Rotary Ni-Ti profile systems for preparing curved canals in resin blocks: influence of operator on instrument breakage

Aim The aim of this study was to determine the incidence of fracture of Pro File 0.4 and 0.6 taper Series 29 nickel-titanium instruments with respect t o operator experience, Methodology A total of 125 simulated root canals in resin blocks with the s ame geometrical shape in terms of angle and radius of curvature and coronal and apical orifice diameter were used. Five operators prepared all the spe cimens using an identical step-down instrument sequence, each one preparing 25 canals. The operators included two endodontists and three general pract itioners. Statistical data concerning the incidence of instrument failure w as compiled using Statlab and Fisher's partial least square difference anal ysis of variance. Results A total of 21 (16.8%) Instruments fractured, all had 0.04 tapers. N ine size 25 instruments failed, 9 size 20 instruments failed and 3 size 15. During the study, the Binary Tree analysis of instrument failure revealed two operator populations belonging to two different study periods. The firs t period. which represented the first 13 root canal preparations, was calle d the 'learning period', and the second period. which represented the next 12 sample preparations, was called the 'application period'. A greater numb er of instruments failed during the first period than during the second. In the 'learning period', both groups of operators learned the same way. In t he 'application period'. two groups could be distinguished; the first group consisted of a general practitioner who produced worse results, and the se cond group consisted of the other four operators. Conclusions The results indicate the necessity of mastering this rotary can al preparation technique, and the importance of improving competence throug h learning and experience.