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Mechanisms of soft palate closure in human embryos Mattson, Melanie


Objectives: The human secondary palate forms between 6-12 weeks of gestation. There has been controversy as to whether palatal shelves in the soft palate join by fusion similar to the hard palate, or whether merging and proliferation of the mesenchyme at the posterior edge of the developing hard palate is the mechanism. The purpose of this study is to examine the mode of soft palate closure in a more representative sample than was used in the single previous study on which all textbooks are based. Methods: Serial sections of secondary palates from 13 human fetuses from 54-74-days of development post conception were stained, photographed and imported into WinSurf 3D software. Anatomical structures were traced including the palatal shelves, midline epithelial seam and palatine aponeurosis, the images aligned and then stacked to create a 3D representation. Results: We analyzed the following numbers of specimens: 54-days-2; 57-days-4; 59 days -2; 64-days-1; 67-days-1; 70-days–2; 74-days-1. At 54-days, a midline seam is present close to the hard palate but more posteriorly the soft palate is open. Between 57 and 59 days a thick midline seam is observed throughout the soft palate. There is some variability between specimens such that the soft palate was closed early in one 59 day specimen and open in a 67-day specimen. One 70-day specimen had no seam whereas the other retained the seam. By 74-days the specimen had complete soft palate union with the presence of a continuous palatine aponeurosis. Overall, our sample included a total of 7 fetuses with a midline seam in the soft palate. Conclusions: The formation of a bilayered epithelial seam followed by breakdown of the seam and mesenchymal fusion is the primary mode of soft palate formation in humans. Epithelial seam removal is rapid and could explain why a seam was not observed in earlier studies.

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