Evaluation of EDM inclusion into the conventional polishing of printed Co-Cr alloy by selective laser melting / Avaliação da inclusão de EDM no polimento convencional da liga de Co-Cr impressa por fusão seletiva a laser

Objective: The selective laser melting (SLM) technique used in manufacturing results in a rougher surface that requires more satisfying processing than conventional hand-finishing operations. The electro discharge machine (EDM) has various possibilities in the adjustment of surfaces. The present study assesses whether the participation of the EDM technique with the conventional finishing and polishing methods enables surface improvement for the Cobalt-Chromium alloy fabricated by SLM. Material and Methods: Twenty discs of cobalt chromium alloy were fabricated by SLM, divided equally into two groups: (TF) control group for finishing and polishing in the conventional method in accordance with the manufacturer's recommendations; and (EF) group for conducting polishing incorporating the EDM method. Results: The EF group recorded the lowest mean value of surface roughness and the highest mean value of micro hardness compared to the TF group. Furthermore, statistically significant differences (P < 0.05) were found for surface roughness as well as micro hardness. Conclusion: Reliance of the electric discharge machine proactively within finishing and polishing procedures promotes competence in the conventional polishing method and improves the surface properties of cobalt chromium alloy printed by SLM technology (AU)

Objetivo: A técnica de fusão a laser seletiva (SLM) usada na fabricação resulta em uma superfície mais rugosa a qual requer um processamento mais satisfatório do que o acabamento manual. A máquina de eletro descarga (EDM) possui várias possibilidades no ajuste de superfícies. O presente estudo avalia se a participação da técnica EDM associada aos métodos convencionais de acabamento e polimento possibilita a melhora da superfície da liga Cobalto-Cromo fabricada através da SLM. Material e Métodos: Vinte discos de liga de cromo-cobalto foram confeccionados por SLM, e divididos igualmente em dois grupos: (TF) grupo controle, realizado acabamento e polimento pelo método convencional de acordo com as recomendações do fabricante; e (EF) grupo do polimento associado ao método EDM. Resultados: O grupo EF registrou o menor valor médio de rugosidade superficial e o maior valor médio de microdureza em relação ao grupo TF. Além disso, diferenças estatisticamente significativas (P < 0,05) foram encontradas para rugosidade superficial, assim como para a microdureza. Conclusão: A confiança na máquina de descarga elétrica proativamente nos procedimentos de acabamento e polimento promove a competência no método de polimento convencional e melhora as propriedades de superfície da liga de cromo-cobalto impressa pela tecnologia SLM(AU)

Titanium Powder Coating Using Metal 3D Printing: A Novel Coating Technology for Cobalt-Chromium Alloy Implants

BACKGROUND: Three-dimensional (3D) printing with a direct metal fabrication (DMF) technology has been innovatively introduced in the field of surface treatment of prostheses. The purpose of this study was to determine whether such modifications on the surface of cobalt-chromium (CoCr) alloy by titanium powder coating using DMF improves the osseointegration ability of CoCr alloy. METHODS: We compared the in vitro and in vivo ability of cells to adhere to DMF-coated CoCr alloy with machining. Biological and morphological responses to human osteoblast cell lines were examined by measuring cell proliferation rate and observing expression of actin filament. For in vivo study, we inserted different specimens in each medulla of the distal femurs of rabbit. After 3 months, the distal femurs were harvested, and a push-out test and histomorphometric analyses were performed. RESULTS: The cell proliferation rate and cell adhesion in the DMF group were higher compared with those in the machined group. Human osteoblast cells on the DMF-coated surface were more strongly adhered and well-proliferated compared with those on the other surface. In the in vivo test, there was a significant difference in the ultimate shear strength between the DMF and machined groups (2.49 MPa vs. 0.87 MPa, respectively, p = 0.001). In the histomorphometric analysis, there was a significant difference in the mean bone-to-implant contact percentages between the DMF and machined groups (72.3 ± 6.2% vs. 47.6 ± 6.9%, respectively, p < 0.001). CONCLUSION: Titanium coating of CoCr alloy with 3D metal printing provides optimal surface characteristics and a good biological surface both in vitro and in vivo.

