A morphometric analysis of craniofacial growth and changes in spatial relations during secondary palatal development in human embryos and fetuses

Abstract

Staged human embryos and fetuses in the Carnegie Embryological Collection were morphometrically analyzed to show craniofacial dimensions and changes in spatial relations, and to identify patterns that would reflect normal developmental events during palatal formation. Normal embryos aged 7-8 weeks postconception (Streeter-O'Rahilly stages 19-23) and fetuses aged 9-10 weeks postconception, in eight groups with mean crown-rump (CR) lengths of 18-49 mm, were studied with cephalometric methods developed for histologic sections. In the 4-week period studied, facial dimensions increased predominantly in the sagittal plane with extensive changes in length (depth) and height, but limited changes in width. Growth of the mandible was more rapid than the nasomaxillary complex, and the length of Meckel's cartilage exceeded the length of the oronasal cavity at the time of horizontal movement of the shelves during stage 23. Simultaneously with shelf elevation, the upper craniofacial complex lifted, and the tongue and Meckel's cartilage extended forward beneath the primary palate. Analysis of spatial relations in the oronasal cavity showed that the palatomaxillary processes became separated from the tongue--mandibular complex as the head extended, and the tongue became positioned forward with growth of Meckel's cartilage. As the head position extended by 35 degrees, the cranial base angulation was unchanged and the primary palate maintained a 90 degrees position to the posterior cranial base. However, the sagittal position of the maxilla relative to the anterior cranial base increased by 20 degrees between stages 19 and 23. In the late embryonic and early fetal periods, the mean cranial base angulation of approximately 128 degrees and the mean maxillary position angulation of approximately 84 degrees were similar to the angulations previously shown to be present later prenatally and post-natally. The results suggest that human patterns of cranial base angulation and maxillary position to the cranial base develop during the late embryonic period when the chondrocranium and Meckel's cartilage form the primary skeleton.

Prenatal Craniofacial Development: New Insights On Normal and Abnormal Mechanisms

“…In this model, restricted space would inhibit both mandibular growth and withdrawal of the tongue from between the shelves. There is some evidence that Meckel's cartilage actually bows out laterally before the tongue is released from between the shelves (presumably because the tongue is anchored to its anterior tip), with the anterior end of the cartilage "springing" forward and the sides narrowing after release of the tongue (e.g., Diewert, 1983). Delayed release could also account for the greater bigonial width observed in affected twins, as could reduced space for embryos in oligohydramnios.…”

“…Earlier studies focused on craniofacial growth (e.g., Diewert, 1983) and embryo movements (e.g., Humphrey, 1969;Walker, 1969) related to removal of the tongue from between the shelves. Other studies focused on the shelf "force" involved in shelf elevation, examining the possible involvement of various intercellular substances (e.g., Brinkley and Morris-Wiman, 1984), neurotransmitters, and other factors including ATP levels (Bulleit and Zimmerman, 1986).…”

Morphometry of the Cranial Base in Subjects with Class III Malocclusion

“…The shape of the cranial base appears to be established during fetal development (Ford, 1956;Diewert, 1983;Burdi et al, 1988), and it remains relatively stable during postnatal growth (Lewis and Roche, 1977;Lestrel and Roche, 1986). A prominent feature of this early growth is a progressive flattening of the cranial base during late prenatal development (Ford, 1956;Burdi, 1969;Diewert, 1983Diewert, , 1985.…”

“…A prominent feature of this early growth is a progressive flattening of the cranial base during late prenatal development (Ford, 1956;Burdi, 1969;Diewert, 1983Diewert, , 1985. Although some reports indicate that a closing of the cranial base angle occurs postnatally (George, 1978;Lang, 1983), morphological instability of nasion casts some doubt on these results (Kerr, 1978).…”

The use of geometric morphometry to study facial asymmetries: relationship between basicranial shape and maxillofacial and occlusal pathologies

“…The modifications of the cranial base during growth 8,18,21,32,33 , the ethnic differences, evolutionary changes between primates and homo sapiens, the relationship with encephalization, upright stature or speech are some subjects that are largely controversial. Further the published results are most often contradictory.…”