Metal-ceramic interface characteristics of Co-Cr alloy fabricated by selective laser melting / 中国组织工程研究

BACKGROUND: Co-Cr ceramic alloys made by selective laser melting technology are widely used in the field of dental restoration, but the influence of selective laser melting technology on the bonding properties of Co-Cr ceramic alloys is still controversial. OBJECTIVE: To explore the metal-ceramic interface characteristics of dental Co-Cr alloy fabricated by selective laser melting. METHODS: Metal-ceramic specimens were prepared by selective laser melting and precision casting, respectively. Metal-ceramic bond strengths, interface characteristics, fracture analysis, microstructures and composition distribution of specimens were obtained with the aid of universal testing machine, metallographic microscope, scanning electron microscope coupled with energy disperse spectrometer. RESULTS AND CONCLUSION: (1) The metal-ceramic bond strengths of precision casting Co-Cr alloy was higher than that of selective laser melting Co-Cr alloy (P < 0.05). (2) Metallographic microscope showed that selective laser melting Co-Cr alloy had fine grains and a more uniform matrix. Precision casting Co-Cr alloy showed typical casting dendritic structure with coarse grains and a large number of island second phase structures. (3) Scanning electron microscopy showed that precision casting Co-Cr alloy had a thicker diffusion layer than the selective laser melting Co-Cr alloy at the metal-ceramic interface. (4) Scanning electron microscopy showed that the metal-ceramic specimens of precision casting Co-Cr alloy tended to cohesive fracture, and the metal-ceramic specimens of selective laser melting Co-Cr alloy tended to adhesive fracture. (5) The results showed that although the bonding strength of selective laser melting Co-Cr alloy was lower than that of precision casting Co-Cr alloy, the bonding strength of selective laser melting Co-Cr alloy could still meet the requirements of standard YY0621.1-2016.

Evaluation of the Effect of Different Surface Treatments on Bond Strength of Heat Cured Acrylic Resin at Co-Cr Alloy and PEEK Polymer Interface

Problem statement: A significant clinical concern in Co-Cr alloy removable prosthodontics is a failure of bonding with acrylic resins and PEEK is introduced on various materials to overcome this problem. The reason for this study was to examine the denture base acrylic resin bond strength to Co-Cr alloy and PEEK polymer using different surface treatment. Materials and method: Total 60 number of disc-shaped specimens were prepared and divided into 2 main groups according to the type of framework material, 30 specimens for Co-Cr alloy and 30 specimens for PEEK polymer, which were then subdivided into 3 groups each one consist of 10 specimens, according to the type of surface treatments. Each group either had a no surface treatment (control group) or air abrasive group (110 μm of alumina oxide) or acid etch (98% sulfuric acid) group. The specimens were thermocycled (3000 cycles) after applications of heat cured acrylic resin. Results: The results for Co-Cr alloy showed that the air abrasive surface treatments had the highest bond strength mean value followed by the control group (no surface treatment), while the acid surface treatment had the least mean value of bond strength. For PEEK polymer, the results revealed that the acid surface treatment had the highest value of bond strength followed by the air abrasive surface treatment while the control group (no surface treatment) had the least bond strength mean value. Conclusion: Air abrasive surface treatment significantly improved bond strength for both Co-Cr and PEEK, while sulfuric acid treatment show counterproductive result with Co-Cr alloy whereas with PEEK play an important role in bonding mechanism. The use of PEEK framework in combination with heat cured acrylic resin can be recommended as a promising non-metallic alternatives framework material for removable of partial dentures.

Influence of porcelain firing and different manufacturing techniques in fit of Co-Cr porcelain crowns / 吉林大学学报(医学版)

