Effect of different cleaning methods on surface contamination of unused endodontic files: a scanning electron microscopy analysis

The aim of this study is to analyze the residual organic film and debris on the surface of new endodontic files following different mechanical cleaning protocols. Fifty new nickel-titanium (NiTi) rotary instruments were used. Initial scanning electron microscope (SEM) images were obtained and debris amounts were scored between 0 and 3. Files were then divided into five groups, each subjected to a different cleaning protocol: 1. group: Autoclave sterilization without mechanical cleaning, 2.group: Ultrasonic cleaning, 3.group: Brushing and ultrasonic cleaning, 4.group: Cleaning with 0.2% chlorhexidine-impregnated sponge and ultrasonic cleaning, 5. group: Cleaning with 70% alcohol-impregnated gauze and ultrasonic cleaning. Post-cleaning Scanning Electron Microscope images were taken, and surface debris was re-scored. Data normality was assessed using visual (histogram, Q–Q plot) and statistical (Shapiro–Wilk test) methods. As the distribution was non-normal, non-parametric tests were used: the Fisher-Freeman-Halton test for intergroup comparisons and the Wilcoxon Signed-Rank test for within-group comparisons. According to the Fisher-Freeman-Halton test, a statistically significant difference was found between groups in terms of post-cleaning scores (p < 0.001). All groups except Group 1 showed a significant decrease in scores after cleaning. The Wilcoxon Signed-Rank test revealed statistically significant differences between pre- and post-cleaning scores in Groups 2, 3, 4, and 5 (p = 0.008, p = 0.004, p = 0.006, and p = 0.004, respectively). Significant reductions in median contamination scores were observed in these groups. In Group 1, no statistically significant difference was found (p = 0.083). Numerically, the lowest median post-cleaning score (1.0) was seen in Groups 3, 4, and 5. The highest median percentage change was observed in Groups 4 and 5 (67%), followed by Group 3 (58%), and Group 2 (33%). No change was observed in Group 1. Within the limitations of this study, it was shown that autoclave sterilization without mechanical cleaning is not sufficient for effective cleaning. Mechanical cleaning prior to sterilization is necessary for proper decontamination of endodontic files. Sponge and gauze-based methods were found to be the most effective, while brushing also provided a notable improvement in surface cleanliness.