Cyclic flexural fatigue resistance of NiTi Controlled Memory and Blue Technology instruments after torsional preloading

Objective: The aim of this study was to evaluate the influence of torsional preloading on the cyclic flexural fatigue resistance of thermally treated NiTi instruments. Material and Methods: Ten new instruments New Hyflex CM (HF 30.06; Coltene/Whaladent Inc.), Typhoon CM (TYP 30.06; Clinician's Choice Dental Products) and Vortex Blue (VB 30.06; Dentsply Tulsa Dental) were chosen, based on geometry and specific characteristics of the manufacturing process. The new instruments of each system were tested in a bench device to determine their fatigue resistance through mean value of number of cycles to failure (Nf) (Control Group – CG). Another group of 10 new HF, TYP and VB instruments were submitted to 20 cycles of torsional straining between 0° and 180° (Experimental Group – EG) and then submitted to fatigue until rupture under the same conditions of the CG. Tested instruments were examined by scanning electron microscopy (SEM). Data were analyzed using one-way analysis of variance and post hoc Tukey’s test (α=.05). Results: Higher fatigue resistance was accomplished by HF instruments, followed by VB and TYP (p<0.05). During the torsional preloading, the lowest mean torque value was observed for TYP instruments (p<0.05). The torsional preload caused a significant reduction in the Nf values (p<0.05) of about 20%, 39% and 45% for instruments HF, VB and TYP, respectively. Longitudinal cracks, generated during the torsional preloading, were present in VB files, but were not observed in the CM instruments (HF and TYP). Conclusions: In conclusion, the flexural fatigue resistance of thermally treated instruments is diminished after cyclic torsional loading

Comparative analysis of electrochemical anodization of α-Ti e β-TiNi substrates to achieve titania nanotubes formation

Submitted by Pedro Resende ([email protected]) on 2020-03-10T15:58:21Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: cfd6801dba008cb6adbd9838b81582ab (MD5) dissertação_completa_bu.pdf: 3050475 bytes, checksum: 0eb577790524c091d59796692fbbd890 (MD5)Approved for entry into archive by Jane Campos ([email protected]) on 2020-03-17T19:13:14Z (GMT) No. of bitstreams: 2 license_rdf: 811 bytes, checksum: cfd6801dba008cb6adbd9838b81582ab (MD5) dissertação_completa_bu.pdf: 3050475 bytes, checksum: 0eb577790524c091d59796692fbbd890 (MD5)Made available in DSpace on 2020-03-26T20:45:40Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: cfd6801dba008cb6adbd9838b81582ab (MD5) dissertação_completa_bu.pdf: 3050475 bytes, checksum: 0eb577790524c091d59796692fbbd890 (MD5) Previous issue date: 2020-02-17CNPq - Conselho Nacional de Desenvolvimento Científico e TecnológicoFAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas GeraisCAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorO titânio e suas ligas são materiais amplamente explorados devido às suas características de boa resistência mecânica e à corrosão, biocompatibilidade, propriedades catalíticas, entre outras. Parte destes campos de utilização se devem à camada de titânia formada em sua superfície, o que torna de primeira importância o controle da morfologia deste filme. Diversas técnicas de finalização de superfícies de titânio são propostas, desde métodos mecânicos e químicos até ópticos. Métodos eletroquímicos são formas eficazes de se funcionalizar uma superfície, pois são de fácil controle operacional, boa relação de custobenefício, alta reprodutibilidade e fácil aplicação em peças de geometrias complicadas. A anodização eletroquímica para obtenção de estruturas nanotubulares de titânia é amplamente estudada em substratos de titânio comercialmente puro e ligas de baixa adição, que possuem em comum o fato de formarem majoritariamente a fase α-Ti. A compreensão de como estes processos podem ser utilizados com mesma finalidade em ligas de estrutura β é escassa. Um exemplo de liga exclusivamente β é o NiTi, que foi utilizado para entender a diferença entre processos aplicados em cada tipo de substrato. Foram utilizadas tiras de titânio puro e de NiTi obtidas comercialmente. Ambos materiais tiveram estrutura investigada e sua superfície foi caracterizada anteriormente aos processos de adequação superficial e após a finalização desta etapa. As amostras foram anodizadas em eletrólitos de composição 0,2%m. NH4F, 1%v. H2O em etilenoglicol. Os potenciais de anodização escolhidos foram 5, 15, 25, 45 e 60 V com duração total de 3 h. As amostras foram caracterizadas por microscopia eletrônica de varredura e as características morfológicas foram observadas por programa de análise de imagens. No titânio puro foram obtidas superfícies de estrutura nanotubular em todas as condições de anodização estudadas, ao contrário do ocorrido para o substrato de NiTi. Neste, apenas a amostra de 5 V apresentou formação similar à amostra de titânio. Amostras obtidas sob potenciais de 15 e 25 V apresentaram formações de aspecto tubular, porém sobre uma matriz porosa e não organizada. As amostras de NiTi anodizadas a 45 e 60 V sofreram corrosão por pite. O mecanismo de crescimento dos filmes anódicos é semelhante, porém apresenta menor organização observada na interface metal/óxido. Foi possível concluir que a obtenção de nanotubos de titânia em substrato de NiTi é viável, assim como no titânio. Os potenciais de anodização eletroquímica do NiTi capazes de produzir esta morfologia devem ser escolhidos cuidadosamente, uma vez que este substrato é mais susceptível à degradação do filme anódico formado.Titanium and its alloys are widely explored in science and technological applications due to its intrinsic characteristics of high mechanical and corrosion resistance, biocompatibility, catalytical properties, among others. Many of these applications are suitable due to the natural titania coat that forms on top of the base metal, which makes its morphology control a primary concern. Several surface finishing techniques have been proposed throughout the years to achieve this goal, since mechanical or chemical to optical processes. Electrochemical processes are efficient ways to functionalize the surface of a base metal once they have relatively easy operational control, are cost-effective, are reproducible and are easy to apply even in complex-shaped pieces. Nanotubular titania films obtained by electrochemical anodization are widely explored in the literature for commercialy pure titanium or mostly α alloys. There is a lack of comprehension how these processes can be used to produce the same kind of nanostructures in pure β alloys. One example of exclusively β alloy is the TiNi phase, which was used to better understand the mechanisms involved in its eletrochemical anodization. Commercially pure titanium and TiNi strips were used in this work. Both materials had its structure determined by X-Ray diffraction and were characterized prior to the electrochemical anodization as well as after the anodic process. The samples were anodized in a electrolyte with a composition of 0,2%m. NH4F, 1%v. H2O in ethyleneglycol. The chosen anodization potentials were 5, 15, 25, 45 and 60 V. The process was set to have 3 hours of duration. The samples were characterized by scanning electron microscopy and its morphological features were assessed by a difital image analyzer. All anodization conditions lead to the formation of nanotubular titania in commercially pure titanium. The same behavior was not observed for TiNi alloys, as the only condition that produced an uniform anodic film was at the anodization potential of 5 V. As the potential increased to 15 and 25 V the degree of organization of the nanostructures was lost and some tubular structures could be observed in a spongy-like oxide matrix. TiNi samples anodized at 45 and 60 V undergone severe corrosion damage and no nanotube formation could be observed. The growth mechanisms of the anodic films seem to be similar for both kinds of substrates, but the result of the TiNi metal/oxide interface has lower degree of organization. It can be concluded that the growth of titania nanotubes in TiNi substrates is feasible as it is in pure titanium substrate. But it is important to choose the anodization potential carefully because the anodic film produced on top of TiNi samples is more prone to suffer degradation from the anodic process du to its higher reactivity