Objective: To explore the influence of different manufacturing techniques and different scanning objects in the marginal and internal fits of the Co-Cr porcelain crowns after procelain firing, and to provide the basis for judging the influencing factors of longevity of restorations. Methods: Five extracted maxillary premolar were selected. According to the prepared tooth, silicone rubber and stone die restoration models, which were fabricated by CAD/CAM and selective laser melting (SLM), the restorations were divided into control group (traditinal casting), tooth-SLM group, silicone rubber-SLM group, stone die-SLM group, tooth-CAD/CAM group, silicone rubber-CAD/CAM group, and stone die-CAD/CAM group. Then all the restorations were fired with the porcelain. The marginal and internal fits of the specinens were measured by micro-compated tomography (Micro-CT). Results: Compared with control group, the AMD of restorations in tooth-SLM and CAD/CAM groups were decresed (P<0. 05), and the MG of restorations in silicone rubber-SLM group was decresed (P<0. 05). Compared with control group, the CA and AW of restorations in silicone rubber-SLM group were decresed (P< 0. 05), the AW of restorations in tooth-CAD/CAM group was the least; compared with control group, the AOT and OA of restorations in stone die-SLM group and CAD/CAM group were decresed (P<0. 05), and the AOT and OA of restorations in silicone rubber-CAD/CAM were the least. Compared with before porcelain firing, the marginal fit and internal fit of restorations after porcelain firing were incresed (P<0. 05). There was positive corrlation between the MG of restorations and fabricated techniques and scanning objects (P<0. 05). There was positive corrlation between the average of internal fit of restorations and fabricated techniques and scanning objects (P<0. 05). Conclusion: The porcelain firing can affect the marginal and internal fits of Co-Cr porcelain crowns. The restorations fabricated by SLM had a better marginal fit and the restorations fabricated by CAD/CAM has a better internal fit.

What is the changing frequency of diamond burs?

PURPOSE: The purpose of this study was to determine the changing frequency of a diamond bur after multiple usages on 3 different surfaces. MATERIALS AND METHODS: Human premolar teeth (N = 26), disc shaped direct metal laser sintered CoCr (N = 3) and zirconia specimens (N = 3) were used in this study. Groups named basically as Group T for teeth, Group M for CoCr, and Group Z for zirconia. Round tapered black-band diamond bur was used. The specimens were randomly divided into three groups and placed with a special assembly onto the surveyor. 1, 5, and 10 preparation protocols were performed to the first, second, and third sub-groups, respectively. The subgroups were named according to preparation numbers (1, 5, 10). The mentioned bur of each group was then used at another horizontal preparation on a new tooth sample. The same procedure was used for CoCr and zirconia disc specimens. All of the bur surfaces were evaluated using roughness analysis. Then, horizontal tooth preparation surfaces were examined under both stereomicroscope and SEM. The depth maps of tooth surfaces were also obtained from digital stereomicroscopic images. The results were statistically analyzed using One-Way ANOVA, and the Tukey HSD post-hoc tests (α=.05). RESULTS: All of the groups were significantly different from the control group (P < .001). There was no significant difference between groups Z5 and Z10 (P=.928). Significant differences were found among groups T5, M5, and Z5 (P < .001). CONCLUSION: Diamond burs wear after multiple use and they should be changed after 5 teeth preparations at most. A diamond bur should not be used for teeth preparation after try-in procedures of metal or zirconia substructures.

Metal-ceramic bond strength between a feldspathic porcelain and a Co-Cr alloy fabricated with Direct Metal Laser Sintering technique

PURPOSE: The aim of the present study was to record the metal-ceramic bond strength of a feldspathic dental porcelain and a Co-Cr alloy, using the Direct Metal Laser Sintering technique (DMLS) for the fabrication of metal substrates. MATERIALS AND METHODS: Ten metal substrates were fabricated with powder of a dental Co-Cr alloy using DMLS technique (test group) in dimensions according to ISO 9693. Another ten substrates were fabricated with a casing dental Co-Cr alloy using classic casting technique (control group) for comparison. Another three substrates were fabricated using each technique to record the Modulus of Elasticity (E) of the used alloys. All substrates were examined to record external and internal porosity. Feldspathic porcelain was applied on the substrates. Specimens were tested using the three-point bending test. The failure mode was determined using optical and scanning electron microscopy. The statistical analysis was performed using t-test. RESULTS: Substrates prepared using DMLS technique did not show internal porosity as compared to those produced using the casting technique. The E of control and test group was 222 ± 5.13 GPa and 227 ± 3 GPa, respectively. The bond strength was 51.87 ± 7.50 MPa for test group and 54.60 ± 6.20 MPa for control group. No statistically significant differences between the two groups were recorded. The mode of failure was mainly cohesive for all specimens. CONCLUSION: Specimens produced by the DMLS technique cover the lowest acceptable metal-ceramic bond strength of 25 MPa specified in ISO 9693 and present satisfactory bond strength for clinical use.