Accuracy evaluation of metal copings fabricated by computer-aided milling and direct metal laser sintering systems

PURPOSE: To assess the marginal and internal gaps of the copings fabricated by computer-aided milling and direct metal laser sintering (DMLS) systems in comparison to casting method. MATERIALS AND METHODS: Ten metal copings were fabricated by casting, computer-aided milling, and DMLS. Seven mesiodistal and labiolingual positions were then measured, and each of these were divided into the categories; marginal gap (MG), cervical gap (CG), axial wall at internal gap (AG), and incisal edge at internal gap (IG). Evaluation was performed by a silicone replica technique. A digital microscope was used for measurement of silicone layer. Statistical analyses included one-way and repeated measure ANOVA to test the difference between the fabrication methods and categories of measured points (alpha=.05), respectively. RESULTS: The mean gap differed significantly with fabrication methods (P<.001). Casting produced the narrowest gap in each of the four measured positions, whereas CG, AG, and IG proved narrower in computer-aided milling than in DMLS. Thus, with the exception of MG, all positions exhibited a significant difference between computer-aided milling and DMLS (P<.05). CONCLUSION: Although the gap was found to vary with fabrication methods, the marginal and internal gaps of the copings fabricated by computer-aided milling and DMLS fell within the range of clinical acceptance (<120 microm). However, the statistically significant difference to conventional casting indicates that the gaps in computer-aided milling and DMLS fabricated restorations still need to be further reduced.

Accuracy evaluation of metal copings fabricated by computer-aided milling and direct metal laser sintering systems

PURPOSE: To assess the marginal and internal gaps of the copings fabricated by computer-aided milling and direct metal laser sintering (DMLS) systems in comparison to casting method. MATERIALS AND METHODS: Ten metal copings were fabricated by casting, computer-aided milling, and DMLS. Seven mesiodistal and labiolingual positions were then measured, and each of these were divided into the categories; marginal gap (MG), cervical gap (CG), axial wall at internal gap (AG), and incisal edge at internal gap (IG). Evaluation was performed by a silicone replica technique. A digital microscope was used for measurement of silicone layer. Statistical analyses included one-way and repeated measure ANOVA to test the difference between the fabrication methods and categories of measured points (alpha=.05), respectively. RESULTS: The mean gap differed significantly with fabrication methods (P<.001). Casting produced the narrowest gap in each of the four measured positions, whereas CG, AG, and IG proved narrower in computer-aided milling than in DMLS. Thus, with the exception of MG, all positions exhibited a significant difference between computer-aided milling and DMLS (P<.05). CONCLUSION: Although the gap was found to vary with fabrication methods, the marginal and internal gaps of the copings fabricated by computer-aided milling and DMLS fell within the range of clinical acceptance (<120 microm). However, the statistically significant difference to conventional casting indicates that the gaps in computer-aided milling and DMLS fabricated restorations still need to be further reduced.

In vitro study on the surface properties of cobalt chromium alloy fabricated by two different methods / 实用口腔医学杂志

Objective:To evaluate the surface free energy and Streptococcus mutans(S.mutans)adhesion on the surfaces of Co-Cr al-loy specimens fabricated by selective laser sintering(SLS)and casting method(SG and W280)respectively.Methods:The specimens of three groups were polished by SiC sandpaper.Surface morphology test,surface contact angle test and surface adhesion test of S.mu-tans were performed.Results:With the same surface roughness value,the surface contact angle of group SLS,W280 and SG was 66.200 ±3.112,74.212 ±3.206 and 67.238 ±2.047(P >0.05),the surface adhesion of S.mutans colone was 8.88 ±2.90,9.25 ± 2.05 and 8.50 ±1.85(P >0.05),respectively.Conclusion:The cobalt chromium alloy fabricated by SLS and casting method have similar surface performance.

Clinical assessment of repair of free second molar residual crowns by glass fiber post and resin core / 实用口腔医学杂志

37 free second molar residual crowns were repaired by glass fiber post and resin core(GF group),and another 37 by cobalt chromium alloy casting post and core(CCA group).The success rate of 1 ~5 years of GF group was 1 00%,1 00%,91 .9%,86.5% and 81 .1 %;that of CCA group 97.3%,91 .9%,83.8%,81 .1 % and 73.0%,respectively(P >0.05).

Casting made simple using modified sprue design: An in vitro study.

