Cyclic fatigue of ProTaper Ultimate and AF-F ONE rotary endodontic nickel-titanium systems in single and double curvature simulated canals at body temperature: a comparative study

Introduction
Despite improvement in endodontic file technology, breakage continues to occur. In this study, cycle fatigue resistance and fragment length were evaluated for ProTaper Ultimate, AF-F ONE, and ProTaper Gold instruments in single- and double-curved canals at 37 ± 1°C.

Objectives
The objective of the current study was to evaluate the resistance of cyclic fatigue and fragment length of ProTaper Ultimate, AF-F ONE, and ProTaper Gold rotary nickel-titanium instruments

Material and methods
Ninety NiTi rotary instruments were divided into three groups: ProTaper Ultimate, AF-F ONE, and ProTaper Gold. Based on single or double curvature, each group had two sub-groups (n = 15). Double-curved canal was characterized by a 60-degree coronal bend, 5-millimeter radius, with additional 70-degree apical curvature, 2 mm radius. Single-curved canal had a 60-degree angle and radius of 5 millimeters. Stainless steel blocks were maintained at 37 ± 1°C in a computerized water bath. Time to fracture was noted, and the number of cycles to failure was evaluated. Length of fractured sections was assessed, and scanning using electron microscopy was performed.

Results
A significant difference in cycles to failure was seen in AF-F ONE instrument compared with other groups in single- and double-curved canals (p < 0.05). No significant differences between ProTaper Ultimate and ProTaper Gold in either canal type (p > 0.05) were observed. The double-curved canal had fewer fracture cycles than the single-curved in all examined files, as shown by independent t-test (p < 0.05). No notable distinction was noted in the length of fractured segments within single- and double-curved artificial canals (p > 0.05), but it was substantially shorter in double-curved ones (p < 0.05).

Conclusions
The AF-F ONE instrument demonstrated superior cyclic fatigue resistance compared with ProTaper Gold and ProTaper Ultimate in either canal type.