Clinical effects of full crown prosthesis on anterior teeth / 中华医学美学美容杂志

Objective To evaluate the clinical effects of anterior teeth repair of three different restorations made of Co-Cr alloy,Ag-Pd alloy and all-ceramic crowns.Methods 90 cases who needed the both maxillary and mandibular anterior teeth restarations were selected and treated respectively with Co-Cr alloy porcelain fused to metal crowns (PFM)(60 teeth),Ag-Pd alloy PFM (46 teeth)and IPS e.max Press Porcelain full crown (38 teeth).Gingival index was observed before restoration and in 6 and 12 months after restoration.Meanwhile,clinical indicators of two restorations were evaluated as cervical margin's coloration,margin fitness degree,color of restorations,fracture of restorations and contour of restorations,etc.Results The healthy condition of gingiva in groups of Ag-Pd alloy PFM and IPS e.max Press Porcelain full crown were superior to the group of Co-Cr alloy PFM (P＜0.05).There was no cervical margin's coloration in groug of all-ceramic PFM.The color and contour of this group was superior to the group of Co-Cr alloy PFM (P ＜0.05).The significant difference between group of Co Cr alloy and group of Ag-Pd alloy was cervical margin's coloration and marginal density of the restoration (P＜0.05).Conclusions The clinical effects of both groups of Ag-Pd alloy PFM and IPS e.max Press Porcelain full crown is superior to the group of Co-Cr alloy PFM.The IPS e.max Press Porcelain full crown group works best.

Comparison of the bond strength of ceramics to Co-Cr alloys made by casting and selective laser melting

PURPOSE: Considering the importance of metal-ceramic bond, the present study aimed to compare the bond strength of ceramics to cobalt-chrome (Co-Cr) alloys made by casting and selective laser melting (SLM). MATERIALS AND METHODS: In this in-vitro experimental study, two sample groups were prepared, with one group comprising of 10 Co-Cr metal frameworks fabricated by SLM method and the other of 10 Co-Cr metal frameworks fabricated by lost wax cast method with the dimensions of 0.5 × 3 × 25 mm (following ISO standard 9693). Porcelain with the thickness of 1.1 mm was applied on a 3 × 8-mm central rectangular area of each sample. Afterwards, bond strengths of the samples were assessed with a Universal Testing Machine. Statistical analysis was performed with Kolmogorov-Smirnov test and T-test. RESULTS: Bond strength in the conventionally cast group equaled 74.94 ± 16.06 MPa, while in SLM group, it equaled 69.02 ± 5.77 MPa. The difference was not statistically significant (P ≤ .05). CONCLUSION: The results indicated that the bond strengths between ceramic and Co-Cr alloys made by casting and SLM methods were not statistically different.

Efeito da soldagem híbrida (plasma + maçarico) na suavização da assinatura torque-ângulo em supraestruturas de COCR sobre minipilares de zircônia ­ parte 1 / Effect of hybrid soldering (plasma + gas torch) technique on suavization of torque-angle signatures at Co-Cr frameworks over zirconia mini-abutmets ­ part I

Objetivo: avaliar as desadaptações em supraestruturas de implantes e a curva de assinatura torque-ângulo dos parafusos protéticos nas condições monobloco e pós-soldagem. Material e métodos: uma base retangular de aço inox recebeu três implantes de hexágono externo (4,1 mm x 10 mm), onde foram parafusados minipilares de zircônia. Após o enceramento e inclusão, as supraestruturas foram fundidas em monobloco com uma liga de cobalto-cromo, e os cilindros foram numerados sequencialmente (1, 2 e 3). A leitura na interface supraestrutura/pilar foi realizada com um microscópio comparador (precisão de 1 µm), três vezes em cada cilindro. A tensão de torque nos parafusos foi medida com um torquímetro eletrônico odontológico (OsseoCare, Nobel Biocare). Depois, as supraestruturas foram seccionadas e soldadas a plasma (pontos de estabilização) e maçarico (preenchimento da área restante). Novamente, as desadaptações e assinaturas dos parafusos foram avaliadas pela mesma metodologia. Resultados: as médias de desadaptações foram maiores nas supraestruturas em monobloco (C1=3,5 µm; C2=0 µm; C3=31,2 µm) do que nas supraestruturas pós-soldagem (C1=3,0 µm; C2=2,9 µm; C3=18,1 µm). Dentro de cada condição, o teste de Kruskal-Wallis mostrou diferença estatisticamente significativa apenas para o cilindro 3 (monobloco: p < 0,00003 / pós-soldagem: p=0,008) em relação aos cilindros 1 e 2. Uma diferença estatisticamente significante foi encontrada apenas no C3, comparando as condições monobloco e pós-soldagem (teste t pareado, p=0,03). A assinatura dos parafusos se mostrou melhor na condição pós-soldagem. Conclusão: a fundição monobloco gera instabilidade na assinatura dos parafusos. A desadaptação nos parafusos protéticos de supraestruturas sobre minipilares de zircônia melhora após secção e soldagem híbrida.

