Ni-Ti alloy remnants after root canal preparation with Ni-Ti engine-driven files: a preliminary report

Aim: Aim of the present study was to assess any signs of Ni-Ti alloy remnants in the root canal after preparation and investigate if this aspect may be influenced by the steam sterilization of the files. Materials and Methods: 20 extracted upper first premolars with complete root formation and apical foramina and three kits of BioRace instruments (FKG, Le Chaux-of-Fonds, Switzerland) were used in the present study. The first BioRace kit was used to prepare 10 teeth (20 canals), without sterilization between the root canal preparations, while the second sample group was subjected to steam sterilization after each tooth (two canals) prepared. The third kit of instruments was used as a control group. Files were then analyzed by means of scanning electron microscope (SEM) using magnifications between 500 and 4.000x. Images were taken on sections D1-D8 of each file. Files weight was measured using a precision weight scale with readability of 0,001g to quantify the possible alloy loss and file degradation occurred during their use. Teeth were then sectioned on their length and submitted to EDX analysis in search of possible alloy particles within the root canals, using magnifications between 30 and 300x. In the same manner, the irrigant used during the root shaping was collected and analyzed. Differences in weight were statistically analysed using the independent sample Student t-test (p<0.05). Results: No file separation was registered in both groups analyzed. Weight measurements and SEM micrographs showed signs of higher degradation for samples from group 2. EDX analysis showed some Ni-Ti particles in roots prepared in group 2. Conclusions: Metal strips, weight loss and micro-fractures appeared on the files subjected to steam sterilization between the uses. Ni-Ti particles detached from files, during their intra-canal use were found on the root canal walls.