Scanning electron microscopy of superficial defects in Twisted files and Reciproc nickel-titanium files after use in extracted molars.

AIM: To evaluate the usage and superficial defects in size 25, 0.08 taper Twisted files (TF) and R25 Reciproc files after root canal instrumentation.
METHODOLOGY: One hundred and twenty mandibular molars with root canal curvature, ranging from 15° to 30° and a 4-5 mm radius, were randomly divided into two groups according to single-file instrumentation: size 25, 0.08 taper TF or R25 files. A total of fifteen files per group were evaluated before and after three, six, nine and 12 uses. The instruments were fixed in custom-made holders and photographed using scanning electron microscopy at ×260 to ×1200 magnifications. The presence of superficial defects (plastic deformation, microcracks, fracture, craters, disruption of the cutting edges and blunt edges) was scored from the pre- and post-usage photographs. Chi-squared test was used to analyse differences after usages in both groups individually. Two-way anova was used to analyse differences between both instruments. The level of significance for all analyses was 5%.
RESULTS: Superficial defects were observed after the instrumentation of six root canals in the TF group and after the instrumentation of nine root canals in the R25 group. Plastic deformation and disruption of cutting edges were the prevalent defects observed in the TF group, and craters and blunt edges were observed in R25 files. The presence of defects was significantly increased with successive usages in both groups (P < 0.05), but TF had more superficial defects than R25 files (P < 0.001). Dentine debris was observed on all instruments. No instruments fractured.
CONCLUSIONS: Instrumentation was possible for six root canals with TF files and nine root canals with R25 files before the presence of superficial defects appeared. Differences in the prevalence and development of superficial defects were observed between the TF and R25 files.