| This study examined the endurance limit (EL) of size 30 ProFile .06, instruments. The EL is the load amplitude below which instrument cycling is almost unrestricted. The EL is the angular deflection of the instrument tip from its long axis below which instrument fracture would not occur after 106 cycles. The instruments' tips were mounted in a torque-sensing device, and the shafts locked into a reversible-geared motor according to the ANSI/ADA Specification #28. Each instrument was rotated to a pre-determined angular deflection and then back to zero, until fracture occurred. Starting at 200°, testing was continued at decreasing angles until 106 cycles were reached without fracture. The mean log number of cycles and standard deviation were calculated and plotted against the corresponding angular deflection. One-way ANOVA showed statistically significant differences (p < 0.001). Larger angular deflections demonstrated fewer cycles to fracture than smaller deflections. The instrument-specific EL (<2.5°) was predicted. |
