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First Premolar Extraction Decisions and Effects Ryan Gregory Bowles University of Tennessee Health Science Center

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First Premolar Extraction Decisions and Effects Ryan Gregory Bowles University of Tennessee Health Science Center University of Tennessee Health Science Center UTHSC Digital Commons Theses and Dissertations (ETD) College of Graduate Health Sciences 5-2005 First Premolar Extraction Decisions and Effects Ryan Gregory Bowles University of Tennessee Health Science Center Follow this and additional works at: https://dc.uthsc.edu/dissertations Part of the Orthodontics and Orthodontology Commons Recommended Citation Bowles, Ryan Gregory , "First Premolar Extraction Decisions and Effects" (2005). Theses and Dissertations (ETD). Paper 30. http://dx.doi.org/10.21007/etd.cghs.2005.0034. This Thesis is brought to you for free and open access by the College of Graduate Health Sciences at UTHSC Digital Commons. It has been accepted for inclusion in Theses and Dissertations (ETD) by an authorized administrator of UTHSC Digital Commons. For more information, please contact [email protected]. First Premolar Extraction Decisions and Effects Document Type Thesis Degree Name Master of Dental Science (MDS) Program Orthodontics Research Advisor Edward Harris, Ph.D. Committee Gregory Hutchins, D.D.S. Quinton Robinson, D.D.S., M.S. DOI 10.21007/etd.cghs.2005.0034 This thesis is available at UTHSC Digital Commons: https://dc.uthsc.edu/dissertations/30 FIRST PREMOLAR EXTRACTION DECISIONS AND EFFECTS A Thesis Presented for The Graduate Studies Council The University of Tennessee Health Science Center In Partial Fulfillment Of the Requirements for the Degree Master of Dental Science From The University of Tennessee By Ryan Gregory Bowles, D.D.S. May 2005 Copyright © Ryan Gregory Bowles, 2005 All rights reserved ii DEDICATION This thesis is dedicated to my parents Dr. Richard Matteson Bowles and Mrs. Sharon White Bowles in recognition of their love, guidance and support of my education iii ACKNOWLEDGMENTS I would like to thank my thesis committee for their help and support over these last three years. Dr. Greg Hutchins and Dr. Chuck Robinson contributed with helpful comments and suggestions and Dr. Edward Harris, my committee chairman and research advisor, guided the overall project. I also deeply appreciate the care and concern of my lovely wife, Glenda, as I persevered on this project and increased her own responsibilities in the process. Thank you for standing with me and being a true helper. Finally, I also thank my two wonderful children Amber and Daniel for accepting less attention whenever I worked on this thesis. Don’t worry kids, daddy’s research days are over! iv ABSTRACT The most common method of resolving substantial tooth size-arch length discrepancies (TSALD) is to treat patients with the extraction of premolars. Not all of the extraction space, however, is needed to eliminate the patient's TSALD. Also, it is typical that some of the extraction space will be lost because the molars are used as anchorage units to retract the anterior teeth. OBJECTIVE: This study developed a method to measure changes in the positions of the canines and second premolars relative to the palatal rugae. These data were used to assess how the extraction space was used in resolving the malocclusion. Data were also collected on the severity of the malocclusion—namely, pretreatment overjet, overbite, incisor irregularity, and TSALD—to test whether these were predictive in the extraction decision. The goal was to better understand first premolar extraction changes and decisions. METHODS: Pretreatment and posttreatment dental casts were available for 50 adolescent North American whites with Class I malocclusion who were treated with first-premolar extractions. Sixty-four landmarks were recorded in all three planes of space with a MicroScribe G2X 3D digitizing system and distances were computer-generated using trigonometric algorithms. RESULTS: Removing a first premolar gave an average of 7.3 mm of space in each quadrant of which 3.8 mm (51%) was consumed by canine retraction, while 3.6 mm (49%) was used as the second premolar moved mesially. Changes in the transverse dimension after premolar extraction treatment were v minor, though second premolar width diminished about 1 mm as these teeth were moved into a narrower segment of the arch (P < 0.01). The extent of incisor irregularity had a significant positive association with the amount of canine retraction (r = 0.33; P = 0.02). CONCLUSION: A four first premolar extraction pattern in Class I patients provides space that is consumed almost equally by the retraction of canines and the mesial movement of the buccal segments in the maxilla. Multivariately, the two significant variables associated with increased canine retraction in these patients were transverse canine change (i.e., buccally displaced canines) and a high level of incisor irregularity. vi TABLE OF CONTENTS Chapter Page I. INTRODUCTION ..