Objective: to evaluate the misfi t at implant frameworks and the torque-angle signature curves at the prosthetic screws at one-piece and after soldering conditions. Material and methods: a stainless steel rectangular base received 3 external hex implants (4.1 x 10 mm) where zirconia mini-abutments were fastened. After wax-up and investing, the frameworks were one-piece cast with a Co-Cr alloy, and the prosthetic cylinders sequentially identified (1, 2, and 3). The misfit at the framework/abutment interface was measured with a microscope (reading error 1 µm) 3 times for each cylinder. The screw tension was investigated with an electronic torqued device (Osseocare, Nobel Biocare). After, the frameworks were sectioned and soldered with plasma (stabilization points) and gas torch (filling of the remaining areas). Again, the misfit and torque-angle signatures were measured as described. Results: mean misfit values were greater for one-piece castings (C1=3.5 µm; C2=0 µm; C3=31.2 µm) than after soldering (C1=3.0 µm; C2=2.9 µm; C3=18.1 µm). Within each condition, the Kruskal-Wallis test demonstrated a statistically significant difference only for C3 (one-piece casting: p < 0.00003 / after soldering: p=0.008) compared to C1 and C2. Between each condition, a significant difference was seen only for C3 in the one-piece and after soldering conditions (paired t test, p=0.03). The torque-angle signatures demonstrated a better behavior after soldering. Conclusion: one-piece castings provide instability at torque-angle signatures. Thus, the seating of the prosthetic abutments over the zirconia mini-abutments improves after sectioning and hybrid soldering.

An experimental study on the fit of Co-Cr basal crowns fabricated by different technology / 实用口腔医学杂志

Objective:To compare the fit of Co-Cr basal crowns fabricated by three kinds of technology. Methods:18 laser cured resin dies were divided into A, B and C groups(n=6) randomly. Co-Cr basal crowns of group A, B and C were made by traditional casting technology, CAD/CAM cutting metal technology and direct metal laser sintering technology( DMLS) respectively. The crowns were cemented to the corresponding dies and the basal crowns and dies were embedded in methyl acrylic. The thickness of the cement layer of the samples was measured under a stero microscope. Data were analyzed with SPSS13. 0 statistical software. Results:Marginal gap of group A, B and C was (66.08 ±3.90) μm, (29.21 ±3.31) μm and (24.96 ±2.99) μm respectively(P0. 05). Conclusion:DMLS technology may make the best marginal fit, CAD/CAM and DMLS technology may pro-duce better internal fit. The marginal fit and the internal fit of the crowns prepared by the 3 methods can meet the clinical requirements.

The effect of Zirconium Nitride coating on shear bond strength with denture base resin in Co-Cr alloy and titanium alloy

PURPOSE: The purpose of this study was to evaluate of Zirconium Nitride (ZrN) coating on shear bond strength with denture base resin in Co-Cr and Ti-6Al-4V alloy. MATERIALS AND METHODS: Co-Cr and Ti-6Al-4V alloy disks (10 mm in diameter, 2.5 mm in thickness; each other: n = 14) were prepared and divided with 2 groups each other by ZrN coating. After primer was applied to disks surface, denture base resin with diameter 6 mm, height 5 mm was bonded on metal disk surface. After surface roughness was measured by Profiler, shear bond strength was determined with Universal testing machine and analyzed with two-way ANOVA. The specimen surfaces and failure mode were examined using a scanning electron microscope. RESULTS: ZrN coated groups showed significantly higher rough surface than non-coated groups (P < 0.05). Irrespective of alloy materials, shear bond strength of ZrN coated groups were lower than non-coated groups (P < 0.001). The scanning electron microscope (SEM) of ZrN coated groups showed mixed and adhesive fractures. CONCLUSION: ZrN coating weakened bonding strength between denture base resin and Co-Cr, Ti-6Al-4V alloy.

