Microscopic evaluation of irrigation solutions and sterilization procedures on the surface alteration of nickel titanium files

The primary goal of the root canal treatment is effectively cleaning, shaping and filling the root canal systems. Chemomechanical root canal preparation is one of the most important step in endodontic treatment. Rotary nickel titanium (Ni-Ti) instruments are esential components of preparation. Various file systems have been marketed by different companies with the development of daily technology. In the field of endodontics, an important innovation has been developed by the manufacturing of Ni-Ti alloy files in recent years. Despite the many advantages of Ni-Ti instruments, unexpected fractures can occur during clinical use. Fracture of files can occure with or without any visible defects of previous permanent deformation. In practice, the potential difficulty according to remaining fractured pieces of the broken instruments is to compromise the outcome of endodontic treatment and result in tooth loss. To date, there is no consensus on how many times rotary Ni-Ti instruments should be used. Some manifacturers recommend single use of Ni-Ti files. But because of their high costs, files are frequently reused after autoclave sterilization. The chemical reactions that occur during disinfection, sterilization or irrigation may cause corrosion and/or deterioration of the instruments, leading to early fracture. The aim of this study was to evaluate the effects of different irrigating solutions and repaeted sterilization cycles on surface deterations of four brands of rotary NiTi instruments [2Shape (Micro Mega, BesanconCedex, France), ProTaper Next (Dentsply Malleifer, Ballaigus, Switzerland), TF-Adaptive (SybronEndo, Orange, CA, USA), HyFlex CM (Coltene Whaledent, Altstatten, Switzerland)]. One group instruments were sterilizied 5 times, and the others were immersed in sodium hypoclorite (NaOCl %2,5), ethylenediaminetetraacetic acid (EDTA %17), Q-Mix (Dentsply, Tulsa, Oklahoma, USA) and MTAD (Dentsply, Tulsa Dental, Oklahoma, USA) solutions for 5 min. dynamically. Topography of them were evaluated using Atomic Force Microscopy (AFM). The RMS values, three dimansionel images and SEM images at various magnifications were obtained. According to RMS and Depth data obtained from AFM analysis, all files except Hyflex CM were affected by irrigation solutions and repeated sterilization procedures. Irrigation solutions and sterilization procedures most often caused deterioration of the surface of the ProTaper Next rotary file system. As a result, irrigation solutions and repeated sterilization procedures caused deterioration of file surfaces. Clinicians should consider the effects that deforme files in order to avoid unexpected errors.