[A comparative study of three different rotary nickel titanium systems in the preparation of curved molar canals].

PURPOSE: To analyze the shaping ability of three different rotary nickel-titanium instruments in curved molar canals. METHODS: Three groups of extracted molars that were balanced in terms of curvature were instrumented by M(two), rotary ProTaper and Hero642 nickel-titanium systems, respectively. The standard digital radiographs were taken to record the profiles of root canals and the positions of the tips of the instruments. At last, the curvature degrees and the apical transportation indexes (ATI) pre- and post instrumentation were compared. All the data were analyzed with SAS6.12 software package. RESULTS: Two Hero642 instruments fractured during preparation and none of the M(two) or rotary ProTaper instruments separated. The mean working time with Hero642 files was significantly longer than that with M(two) or ProTaper instruments (P<0.01).The change of curvature degree before and after instrumentation for three systems was statistically significant (P<0.05). And the difference of ATI for three systems was not significant (P>0.05). CONCLUSION: M(two) and ProTaper systems tested in this study are effective in shaping curved molar canals in extracted teeth.