Changes in human palatine bone location and tongue position during prenatal palatal closure

Closure of the palatal shelves during normal prenatal palate formation is commonly supposed to be the result of a complex interaction between tissue growth processes and functional factors such as mandibular and tongue movements. The purpose of the present study was to analyze tongue and palatine bone positions during palatal shelf closure. The material consisted of 40 normal human fetuses (CRL 26-57 mm). The series covers the developmental stages in which palatal shelf closure takes place. The spatial relation between the tip of the tongue and the lips was examined by visual inspection, and radiographic/cephalometric methods were used for analyzing palatine bone positions. On axial radiographs of the upper jaws, the angle in the horizontal plane between the vertical plates of the palatine bones was measured. The study revealed that the vertical plates of the palatine bones rotate on their vertical axes during palatal closure, the mean interpalatine angle changing from 23.7 degrees (SD 2.0 degrees) to 13.3 degrees (SD 3.2 degrees), P < 0.001. The rotation of the palatine bones occurred while the cranial base was still unossified. Moreover, the tip of the tongue became visible between the lips immediately after palate closure. In the present study the rotational changes observed in skeletal tissue provided information about soft tissue changes during palatal closure. These normal developmental aspects are discussed in relation to skeletal deviations in congenital cleft palate malformations.