3D FEA of post-core design of restoring weakened roots on stress distribution between post&core and tooth interface －Cohesive element approach

由於bonding agent和resin cement及fiber post不斷進步，還有『Monoblock』的概念的出現，進而洐生出可以利用composite resin來強化齒質的說法，使得過去歸類預後不好的牙齒，還可能留下來繼續重建使用！因此重建缺損過大根管治療後的牙齒，觀念慢慢的與以往不同，治療方式也有更多的選擇，因此近來有許多FEA的文獻在討論這一個區塊。但之前FEA文獻則因為往往(1)沒有辦法模擬出黏合劑將fiber post與root dentin膠合後的樣子，而時常把fiber post與dentin設定成為一體，高估resin cement的作用，導致實驗結果與臨床有所誤差；(2)另一方面無法得知resin cement介面的受力及崩解狀況，無法準確分析實驗樣本的結果。 因此本篇利用Abaqus軟體製模擬缺損過大的根管治療後牙齒，且以『cohesive element』模擬resin cement將fiber post與dentin膠合的狀態。而應力常常存在於牙齒與冠心或牙根柱的界面上，導致根管治療後的牙齒往往都是沿著界面發生牙齒斷裂或是在界面上發生debonding。因此本篇論文以剩餘齒質所受應力大小與分佈及resin cement介面的應力與崩解情形，來分析重建缺損過大根管治療後的牙齒應該如何在(1) Ferrule的有無; (2)冠心與牙根柱的材質; (3)牙根柱的長短與粗細，這幾個方面作為考量。 本實驗結果發現 (1)對於Fiber post來講Ferrule effect更顯得重要，尤其在靠近冠心與齒質界面處，若沒有2mm ferrule length將會使應力增加，最大幅度甚至有4倍之多; (2)Elastic modulus與牙齒相接近的材料，應力不易集中於膠合界面中，較不會發生post deboning或是root fracture的現象; (3)對於Fiber post的選用，若有Ferrule effect下，應選用較細的fiber post以避免傷害更多的齒質；若臨床上無法提供Ferrule effect下，則建議使用較細且較長的fiber post ，會有最好的應力分散較果。As improvements on bonding agent, resin cement and fiber post occurred and the concept of『Monoblock』arose, that of which flourished into the idea of using composite resin to strengthen tooth structure, made it possible for the prognosis compromised teeth to kept for rehabilitation! Hence, the concept of restoring excessively weakened endodontically treated tooth becomes different from before and there are more options for treatments. As a result of the modification in the concept, FEA provided numerous studies on excessively weakened endodontically treated tooth in these recent years. Different conclusions can be found in in vitro studies due to differences in methodology in which these methodologies do not closely simulate to the clinical situations and thus the results became unreliable. The previous related FEA studies cannot simulate the image of the fiber post and root dentin after they are adhered by the cement and often presented fiber post and root dentin as a whole. On one hand, the function of resin cement has been overestimated by doing so and as a result, errors between experimental results and clinic would occur. On the other hand, the interfacial stress and the debonding situation of resin cement cannot be known and the results of the experimental samples cannot be analyzed precisely. This current study relied on the software Abaqus to simulate excessively weakened endodontically treated tooth and used “cohesive element” to simulate the image (status) of fiber post and dentin being adhered by resin cement. Stress usually occurred on the interface between the tooth and the center of the crown or the post which leads to fractures or debonding along the interface of the tooth that had undergone endodontic treatments. The present study will analyze (1) designs of ferrule; (2) the materials chosen for core and post; (3) the length and width of the post by discussing the intensity and distribution of the stress on the remaining tooth structure. The interfacial stress and debonding condition of resin cement will also be investigated as way of rehabilitation for excessively weakened endodontically treated tooth. This current study finds out (1) Ferrule effect is more important to fiber post, especially at interface between core and dentin. If it doesn’t have 2 mm ferrule length, the stress of interface will increase 4 times. (2) The material similar to tooth has less stress at interface between post and tooth. The chances of post debonding and post fracture will decrease. (3) If tooth has 2mm ferrule length, we have to choose thinner post; If tooth doesn’t have ferrule length, we have to choose thinner and longer post in order to get better stress distribution