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.

The study of cytocompatibility of Co-Cr alloy and Ti alloy / 天津医药

Objective To investigate the cytocompatibility of the liching liquids of Co-Cr alloy and Ti alloy on human gingival fibroblasts (HGF). Methods The HGF were treated in vitro with leaching liquids of Co-Cr alloy and Ti alloy, respectively. The DMEM cell medium containing 10% fetal bovine serum was served as a negative control. The viability of HGF treated by two dental alloys were evaluated by means of MTT, and the contents of intracellular reduced glutathione (rGSH) were assayed by kits. The tumor necrosis factor-α(TNF-α) contents were determined in the culture supernatant by ELISA in two groups. The effects of these alloys on the expression of caspase-3 were examined by real time-PCR method. Results Compared with the control group, HGF treated with Co-Cr alloy leaching liquids showed a lower viability ( P ＜0.05), while Ti alloy leaching liquid promoted the proliferation of HGF. In Co-Cr alloy group, the rGSH content was significantly decreased (P＜0.05), while TNF-α content was significantly increased (P＜0.05) compared with control group. There were no significant differences in rGSH and TNF-α contents between the Ti alloy group and control group (P＞0.05). The expression of caspase-3 was significantly higher in Co-Cr alloy group than that of control group (P＜0.05), while there was no significant difference in the expression of caspase-3 between Ti alloy group and control group. Conclusion Results suggest that Co-Cr alloy possesses cytotoxicity, while there is better cell compatibility for Ti alloy.

Comparative study on the compressive strength of porcelain crown with different base materials / 实用口腔医学杂志

Objective:To compare the compressive strength of porcelain crown with Co-Cr,CAD/CAMpure titanium and CAD/CAM zirconia respectively.Methods:Metal models of simulating crown core of the ideal premolar were manufactured,digital data of the met-al model were obtained by CAD/CAMsystem,the basement crowns of Co-Cr,CAD/CAMpure titanium and CAD/CAMzirconia were respectively made(n =5),size of each crown was kept the same and the spcimens were set as group A,B and C respectively.Then masking porcelain and body porcelain were fired on basement crowns according to the instructions.The thickness of the porcelain was kept the same.All of the porcelain crowns were located on the Instron testing machine,the compression strength force values were measured.Data were statistically analysed by SPSS 1 3.0 software.The bonding surface of basement material and porcelain was observed by SEMafter compressive failure.Results:The compressive strength(N)of group A,B and C was 2 990 ±1 88,2 305 ±1 57,2 1 50 ± 1 31 ,A vs B or C,P 0.05.Conclusion:All the 3 base materials with porcelain crown satisfy the clinical require-ments.The compressive strength of Co-Cr porcelain crown is stronger than that of CAD/CAMpure titanium porcelain crown and CAD/CAMzirconia porcelain crown.

Evaluation and comparison of the marginal adaptation of two different substructure materials

PURPOSE: In this study, we aimed to evaluate the amount of marginal gap with two different substructure materials using identical margin preparations. MATERIALS AND METHODS: Twenty stainless steel models with a chamfer were prepared with a CNC device. Marginal gap measurements of the galvano copings on these stainless steel models and Co-Cr copings obtained by a laser-sintering method were made with a stereomicroscope device before and after the cementation process and surface properties were evaluated by scanning electron microscopy (SEM). A dependent t-test was used to compare the mean of the two groups for normally distributed data, and two-way variance analysis was used for more than two data sets. Pearson's correlation analysis was also performed to assess relationships between variables. RESULTS: According to the results obtained, the marginal gap in the galvano copings before cementation was measured as, on average, 24.47 +/- 5.82 microm before and 35.11 +/- 6.52 microm after cementation; in the laser-sintered Co-Cr structure, it was, on average, 60.45 +/- 8.87 microm before and 69.33 +/- 9.03 microm after cementation. A highly significant difference (P<.001) was found in marginal gap measurements of galvano copings and a significant difference (P<.05) was found in marginal gap measurements of the laser-sintered Co-Cr copings. According to the SEM examination, surface properties of laser sintered Co-Cr copings showed rougher structure than galvano copings. The galvano copings showed a very smooth surface. CONCLUSION: Marginal gaps values of both groups before and after cementation were within the clinically acceptable level. The smallest marginal gaps occurred with the use of galvano copings.

