Rapisarda E, Tripi T R, Bonaccorso A
Università degli Studi-Catania.
Minerva Stomatol. 2000 Mar;49(3):93-9.
Technological progress in the endodontic field has allowed the creation of innovative nickel-titanium endodontic instruments, made with a superelastic alloy with a reduced modulus of elasticity. The elastic properties of the NiTi alloy can undergo significant variations in connection with mechanical movements and cyclic fatigue induced on the instruments caused by their repeated usage, especially in canals which are anatomically difficult to shape. The state of tension of the instrument determines a deformation of the geometry of the files and, therefore, a modification in their properties. Similarly to mechanical stress, thermal treatments can influence the properties of the alloy. The aim of the study is to subject the NiTi alloy to repeated thermomechanical cycles, examining the influence of the mechanical and thermal stress on the temperature at the beginning and end of the martensite transformation, on the increase of recovery of deformation during the cooling phase and on the change in the internal structure of the material.
The instruments (30 ProFile Maillefer) were subdivided into 5 groups: Group I, composed of 6 new ProFiles submitted to 14 sterilization cycles in an autoclave for 30 minutes each; Group II, formed by 6 unused ProFiles subjected to one sterilization cycle in an autoclave; Group III made up of 6 new ProFiles used as controls; Group IV made up of 6 ProFiles submitted to clinical use on endodontic simulators in plexiglas for a total time of 240 seconds; Group V consisting of 6 ProFiles used on endodontic simulators for a total time of 480 seconds. All the above mentioned samples were tested using a thermomechanic dynamic analyzer (DMTA) produced by Rheometric Scientific.
The files from Group III (control) show an elastic deformation curve typical of nickel-titanium instruments. The samples from Groups IV and V subjected to sequential use on endodontic simulators evidenced modifications in their elastic behaviour compared to the control instruments. The operative use caused modifications in the original properties of the alloy, with a reduction in elasticity proportional to the number of uses. The instruments that underwent 14 cycles of sterilization in the autoclave (I group) present dynamic analysis curves which are different compared to the new unsterilized ProFiles. After 14 cycles there is a modification in the response of the instruments to thermodynamic stress.
Both the samples undergoing repeated mechanical stress on Plexiglas endodontic simulators and those sterilized in the autoclave at thermodynamic analysis show significant modification in modulus of elasti- city. The different taper does not influence the experimental results, there not being any significant differences found in the elastic behaviour between ProFiles.
牙髓病学领域的技术进步使得创新型镍钛牙髓器械得以问世，这些器械由弹性模量降低的超弹性合金制成。镍钛合金的弹性特性会因器械反复使用所引发的机械运动和循环疲劳而发生显著变化，尤其是在解剖结构复杂难以塑形的根管中。器械的拉伸状态会导致锉的几何形状发生变形，进而改变其性能。与机械应力类似，热处理也会影响合金的性能。本研究的目的是使镍钛合金经受反复的热机械循环，研究机械应力和热应力对马氏体转变开始和结束时的温度、冷却阶段变形恢复增加情况以及材料内部结构变化的影响。
将器械（30根Maillefer ProFile锉）分为5组：第一组，由6根新的ProFile锉组成，在高压灭菌器中进行14次灭菌循环，每次30分钟；第二组，由6根未使用过的ProFile锉组成，在高压灭菌器中进行一次灭菌循环；第三组由6根新的ProFile锉组成，用作对照；第四组由6根ProFile锉组成，在有机玻璃牙髓模拟器上进行临床使用，总时长240秒；第五组由6根ProFile锉组成，在牙髓模拟器上使用，总时长480秒。使用Rheometric Scientific生产的热机械动态分析仪（DMTA）对上述所有样品进行测试。
第三组（对照）的锉显示出典型的镍钛器械弹性变形曲线。在牙髓模拟器上连续使用的第四组和第五组样品与对照器械相比，其弹性行为有改变。实际使用导致合金原始性能发生改变，弹性降低与使用次数成正比。在高压灭菌器中进行14次灭菌循环的器械（第一组）呈现出与未灭菌的新ProFile锉不同的动态分析曲线。14次循环后器械对热力学应力的响应发生了改变。
在有机玻璃牙髓模拟器上经受反复机械应力的样品以及在热力学分析中在高压灭菌器中灭菌的样品，其弹性模量均有显著改变。不同的锥度不影响实验结果，不同ProFile锉之间的弹性行为未发现显著差异。
