根管彎曲度的新參數及其在臨床上的意義

Abstract

對於臨床的牙醫師尤其針對沒有接受過長期且專業根管專科訓練的醫師而言，如何能快速且準確的判斷一顆牙齒其根管治療的難易度是非常重要的，大部分的狀況都是藉由一張術前X光片來評估，難易度大致上是和根管的彎曲度成正比，然而先前一些學者提出的一些角度的量測方法都十分複雜，且各種方法都有其優缺點，所以我們在這裡希望能簡單的在X光片上畫幾條直線，找尋新的參數來評估根管的彎曲度，以代替複雜的角度量測。 本實驗先選擇在臨床上需要做根管治療的30顆人類下顎第一顆大臼齒，利用Günday在2005年發表的方法加以改良，並且加入長度這個參數，測量各個參數及其之間的相關係數；再利用我們提出的new technique量測同樣的30顆牙齒，一樣測量我們新定義的參數(X、Y、Z)並且分析參數間的關係，統計方面使用Pearson correlation；之後我們又設計了一個靜態彎曲測試的模具，希望藉由鎳鈦旋轉器械的彎曲來模擬根管的彎曲度，藉由此彎曲度驗證我們提出的方法，並且找尋各參數間的相對應數值，再利用負載三段式曲線圖定義出臨界點，找出修型時的絕對安全區、相對安全區、絕對危險區；最後再利用有限元素分析法進行靜態彎曲測試的模擬，看與實體實驗之間是否可相呼應。 我們發現利用Günday technique改良版來測量的結果，Coronal Access Angle是多餘的，它可以被X/Y這個比值所取代，因為他們是三角函數tan的關係，且發現根管長度對於彎曲度的形容來說也是一個可用的參數；而利用我們新定義的new technique來測量時，會發現可將根管彎曲的地方分成上下半部來思考，上半部可視為彎曲的起始，可以用Schneider角度來表示，下半部可視為彎曲的結束，可以用Weine角度來表示，並且又可以把上下半部根管長度列入新的參數來取代上述兩種角度參數。 利用我們設計的靜態彎曲測試會發現SA和X/(Y+Z)、X/Y有很高的正相關，WA和X(Y+Z)、X/Z有很高的正相關，也就是先前學者提出的角度參數SA、WA可以被我們提出的線性參數間比值X/(Y+Z)、X/Y、X/Z所代替。至於有限元素分析的部分，在器械彎曲的程度和實體實驗之間比較起來相似度頗高，以後可以利用在模擬方面，以減低我們需大量器械做實驗時的成本。 結論是當我們今天遇到一個彎曲的根管要來形容時，我們可以畫幾條直線且用三個線性參數(X、Y、Z)來表達，第一個就是X/(Y+Z)，可大略的知道最彎的程度為何？再來就是Y/(Y+Z)，可知道根管最彎處位在整個根管的那個地方(前、中、後段？)，再來若想更深入的探討彎曲的地方，可利用X/Y來形容彎曲的起始處，再利用X/Z來形容彎曲的結束。

It is important for a dentist to diagnose the difficulty of root canal therapy quickly and definitely. In most situation, we usually use a pre-operative radiography as a guide and the difficulty of root canal therapy is propose to the root canal curvature. Although many methods about the root canal curvature were published, but they still had many disadvantages and been very complicated. The purpose of this study is to find new linear parameters to describe the root canal curvature instead of the complicated angular parameters. Thirty human mandibular first molar which need root canal therapy were collected. First we use digital X-ray system (Digoraâ) to take pre-operation radiography and then determine the parameters of Günday technique. We also determine the same thirty teeth with the linear parameters of new technique. The resultant values were evaluated statistically using Pearson correlation. A new designed statistic bending test model were used to stimulate the root canal curvature. After analyzing the relationships between the linear and angular parameters, we can find a rule to define the root canal curvature with a new definition. Then the preparation sequence and the difficulty of root canal therapy can be defined. Finally we use finite element method to simulate the statistic bending test. The parameter Coronal Access Angle seems to be excrescent in Günday technique and can be replaced by the specific value X/Y. The previous angular parameter Schneider’s angle can be replaced by the specific values X/(Y+Z) and X/Y in new technique. The Weine’s angle can be replaced by X/(Y+Z) and X/Z. A significant correlation was seen between the finite element method and the statistic bending test. We can use the finite element method to replace the complicated actual study and made it efficiently and economically. If we want to describe a root canal curvature with our new definition. We can use the special value X/(Y+Z) to show the generalized curvature. And then we use the value Y/(Y+Z) to define the most curved point is at what level in the whole canal (coronal, middle, or apical part?). Finally, if we want to describe the curvature definitely. We can use the value X/Y to describe the initial part of the curve and use the value X/Z to describe the posterior part of the curve.