Development of Nondestructive Testing and Application of Surface Treatment in Nickel Titanium Rotary Instruments

• Main Authors: Uei-Ming Li, 李偉明
• Other Authors: Chun-Pin Lin
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/11568653405666136182

博士 === 國立臺灣大學 === 臨床牙醫學研究所 === 95 === In the past 10 years, the revolutionary development of incorporating nickel-titanium (Ni-Ti) into endodontic files has greatly transformed the methods of root canal instrumentation. However, there are still a lot of problems demanding solutions till now. Instruments separation and surface blunt after repeated uses are the most concerned problems among them. Although a great deal of research has been undertaken to understand the reasons for instrument fracture, unexpected fractures of previous permanent deformation still occurred. Therefore, develop a possible nondestructive integrity assessment method for Ni-Ti rotary instrument and improve the surface character of Ni-Ti rotary instrument to increase its wear resistance and cutting ability are well worth making our efforts. This study was divided into three chapters: Chapter 1 was dedicated to application of nondestructive testing in cyclic fatigue of endodontic Ni-Ti rotary instruments. Utilizing a device to monitor its stiffness by using two strain gages in four different directions, we could develop a convenient nondestructive turn-key system that allows assessment of the integrity of Ni-Ti instruments in the clinic. The specific aim of chapter 2 was to investigate the effects of thermal nitriding surface treatment of Ni-Ti instruments on the wear resistance, cutting efficiency and anticorrosion. Chapter 3 focused on the application of plasma immersion ion implantation (PIII) for the surface treatment of Ni-Ti rotary instruments by utilizing x-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and micro x-ray diffraction (micro-XRD). Through these tests, we found that crack initiation occurred near final fracture. That means, if the life span of the instrument mainly depends on crack initiation and the duration of crack growth before final fracture is very short. A possible nondestructive integrity assessment method for Ni-Ti rotary instrument was developed. In addition, the nitrogen ions were successfully introduced onto the surface of Ni-Ti instruments by using thermal nitriding. Post-nitrided files at a controlled temperature of < 300 ºC showed increased wear resistance, cutting efficiency as well as corrosion resistance. More importantly, the surfaces of Ni-Ti instruments could be successfully modified by the nitrogen PIII and a light golden TiN layer was present under XPS analysis. The PIII technique did not alter the superelastic character of the Ni-Ti instruments by way of DSC analysis. In conclusion, although no surface morphological changes were evident, studies of the effects of cutting on PIII instrument surfaces are needed and are in progress.