Cyclic fatigue of instruments for endodontic glide path.

Endodontic glide path is the creation of a smooth patency from canal orifice to apex, which can be performed manually or with small tapered NiTi rotary instruments. The use of stainless steel (SS) hand K-files inserted in a reciprocating handpiece can be a possible alternative to create a mechanical glide path. The aim of this study was to compare the cyclic fatigue resistance between SS K-files used in a reciprocating motion and NiTi rotary instruments in artificial curved canals. Ten SS size 15 K-files used with the M4 handpiece (SybronEndo, Glendora, CA, USA) and ten PathFiles (Maillefer-Dentsply, Ballaigues, CH, Switzerland) NiTi rotary instruments size 16, 0.02 taper were tested for resistance to cyclic fatigue. The time to fracture inside an artificial curved canal was recorded for each instrument. Data were analyzed by one-way ANOVA and Tukey HSD test. Mean time (and SD) to failure was 464 s (±40.4) for the Group PF (NiTi rotary PathFile), and 1049 s (±24.8) for the Group M4 (SS K-files reciprocating) with a statistically significant difference between the two groups (p = 0.033). The SS 15 K-files used with the M4 handpiece showed a significant greater resistance to cyclic fatigue when compared to the NiTi rotary PathFiles. Therefore, the use of small size SS files in a reciprocating motion might be a rational choice for the creation of a mechanical endodontic glide path in curved root canals.

Flexibility and resistance to cyclic fatigue of endodontic instruments made with different nickel-titanium alloys: a comparative test.

AIM: A new manufacturing method aiming at to producing more flexible and resistant NiTi endodontic instruments has been recently developed (Hyflex, produced with CM wire). The purpose of the study was to determine whether this new manufacturing method produces NiTi instruments (Hyflex) of superior flexibility and/or superior resistance to cyclic fatigue, when compared with instruments produced by a traditional manufacturing process or thermally treated NiTi alloy (M-wire). MATERIALS AND METHODS: Twelve .06 size 25 Hyflex instruments (Coltene, Allstatten, Switzerland), and twelve 06.25 Vortex instruments (Dentsply-Tulsa, OK, USA) and twelve 06.25 Endosequence instruments (Brasseler, Savannah, GA, USA) were initially evaluated for stiffness on bending, followed by a cyclic fatigue test. For the stiffness test test procedures strictly followed ISO 3630-1, and bending moment was measured when the instrument attained a 45 degrees bend. The cyclic fatigue test was performed in a customized artificial stainless steel canal (60° degree curvature with 5 mm radius). Instruments were rotated at 300 rpm until fracture. All data obtained were recorded and statistically analyzed using an ANOVA test. RESULTS: Statistical analysis of data showed that bending moments were significantly greater (P < .05) for Vortex and EndoSequence instruments (mean values 59.06 g/cm and 48,98 g/cm respectively), compared to the Hyflex instruments (mean value 35.60 g/cm). For the cyclic fatigue test Hyflex and Vortex were significantly more resistant than EndoSequence instruments (P < .05). CONCLUSIONS: Results of the present study demonstrate the ability of the new CM-wire manufacturing process to produce NiTi rotary instruments more flexible and more resistant to cyclic fatigue than instruments produced by a traditional manufacturing process or a thermally treated NiTi alloy (M-wire).

Bending properties of a new nickel-titanium alloy with a lower percent by weight of nickel.

INTRODUCTION: The aim of the present study was to evaluate the bending properties of Hyflex instruments, which exhibit a lower percent in weight of nickel (52 Ni %wt) and compare them with other commercially available nickel-titanium (NiTi) rotary instruments. METHODS: Ten instruments with tip size 25, 0.06 taper of each of the following NiTi rotary instrumentation techniques were selected for the study: Hyflex, EndoSequence, ProFile, Hero, and Flexmasters. All instruments from each group were tested for stiffness by comparing their bending moment when they attained a 45-degree bend. Experimental procedures strictly followed testing methodology described in ISO 3630-1. All data were recorded and subjected to statistical evaluation by using analysis of variance test. Statistical significance was set at P < .05). RESULTS: Statistical analysis of the data revealed that Hyflex files were found to be the most flexible instruments, with a significant difference (P < .05) in comparison with the other instruments. Among the other files, a significant difference has been reported for EndoSequence instruments compared with ProFile, Hero, and FlexMaster (P < .05), whereas no significant differences have been reported among those 3 files (P > .05). CONCLUSIONS: Results of the present study have illustrated an increased flexibility of the new NiTi alloy over conventional NiTi alloy, and they highlight the potential of the new manufacturing process.

A SEM study of canal cleanliness after a new nickel-titanium rotary instrumentation technique.

The purpose of this in vitro study was to evaluate the degree of smear layer removal after root canal preparation with TF(®) instruments, combined with two different irrigating solutions.For the present study twenty-two freshly extracted human roots were selected. All teeth had been extracted for periodontal purpose. Crown were cut off with a separating disk, so all roots were approximately 10-12 mm long.After having chosen the two control roots, the remaining ones were randomly divided into two groups each containing 10 roots. The two experimental groups were prepared as follows.A crown-down instrumentation technique was used, following TF(®) manufacturer's instructions.Irrigation of Group A consisted of 2 ml of solution: 6% sodium hypochlorite (Chlor-Extra(®), Vistadental Racine, Mi, USA) after each instrument followed at the end by a 17% EDTA minute (Smear Clear(®), SybronEndo, Orange, Ca) irrigation for 1 min. Both irrigants contain tensioactive agents.Group B specimens were irrigated with 2 ml of sterile saline solutions after each instrument. Two control roots were not instrumented and irrigated. Teeth were then examined by scanning electron microscopy.Values obtained were tabulated and statistical analyses were carried out using a non parametric tests.RESULTS SHOWS SIGNIFICANT DIFFERENCES IN THE MEAN SCORE BETWEEN THE TWO GROUPS: most experimental group A canals showed clean or minimal debris in the observed areas, especially in the coronal and middle thirds.