Document Type

Thesis

Date of Degree

Spring 2013

Degree Name

MS (Master of Science)

Degree In

Orthodontics

First Advisor

Thomas E. Southard

Abstract

Objective: The purpose of this study to assess the relationship between masticatory function and symphyseal biomechanical properties using a longitudinal sample. Known differences in male and female maximum bite forces manifest during adolescence. If symphyseal bending rigidity is affected by function during ontongeny, we would expect variation in male and female growth allometries of certain biomechanical properties of the symphysis.

Methods and Materials: Subjects were chosen from the Iowa Growth Study records for completeness and quality of radiographic images longitudinally. 19 females and 20 males were chosen. Lateral ceph images from 9 timepoints (age 3-20) were used to trace the external cortical outline of the symphysis. The biomechanical parameters (second moments of area (Ix, Iy, Imax, Imin)) were calculated from the external contours of the symphysis. Mandibular length was used as a proxy for overall mandibular size. All variables were scaled and growth allometries calculated by a reduced major axis regression. Clarke's T-test was used to test for significance. ANCOVA was used assess the interaction between symphyseal properties and sex, mandibular length, and sex+mandibular length.

Results: No significant differences in symphyseal growth allometries of males and females were found (p>.05). No significant interactions between symphyseal properties and sex, and sex+mandibular length. (p>.05). A significant interaction between symphyseal properties and mandibular length was found (p<.05).

Conclusions: Despite greater bite forces in males that manifest during adolescence, there were no differences in symphyseal growth allometries between males and females. Perhaps function does not play a significant role in development of symphyseal form. Perhaps the subtle effects of function on symphyseal morphology cannot be assessed by using only external cortical outlines for evaluation of symphyseal biomechanical parameters.

Pages

v, 45 pages

Bibliography

Includes bibliographical references (pages 41-45).

Copyright

Copyright 2013 Laura Lynn Bonner

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