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Avaliação da Resistência à Fadiga de Limas de Endodontia Sujeitas a Flexão Rotativa e da sua Integridade Estrutural com Recurso à Utilização de Termografia e de Correntes Induzidas
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O propósito deste estudo é comparar a resistência mecânica à fadiga, por flexão
rotativa, de limas endodônticas de diferentes gerações, fabricadas em Níquel-Titânio
(NiTi). Adicionalmente pretende-se averiguar a possibilidade de utilização de Ensaios
Não Destrutivos (END), através dos métodos de correntes induzidas (CI) e termografia,
na deteção de fissuras de fadiga, responsáveis por grande parte das fraturas das limas
em ambiente clínico.
Os instrumentos foram colocados em rotação numa montagem experimental,
projetada para simular um canal radicular com um raio de curvatura igual a 4.7 mm
aplicado ao longo de um ângulo de 45°. Foram testadas seis limas rotativas HyFlex™
EDM (Coltene, Suíça), de dois tamanhos diferentes, e comparadas com os resultados
obtidos para duas limas HyFlex™ CM de tamanho 20/.04. Foram ainda avaliadas as suas
superfícies de fratura com auxílio de um microscópio eletrónico Leica DMI 5000 M.
Para a aplicação dos END, introduziu-se um defeito artificial na região apical de uma
lima HyFlex CM. Seguidamente, foram produzidas e validadas experimentalmente dez
sondas de CI, especificamente concebidas para a sua inspeção. Foram ainda realizadas
simulações numéricas, replicando-se os parâmetros e as condições das duas sondas que
revelaram melhor capacidade de detetabilidade. Por fim, fez-se uma inspeção
termográfica ao instrumento defeituoso, utilizando-se uma câmara Fluke Ti 400.
Os resultados experimentais mostraram que a geração de instrumentos mais
recente (EDM), fabricados através do processo de eletroerosão, são bastante mais
resistêntes à fratura por fadiga quando comparados com as limas CM (Control Memory).
Em relação aos END, as metodologias desenvolvidas para a inspeção das limas
através das CI revelaram-se incapazes de detetar a região defeituosa, em grande
medida devido à sua conicidade. As simulações numéricas corroboraram os resultados
experimentais. Por outro lado, conseguiu-se detetar o defeito através da termografia,
embora com alguma dificuldade devido às suas reduzidas dimensões.
The purpose of this study is to compare the fatigue resistance to rotational bending of endodontic files of different generations, made of nickel-titanium (NiTi). Additionally, it is intended to investigate the possibility of using Non-Destructive Tests (NDT), mainly eddy currents (EC) and thermography, in the detection of fatigue microcracks, responsible for most of the fractures of the files in clinical environment. The instruments were placed in rotation in an experimental setup designed to simulate a root canal with a radius of curvature of 4.7 mm applied over an angle of 45 °. Six HyFlex ™ EDM rotary files (Coltene, Switzerland) of two different sizes were tested, and compared with the results obtained for two HyFlex ™ CM files of size 20 / .04. Their fracture surfaces were also analysed using a Leica DMI 5000 M electronic microscope. For NDT application, an artificial defect was introduced in the apical region of a HyFlex CM file. Subsequently, ten EC probes, specifically designed for their inspection, were produced and validated experimentally. Numerical simulations were carried out, replicating the parameters and conditions of the two probes that showed better detectability. Finally, a thermographic inspection of the defective instrument was performed using a Fluke Ti 400 thermographic camera. Experimental results showed that the newer generation of instruments (EDM) manufactured by the electroerosion process are much more resistant to fatigue fracture when compared to CM files. With respect to NDT, the methodologies developed for the inspection of files through ECs proved unable to detect the faulty region, largely due to their taper and the electromagnetic properties of NiTi alloys. In addition, numerical simulations corroborated the experimental results. On the other hand, the defect introduced in the endodontic file could be detected by thermography, although with some difficulty due to its small size.
The purpose of this study is to compare the fatigue resistance to rotational bending of endodontic files of different generations, made of nickel-titanium (NiTi). Additionally, it is intended to investigate the possibility of using Non-Destructive Tests (NDT), mainly eddy currents (EC) and thermography, in the detection of fatigue microcracks, responsible for most of the fractures of the files in clinical environment. The instruments were placed in rotation in an experimental setup designed to simulate a root canal with a radius of curvature of 4.7 mm applied over an angle of 45 °. Six HyFlex ™ EDM rotary files (Coltene, Switzerland) of two different sizes were tested, and compared with the results obtained for two HyFlex ™ CM files of size 20 / .04. Their fracture surfaces were also analysed using a Leica DMI 5000 M electronic microscope. For NDT application, an artificial defect was introduced in the apical region of a HyFlex CM file. Subsequently, ten EC probes, specifically designed for their inspection, were produced and validated experimentally. Numerical simulations were carried out, replicating the parameters and conditions of the two probes that showed better detectability. Finally, a thermographic inspection of the defective instrument was performed using a Fluke Ti 400 thermographic camera. Experimental results showed that the newer generation of instruments (EDM) manufactured by the electroerosion process are much more resistant to fatigue fracture when compared to CM files. With respect to NDT, the methodologies developed for the inspection of files through ECs proved unable to detect the faulty region, largely due to their taper and the electromagnetic properties of NiTi alloys. In addition, numerical simulations corroborated the experimental results. On the other hand, the defect introduced in the endodontic file could be detected by thermography, although with some difficulty due to its small size.
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Palavras-chave
Limas Endodônticas Fadiga Mecânica Ensaios Não Destrutivos (END) Correntes Induzidas (CI) Termografia