Shaping ability of Mity Roto 360 degrees and Naviflex rotary nickel-titanium instruments in simulated root canals. Part 2.

The aim of this study was to determine the shaping ability of Mity Roto 360 degrees and Naviflex rotary nickel-titanium instruments in simulated canals. Forty simulated root canals made up of four different shapes in terms of angle and position of curvature were prepared by both sets of instruments using a stepdown approach. This study describes the efficacy of the instruments in terms of prevalence of canal aberrations, the amount and direction of canal transportation, and thus the overall postoperative shape. Pre- and postoperative images of the canals were taken using a videocamera attached to a computer with image analysis software. The pre- and postoperative views were superimposed to highlight the amount and position of material removed during preparation. Neither Mity Roto 360 degrees nor Naviflex instruments created any zips or elbows. Ledges were produced in 20 (50%) canals prepared with Mity instruments and in 29 (72%) canals prepared with Naviflex instruments. Statistically significant differences (p < 0.001) between canal shapes occurred in relation to the incidence of ledges with 40 degrees canals (35) associated with more aberrations than 20 degrees canals (14); the position of the beginning of the curve had no effect. The distance of ledges from the end point of preparation was also affected significantly (p < 0.01) by canal shape. Neither instrument created any perforations or danger zones. At specific positions along the canal length, canal shape had a significant influence on total width and the amount of material removed from the inner and outer aspects of the canal curve. The direction of canal transportation at the end point of preparation was most frequently toward the outer aspect of the curve in canals prepared with Naviflex instruments, whereas the Mity instruments produced a more balanced preparation. At the apex and beginning of the curve, transportation with both instruments was generally toward the outer aspect of the curve. Overall, mean absolute transportation was small and was below 0.1 mm at every position except the orifice. Under the conditions of this study, Mity Roto 360 degrees and Naviflex rotary instruments prepared canals with a high incidence of ledges. However, in the absence of other aberrations, both instruments would seem to be a valuable addition to the endodontic armamentarium.