Radiographic inspection of porosity in Ti-6Al-4V laser-welded joints

Widely used in dentistry, Ti-6Al-4V alloy is difficult to cast and solder, as it frequently exhibits pores inside the structure. This study was conducted to evaluate the effect of joint openings and diameters of laser-welded joints executed in Ti-6Al-4V structures on the presence of pores as checked by radiographic procedures. Sixty dumbbell rods with central diameters of 1.5, 2.0 and 3.5 mm were created from Ti-6Al-4V-wrought bars. Specimens were sectioned and welded using two joint openings (0.0 and 0.6 mm). The combination of variables created six groups (n = 10). Laser welding was executed using 360V/8ms (1.5 and 2.0 mm) and 380V/9ms (3.5 mm), with the focus and frequency set to zero. The joints were finished, polished and submitted to radiographic examination. The radiographs were visually examined for the presence of pores in the joints, qualitatively. The percentage of radiographic presence of pores was calculated without counting pores per joint. Data were analyzed using a chi-square test (α = 0.05). For the 1.5-mm specimens, the incidence of pore presence was significantly higher (p = 0.0001) when using 0.6-mm joint openings (40 percent) compared to 0.0-mm openings (0 percent). For the 2.0-mm specimens, there was no significant difference between groups (p = 0.2008). However, for the 3.5-mm specimens, the incidence of pore presence was lower (p = 0.0061) for 0.6-mm openings (50 percent) compared to 0.0-mm openings (70 percent). Therefore, laser welding of Ti-6Al-4V structures with thin diameters provides the best condition for the juxtaposition of the parts.

Análise radiográfica de uniões soldadas a laser executadas no titânio comercialmente puro fundido, em diversas situações clínicas simuladas / Radiographic analysis in casting titanium laser-joints in diverse clinical situations

Esse estudo foi conduzido para avaliar a possibilidade de visualização de porosidade interna em radiografias periapicais de uniões soldadas a laser, confeccionadas em estruturas de titânio (Ti) comercialmente puro (cp), em diferentes situações de soldagem. Foram confeccionados halteres em resina acrílica, com diâmetros centrais de 1,5; 2,0; e 3,5 mm, por meio de uma matriz metálica bipartida. Os halteres em resina foram fundidos em Ti cp e após acabamento e polimento, seccionados em duas partes iguais. As partes foram alinhadas e fixadas de tal forma que as distâncias entre elas fossem 0,0 e 0,6 mm. A combinação entre as variáveis (distância de soldagem e diâmetro dos halteres) gerou seis grupos (n=10). A soldagem a laser foi realizada com as seguintes especificações: 360V/8ms (1,5 e 2,0 mm) e 380V/9ms (3,5 mm), com foco e freqüência regulados em zero, em um aparelho de soldagem a laser Desktop-F. As uniões obtidas receberam acabamento, polimento e foram submetidas à análise radiográfica com exposição à radiação (90 KV, 15 mA, 0,6 seg e 10 a 13 mm de distância) utilizando filme periapical. As radiografias foram analisadas visualmente quanto à presença de porosidade nas uniões soldadas, e os dados obtidos, submetidos ao teste Qui-Quadrado (5%). Com isso, verificou-se ser possível visualizar porosidade interna nessas uniões. Em corpos de prova de menores diâmetros, 1,5 e 2,0 mm, a incidência é maior quando a distância é 0,6 mm. Entretanto, em corpos de prova de 3,5 mm, a incidência é alta para ambas as uniões, não diferindo estatisticamente entre si.

This study was conducted to evaluate the possibility of porosity inspection in laser-weld joints executed in cp titanium structures, by radiographic analyses. Sixty acrylic dumbbells rods with 1.5, 2.0 and 3.5 mm central diameter were prepared by lost-wax casting procedure. The casted specimens were finished, polished and sectioned in two halves. The parts were lined up in a metal matrix and fixed according two welding distances (0.0 and 0.6 mm). The combination between diameter and welding distance created a total of six groups (n = 10). The laser welding was executed as follows: 360V/8ms (1.5 and 2.0 mm) and 380V/9ms (3.5 mm) with focus and frequency regulated to zero. The achieved joints were finished, polished and submitted to radiographic examination (90 KV, 15 mA, 0.6 second and 10 to 13 mm of distance) with periapical film. The radiographies were visually analyzed for the presence of internal porosity in the joints. The data was submitted to Chi-Square test (5%). Herewith, it was possible to visualize internal porosity in the analyzed joints. In thin specimens, 1.5 and 2.0 mm, the porosity incidence was higher when the joint distance was 0.6 mm. However, in 3.5 mm specimens, this incidence was high for both joint openings.

Porcelain application and simulation of firing cycle: effect on marginal misfit of implant-supported frameworks

Aim: Success of implant-supported prostheses is related to the frameworks’ passive fit, henceinaccuracies can generate stress, leading to bone resorption and rehabilitation failure. This study evaluated misfit levels of implant-supported frameworks after different coverage treatments.Methods: Twenty commercially pure titanium (CP Ti) frameworks were manufactured with 5Branemark type multi-unit abutments. Frameworks were distributed in two groups as follows: G1- porcelain application (n=10); G2 - porcelain firing cycle simulation (n=10). Using a traveling microscope, marginal misfit was measured before and after undertaking the techniques, following the single-screw test protocol. All data were submitted to ANOVA and Tukey’s test (p<0.05).Results: Initial marginal misfit values were not significantly different, but both groups presented significantly higher misfit values after treatment: G1: 233.99 ìm (p=0.0003); G2: 119.75 ìm(p<0.0001). In addition, G1 presented higher misfit than G2 (p<0.0001). Conclusions: Porcelain application promoted significantly higher increase of misfit, which indicates that such procedure should be considered on misfit analysis of implant-supported prostheses.