Influence of operator experience on vertical force during instrumentation using Neoniti rotary files

Aim: This study aimed to measure the vertical force developed during canal instrumentation with Neoniti rotary files at predetermined torque in relation to the operator’s experience. Methodology: The research was performed on 60 human maxillary and mandibular incisors extracted for periodontal reasons. Each group of 20 teeth (10 maxillary and 10 mandibular incisors) was prepared by three different operators with different levels of experience in endodontics: a fresh dental school graduate, a postgraduate student training in endodontics and an endodontic specialist. Maxillary incisors represented the experimental model of wide root canals while mandibular incisors represented a model of narrow root canals. Root canals were prepared employing Neoniti files and TCM Endo unit at speed and torque recommended by the manufacturer. Vertical force measurement was performed utilizing device constructed for this purpose. Statistical analysis was accomplished using Mann-Whitney U test, Kruskal-Wallis test and Spearman’s rank correlation. Results: The amount of vertical force was significantly higher in narrow than in wide root canals (P=0.001). Comparison of vertical forces developed by three different operators demonstrated significant differences (P<0.001). Median vertical force developed by postgraduate student was significantly lower than in other two operators (both P<0.01). In postgraduate student, a significant positive correlation between number of shaped root canals and vertical force was demonstrated (ρ=.490; P=0.003). Conclusions:  The postgraduate with limited experience in rotary instrumentation had on average lowest values of vertical force as opposed to other two operators. However, these values increased with the number of shaped root canals.