The effect of sterilization procedures and different irrigation solutions on the surface roughness of nickel titanium files: An atomic force microscope study

This study aims to examine the effects of different irrigation solutions and sterilization procedures on the surface properties of ProTaper Next (PTX) and Reciproc blue files. The research sample comprises a total of 60 files as 30 of each PTX and Reciproc Blue. PTX and Reciproc Blue files were divided into five sub-groups and 6 files tested in each group (n=6). No treatment was applied to the files in the control group. The other groups were continuously applied to the irrigation solutions of 5.25% sodium hypochlorite, 18% Etidronic acid and BioAkt for 5 minutes, respectively. The files of the last group were packaged, and the sterilization process wasapplied for 5 times with an autoclave at 134 °C for 20 minutes. The files in each group were prepared for examination after cutting the apical 5mm sections with a carbon separator. Scanning was performed with silicon nitride tips suitable for tapping (non-contact) mode at 5 different points in each sample atomic force microscope (AFM) in a 5μmX5μm area to examine the surface properties of the prepared samples. Three-dimensional analysis images, Depth analysis, visualizing the difference of the deepest and highest region in the scan area, and the RMS data indicating surface roughness for numerical comparison were obtained. Statistical analysis of the data was performed through IBM SPSS V. 22.0 statistics program. The compliance with a normal distribution regarding quantitative variables was assessed using the Kolmogorov-Smirnov test. Descriptive statistics are presented with mean ± standard deviation. One-way ANOVA was applied to compare quantitative measurements among several independent groups, and then a post-hoc LSD test was used for paired comparisons. The significance level was chosen as p˂0.05. Surface roughness was measured at the production phase of both PTX and Reciproc Blue files in the control group. After the Ni-Ti files were treated in NaOCI, the RMS value, the numerical data of the surface roughness, and the DEPTH value, the maximum depth, increased in comparison to the control group (P˂0.05). RMS and DEPTH values increased in both Ni-Ti files treated in BioAkt solution (P˂0.005). Etidronic acid significantly increased RMS and DEPTH values in PTX and Reciproc Blue files in the experimental group (P˂0.005). The sterilization procedure applied to PTX and Reciproc Blue files increased RMS and DEPTH values for the experimental group (P˂0.005). The groups with the highest increases in the surface roughness of PTX and Reciproc Blue files are the Etidronic acid and sterilization group. While the group with the lowest RMS and DEPTH values belongs to the control group with Reciproc Blue files. The group with the highest RMS and DEPTH values is the sterilization group with PTX files. The irrigation processes and repeated sterilization processes increased the file surface roughness. Clinicians should consider the deforming effects to avoid unexpected fractures on Ni-Ti files. Keywords: Reciproc Blue, ProTaper Next, Surface Analysis, Atomic Force Microscope, RMS, DEPTH