Publication: Análisis de los factores que influyen en la resistencia de los instrumentos de Níquel-Titanio a la fatiga cíclica flexural
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2017-08-03
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Universidad Complutense de Madrid
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Abstract
El Níquel-Titanio (NiTi) fue desarrollado por WH. Buehler para el programa espacial del Laboratorio de Ordenanza Naval (EEUU). Esta aleación tiene características de superelasticidad (capacidad de recuperar su forma inicial tras ser deformada) y de memoria de forma (si se somete a un tratamiento térmico) debido a la transición de austenita a martensita (dos posibles fases microestructurales con diferentes propiedades mecánicas). Aunque Civjan (1975) fue quién primeramente sugirió la superioridad de los alambres de NiTi para la creación de instrumentos endodónticos, no fue hasta 1988 cuándo Walia publicó la mayor flexibilidad y resistencia horaria y antihoraria a la rotación de instrumentos de NiTi cuando eran comparados con limas de acero inoxidable. Desde entonces hasta hoy, los sistemas de conformación de NiTi han evolucionado hasta convertirse en la herramienta estándar para trabajar los conductos radiculares debido a su alta flexibilidad, capacidad de corte y porque son capaces de crear preparaciones centradas de una forma más rápida. Sin embargo, estos instrumentos tienden a fracturarse de forma inesperada debido a la fatiga cíclica flexural (FCF), la cual se produce por los ciclos de tensión-compresión a los que son sujetos cuando son flexionadas y rotadas en la región de máxima curvatura. Varios factores pueden influir en la resistencia a la FCF. En primer lugar, los principales factores que puede determinar la resistencia a la FCF son los factores anatómicos como el radio y ángulo de curvatura del conducto radicular (descrito por Pruett en 1997). En segundo lugar, algunas características de los instrumentos como la aleación, diámetro y diseño pueden influir en la resistencia de los instrumentos. Otros factores como el uso clínico, el proceso de esterilización o el contacto de la lima con soluciones corrosivas pueden también afectar a la resistencia a la FCF. Estudios publicados han descrito que la tasa de fractura de las limas puede variar del 1.67% al 5% durante los tratamientos de conductos radiculares e indican que algunas de estas fracturas no mostraron signos de fatiga previamente, convirtiendo el suceso en algo poco predecible...
WH Buehler developed Nickel-Titanium (NiTi) alloy for the spacial program of the Naval Ordenance Laboratory. This alloy has the characteristics of super-elasticity (ability to recover the initial shape after being deformed) and shape memory (when subjected to a controlled thermal treatment) due to the transition from and to austenite and martensite (two possible microstructural phases) with different mechanical properties. Although Civjan (1975) was the first one suggesting the use of NiTi wires for endodontic instruments to benefit from its superiority, it was not until 1988 that Walia published the greater flexibility and resistance to clockwise and counterclockwise rotation of NiTi instruments when compared to conventional stainless steel (SS) files. Since then, NiTi rotary shaping systems have evolved to become a standard tool with which to shape root canals because of their high flexibility and cutting ability and because they create centered preparations more rapidly. However, they tend to unexpectedly breakage because of flexural cyclic fatigue (FCF), which is induced by the alternating tension-compression cycles to which they are subjected to when flexed in the maximum curvature region of the canal and rotated. Many factors are believed to influence FCF resistance of files. Firstly anatomical factors such as radius and angle of curvature, as described by Pruett in 1997, are the main factors that can determine the resistance of files to FCF. Second, some instrument characteristics such as alloy, diameter and design has been also reported. Other factors like use mechanisms, autoclaving or the contact of the file with corrosive solutions may also have an influence in FCF resistance of files. Published studies have reported varying incidences from 1,67% to 5% of file breakages during root canal treatments and shown that some of them do not show signs of fatigue and therefore breakage is somehow unexpected in some of them. Many FCF test has been published in the last years using different protocols and different devices. Plotino et al. (2009) reviewed all these studies and concluded that the differences in the methodology affected the results on fatigue behavior of these studies...
WH Buehler developed Nickel-Titanium (NiTi) alloy for the spacial program of the Naval Ordenance Laboratory. This alloy has the characteristics of super-elasticity (ability to recover the initial shape after being deformed) and shape memory (when subjected to a controlled thermal treatment) due to the transition from and to austenite and martensite (two possible microstructural phases) with different mechanical properties. Although Civjan (1975) was the first one suggesting the use of NiTi wires for endodontic instruments to benefit from its superiority, it was not until 1988 that Walia published the greater flexibility and resistance to clockwise and counterclockwise rotation of NiTi instruments when compared to conventional stainless steel (SS) files. Since then, NiTi rotary shaping systems have evolved to become a standard tool with which to shape root canals because of their high flexibility and cutting ability and because they create centered preparations more rapidly. However, they tend to unexpectedly breakage because of flexural cyclic fatigue (FCF), which is induced by the alternating tension-compression cycles to which they are subjected to when flexed in the maximum curvature region of the canal and rotated. Many factors are believed to influence FCF resistance of files. Firstly anatomical factors such as radius and angle of curvature, as described by Pruett in 1997, are the main factors that can determine the resistance of files to FCF. Second, some instrument characteristics such as alloy, diameter and design has been also reported. Other factors like use mechanisms, autoclaving or the contact of the file with corrosive solutions may also have an influence in FCF resistance of files. Published studies have reported varying incidences from 1,67% to 5% of file breakages during root canal treatments and shown that some of them do not show signs of fatigue and therefore breakage is somehow unexpected in some of them. Many FCF test has been published in the last years using different protocols and different devices. Plotino et al. (2009) reviewed all these studies and concluded that the differences in the methodology affected the results on fatigue behavior of these studies...
Description
Tesis inédita de la Universidad Complutense de Madrid de la Facultad de Odontología del Departamento de Estomatología II, leída el 30 de Septiembre de 2016. Tesis formato europeo (compendio de artículos)