Role of cranial base flexure in developing sagittal jaw discrepancies

The aim of this longitudinal cephalometric study was to investigate skeletal features in patients with small and large cranial base angles. Two groups of untreated subjects were formed on the basis of a small and large cranial base angle N-S-Ar at the age of 5 years: the large cranial base angle group (n = 22) consisted of subjects with an N-S-Ar angle larger than 125 degrees (mean, 128.1 degrees ), and the small cranial base angle group (n = 20) included subjects with an N-S-Ar angle of less than 120 degrees (mean, 117.6 degrees ). Cephalometric data of the 2 groups were analyzed at subject ages 5 and 12 years. At both ages, the groups showed significant differences of the variables SNA, SNB, individualized ANB, and Y axis. The unadjusted ANB angle and the angle of convexity N-A-Pg were not significantly different between the 2 groups. According to the individualized norm of the ANB angle, subjects with a large cranial base angle in the primary dentition demonstrated a skeletal Class II tendency both at the initial observation and at the longitudinal follow-up. On the basis of cephalometric variables at 12 years of age, it was possible to classify 88.1% of the initial large and small cranial base angle individuals, indicating a constancy of the skeletal pattern during the longitudinal follow-up. The relationship between cranial base flexure and skeletal pattern of the jaws seems to be established before the age of 5 years.