Abstract
Protaper Universal (PTU), Protaper Gold (PTG) (Maillefer, Ballaigues, CH), EdgeTaper (ET), and EdgeTaper Platinum (ETP) (Albuquerque, NM, USA) were tested for both torsional and flexural resistance. The aim of the present study was to evaluate the influence of proprietary heat treatment on the metallurgical properties of the aforementioned instruments. Four groups of 30 different instruments (size 20.07) were tested, then divided into two subgroups of 15 instruments—one for the cyclic fatigue test in a curved canal (90°—2 mm radius) at 300 rpm and 2.5 Ncm. The time to fracture (TtF) and fragment length (FL) were recorded. The other subgroup was subjected to the torsional test (300 rpm, 5.5 Ncm). The torque to fracture and TtF were recorded. All the instruments underwent a SEM analysis. The heat-treated instruments showed a significantly higher fatigue resistance than the non-heat-treated instruments (p < 0.05). No significant differences were found in the torsional resistance between the ET and PTU, and the ETP and PTG. However, when comparing all the groups, the heat-treated instruments showed less torsional resistance. The improvement from heat treatment was mainly found in the cyclic fatigue resistance.
Highlights
The intracanal fracture of nickel–titanium (NiTi) rotary files is still one of the main concerns during root canal therapy
The mechanical resistance of NiTi rotary files has been tested in two different ways: cyclic fatigue tests and the torsional test
The EdgeTaper Platinum (ETP) is made of an annealed heat treated (AHT) nickel–titanium alloy brand, named Fire-wire
Summary
The intracanal fracture of nickel–titanium (NiTi) rotary files is still one of the main concerns during root canal therapy. It has been demonstrated by many authors that rotary NiTi files essentially fail for two main reasons: flexural (cyclic) fatigue and torsional failure [1,2]. The mechanical resistance of NiTi rotary files has been tested in two different ways: cyclic fatigue tests and the torsional test. Instruments are usually rotated inside an artificial curved canal until a fracture occurs at the recommended rotation speed. When investigating the torsional resistance, based on the ADA testing recommendations for stainless steel manual files, the tip is usually locked at 2 mm and its rotation speed is 2 rpm.
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