Deformation and Fracture of NiTi Instruments Using Adaptive Reciprocation Intelligent or Fixed-Angle Reciprocation...

To compare the canal number at first visible deformation, the number of simulated canals completely prepared before fracture, and fractured-fragment length of One RECI instruments operated using fixed-angle conventional reciprocation or the Adaptive Reciprocation Intelligent (ARI) setting.

Twenty-six One RECI instruments were allocated to conventional reciprocation or ARI groups (n = 13). Fixed-angle reciprocation used parameters of 170° counterclockwise/60° clockwise, 4.0 Ncm, and 400 rpm. ARI initially used the same parameters but automatically changed to 90° counterclockwise/30° clockwise, 0.4 Ncm and 500 rpm when resistance to instrument advancement was detected. A single experienced operator repeatedly prepared simulated canals in transparent resin blocks until instrument fracture. Each canal was prepared using successive sequences of three gentle in-and-out pecking movements, with instrument cleaning and inspection, canal irrigation with 5 mL of distilled water, and recapitulation with a size 15 K-file between sequences, until the working length was reached. The canal number at first visible deformation and the number of canals completely prepared before fracture were recorded. Fractured-fragment length was measured digitally from the instrument tip to the fracture line. Groups were compared using two-sided Mann-Whitney U tests (α = 0.05).

First visible deformation was detected at a significantly higher simulated canal number with ARI than with conventional reciprocation (median [interquartile range], 3 [1-5] versus 1 [1-2]; P = 0.037). ARI also increased the number of canals completely prepared before fracture (20 [18-30] versus 6 [5-11]; P < 0.001). Fractured-fragment length did not differ significantly between ARI and conventional reciprocation (14.15 [11.65-14.43] mm versus 13.77 [13.61-14.51] mm; P = 0.644).

The ARI setting delayed visible deformation and markedly increased the number of simulated canals prepared before fracture of One RECI instruments, without significantly affecting fractured-fragment length.