A comparison of cranial base growth in Class I and Class II skeletal patterns.

The purpose of this retrospective longitudinal study was to compare 7 cephalometric measurements of the cranial base in subjects with Class I and Class II skeletal patterns at ages 1 month, 2 years, and 14 years. A sample of 22 Class I and 21 Class II subjects was selected; the inclusion criteria were overjet, ANB, and Harvold unit difference. Analyses of head circumference, crown-rump length, and weight revealed no significant (P >.15) differences between the Class I and Class II infant subjects at the initial age (1 month). One angular and 6 linear measurements were first compared with a multivariate analysis of variance, which revealed significant effects for age (P <.0001) and the age by skeletal pattern interaction (P =.0266) but not for skeletal pattern (P =.3705). Analyses of variance showed significant (P <.0001) age effects for each of the cephalometric variables but no significant skeletal pattern effects (P >.10). The anterior cranial base measurement of nasion to sphenoethmoidal suture was the only variable found to have a significant age by skeletal pattern interaction (P <.006), which revealed a difference in the timing of its growth spurt that occurred between 1 month and 2 years in the Class I subjects and between 2 years and 14 years in the Class II subjects. There were no significant differences between the skeletal classes at any of the 3 ages evaluated. Conclusions from this study indicate that cranial base growth patterns are similar for Class I and Class II subjects and that the premise of a more obtuse "saddle angle" or cranial base angle in Class II skeletal patterns was not supported.