MORPHOLOGICAL DEFICIENCY IN THE PRENATAL ANTERIOR CRANIAL BASE OF MIDFACIALLY RETROGNATHIC MICE

The role of the anterior cranial base in the establishment of midfacia l retrognathia remains unclear. The purpose of this study was to deter mine whether morphological deficiencies occur in the developing anteri or cranial base of the retrognathic Brachyrrhine (3H1 Br/+) mouse muta nt shortly after overt cartilaginous differentiation and to localise a ny malformations. Crania from 2 groups of 3H1 Br/+ and +/+ mice, each consisting of 15 animals, were collected at gestational days 15, 17 an d 19 (Theiler stages 23, 25, 27). The anterior cranial base from each specimen was subjected to computerised reconstruction and 8 homologous anatomical landmarks were digitised on each model. The landmark confi gurations were subjected to Procrustes analysis and significant differ ences between models were determined at each age. In order to localise differences between forms, average landmark configurations derived fr om Procrustes analysis were subjected to finite-element analysis. Two cluster models were generated based on size-change values. One cluster was located anteriorly and superiorly while the second was located po steriorly and inferiorly within the anterior cranial base. Results ind icate that the size-change values for the posterior and inferior clust er increased more rapidly compared with the anterior and superior regi on over the age range tested. These data indicate that the midfacial r etrognathia in Br/+ mice is associated with abnormal growth activity i n the presphenoid component of the presumptive anterior cranial base. In addition, the deficiency is present in the presphenoid at the time of overt cartilaginous differentiation.