Maxillary ossification in a series of six human embryos and fetuses aged from 9 to 12 weeks of amenorrhea: clinical implications.

An anatomic controversy exists concerning the number of nuclei of ossification of the maxilla in human embryos and fetuses. Many authors have described two maxillary ossification nuclei, an incisor nucleus and a maxillary nucleus properly so-called. Some of these have explained congenital labiomaxillary clefts by a defect of bony fusion between these two ossification nuclei. Others consider that there is only a single nucleus for maxillary ossification. In order to settle this question we performed a histologic study in six heads of embryos and fetuses aged from 9 to 12 weeks of amenorrhea (WA) to demonstrate the presence of one or more sites of maxillary ossification at the earliest stages. Our study revealed, on each side, a single zone of maxillary ossification, present from 9 WA, in the form of a sheet of osteoid tissue situated in close contact with the dental lamina. Maxillary ossification then progressed in the lateromedial direction, preserving a median transverse and ventral mesenchymal septum. This septum may constitute the phylogenetic remnant of an ancestral premaxilla.