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This study aimed to assess the effect of mechanical loading and heating on the cyclic fatigue and torsional fracture resistances of heat-treated nickel-titanium files after usage and autoclaving. Sixty files (One Curve) were tested for cyclic fatigue and torsional fracture resistances using customized devices. The files were divided into three groups according to the test conditions (n = 10); new (group-N), used for simulated canal shaping (group-U), and sterilized after use (group-S). For cyclic fatigue resistances, the files were freely rotated in a curved metal canal under body temperature; the time elapsed to fracture was recorded and the numbers of cycles to fracture (NCF) were calculated. For the torsional resistances, the file tip was fixed and rotated until the file fractured. The maximum torsional load and distortion angle were recorded. The toughness was calculated. Fracture fragments were examined with a scanning electron microscope. Data were analyzed using a one-way analysis of variance and Tukey's post hoc test at the significance level of 95%. Group-U showed significantly higher NCF than group-S (p < 0.05). However, there was no significant differences between groups-N and -S in the NCF (p > 0.05). Group-N showed a significantly bigger distortional angle and higher torsional toughness than groups-U and -S, but the ultimate torsional strength did not have significant difference between the groups. Under the limitation of this study, autoclave sterilization after single-usage did not improve the fracture resistance of heat-treated One Curve nickel-titanium files.
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INTRODUCTION: This study aimed to evaluate the dynamic cyclic fatigue resistance of heat-treated nickel-titanium (NiTi) files after usage and autoclaving. METHODS: Two heat-treated NiTi file systems with tip sizes of #25 (ie, ProTaper Gold F2 [Dentsply Sirona, Charlotte, NC] and TruNatomy Prime [Dentsply Sirona]) were selected. Files of each system were divided into 3 experimental subgroups (n = 10). For subgroup 1, new files were tested to establish the baseline number of cycles to failure (NCF). For subgroup 2, files underwent canal instrumentation in a simulated J-shaped canal block with 35° of curvature and a 16.5-mm length. The simulated canals were pre-enlarged using stainless steel files #10K and #15K. After instrumentation, the files were tested. For subgroup 3, files underwent canal instrumentation as in subgroup 2 followed by autoclave sterilization and then were tested for cyclic failure. The cyclic fatigue test was performed in dynamic pecking motion under body temperature. The time to fracture was recorded and calculated into NCF. Fracture fragment lengths were measured using a digital microcaliper. Statistical analysis was conducted using the independent t test and multifactorial analysis of variance with 95% significance. Scanning electron microscopy was used to examine the topographic characteristics after cyclic fatigue tests. RESULTS: There were no significant differences between file systems in subgroup 1 using new files (P < .05). Although PG reduced the NCF after use, TN showed a significantly increased NCF (P < .05). However, after sterilization, TN showed a reduced NCF compared with the used one (P < .05). CONCLUSIONS: Cyclic loading by usage and heat treatment during sterilization may result in different cyclic fatigue resistance according to the geometry and alloy characteristics.
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Níquel , Titanio , Instrumentos Dentales , Calor , Acero Inoxidable , Ensayo de Materiales , Falla de Equipo , Aleaciones , Esterilización , Oro , Preparación del Conducto RadicularRESUMEN
Hereditary spastic paraplegia (HSP) describes a heterogeneous group of inherited neurodegenerative disorders in which the cardinal pathological feature is upper motor neurone degeneration leading to progressive spasticity and weakness of the lower limbs. Using samples from a large Omani family we recently mapped a gene for a novel autosomal recessive form of HSP (SPG35) in which the spastic paraplegia was associated with intellectual disability and seizures. Magnetic resonance imaging of the brain of SPG35 patients showed white matter abnormalities suggestive of a leukodystrophy. Here we report homozygous mutations in the fatty acid 2-hydroxylase gene (FA2H) in the original family used to define the SPG35 locus (p.Arg235Cys) as well as in a previously unreported Pakistani family with a similar phenotype (p.Arg53_Ile58del). Measurement of enzyme activity in vitro revealed significantly reduced enzymatic function of FA2H associated with these mutations. These results demonstrate that mutations in FA2H are associated with SPG35, and that abnormal hydroxylation of myelin galactocerebroside lipid components can lead to a severe progressive phenotype, with a clinical presentation of complicated HSP and radiological features of leukodystrophy. (c) 2010 Wiley-Liss, Inc.