臺灣博碩士論文加值系統

錨定的控制，在牙科矯正治療當中扮演一個重要的角色，是影響治療成功與否的關鍵因素。近年來，屬於臨時植體的微骨釘已廣泛地應用於臨床上的錨定控制，相對於傳統牙科贗復植體的錨定系統，微骨釘具有較易於植入與取出、手術創傷較小、可種植的部位較多、可立即受力和價格較便宜等優點。然而，在臨床使用上的失敗率仍然困擾著矯正醫師。而造成微骨釘失敗的可能原因是病患本身的骨質條件、微骨釘的尺寸、植入的深度、露出的長度和施力的狀況。所以，本研究目的是利用臨床病例分析與有限元素法來探討影響微骨釘於矯正錨定應用的生物力學的因素。在臨床病例分析上蒐集了11位共使用20支微骨釘當作矯正錨定的病患。在有限元素法模擬部分則是建立包含微骨釘和骨塊的立體模型，模擬各種不同的參數，包括皮質骨厚度、髓質骨密度、微骨釘直徑、微骨釘長度、植入深度、露出長度、施力大小和施力方向，進行有限元素分析，探討在皮質骨的最大von Mises應力和微骨釘的最大位移。結果顯示在所有的模型中，皮質骨的最大von Mises應力都是集中在靠近微骨釘的受壓力面，而微骨釘的最大位移都是在頭部的頂端。此應力與位移，對於各種模擬參數的相關性是類似的。應力值與位移量，是隨著皮質骨厚度的減少而增加、隨著微骨釘直徑的減少而增加、隨著露出長度的增加而增加、與施力大小成正比、且施力方向在90°有最大值；而微骨釘在大於2 mm的植入深度且在相同的露出長度下所產生的應力值與位移量幾乎不變；而在皮質骨厚度大於0.5 mm與不同的髓質骨彈性模數下結果也幾乎相等。經由本研究的結果可以得知：大於0.5 mm的皮質骨厚度、大於1.2 mm的微骨釘直徑、大於2 mm的植入深度、儘可能減少露出長度、施力大小依臨床所需、施力方向避免與微骨釘成垂直等條件之下，將可增加微骨釘在矯正錨定應用的成功率。

Anchorage control plays an important and determinant role in successful orthodontic treatment. Recently, orthodontic miniscrews, used as temporary implants, have been widely used for anchorage control in clinical practice. Compared to the traditional dental implant anchorage systems, the advantages of miniscrew are simple to insert and to remove, less trauma surgery, less limitation in implant position, immediate loading and less cost. However, the failure of miniscrews in clinic is still bothering the orthodontists. It was hypothesized that bone quality, miniscrew dimensions, implanted depth, exposed length and force conditions would contribute to the failure of miniscrew. The aim of the present study was to investigate the biomechanical influences of these factors in miniscrews for orthodontic anchorage by finite element method and clinical data analysis. Eleven patients were included with total 20 miniscrews applied for orthodontic anchorage for clinical analysis. In finite element simulations, the three-dimensional model of bone block integrated with miniscrew was built. The evaluated parameters included cortex thickness, cancellous bone property, miniscrew diameter, miniscrew length, implanted depth, exposed length, force magnitude and force direction. The maximum von Mises stress of cortex and displacement of miniscrew were investigated and compared. The results showed that the maximum von Mises stress of cortex concentrated in the compressed surface adjacent to the miniscrew and the maximum displacement of miniscrew located at the top of screw head in all models. The tendency of changes of the stress and displacement related to these parameters were similar. In general, both stress and displacement increased with the decreasing of cortex thickness, decreasing of miniscrew diameter, increasing of exposed length, and were linearly proportioned to the force magnitude and had the largest values in 90° force direction. For various lengths of miniscrew, these two indices were almost unchanged when the exposed lengths were equal with the implanted depths larger than 2 mm. For the same miniscrew, both stress and displacement varied insignificantly under various cancellous bone properties with cortex thickness greater than 0.5 mm. This study concluded that to increase the clinical success rate of miniscrew anchorage, the cortex should be thicker than 0.5 mm; the miniscrew diameter should be greater than 1.2 mm; the implanted depth should be longer than 2 mm; the exposed length should be as short as possible; the force magnitude should not exceed the clinical indications; and the force direction should prevent perpendicular to the miniscrew axis.

Abstract …………………………………………………………………… I
Acknowledgments ………………………………………………………… III
List of Tables …………………………………………………………… VI
List of Figures …………………………………………………………… VII

Chapter 1 Introduction
1.1 Background ………………………………………………………………1
1.2 Literature review …………………………………………………… 3
1.3 Motivation ………………………………………………………………7
1.4 Objectives ………………………………………………………………7

Chapter 2 Material and methods
2.1 Clinical data analysis ………………………………………………8
2.2 Finite element analysis …………………………………………… 13

Chapter 3 Results
3.1 Clinical data analysis ………………………………………………22
3.2 Finite element analysis …………………………………………… 25
3.2.1 Stress distribution ……………………………………………… 26
3.2.2 Maximum von Mises stress in bone ………………………………30
3.2.3 Maximum displacement in miniscrew …………………………… 39

Chapter 4 Discussion
4.1 Clinical data analysis ………………………………………………47
4.2 Finite element method ……………………………………………… 50
4.3 Modeling rationale ……………………………………………………51
4.3.1 Model size ……………………………………………………………51
4.3.2 Miniscrew dimensions ………………………………………………52
4.3.3 Implanted depth …………………………………………………… 52
4.3.4 Bone quality …………………………………………………………52
4.3.5 Material complexity ……………………………………………… 53
4.3.6 Interface condition ……………………………………………… 55
4.3.7 Force ………………………………………………………………… 55
4.3.8 Convergence ………………………………………………………… 56
4.4 Contact interface …………………………….………………………57
4.5 Bone resorption related to stress/strain ………………………59
4.6 Miniscrew stability related to displacement ………………… 60
4.7 Bone effects to stress and displacement ……………………… 61
4.8 Miniscrew effects to stress and displacement …………………64
4.9 Force effects to stress and displacement ………………………66
4.10 Clinical implications ………………………………………………67
4.11 Limitations ……………………………………………………………69
4.12 Future works ………………………………………………………… 70

Chapter 5 Conclusions …………………………………………………… 71

References …………………………………………………………………… 72

Appendix I ……………………………………………………………………78
Appendix II …………………………………………………………………90

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