- 學位論文
根管幾何型態對於鎳鈦旋轉器械之力學行為分析
Influence of Canal Geometry on the Mechanics of Nickel-Titanium Endodontic Rotary Instrumentation
摘要
根管製備主要是在於良好的根管清潔與修形。良好的根管修形目的是要適度擴大與建立一有錐度平滑之根管。近年來，根管製備的器械有很大的進展，其中鎳鈦合金因良好的生物相容性、獨特的記憶金屬與超彈性特性，被廣泛應用於根管清創器械，彌補過去臨床上使用不鏽鋼器械製備彎曲根管常發生之副作用。雖然鎳鈦旋轉器械對於修形彎曲根管有良好的成形能力，但發現斷裂一直是值得注意的問題。因此，本研究目的利用有限元素分析方法探討根管幾何型態對於根管清創器械影響，以及提出將來設計根管清創器械之建議。本論文共分為三個部分。第一部份：利用斜塊下壓ProTaper Universal System器械尖端，得到其彎曲力學行為。結果顯示，ProTaper Universal System有較ProTaper Sytem彎曲能力。第二部分：探討根管幾何參數對器械力學行為影響，一、利用2-D彎道作為模擬探討鎳鈦旋轉器械對疲勞斷裂之抵抗能力，使用三種不同的角度(20°, 40°, 60°) ，三種不同曲率半徑(5mm, 7.5m, 10mm)，二、建構出不同幾何彎曲位置(冠端、中間、尖端)、擴根管口程度(1.3mm、2mm、2.6mm)之人工根管，模擬鎳鈦旋轉器械進入根管情況，可清楚看出器械與根管壁之接觸情形。不鏽鋼彎道分析結果顯示，曲率半徑越大及彎曲角度越小，器械上最大主應力值會越小。而於不同幾何型態之根管結果顯示，彎曲位置越往根尖接近，器械上最大主應力值會越小且有愈往器械尖端移動之趨勢且彎曲角度會變小；擴根管口對於彎曲位置越接近根尖之根管，角度變化量越不明顯，表示越接近根尖之彎曲，擴大根管口可能不會降低對器械之危害。第三部分：探討新型器械之力學行為。改良本研究團隊之設計，將上方無螺紋部分以螺紋漸進縮小直徑形式，發現當進入彎曲根管時，可降低應力值減少不預期斷裂危險，且建議不應在幾何上做突然的變化。
並列摘要
The important objectives of endodontic treatment are to achieve good canal shaping and cleaning. The goal of shaping is to attain a continuous taper from the coronal access to the apex. In recent years, Ni-Ti alloy has been used widely for endodontic instruments due to its bio-compatibility, high flexibility, and stronger in fatigue resistance than stainless steel in curved canal treatment. It is known that changes in the shape of instrumentation in curved canal may have a crucial influence on the success of root canal treatment and may cause instrument fracture. In clinical practice, many of the instrument fractures happen unexpectedly with no visible sign of permanent deformations. It is a serious concern in root canal preparation. Therefore, the purpose of this study was to investigate the influence of canal geometry on the mechanics of Ni-Ti endodontic rotary instrumentation by using finite element analysis and to provide suggestions for product designs. The current thesis was divided into three main parts. Part 1: The tip of ProTaper Universal System file was pressed down by a wedge-shaped block and the stress distributions were analyzed. Results indicated that ProTaper Universal System file has better bending-resistance ability than Protaper System file. Part 2: first, the stress distributions of files pushed into different types of 2-D curved routes were compared. Three different angles of curvature (20°, 40°, 60°) and three different radii of canal (5mm, 7.5m, 10mm) were considered, respectively. Second, we compared the effects of different canal geometries on the file stress distribution. Three different starting locations and extents of curved canal (coronal, middle and apical part) were considered. Also, different diameters of root canal orifice enlargement (1.3, 2, and 2.6mm) were taken into account. Results indicated that when under the condition of an increase in the radius of curvature, a decrease in the curvature extent, a decrease in the starting curved distance, and an increase in the root canal orifice diameter, it will lead to a decrease in the maximum principal stress of the file. The curvature of file was decreased when the staring curvature distance decreased from the root canal foramen. But the variation of curvature is not obvious when both the root canal orifice was enlarged and the staring curvature distance was decreased from the root canal foramen. Part 3: A new type of file was designed and analyzed. The smooth area of the file was replaced by a threaded and tapered part. The results revealed the stress was reduced and therefore it is suggested that sharp variation should be avoided when designing root canal files in order to reduce stress concentration.