Document Type


Date of Degree

Spring 2013

Degree Name

MS (Master of Science)

Degree In


First Advisor

Staley, Robert N

First Committee Member

Moreno, Lina

Second Committee Member

Qian, Fang


Objective: The purpose of this study was to use the University of Iowa Meredith Growth Study to limit selection bias in selecting subjects to determine interarch tooth-size discrepancies (ITSD) by measuring and comparing the mesiodistal widths of maxillary and mandibular teeth.

Methods: Thirty-two males and twenty-four females were selected from the Iowa Growth Study. They were selected on the basis of normal occlusions which were defined as Class I molars with mild (<2mm crowding/spacing) or moderate (2-4mm crowding/spacing) tooth-size arch length discrepancies. The mesiodistal widths of the maxillary and mandibular teeth were measured and anterior and overall ratios were developed. Descriptive statistics were computed. A two-sample t-test was used to detect the differences between the genders and between two crowding groups under different conditions. The Shapiro-Wilk test was used to check for the normality of the variables.

Results: All subjects had a combined mean overall ITSD ratio of .914, a SD of .021 and a range of .875-.960. All subjects had a combined mean anterior ITSD ratio of .778, a SD of .025 and a range of .714-.863. No significant differences in ITSD were found between the two crowding groups nor differences found between the genders (p>0.05 in each instance). No significant differences in overall ratios were found between Bolton's data and this study's data for all subjects (p=0.7934) or anterior ratios (p=0.9786).

Conclusions: The determined overall ITSD ratio of 91.4% +/- 2.1% and anterior ratio of 77.8% +/- 2.5% are remarkably similar to the original Bolton analysis that is still frequently used in orthodontics today. The results of this study validate and strengthen the findings of Bolton's study and support the use of the Bolton analysis in the determination of ITSD before orthodontic treatment as a tool to assist in the development of an orthodontic treatment plan.


vi, 72 pages


Includes bibliographical references (pages 68-72).


Copyright 2013 Jordan Poss