- 期刊
下顎不同局部活動義齒設計之應力分佈
Stress Distribution of Mandibular Removable Partial Dentures with Different Designs
摘要
遠心游離端(distal free-end)缺牙以局部活動義齒來修復時，其設計有以保護支柱牙為主之緩壓裝置的設計，此種設計的理念或稱為flexible support。而flexible support的設計已發展近半世紀。相對於此的為rigid support的設計理念。此兩種不同的製作理念，常造成牙醫師在設計製作時的困惑。故本研究之目的乃是探討這兩種不同理論的固位裝置(retainer)其受力時應力分布的差異，以作為臨床製作時的參考。實驗選用下顎單側游離端缺損Kennedy Ⅱ級modification Ⅰ的模型以類三次元光彈應力分析法來研究。在右側游離端最終支台齒上設計五種不同的固位裝置，分別有鍛製金屬線牙鉤(wrought-wire clasp)、RPI clasp、鑄造環周牙鉤(cast circumferential clasp)、RPPI clasp及conical crown telescope。並以超小型應力負荷感應器放置於特殊設計的義齒基底中，於咬合壓力下，分別量測不同固位設計的局部活動義齒，其義齒基底所分擔的咬合力比率。在咬合施力的同時並照相記錄局部活動義齒光彈模型在光彈組合上的等色線圖以做為應力分布的比較。實驗結果顯示，以鍛製金屬線牙鉤設計分佈之固位裝置，在支柱牙會有較小的應力，然而在齒槽骨嵴則有明顯的應力集中。由義齒基底所分擔的咬合應力來看，鍛製金屬線牙鉤設計的也分擔較高比率的咬合力。本研究的結論為製作理想的局部活動義齒，在支柱牙及殘存嵴間的應力分佈應為最小是很重要的。
並列摘要
When a removable partial denture RPD is anticipated to restore the missing teeth of distal free-end edentulous ridge, how to design the distal extension RPD always make dentists so puzzles. To prevent abutment teeth from being harmed, some designs and devices called stress-breakers sometimes referred to as flexible support design have been developed over the past half-century. On the contrary, the other controversial design philosophy-the ”rigid support” design, also advocated in a lot of articles. Therefore, the purposes of this study were to compare the various retainer designs that belonged to the two different designing philosophies. The technique of quasi-three dimensional photoelastic stress analysis was used for this investigation. Photoelastic model was made with individual simulative materials for tooth structure (PL-1) and alveolar bone (PL-2). A model was fabricated that included the anterior teeth, right 1(superscript st) premolar, left 1(superscript st) premolar and 2(superscript nd) molar. Some types of retainers will be selected to fabricate for the analyses, they are wrought wire clasp, RPI clasp, the conical crown telescopic retainer, RPPI clasp and cast circumferential clasp. For each experimental RPD, one micro load cell transducer will be put between the two layers of the specially fabricated double denture bases to measure the denture base shearing load of occlusal force. After load vertically on the occlusal table of RPD, photoelastic stress distribution isochromatics, and denture base shearing load will be obtained. The results indicated that the unfavorable stress gradient was found in wrought wire clasp design, the maximum stress concentrated at the residual ridge while the minimum stress occurred at the abutment. This study concluded that minimum stress gradient between the abutments and the residual ridge might be most important issue when fabricated an adoptable RPD.