根管治療用鎳鈦旋轉器械之幾何形態與撓曲度之力學分析

Mechcnics Analysis of Geometry and Bedning Angulation of Endodontic Nickel - Titanium Rotary Instrumentation

呂志明(Chih-Ming Lu)

指導教授 ： 林俊彬

共同指導教授 ： 陳文斌

國立臺灣大學/醫學院/臨床牙醫學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.02596

摘要

彈性極佳的鎳鈦旋轉器械被賦予期望能夠去減少根管修形產生肩台形成、根尖孔敞開、根尖區穿孔、根管偏移等併發症的機會，並藉此提高彎曲牙根根管治療的成功率；可是上述根管修形之併發症依然是時有所聞，不易移除的器械斷裂病例更是曾出不窮，因此有必要對鎳鈦旋轉器械的基本金屬特性再加以深入探討；雖然先前學者的動態或是靜態研究，對此類問題也提出了看法，例如週期性疲勞、或者是不當施力方式等，但是並無研究是針對器械本身不同幾何形狀的變化，以及其受力負載後的撓曲力學行為影響。所以本研究的目的，是使用有別於ADA 28號的測試方式，探討鎳鈦旋轉器械進入不同長度之彎曲根管後、器械本身的幾何形態與撓曲度之力學變化，並找出鎳鈦旋轉器械進入根管修形時，器械的彎曲之模式、進而對臨床醫師及一般研究者提出預防器械斷裂與如何達到安全的根管修形之建議。本研究的前導實驗，分析出台灣牙醫師最常用的鎳鈦旋轉器械為ProTaper system，為了模擬鎳鈦旋轉器械進入彎曲根管，所形成的彎曲行為，我們使用一塊斜度為十五度的金屬塊負載於不同的鎳鈦旋轉器械（ProTaper system F1, F2 & F3)之上，使得鎳鈦旋轉器械在不同的彎曲限制點(3, 6 & 9 mm)改變下，受力下壓位移至少使得鎳鈦旋轉器械彎曲超過Schneider角度50°，過程中除了記錄負載力量之大小、下壓位移的距離外、我們並使用數位影像記錄來進行鎳鈦旋轉器械的Schneider角度與Pruett角度之分析，本實驗的彎曲測試的結果，並將與三維有限元素法之彎曲測試結果來做比較分析。
　　當以Schneider技術來評估不同限制點的同一鎳鈦器械時，結果顯示、當限制點越往後移動時，鎳鈦旋轉器械受力彎曲時，產生大量金屬分子晶相由Austenite轉變到Martensite的彎曲角度也會隨之減小；但是在彈性限度的臨界角度的比較上，卻是不受器械與限制點的影響，都是45°，此時鎳鈦器械都會脫離超彈性的特性，因而進入永久形變區。另一方面在Pruett角度的評估上，我們的實驗的結果也顯示，當限制點向後移動時、就單一器械本身來說，F2與F3的大量金屬分子之晶相轉換角度有逐漸減小的趨勢，而F1卻是無明顯的差異；在限制點位於9 mm時，F1，F2與F3因受力彎曲而進入大量分子參與晶相轉變的角度相近，並且有相近的，重要的是彈性限度的臨界角度也相近；總而言之、鎳鈦旋轉器械進入不同長度之彎曲根管時、不僅僅是根管彎曲的角度與曲率半徑對根管修形的難度，或是說對器械本身的撓曲力學行為會有所改變、在限制點的位置不同所模擬彎曲根管的長度，或是說進入此長度的器械尺寸，都扮演極為重要的角色；也就說當根管彎曲角度越大，曲率半徑越小，彎曲根管的長度越長、或者是器械尺寸越大，對於彎曲根管的修行來說都是較不利的。三維有限元素法之彎曲測試結果也顯示與本實驗各項結果有極高的相關連性，證明本實驗設計與結果足以提供臨床醫師與研究人員當成參考指標。

關鍵字

鎳鈦旋轉器械 ； 限制點 ； Schneider角度 ； Pruett角度 ； 曲率半徑 ； 三維有限元素法

並列摘要

With the advantages of material technology, nickel titanium (Ni-Ti) files are introduced to facilitate the instrumentation of curved canals due to its superior flexibility to minimize operative complications, such as ledging, elbow, perforation and transportation. They also have been expected for-ward to increase the success rate of root canal therapy. Nevertheless, separation is still a subject of debate with Ni-Ti rotary instruments. Thus, the purpose of this study was aimed to compare the mechanical behaviors of different geometries of endodontic Ni-Ti rotary instruments via simula-tive variable curvatures of root canal during shaping. ProTaper® F1, F2, and F3 were selected due to the different geometries of design and most ex-ercised in Taiwan. Each group contained 10 files progressing static bending test in different restricted points experimentally by universal testing ma-chine. The results showed that according to the evaluation of Schneider Technique, the restricted points move backward from 3 mm to 9 mm, the bending angle of maximal crystal transformation will be minimized, which is getting abundantly transforming Austenite into Martensite. However, among the ProTaper R F1, F2, and F3 or the different restricted points, the critical angle of elasticity always came close to 45。. On the other hand, ac-cording to the evaluation of Pruett Technique, our results also showed when the restricted point moving backward from 3 mm to 9 mm, the bending an-gle of maximal crystal transformation of ProTaper R F2 and F3 had the ten-dency to reduce gradually, but F1 did not have obvious difference; ProTa-per R F1, F2, and F3 have the approximative angle, whatever the bending angle of maximal crystal transformation, the critical angle of elasticity. It means that if the root canals have a severe angle, a small radius of curve, a long working length or the usage of large instruments, there are more unfa-vorable to the shaping of root canals. And The experimental results corre-lated very well with FEM analysis. In conclusion, these data of static bend-ing test can provide useful information for instrument under cyclic tensile and compressive stresses which can cause fracture failure. Furthermore, it is important that the limitations of instruments using rotary Ni-Ti instruments should be known and the modification of geometry and material should be further investigated in the future.

並列關鍵字

Ni-Ti rotary instruments ； restricted point ； Schneider angle ； Pruett angle ； radius of curve ； Finite element method

參考文獻

呂玉蓉、林俊彬、陳文斌，根管治療用之鎳鈦旋轉器械力學行為分析 2005.

Buehler WH, Gilfrich JV, Wiley RC. Effect of low temperature phase changes on the mechanical properties of alloy near composition Ni-Ti. Journal of Applied Physics 1963; 34; 1475-1477.

Bramante CM, Betti LV. Comparative analysis of curved root canal preparation using nickel-titanium instruments with or without EDTA. J. Endodon 2000;26:278–80.

Berutti E, Giorgio C, Gaviglio I, Eng D, Andrea I, Eng D. Comparative Analysis of Torsional and Bending Stresses in Two Mathematical Models of Nickel-Titanium Rotary Instrument: ProTaper versus ProFile. The American Association Endodon 2003; 29:15-19.

Bahia MGA, Martins RC, Gonzalez BM & Buono VTL. Physical and mechanical characterization and the influence of cyclic loading on the behaviour of nickel-titanium wires employed in the manufacture of rotary endodontic instruments. Int. Endodon. J., 38, 795–801, 2005.