Stress Distribution in Co-Cr Implant Frameworks after Laser or TIG Welding

Lack of passivity has been associated with biomechanical problems in implant-supported prosthesis. The aim of this study was to evaluate the passivity of three techniques to fabricate an implant framework from a Co-Cr alloy by photoelasticity. The model was obtained from a steel die simulating an edentulous mandible with 4 external hexagon analog implants with a standard platform. On this model, five frameworks were fabricated for each group: a monoblock framework (control), laser and TIG welding frameworks. The photoelastic model was made from a flexible epoxy resin. On the photoelastic analysis, the frameworks were bolted onto the model for the verification of maximum shear stress at 34 selected points around the implants and 5 points in the middle of the model. The stresses were compared all over the photoelastic model, between the right, left, and center regions and between the cervical and apical regions. The values were subjected to two-way ANOVA, and Tukey's test (α=0.05). There was no significant difference among the groups and studied areas (p>0.05). It was concluded that the stresses generated around the implants were similar for all techniques.

Resumo A falta de passividade tem sido associada a problemas biomecânicos em próteses implantossuportadas. A proposta deste estudo foi avaliar, por meio da fotoelasticidade, a influência de três diferentes de fabricação de infraestrutura em liga de Co-Cr na passividade destas. O modelo foi obtido a partir de uma matriz de aço simulando uma mandíbula edêntula com 4 análogos de implantes de hexágono externo com plataforma padrão. Neste modelo, foram confeccionados cinco amostras para cada grupo: infraestruturas em monobloco, infraestruturas soldadas a laser e soldadas a TIG. O modelo fotoelástico foi feito com uma resina epóxi flexível (GIII, Polipox Industria e Comercio Ltda.). Na análise fotoelástica, as infraestruturas foram aparafusadas no modelo para a verificação da tensão de cisalhante máxima em 34 pontos selecionados ao redor dos implantes e 5 pontos na região média do modelo. Foram comparadas as tensões em todo o modelo fotoelástico, entre as regiões direita, esquerda e centro e também entre as regiões cervical e apical. Os valores foram submetidos à análise de variância a dois critérios, seguido pelo teste de Tukey (α=0,05). Os resultados não mostraram diferença significativa entre as tensões presentes nos grupos e nas áreas estudadas. Conclui-seque as tensões geradas ao redor dos implantes foram semelhantes entre as diferentes técnicas de confecção e entre todas as regiões analisadas. .

Effect of plasma welding parameters on the flexural strength of ti-6al-4v alloy

The aim of this study was to assess the effect of different plasma arc welding parameters on the flexural strength of titanium alloy beams (Ti-6Al-4V). Forty Ti-6Al-4V and 10 NiCr alloy beam specimens (40 mm long and 3.18 mm diameter) were prepared and divided into 5 groups (n=10). The titanium alloy beams for the control group were not sectioned or subjected to welding. Groups PL10, PL12, and PL14 contained titanium beams sectioned and welded at current 3 A for 10, 12 or 14 ms, respectively. Group NCB consisted of NiCr alloy beams welded using conventional torch brazing. After, the beams were subjected to a three-point bending test and the values obtained were analyzed to assess the flexural strength (MPa). Statistical analysis was carried out by one-way ANOVA and Tukey's HSD test at 0.05 confidence level. Significant difference was verified among the evaluated groups (p<0.001), with higher flexural strength for the control group (p<0.05). No significant differences was observed among the plasma welded groups (p>0.05). The NCB group showed the lowest flexural strength, although it was statistically similar to the PL 14 group (p>0.05). The weld depth penetration was not significantly different among the plasma welded groups (p=0.05). Three representative specimens were randomly selected to be evaluated under scanning electron microcopy. The composition of the welded regions was analyzed by energy dispersive X-ray spectroscopy. This study provides an initial set of parameters supporting the use of plasma welding during fabrication of titanium alloy dental frameworks.

O objetivo deste estudo foi avaliar o efeito de diferentes parâmetros de solda a plasma verificando a resistência flexural de barras de liga de titânio (Ti-6Al-4V). Quarenta espécimes de Ti-6AL-4V e dez espécimes de liga de NiCr foram preparados (40 mm de altura e 3,18 mm de diâmetro) e divididos em 5 grupos (n=10). As barras de liga titânio do grupo controle não foram seccionadas e nem submetidas a processo de soldagem. Os grupos PL10, PL12 e PL14, continham barras de titânio seccionadas e soldadas com uma corrente de 3 A por períodos de 10,12 e 14 ms, respectivamente. O grupo NCB consistiu de barras de liga de NiCr soldadas pelo método de brasagem convencional. Em seguida as barras foram submetidas ao teste de flexão de três pontos e os valores obtidos foram transformados em resistência flexural (MPa). Análise estatística foi realizada usando ANOVA de fator único e o teste Tukey com o nível de significância de 0,05. Diferença estatística foi verificada entre os grupos avaliados (p<0,001), com os maiores valores pra o grupo controle. Não foram encontradas diferenças entre os grupos de solda plasma (p>0,05). O grupo NCB apresentou os menores valores de resistência flexural embora tenha sido estatisticamente semelhante ao grupo PL14. Não houve diferença significante na profundidade de penetração entre os grupos de solda plasma (p=0,05). Três espécimes representativos foram aleatoriamente selecionados para serem avaliados por meio de microscopia eletrônica de varredura. A composição das regiões soldadas foi verificada por meio de espectroscopia por energia dispersiva. Este estudo fornece informações iniciais de parâmetros para permitir a utilização de soldagem plasma durante a fabricação de estruturas em liga de titânio.