Effects of R-Phase on Mechanical Responses of a Nickel-Titanium Endodontic Instrument: Structural Characterization and Finite Element Analysis

The effects of the presence of the R-phase in a near-equiatomic NiTi alloy on the mechanical responses of an endodontic instrument were studied by using finite element analysis. The input data for the constitutive model in the simulation were obtained by tensile testing of three NiTi wires: superelastic austenite NiTi, austenite + R-phase NiTi, and fully R-phased NiTi. The wires were also characterized by X-ray diffraction and differential scanning calorimetry. A commercially available endodontic instrument was scanned using microcomputed tomography, and the resulting images were used to build the geometrical model. The numerical analyses were performed in ABAQUS using load and boundary conditions based on the ISO 3630-1 specification for the bending and torsion of endodontic instruments. The modeled instrument containing only R-phase demanded the lowest moment to be bent, followed by the one with mixed austenite + R-phase. The superelastic instrument, containing essentially austenite, required the highest bending moment. During bending, the fully R-phased instrument reached the lowest stress values; however, it also experienced the highest angular deflection when subjected to torsion. In summary, this simulation showed that NiTi endodontic instruments containing only R-phase in their microstructure would show higher flexibility without compromising their performance under torsion

Cyclic flexural fatigue resistance of NiTi Controlled Memory and Blue Technology instruments after torsional preloading

Abstract Objective The aim of this study was to evaluate the influence of torsional preloading on the cyclic flexural fatigue resistance of thermally treated NiTi instruments. Material and Methods Ten new instruments New Hyflex CM (HF 30.06; Coltene/Whaladent Inc.), Typhoon CM (TYP 30.06; Clinician's Choice Dental Products) and Vortex Blue (VB 30.06; Dentsply Tulsa Dental) were chosen, based on geometry and specific characteristics of the manufacturing process. The new instruments of each system were tested in a bench device to determine their fatigue resistance through mean value of number of cycles to failure (Nf) (Control Group – CG). Another group of 10 new HF, TYP and VB instruments were submitted to 20 cycles of torsional straining between 0° and 180° (Experimental Group – EG) and then submitted to fatigue until rupture under the same conditions of the CG. Tested instruments were examined by scanning electron microscopy (SEM). Data were analyzed using one-way analysis of variance and post hoc Tukey’s test (α=.05). Results Higher fatigue resistance was accomplished by HF instruments, followed by VB and TYP (p<0.05). During the torsional preloading, the lowest mean torque value was observed for TYP instruments (p<0.05). The torsional preload caused a significant reduction in the Nf values (p<0.05) of about 20%, 39% and 45% for instruments HF, VB and TYP, respectively. Longitudinal cracks, generated during the torsional preloading, were present in VB files, but were not observed in the CM instruments (HF and TYP). Conclusions In conclusion, the flexural fatigue resistance of thermally treated instruments is diminished after cyclic torsional loading