Growth-related shape changes in the fetal craniofacial complex of humans (Homo sapiens) and pigtailed macaques (Macaca nemestrina): a 3D-CT comparative analysis.

This study investigates whether macaques and humans possess a common pattern of relative growth during the fetal period. The fetal samples consist of 16 male pigtailed macaques (mean age, 20.5 gestational weeks) and 17 humans (9 males and 8 females; mean age, 29.5 gestational weeks). For each individual, three-dimensional coordinates of 18 landmarks on the skull were collected from three-dimensional computed tomographic (CT) reconstructed images and two-dimensional CT axial slices. Early and late groups were created from the human (early mean age, 24 weeks, N = 8; late mean age, 34 weeks, N = 9) and macaque samples (early mean age, 17.7 weeks, N = 7; late mean age, 23 weeks, N = 9). Inter- and intraspecific comparisons were made between the early and late groups. To determine if macaques and humans share a common fetal pattern of relative growth, human change in shape estimated from a comparison of early and late groups was compared to the pattern estimated between early and late macaque groups. Euclidean distance matrix analysis was used in all comparisons. Intraspecific comparisons indicate that the growing fetal skull displays the greatest amount of change along mediolateral dimensions. Changes during human growth are primarily localized to the basicranium and palate, while macaques experience localized change in the midface. Interspecific comparisons indicate that the two primate species do not share a common pattern of relative growth, and the macaque pattern is characterized by increased midfacial growth relative to humans. Our results suggest that morphological differences in the craniofacial skeleton of these species are in part established by differences in fetal growth patterns.

Mandibular growth rates in human fetal development.

A morphometric analysis of changing proportions in the developing mandible was undertaken in 18 human embryos and fetuses of both sexes (developmental age from 8 to 14 weeks, crown-rump length, CRL, from 34 to 110 mm), previously cleared and stained with a specific method for bone (alizarin red S). Reference points were located on the mandible, i.e. condylar process (Pcl), coronoid process (Pco), gnathion (GN), gonion (GO), superior symphyseal point (SSP), for measuring linear dimensions, i.e. Pcl-GN, Pcl-Pco, Pco-GN, GO-GN, SSP-GN. The gonial (Pcl-GO-GN) and the (Pcl-GN-Pcl) angles were also measured. All linear dimensions were correlated with the CRL by bivariate allometry (1n y = 1n a+b 1n x): they all grew with positive allometry, except GO-GN with isometry. The mandibular ramus grew relatively faster than the body, both in length and height, and the greatest growth rate was found for ramus height. The relation between mandibular shape and the craniofacial structures was investigated using scale drawings obtained from photographs of fetal skulls in lateral view. In the youngest fetuses the mandible was prognathic, then became retrognathic. During the period investigated the zygomatic process and squama of the temporal bone were in a lower and more inclined position in relation to the transverse plane passing through the zygomatic arch than in the newborn and adult. This study identifies parameters fitting changing trends in height, length and shape of the human mandible during the prenatal period (8-14 weeks); moreover, it emphasizes that the mandibular growth patterns differ significantly from those of successive development periods.

[Dynamics of changes of anteroposterior jaw positions relative to the cranial base during the second trimester of normal intrauterine growth]. / Dinamika menjanja anteroposteriornog polozaja vilica prema bazi lobanje tokom drugog tromesecja normalnog intrauterinog rastenja.

The aim of this investigation was to estimate dynamics of changes of maxillary (SNAns) and mandibular (SNMe) prognathism relative of the cranial base from 14th to 24th week of normal intrauterine growth. Investigation was performed on lateral cephalometric radiographs of 50 fetuses, both sexes, derived from artificial abortions in advanced uncomplicated pregnancies, due to social indication. Estimation of gestational ages was made according to contemporary ultrasonic standards of the normal fetal growth. The results obtained from this study showed that enlargement of the SNAns angle was relatively more rapid and regular (2.806 degrees +/- 0.483 degrees per week). The average change of this angle was from 61.047 degrees (in 14th week) to 89.107 degrees (in 24th week), with total change of 28.060 degrees during the period investigated. On the other hand, enlargement of the SNMe angle was, relatively, moderate an variably of 1.678 degrees +/- 0.597 degrees per week. Changes of this angle were ranged, in average from 46.295 degrees (in 14th week) to 63.074 degrees (in 24th week), with the total change of the 16.780 degrees during the same period. Rhythm of enlargement of SNAns angle was 76.222% more rapid than in SNMe angle (p less than 0.05). However, individual variability of SNMe angle enlargement was 23.602% higher compared with SNAns angle (p greater than 0.05). The author concluded that changes of anteroposterior position of the upper jaw relative to the cranial base ranged from marked retrognathism to mild prognathism. During the period investigated, changes of anteroposterior position of the lower jaw relative to the cranial base ranged from marked to moderate retrognathism.