Background: Success in dental casting restorations for fixed partial dentures (FPDs) depends on the castability. Castability is described as the ability of an alloy to faithfully reproduce sharp detail and fine margins of a wax pattern. The goal of a prosthodontist is to provide the patient with restorations that fit precisely. Regardless of the alloy used for casting, the casting technique should yield a casted alloy, which should possess sufficient mass, surface hardness and minimal porosity after casting. Materials and Methods: Twenty patterns for casting were made from three‑dimensional printed resin pattern simulating a 3 unit FPD and casted using modified sprue technique. Later test samples were cemented sequentially on stainless steel model using pressure indicating paste and evaluated for vertical marginal gap in eight predetermined reference areas. Marginal gap were measured in microns using Video Measuring System (VMS2010F‑CIP Corporation, Korea). A portion of the axial wall of the cast abutments depicting premolar and molar were sectioned and embedded in acrylic resin and tested for micro hardness using Reichert Polyvar 2 Met Microhardness tester (Reichert, Austria) and porosity using Quantimet Image Analyzer (Quantimet Corporation London, England). Results: The results obtained for marginal gap, micro hardness, and porosity of all test samples were tabulated, descriptive statistics were calculated and the values were found to be within the clinically acceptable range. Conclusion: The new sprue technique can be an alternative and convenient method for casting which would minimize metal wasting and less time consuming. However, further studies with same technique on various parameters are to be conducted for its broad acceptance.

The effect of remelting various combinations of new and used cobalt-chromium alloy on the mechanical properties and microstructure of the alloy.

Context: Remelting previously cast base metal alloy can adversely affect the mechanical properties of the alloy and necessitates addition of new alloy. Aims: To study the effect of remelting different combinations of new and used cobalt-chromium (Co-Cr) alloy on its mechanical properties and microstructure. Materials and Methods: Using induction casting, 24 tensile test specimens were prepared for eight different combinations of new and used Co-Cr alloy. The test specimens were assessed for yield strength and percentage elongation. Microhardness was evaluated using Vickers's hardness tester. The tensile testing was carried out on a 50 kN servo-hydraulic universal testing machine. Microstructure analysis was done using an optical photomicroscope on the fractured samples after acid etching. Statistical Analysis: The mean values (±standard deviation) and coefficient of variation were calculated. Student's 't' test was used for statistical analysis. Statistical significance was assumed at P=.05. Results: The mean yield strength of eight different combination groups were as follows: group A: 849 MPa, group B 1 : 834 MPa, group B 2 : 915 MPa, group B 3 : 897 MPa, group C 1 : 874 MPa, group C 2 : 859 MPa, group D 1 : 845 MPa, and group D 2 : 834 MPa. The mean percentage elongation for the different groups were as follows: group A: 7%, group B 1 : 7%, group B 2 : 8%, group B 3 : 7%, group C 1 : 8%, group C 2 : 7%, group D 1 : 7%, and group D 2 : 8%. The mean hardness values were as follows: group A: 373 VHN, group B 1 : 373 VHN, group B 2 : 346 VHN, group B 3 : 346 VHN, group C 1 : 364 VHN, group C 2 : 343 VHN, group D 1 : 376 VHN, and group D 2 : 373 VHN. Conclusion: Repeated remelting of base metal alloy for dental casting without addition of new alloy can affect the mechanical properties of the alloy. Microstructure analysis shows deterioration upon remelting. However, the addition of 25% and 50% (by weight) of new alloy to the remelted alloy can bring about improvement both in mechanical properties and in microstructure.

Mechanical properties of laser welded Co-Cr alloy / 대한치과보철학회지

STATEMENT OF PROBLEM: The joints of removable partial denture alloys have failed frequently after routine usage. PURPOSE: The purpose of this study was to evaluate the mechanical properties of the laser welded Co-Cr alloys. MATERIAL AND METHOD: For this study, 20 Co-Cr specimens were casted and 10 of them were seperated on the middle area and laser welded with Alpha laser welding machine(Siro Lasertec, Pforzheim, Germany). Rest of them which were as cast, were used as a control group. For the section of the experimental specimens, wire cutting machine was used to make a even gap of the all specimens. Laser welding was done with manufacturer's instrunction and tested each specimen by Instron Machine. Tensile strength, 0.2% yield strength and % elongations were recorded. Fractured surfaces were investigated with SEM. RESULTS: The results were as follows : 1. The tensile strength of the laser welded group(617.7MPa) was about 75% of the as cast group(820.4MPa). It had stastically singnificant diffrences(p<0.05). 2. The % elongation of the experimental group was 6.6 which was lower than the control group(14.3). 3. Fracture of the experimental group occured in the welded surface and showed many voids. In contrast, the fracture surface of the control group was showed rough surfaces without any voids. CONCLUSION: The tensile strengths of the as-cast joints were higher than those for the laserwelded joints, and the % elongation of the experimental group was lower than the control group. Porosity was found in laser-welded joints.