Mechanical and interfacial characterization of laser welded Co-Cr alloy with different joint configurations

PURPOSE: The mechanical and interfacial characterization of laser welded Co-Cr alloy with two different joint designs. MATERIALS AND METHODS: Dumbbell cast specimens (n=30) were divided into 3 groups (R, I, K, n=10). Group R consisted of intact specimens, group I of specimens sectioned with a straight cut, and group K of specimens with a 45degrees bevel made at the one welding edge. The microstructure and the elemental distributions of alloy and welding regions were examined by an SEM/EDX analysis and then specimens were loaded in tension up to fracture. The tensile strength (TS) and elongation (epsilon) were determined and statistically compared among groups employing 1-way ANOVA, SNK multiple comparison test (alpha=.05) and Weibull analysis where Weibull modulus m and characteristic strength sigmaomicron were identified. Fractured surfaces were imaged by a SEM. RESULTS: SEM/EDX analysis showed that cast alloy consists of two phases with differences in mean atomic number contrast, while no mean atomic number was identified for welded regions. EDX analysis revealed an increased Cr and Mo content at the alloy-joint interface. All mechanical properties of group I (TS, epsilon, m and sigmaomicron) were found inferior to R while group K showed intermediated values without significant differences to R and I, apart from elongation with group R. The fractured surfaces of all groups showed extensive dendritic pattern although with a finer structure in the case of welded groups. CONCLUSION: The K shape joint configuration should be preferred over the I, as it demonstrates improved mechanical strength and survival probability.

Effect of chloride ion on corrosion of two commonly used dental alloys / 中南大学学报(医学版)

Objective: To investigate the effect of chloride concentration on the corrosion of Co-Cr alloy and pure Ti in a simulated oral environment. Methods: The electrochemical corrosion tests of pure Ti and Co-Cr alloy were carried out in neutral artiifcial saliva solutions with different NaCl concentrations (0.9%, 2.0%, and 3.0%). hTe morphologies of corroded surface for pure Ti and Co-Cr alloy were observed by scanning electron microscope (SEM). Results: hTe changes in the self-corrosion potentials (Ecorr) for pure Ti and Co-Cr alloy in three kinds of artificial saliva solutions was not obvious. However, the self-corrosion current densities (Icorr) of pure Ti were much lower than those of Co-Cr. TheIcorr of Co-Cr alloy increased in a concentration-dependent manner of NaCl, whereas the breakdown potential (Eb) of Co-Cr alloy decreased in a concentration-dependent manner. hTe potential ranged for the breakdown of oxide film (Ev) was shortened in a concentration-dependent manner of NaCl. There was no obviousdifference in theIcorr of pure Ti with different concentrations of NaCl. hTe breakdown potential was not seen according to the polarization curves. Conclusion: In a certain range, the increase of the concentration of Cl- leads to accelerate the corrosion behavior of Co-Cr alloy, but it does not affect pure Ti.

Evaluation of shear bond strength of repair acrylic resin to Co-Cr alloy

PURPOSE: The purpose of this study was to investigate the impact of different surface treatment methods and thermal ageing on the bond strength of autopolymerizing acrylic resin to Co-Cr. MATERIALS AND METHODS: Co-Cr alloy specimens were divided into five groups according to the surface conditioning methods. C: No treatment; SP: flamed with the Silano-Pen device; K: airborne particle abrasion with Al2O3; Co: airborne particle abrasion with silica-coated Al2O3; KSP: flamed with the Silano-Pen device after the group K experimental protocol. Then, autopolymerized acrylic resin was applied to the treated specimen surfaces. All the groups were divided into two subgroups with the thermal cycle and water storage to determine the durability of the bond. The bond strength test was applied in an universal test machine and treated Co-Cr alloys were analyzed by scanning electron microscope (SEM). Two-way analysis of variance (ANOVA) was used to determine the significant differences among surface treatments and thermocycling. Their interactons were followed by a multiple comparison' test performed uing a post hoc Tukey HSD test (alpha=0.05). RESULTS: Surface treatments significantly increased repair strengths of repair resin to Co-Cr alloy. The repair strengths of Group K, and Co significantly decreased after 6,000 cycles (P<.001). CONCLUSION: Thermocycling lead to a significant decrease in shear bond strength for air abrasion with silica-coated aluminum oxide particles. On the contrary, flaming with Silano-Pen did not cause a significant reduction in adhesion after thermocycling.

