Influence of rotational speed, torque and operator's proficiency on ProFile failures

Aim The purpose of this study was to evaluate the influence of rotational s peed, torque, and operator experience with a specific Ni-Ti rotary instrume ntation technique on the incidence of locking, deformation and separation o f instruments. Methodology Profile Ni-Ti rotary instruments (PRI) sizes 40-15 with a 6% ta per were used in a crown-down technique. In one group of canals (n = 300) s peeds of 150, 350 and 350 rpm (subgroups 1, 2 and 3) were used. Each one of the subgroups included 100 canals. In a second group (n = 300) torque was set at 20, 30 and 55 Ncm (subgroups 4, 5 and 6). In the third group (n = 30 0) three operators with varying experience (subgroups 7, 8 and 9) were also compared. Each subgroup included the use of 10 sets of PRI and 100 canals of extracted human molars. Each set of PRI was used in up to 10 canals and then sterilized before each case. NaOCl 2.5% was used as an irrigant. The n umber of locked, deformed, and separated instruments for the different grou ps, and within each part of the study was analysed statistically for signif icance with chi-squared tests. Results In group 1 only one instrument was deformed in the 150-rpm group an d no instruments separated or locked. In the 250-rpm group instrument separ ation did not occur, however, a high incidence of locking, deformation and separation was noted in the 350-rpm group. In general, instrument sizes 30- 15 looked, deformed and separated. Chi-squared statistics showed a signific ant difference between the 150 and 350 rpm groups but no difference between the 150 and 250 rpm groups with regard to instrument separation. Overall, there was a trend toward a higher incidence of instrument deformation and s eparation in smaller instruments. Locking and separation occurred during th e final passage of the instruments, in the last (tenth) canal in each subgr oup. In the second group, neither separation nor deformation and locking oc curred during the use of the ProFile instruments, at 150 rpm, and at the di fferent torque values. In the third group, chi-squared analysis demonstrate d that significantly more instruments separated with the least experienced operator. Instrument locking, deformation, and separation did not occur wit h the most experienced operator. Conclusions Preclinical training in the use of the PRI technique with crown -down at 150 rpm were crucial in avoiding instrument separation and reducin g the incidence of instrument locking and deformation.