Application of Thin Film Metallic Glasses on Surface Modification of Nickel Titanium Rotary Instruments: Analysis of Fracture Mechanism and Cutting Efficiency

Endodontic treatment is a crucial and significant procedure of dental treatments. The primary purpose of endodontic treatment is to remove inflamed tissue and infectious pathogens. Proper canal shaping could facilitate intracanal mechanical debridement and chemical cleaning. However, the curved canals would be deviated and perforated with the stainless steel files and the prognosis would be poor. In these decades, the philosophy of root canal shaping have improved with NiTi alloy due to its super-elastic and shape memory properties. However, there were still many issues of Ni-Ti instruments need to be improved. Unpredictable separated instrument and insufficient cutting ability were the major limitations of NiTi rotary instruments. In recent years, relevant studies have proposed to resolve these problems with instrument geometry and alloy modification etc., but the problems have not been improved. Hence, for enhancing the abilities of cutting and fracture resistance of instruments, development of instruments processing is a clinically valuable research topic. In the meantime, the mechanisms of cutting ability and fracture patterns are also important research agendas of improving clinical performance of instruments. Therefore, this research was divided into three chapters. Chapter I was focused on the composition and performance of mechanical properties of thin film metallic glass under different parameters of sputtering. According to results of mechanical properties, electrochemical characteristics and biocompatibility, it was meant to find the most suitable parameters of thin film metallic glass to apply on clinical instruments. Chapter II was utilizing different thickness of thin film metallic glass on Ni-Ti rotary instruments to explore the mechanism of cutting ability. Chapter III was focusing on mechanisms of torsional and fatigue fracture of NiTi instruments treated with Ti-Zr-B thin film metallic glass. To summarize the results of this experiment, Ti-Zr-B thin film metallic glass could be denser and would have better corrosion resistance when the content of Boron increased. As for the application of Ni-Ti rotary instruments, the ones with thicker coating appeared to have relatively smooth morphologies on instruments surface and achieved optimal cutting efficiency and resistance to fatigue fracture. Meanwhile, the results showed that metallic glass sputtering techniques would not affect the nature of super-elastic of the instrument itself. Further exploring the mechanism of fatigue fracture of Ni-Ti rotary instruments, it was found that, among the overall fatigue life, thin film metallic glass mainly changed the surface features of the instrument and improved its resistance of fracture initiation ability. In summary, the technique of Ti-Zr-B metallic glass thin film is a satisfied surface modification for improving surface features of an instrument to advance its clinical performance.