根管治療手術之力感測器設計與銼針力學分析

Abstract

牙髓病科為牙醫學系的一門專科，俗稱根管治療。由於銼針在根 管治療手術中佔有舉足輕重的地位，因此銼針的力學分析扮演著重要 的角色。在手術過程中鎳鈦合金銼針進入彎曲的根管中，且高剛性的 鎳鈦銼針能夠避免不必要的變形，同時提升清創效率，而銼針的應力 分布則可以用來預測銼針的破損。為了輔助根管治療手術，本研究設 計並製作了同時可量測彎曲力矩與軸向力之力感測器，藉由量測彎曲 力矩可以得知銼針的彎曲度，而軸向力的量測也是不可或缺，過大的 軸向力可能導致銼針挫曲，甚至是根管的穿孔。因此本研究分為二個 主軸，分別為(1)根管銼針之力學分析、(2)力感測器的設計。 首先對根管銼針進行彎曲負載下的非線性變形分析，公式解之結 果是由尤拉伯努力非線性方程式所推導求得，並且考量到了鎳鈦銼針之螺紋節距的變化。研究結果發現最大的曲率發生在接近銼針的尖端 處。本研究並且根據彈性力學推導扭轉理論的公式，考量銼針之三角 形橫切面與錐面形狀，研究結果發現最大的應力是位於尖端處，且位 於橫切面的腰間處。此外公式解的結果也藉著有限元素分析的結果所 驗證，兩者方法相比較，公式解的方法較為方便且有效率。力感測器 部分，選用了壓阻式的壓力感測片做為量測材料，因為它可以直接量 測負載，且尺寸可以微小化，力的量測範圍亦滿足牙醫師的需求。藉 由機構的設計，力感測器所能量測的力，包含正向力和彎曲力矩。而 每一個感測體包含了壓感導電橡膠與電極。實驗結果包含了遲滯性、 重複性、非線性，以驗證此感測器之可行性。

Endodontics is a branch of dental therapy, commonly known as root canal treatment. Endodontic files play an important role in the process of endodontic therapy, the mechanics analysis of file is necessary. In treatment, a NiTi file enters the curved root canal, and the higher rigidity of NiTi instrument can not only avoid unnecessary deformation, but also improve the efficiency of debridement. And the stress distribution of endodontic instruments can be used to predict file failures. To assist endodontic therapy, in this study, a force sensor has been designed and fabricated for measuring the axial force and the bending moment simultaneously. By detecting the bending moment, one can know the severity of bending. Axial force detection is also desired, since excessive axial forces may result in file buckling or even root canal perforation. Therefore, this study can be divided into two main parts, which include (1) mechanics analysis of endodontic instruments (2) design of a force sensor. First, we investigate the nonlinear deformation of files under bending load. Analytical results are derived by using Euler-Bernoulli nonlinear differential equations that took into account screw pitch variation of NiTi instruments. The maximum curvature of the instrument is found in this study to occur near the instrument tip. Second, torsional results are derived by using the elasticity theory that take into account triangular cross-sections and tapered shapes of NiTi instruments. This study discovered that the maximum stress occurs near the instrument tip and the middle side of a triangular cross-section. The analysis based on the analytical model and the finite element nonlinear analyses are carried out. The proposed analytical models are validated by numerical results in analyzing NiTi instruments. Third, this study uses a piezoresistive material as a force sensing material, because it can sense loads directly and the size can be miniaturized. The force range that the force sensor can measure meets dentists’ needs. The force types that can be measured include the normal force and bending force. Each sensing cell consists of a pressure-sensitive electric conductive rubber and an electrode. Experimental results on hysteresis, repeatability, and nonlinearity are presented to validate the proposed sensor.