[Dynamics of changes of anteroposterior jaw positions relative to the cranial base during the second trimester of normal intrauterine growth].

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.