Date of Degree
MS (Master of Science)
Southard, Thomas E.
First Committee Member
Marshall, Steven D.
Second Committee Member
Holton, Nathan E.
Third Committee Member
Fourth Committee Member
Introduction: The purpose of this study was to evaluate the changes in marginal ridge alignment occurring through normal growth and development from early childhood to late adulthood and to examine if any statistical variation exists between males and females.
Methods: Dental casts of 38 subjects (15 females and 23 males) from the Iowa Growth Study were selected. The marginal ridge discrepancy was measured as the absolute value difference between adjacent marginal ridges of 20 interproximal contacts with both the ABO tool (data not shown) and a vertically mounted digital caliper. Upper and lower casts were tripoded to a level plane defined by the most posterior tooth and central point of the most erupted central incisor. A 15 subject calibration was used to measure inter-examiner reliability using the Cronbach’s Alpha and Kappa tests. The independent samples t test was used to examine the correlation of marginal ridge discrepancies between males and females.
Results: Cronbach alpha (p ≤ .001) and Kappa test (p ≤ .01) show excellent inter-rater reliability. The independent sample t test showed no statistical significance, with minimal exception, in marginal ridge discrepancies between males and females matched for age (p > .05). Group 1 showed significantly higher number of marginal ridge discrepancies within ABO range of 0 – 0.5 mm of males and females compared to Group 2.
Conclusion: Based on this study, no statistically significant differences were found in marginal ridge discrepancies between males and females. Also, the magnitude of marginal ridge discrepancies of erupting permanent teeth shows a decrease as an individual proceeds through growth and development and they remain relatively “level” during primary dentition.
Due to the limited amount of research about the alignment of a person’s bite as they grow, it was important to look at how teeth erupt into the mouth from a child to an adult (2nd decade). Therefore, we used dental models from 38 people from the Iowa Growth Study to measure height differences as the teeth erupt into the mouth and align themselves as each person grows and matures. Also, we wanted to see if any differences occurred between males and females in their tooth alignment measurements. A specific tool was fabricated to make accurate measurements to reduce the risk of ambiguity that could introduced with a less accurate tool. Because a large age range existed we split the ages into three groups: Group1 (5 – 9yrs), Group 2 (>9 – 14) and Group 3(15 – 29). Our findings indicated little to no differences between males and females in how the teeth erupt and align during growth. Also Group 1 had a much higher number of level (0 – 0.5 mm) teeth compared to Group 2. In addition to little differences between males and females, height differences between permanent teeth showed a levelling trend as the individuals proceeded through growth into adulthood (2nd decade).
American Board of Orthodontics, curve of Spee, marginal ridge, root angulation
vii, 37 pages
Includes bibliographical references (pages 36-37).
Copyright © 2017 Mason Andrew Dearing
Dearing, Mason Andrew. "Changes in marginal ridge alignment from early childhood to late adulthood in an untreated Caucasian population using the Iowa growth study sample." MS (Master of Science) thesis, University of Iowa, 2017.