Date of Award

Spring 2000

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)



First Advisor

Kittleson, Russell T.

Second Advisor

Bradley, Gerald T.

Third Advisor

Iacopino, Anthony M.


The controversy between extraction and nonextraction treatment and its effect on the vertical dimension of the face still exists today. The purpose of this study was to evaluate the effects of four-first bicuspid extraction and nonextraction methods on the skeletal vertical dimension of African American adolescents with high mandibular plane angles (MPA). The sample groups consisted of 30 extraction (15 males, 15 females) and 31 nonextraction (15 males, 16 females) subjects. In the extraction group, the mean pretreatment age for males and females was 12.41 ± 2.1 and 11.01 ± 2.80 years, respectively. In the nonextraction group, the mean pre-treatment age for males and females was 12.21 ± 2.51 and 12.33 ± 2.02 years, respectively. The average treatment duration for the extraction and nonextraction groups was 2.38 years and 2.20 years, respectively, and all of the patients completed treatment prior to age 17. A total of 122 pre- and post-treatment lateral cephalometric radiographs were traced and digitized. Twelve skeletal measurements (five angular, seven linear) and three linear dental measurements were recorded and analyzed. The linear measurements included the ratios of the absolute linear measurements. The null hypotheses tested were as follows: (1) There is no difference in the skeletal vertical dimension of high-angle African American adolescents following the extraction of four-first bicuspids versus nonextraction therapy, (2) There is no difference between pre- and post-treatment vertical dimension within each treatment group, and (3) There is no difference in the skeletal vertical dimension based upon gender, following extraction and nonextraction therapy. A Paired t-test compared the pre- and post-treatment mean differences as a function of the treatment therapy regardless of gender. A Two-Factor Multivariate Repeated Measures Analysis of Variance (ANOVA) evaluated the effects of treatment therapy regardless of gender and evaluated the effects of gender regardless of treatment therapy. The Two-Factor ANOVA also assessed the mean changes for interactions between the treatment therapies and gender. Lastly, a One-Factor Multivariate Repeated Measures Analysis of Variance (ANOVA) further examined the effects of gender by analyzing the mean changes of extraction and nonextraction therapy as a function of gender. The results showed that the mean changes between treatment therapies that were statistically significant at the level P< 0.05 were the Gonial angle, TAFH, LAFH, U6-PP, L6-MP, and U6-PTV. Therefore, the first null hypothesis was rejected. There were statistically and clinically significant differences in the mean changes within each treatment group, thus the second null hypothesis was rejected. The effects of gender revealed a statistical significance for the Y-axis, Genial angle, PFH, TAFH, UAFH, LAFH, U6-PP, L6-MP, and U6-PTV, and showed that an interaction between treatment therapy and gender existed for LAFH/TAFH and UAFH/LAFH. Consequently, the third null hypothesis was also rejected. Further studies with larger samples may be needed in order to confirm the effects of gender. The results of this study do not support the theory that bicuspid extraction therapy would decrease the vertical dimension in African American patients with high MPA, but rather it showed that overall there were greater increases in the linear than the angular skeletal vertical dimensions.



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