rates at 8th–10th months period – 1100-1200 mm2. The angulated course of omohyoid muscle is visible at late prefetal and early fetal periods (3-4th month; 80,0-130,0 PCL) as well as the presence of intermediate tendon. Peaks of the area of sternocleidomastoid region area evaluation was observed in 190,0-210,0 mm PCL and 260,0-270,0 mm PCL human fetuses; 6th and 7,5th months accordingly.
Conclusions: The critical periods for the AT and SCM regions should be considered 6th and 8th months of the IUD. Prefetal period shows the presence of AT and border structure for the IH neck – precursor of HB. Fetal period of IUD (4th – 10th months of IUD) should be considered as such that represents an adult-alike morphology of IH neck: presence of IH triangles with fully developed vascular, muscular and fascial content.
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