………………………………….………………… 1 II. REVIEW OF THE LITERATURE…………………………………….. 3 Quantifying Extraction Decisions……………………………....... 3 First Premolar Extractions………………………………… 4 Second Premolar Extractions……………………………… 5 Other Considerations……………………………………… 7 Premolar Extraction Effects……………………………………….. 8 Incisor Angulation………………………………………… 9 Incisor versus Molar Changes…………………………… 11 Incisor Retraction………………….……………… 11 Molar Protraction…………………………………. 15 Occlusal Plane……………………………………………... 17 Vertical Dimension……………………………………….. 18 Arch Changes……………………………………………… 18 Arch Width…………………………………………. 19 Arch Depth…………………………………………. 21 Tooth Size-Arch Length Discrepancy…………………… 21 Tooth-Size Discrepancy………………..……….………... 22 Stability of Palatal Rugae……………………………………….... 23 vii Chapter Page Summary and Conclusions…………….………………………… 28 III. MATERIALS AND METHODS ………..…………………………… 29 Materials…………………………………………………………… 29 Sample Characteristics……………………………………. 29 Data Analysis……………………………………………… 30 Methods……………………………………………………………. 31 Cast Analysis……………………………………………… 31 Statistical Analysis………………………………………… 37 IV. RESULTS ………………………………………………………………. 39 Side Differences…………….……..……….….…………………… 39 Sexual Dimorphism……………………………………………….. 43 Extraction Space…….……………………………………………… 47 Use of the Extraction Space………….……………………………. 54 Multivariate Model..………………….…………………………… 60 V. DISCUSSION …………………………………………………………. 63 Side Differences………………….…………………………………. 64 Sexual Dimorphism.……………………………………………….. 65 Extraction Space.…………………………………………………… 67 Mesiodistal Dimension…..……………………………….. 67 Transverse Dimension……………………………………. 69 viii Chapter Page Predictive Models……………………………………………….. 70 VI. SUMMARY AND CONCLUSIONS ………..………………..…... 72 LIST OF REFERENCES………………………..…………………… 76 APPENDIX ……………………………………..………………….. 84 VITA ………………………………………………………………… 135 ix LIST OF TABLES Table Page 1 Summary of the average amounts of maxillary incisor retraction as measured in four studies with five different references ………………………..…...……………… 14 2 Results of paired t-tests assessing side differences in the mesiodistal plane…………………………………………………. 41 3 Results of paired t-tests assessing side differences in the transverse plane…………………………………………………… 42 4 Results of one-way ANOVA testing for sexual dimorphism in dental movements…………………………….……….. 45 5 Results of one-way ANOVA testing for sexual dimorphism in dental relationships………..…………………………… 46 6 Descriptive statistics for changes in tooth positions……………………..…………………………………………….. 49 7 Results of linear regression predicting the amount of canine retraction…………….……….………………………….…….. 56 8 Results of stepwise linear regression predicting the amount of canine retraction.…………..……..………………………....... 61 x LIST OF FIGURES Figure Page 1 Demonstration of the effect of occlusal plane tipping on the molar’s relationship to the medial ruga point…………………. 27 2 Pretreatment cast landmarks (Points 1-34)………………...................... 32 3 Posttreatment cast landmarks (Points 37-66)………………………….. 33 4 Sequenced array of cases according to the amount of observed mesiodistal change in the distal contact of the maxillary canine.………………………………….……………….. 50 5 Sequenced array of cases according to the amount of observed mesiodistal change in the mesial contact of the maxillary second premolar………………..……………………. 51 6 Sequenced array of cases according to the amount of observed transverse change in the distal contact of the maxillary canine ……………………………………...………….. 52 7 Sequenced array of cases according to the amount of observed transverse change in the mesial contact of the maxillary second premolar...……..…………………………. …. 53 8 The association between the amount of canine retraction and the degree of maxillary incisor irregularity at pretreatment….…………………………………………. 57 9 The association between the amount of canine retraction and the amount of transverse change in canine position........................................................................................ 58 xi CHAPTER I INTRODUCTION A common orthodontic problem occurs when the tooth crown dimensions exceed the available space in the alveolar arch. This discrepancy occurs when the sum of the mesiodistal crown diameters exceed the bony arch perimeter available for the teeth to be properly aligned. As methods are unavailable to increase arch size by promoting bone growth, the common alternative is to reduce tooth size. By far, the most common method of resolving substantial tooth size-arch length discrepancies (TSALD) is to treat patients with the extraction of premolars. Extracting a premolar can create more space than is needed to resolve the discrepancy. Premolar extraction is a quantum event in that removing a tooth provides about 7 mm of space whereas the alternative, nonextraction, provides none. It is unlikely, however, that all of the extraction space
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