Dentofacial changes in Norwegian and Iowan populations between 6 and 18 years of age

The purpose of this study was to compare the dentofacial changes in Norwegian and Iowan populations between 6 and 18 years of age. Comparisons of the absolute and incremental changes were made both longitudinally and cross-sectionally. The Norwegian sample consisted of 39 females and 35 males, the Iowa sample consisted of 15 females and 20 males, for whom complete sets of data were available for the period of the study. All subjects had a clinically acceptable occlusion and had not undergone previous orthodontic treatment. Descriptive statistics summarized the changes in 29 parameters. Longitudinal comparison of the growth curves evaluated the curve profiles and curve magnitudes for the two populations for both males and females. The analysis of variance was also used to compare the absolute and incremental changes at ages 6, 9, 12, 15, and 18 years. The study resulted in the following findings: 1. The longitudinal growth profile comparisons of the various dentofacial parameters indicated that the growth trends of the Norwegian and Iowa groups were essentially similar. 2. The comparisons of the growth profiles of the males and females from the two populations also indicated that there were no significant differences between the shape of their growth curves. 3. The comparisons of the curve magnitude, as well as the results of the cross-sectional comparisons, indicated that Norwegians had significantly greater maxillary and mandibular protrusion, and larger proclination of the upper and lower incisors than the Iowans.