MANDIBULAR GROWTH-RATES IN HUMAN FETAL DEVELOPMENT

A morphometric analysis of changing proportions in the developing mand ible was undertaken in 18 human embryos and fetuses of both sexes (dev elopmental age from 8 to 14 weeks, crown-rump length, CRL, from 34 to 110 mm), previously cleared and stained with a specific method for bon e (alizarin red S). Reference points were located on the mandible, i.e , condylar process (Pcl), coronoid process (Pco), gnathion (GN), gonio n (GO), superior symphyseal point (SSP), for measuring linear dimensio ns, i.e. Pcl-GN, Pcl-Pco, Pco-GN, GO-GN, SSP-GN. The genial (Pcl-GO-GN ) and the (Pcl-GN-Pcl) angles were also measured. All linear dimension s were correlated with the CRL by bivariate allometry (in gamma = In a + b In x): they all grew with positive allometry, except GO-GN with i sometry. The mandibular ramus grew relatively faster than the body, bo th in length and height, and the greatest growth rate was found for ra mus height. The relation between mandibular shape and the craniofacial structures was investigated using scale drawings obtained from photog raphs of fetal skulls in lateral view. In the youngest fetuses the man dible was prognathic, then became retrognathic. During the period inve stigated the zygomatic process and squama of the temporal bone were in a lower and more inclined position in relation to the transverse plan e passing through the zygomatic arch than in the newborn and adult. Th is study identifies parameters fitting changing trends in height, leng th and shape of the human mandible during the prenatal period (8-14 we eks); moreover, it emphasizes that the mandibular growth patterns diff er significantly from those of successive developmental periods.