Differences in palatal shelf epithelial stiffness between the lingual/nasal and buccal/oral surfaces during palatal shelf elevation in developing mice.

Background: During secondary palate formation, bilateral palatal shelves grow vertically to a horizontal position. This morphological change of the palatal shelves, defined as the palatal shelf elevation, occurs from embryonic day (E)-13.5 to E14 in mice. Palatal shelves show regional differences in elevation patterns along the anterior-posterior (AP) axis; however, the underlying mechanisms remain unclear. Material properties of the lingual/nasal and buccal/oral surfaces, especially stiffness, possibly contribute to different elevation patterns.

Results: Indentation test using atomic force microscopy was performed to measure the stiffness at the epithelial surface of the palatal shelf. Measurement of palatal shelf stiffness along the AP axis before and after elevation revealed that the lingual/nasal surface was softer than the buccal/oral surface in the posterior region before elevation and that the palatal shelf was stiffer after elevation than before elevation. Moreover, the thickness of epithelial cells on the lingual/nasal side was lower than that on the buccal/oral side before elevation.

Conclusion: Overall, our results suggest that epithelial cell thickness affects epithelial surface stiffness, causing regional differences in elevation patterns.