Microstructure, mechanical performance and corrosion properties of base metal solder joints.

Context: Alloys have been considered to be of paramount importance in the field of prosthodontics. Long span prosthesis may often require joining of one or more individual castings to obtain better fit, occlusal harmony and esthetics in comparison to one-piece casting. Aim: This study was undertaken to evaluate the mechanical properties of base metal alloys joined by two different techniques, namely, gas oxygen torch soldering and laser fusion, compared to a one-piece casting. Mechanical properties evaluated were tensile strength, percentage of elongation and hardness of the solder joint. In addition, corrosion properties and scanning electron microscopic appearance of the joints were also evaluated. Materials and Methods: The samples were prepared according to American Society for Testing Materials specifications (ASTM, E8). Specimens were made with self-cure acrylic and then invested in phosphate-bonded investment material. Casting was done in induction casting machine. Thirty specimens were thus prepared for each group and compared with 30 specimens of the one-piece casting group. Statistical Analysis Used: SPSS software (version 10.0, Chicago, IL, USA) was used for statistical analysis. ANOVA and Benferroni post hoc tests were done for multiple comparisons between the groups and within the groups for mean difference and standard error. Results: Results showed that tensile strength of the one-piece casting was higher than laser fused and gas oxygen torch soldered joints. Laser fused joints exhibited higher hardness values compared to that of gas oxygen torch soldered joints. Scanning electron microscopic examination revealed greater porosity in the gas oxygen torch soldered joints. This contributed to the reduction in the strength of the joint. Gas oxygen torch soldered joints showed less corrosion resistance when compared to laser fused joints and one-piece casting. Conclusion: Laser fusion, which is a recent introduction to the field of prosthodontics, produces joints which have properties between those of one-piece casting and the gas oxygen torch soldering.

Avaliação comparativa de propriedades geradas pelos processos de soldagem TIG e brasagem em uma liga odontológica à base de Ni-Cr / Comparative assessment of properties generated by the process of TIG welding and brazing in a Ni-Cr dental alloy

O objetivo deste trabalho foi comparar, por meio de teste de microdureza e técnicas de caracterização metalúrgica, que inclui a metalografia, microscopia óptica, microscopia eletrônica de varredura (MEV) e espectroscopia por dispersão de energia (energy dispersive spectroscopy – EDS), propriedades mecânicas e metalúrgicas de juntas soldadas pelos métodos TIG e brasagem em uma liga odontológica à base de Ni-Cr (FIT-CAST SB). As regiões estudadas em cada amostra foram o metal de base (MB), a zona termicamente afetada (ZTA) e a zona de fusão (ZF). Foram confeccionados 40 corpos-de-prova cilíndricos, em forma de bastão, com 2,5mm de diâmetro e 18,0mm de comprimento, obtidos apartir de fundição odontológica por centrifugação (técnica da cera perdida). Foram separados vinte cilindros para cada técnica, que após a soldagem formaram grupos de dez amostras para cada procedimento. A microestrutura do MB apresentou-se como uma matriz de uma solução sólida à base de Ni-Cr contendo um típico arranjo dendrítico de estrutura eutética. A liga apresentou precipitados metálicos na região interdendrítica da estrutura eutética. A análise química semi-quantitativa obtida através da técnica de EDS apresentou resultados compatíveis com a composição química quantitativa fornecida pelo fabricante da liga. Na brasagem, o MB e a ZF apresentaram microestruturas distintas. A ZF apresentou uma morfologia dendrítica grosseira com a presença de precipitados e porosidades. A análise química semi quantitativa por EDS da ZF mostrou-se bastante semelhante aos resultados obtidos para o MB...

The purpose of this study was to compare, by means of microhardness testing and metallurgical characterization techniques as metallography, optical microscopy, scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS), mechanical and metallurgical properties of welded joints by TIG and brazing methods in a dental alloy based on Ni-Cr (FIT-CAST SB). The studied regions in each sample were the base metal (MB), the heat affected zone (ZTA) and the fusion zone (ZF). Forty cylindrical bodies-of-proof, stick-shaped, with 2.5mm diameter and 18.0mm in length were made from dental casting by centrifugation (lost wax technique). Twenty cylinders were used for each technique, which formed, after the welding, groups of ten samples for each procedure. The microstructure of the MB is presented as a matrix of a solid solution based on Ni-Cr with a typical dendritic arrangement of eutectic structure. The alloy presented metallic precipitates in the interdendritic region of the eutectic structure. The semiquantitative chemical analysis obtained by EDS technique showed results consistent with the quantitative chemical composition provided by the alloy manufacturer. In the brazing method, the MB and ZF showed different microstructures. The ZF showed a rough dendritic morphology with the presence of precipitates and porosities. The semiquantitative chemical analysis by EDS of the ZF had very similar results to those obtained for the MB...