Comparison of the mechanical properties and microstructures of fractured surface for Co-Cr alloy fabricated by conventional cast, 3-D printing laser-sintered and CAD/CAM milled techniques / 대한치과보철학회지

PURPOSE: The purpose of present study is to compare mechanical properties and microstructural characteristics of fractured surface for cast, 3-D printing laser sintered and CAD/CAM milled cobalt-chromium (Co-Cr) alloy specimens and to investigate whether laser sintered technique is adequate for dental applications. MATERIALS AND METHODS: Thirty six flat disc shape Co-Cr alloy specimens were fabricated for surface hardness test and divided into three groups according to the manufacturing methods; 12 specimens for casting (n=12), 12 specimens for laser sintered technology (n=12) and 12 specimens for milled technology (n=12). Twelve dumbbell shape specimens for each group were also fabricated for a tensile test. Statistical comparisons of the mechanical properties for the alloys were performed by Kruskal-Wallis test followed by Mann-Whitney and Bonferroni test. The microstructural characteristics of fractured surfaces were examined using SEM. RESULTS: There were significant differences in the mean Vickers hardness values between all groups and the cast specimen showed the highest (455.88 Hv) while the CAD/CAM milled specimen showed the lowest (243.40 Hv). Significant differences were found among the three groups for ultimate tensile strength, 0.2% yield stress, elongation, and elastic modulus. The highest ultimate tensile strength value (1442.94 MPa) was shown in the milled group and the highest 0.2% yield strength (1136.15 MPa) was shown in the laser sintered group. CONCLUSION: Different manufacturing methods influence the mechanical properties and microstructure of the fractured surfaces in Co-Cr alloys. The cast Co-Cr alloy specimens showed the highest Vickers hardness, and the CAD/CAM milled specimens revealed the highest tensile strength value. All alloys represent adequate mechanical properties satisfying the ISO standards of dental alloy.

Physico-mechanical properties and prosthodontic applications of Co-Cr dental alloys: a review of the literature

Cobalt-Chromium (Co-Cr) alloys are classified as predominantly base-metal alloys and are widely known for their biomedical applications in the orthopedic and dental fields. In dentistry, Co-Cr alloys are commonly used for the fabrication of metallic frameworks of removable partial dentures and recently have been used as metallic substructures for the fabrication of porcelain-fused-to-metal restorations and implant frameworks. The increased worldwide interest in utilizing Co-Cr alloys for dental applications is related to their low cost and adequate physico-mechanical properties. Additionally, among base-metal alloys, Co-Cr alloys are used more frequently in many countries to replace Nickel-Chromium (Ni-Cr) alloys. This is mainly due to the increased concern regarding the toxic effects of Ni on the human body when alloys containing Ni are exposed to the oral cavity. This review article describes dental applications, metallurgical characterization, and physico-mechanical properties of Co-Cr alloys and also addresses their clinical and laboratory behavior in relation to those properties.

The Tribological and Lubrication Responses of a Cobalt-Chromium Femoral Head in Total Hip Arthroplasty

PURPOSE: This study aimed at investigating the role of albumin as a boundary lubricant in the lubrication of the Co-Cr femoral head of artificial hip implants by measuring the tribological parameters of the Co-Cr femoral head with Atomic Force Microscope (AFM) techniques. MATERIALS AND METHODS: Samples were prepared from the main wear region of a Co-Cr femoral head from revision hip surgery. Two types of solutions were prepared as lubricants: PBS (Phosphate Buffered Saline) as a control solution and BSA (Bovine Serum Albumin) as a lubricant at concentrations of 10, 20, 30 and 40 mg/ml in PBS solution. RESULTS: There were statistically significant differences in the frictional coefficients (micron) of a Co-Cr head between the PBS control and all the concentrations of BSA (10, 20, 30, 40 mg/ml) (P<0.001). Similarly, there were statistically significant differences for the micron between the BSA concentrations of 10, 20, 30 and 40 mg/m for all the cases except between the BSA of 30 and 40 mg/ml (P<0.01). CONCLUSION: There exists a maximum protein concentration of BSA to play a role as an effective boundary lubricant through adsorption on the surface of Co-Cr femoral head.