Date of Award

Spring 1999

Document Type

Thesis - Restricted

Degree Name

Master of Science (MS)

Department

Dentistry

First Advisor

Bradley, Gerald T.

Second Advisor

Kittleson, Russell T.

Third Advisor

Connell, Todd

Abstract

A pleasing profile and esthetic harmony are among the most important goals for successful orthodontic treatment. The balance of the facial structure is affected not only by orthodontic treatment but also by growth. The literature has suggested that soft tissue changes with growth do not directly follow the underlying skeletal structures. They are sex- and age specific. The nose and chin continue to grow, with the nose growing relatively more forward than the chin. The length and thickness of the lips increase, with the largest incremental change occurring during the adolescent growth period. The literature has also suggested that there is conflicting and contradictory information on the soft tissue changes associated with tooth movement. The controversy rests with soft tissue changes following either extraction or nonextraction mechanics. Some studies have indicated the soft tissue profile improved or was within the desired esthetic range after extraction of premolars. Other studies suggested that orthodontic treatment involving the extraction of premolars cause undesirable retrusion of the lips along with unfavorable profile changes. Interest in the literature has also centered on the prediction of a ratio between upper lip and upper incisor retractions after treatment. Many ratios have been developed but with different reference planes. All the above studies have used lateral cephalometric radiographs that were taken prior to, and after orthodontic treatment. In most of these studies, they have differences in malocclusion status, gender, extraction pattern, and stage of growth. It is important to use a sample consisting of the same gender patients with one type of malocclusion, same extraction pattern and little growth left for the evaluation of soft tissue profile changes after extractions. The null hypotheses of this study are: 1) profile will not change after premolar extraction; 2) there is no correlation between the retraction of the upper lip and the upper incisors. In the present study, every effort was made to standardize the sample and to control other dependent variables in order to evaluate cephalometric changes in soft tissue profile after different premolar extraction patterns. The sample consisted of 104 pre and post-treatment lateral cephalometric radiographs from 52 Caucasian postadolescent female patients who were at least 16 years old before treatment. Two treatment groups are: 1) patients (n = 26, class II division 1) had extractions of 2 upper first premolars (2UFPE); 2) patients (n = 26, class I) had extractions of 4 first premolars (4FPE). All the patients were selected from a Milwaukee based orthodontic practice. Combinations of 31 soft and hard tissue measurements were chosen in the study. Statistical comparisons were made between the pre- and post-treatment measurements in each group and between two groups. Correlations between every two measurements and ratios between lip and incisor retraction were also calculated.

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