| 1. |
- Adnan, Safdar, et al.
(författare)
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Effect of process parameters settings and thickness on surface roughness of EBM produced Ti-6Al-4V
- 2012
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Ingår i: Rapid prototyping journal. - : Emerald Group Publishing Limited. - 1355-2546 .- 1758-7670. ; 18:5, s. 401-408
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Tidskriftsartikel (refereegranskat)abstract
- Purpose – Ti-6Al-4V is one of the most attractive materials being used in aerospace, automotive and medical implant industries. Electron beam melting (EBM) is one of the direct digital manufacturing methods to produce complex geometries of fully dense and near net shape parts. The EBM system provides an opportunity to built metallic objects with different processing parameter settings like beam current, scan speed, probe size on powder, etc. The purpose of this paper is to determine and understand the effect of part's thickness and variation in process parameter settings of the EBM system on surface roughness/topography of EBM fabricated Ti-6Al-4V metallic parts. Design/methodology/approach – A mathematical model based upon response surface methodology (RSM) is developed to study the variation of surface roughness with changing process parameter settings. Surface roughness of the test slabs produced with different parameter settings and thickness has been studied under confocal microscope. Response surface methodology was used to develop a multiple regression model to correlate the effect of variation in EBM process parameters settings and thickness of parts on surface roughness of EBM produced Ti-6Al-4V. Findings – It has been observed that every part produced by EBM system has detectable surface roughness. The surface roughness parameter Ra varies between 1-20 µm for different samples depending upon the process parameter setting and thickness. The Ra value increases with increasing sample thickness and beam current, and decreases with increase in offset focus and scan speed. Originality/value – Surface roughness is related to wear and friction property of the material and hence is related to the life time and performance of the part. Surface roughness is an important property of any material to be considered as biomaterial. The surface roughness of the material depends upon the manufacturing method and environment and hence it is controllable either during fabrication or by post processing. From the 1st order regression model developed in this study, it is also evident that sample thickness, scan speed and beam current have relatively more effect on roughness value then the offset focus. With the model obtained equation, a designer can subsequently select the best combination of sample thickness and process parameter values to achieve desired surface roughness.
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| 2. |
- Chávez de Paz, Luis E.
(författare)
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Development of a Multispecies Biofilm Community by Four Root Canal Bacteria
- 2012
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Ingår i: Journal of Endodontics. - : Elsevier. - 0099-2399 .- 1878-3554. ; 38:3, s. 318-323
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Tidskriftsartikel (refereegranskat)abstract
- The development of multispecies biofilm models are needed to explain the interactions that take place in root canal biofilms during apical periodontitis. The aim of this study was to investigate the ability of 4 root canal bacteria to establish a multispecies biofilm community and to characterize the main structural, compositional, and physiological features of this community. Methods Four clinical isolates isolated from infected root canals, Actinomyces naeslundii, Lactobacillus salivarius, Streptococcus gordonii, and Enterococcus faecalis, were grown together in a miniflow cell system. Simultaneous detection of the 4 species in the biofilm communities was achieved by fluorescence in situ hybridization in combination with confocal microscopy at different time points. The LIVE/DEAD BacLight technique (Molecular Probes, Carlsbad, CA) was used to assess cell viability and to calculate 3-dimensional architectural parameters such as biovolume (μm3). Redox fluorescence dye 5-cyano-2,3-ditolyl tetrazolium chloride was used to assess the metabolic activity of biofilm bacteria. Results The 4 species tested were able to form stable and reproducible biofilm communities. The biofilms formed in rich medium generally showed continuous growth over time, however, in the absence of glucose biofilms showed significantly smaller biovolumes. A high proportion of viable cells (>90%) were generally observed, and biofilm growth was correlated with high metabolic activity of cells. The community structure of biofilms formed in rich medium did not change considerably over the 120-hour period, during which E. faecalis, L. salivarius, and S. gordonii were most abundant. Conclusions The ability of 4 root canal bacteria to form multispecies biofilm communities shown in this study give insights into assessing the community lifestyle of these microorganisms in vivo. This multispecies model could be useful for further research simulating stresses representative of in vivo conditions.
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| 3. |
- Chavez de Paz, Luis E., et al.
(författare)
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Role of (p)ppGpp in Biofilm Formation by Enterococcus faecalis
- 2012
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Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 78:5, s. 1627-1630
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Tidskriftsartikel (refereegranskat)abstract
- Enterococcus faecalis strain OG1RF and its (p)ppGpp-deficient ΔrelA, ΔrelQ, and ΔrelA ΔrelQ mutants were grown in biofilms and evaluated for growth profiles, biofilm morphology, cell viability, and proteolytic activity. E. faecalis lacking (p)ppGpp had a diminished capacity to sustain biofilm formation over an extended period of time and expressed abundant proteolytic activity.
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| 4. |
- Chavez de Paz, Luis E., et al.
(författare)
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Strains of Enterococcus faecalis differ in their ability to coexist in biofilms with other root canal bacteria
- 2015
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Ingår i: International Endodontic Journal. - : Wiley. - 0143-2885 .- 1365-2591. ; 48:10, s. 916-925
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Tidskriftsartikel (refereegranskat)abstract
- AimTo investigate the relationship between protease production and the ability of Enterococcus faecalis strains to coexist in biofilms with other bacteria commonly recovered from infected root canals. MethodologyBiofilms with bacteria in mono-, dual- and four-species communities were developed in flow chambers. The organisms used were Lactobacillus salivarius, Streptococcus gordonii and Actinomyces naeslundii and E.faecalis strains, GUL1 and OG1RF. Biovolume and species distribution were examined using 16S rRNA fluorescence insitu hybridization in combination with confocal microscopy and image analysis. The full proteome of the E.faecalis strains was studied using two-dimensional gel electrophoresis. Spots of interest were identified using tandem mass spectroscopy and quantified using Delta 2D software. ResultsAll bacteria formed biofilms and an anova analysis revealed that the biofilm biomass increased significantly (P0.01) between 6 and 24h. L.salivarius, S.gordonii and A.naeslundii formed mutualistic biofilm communities, and this pattern was unchanged when E.faecalis GUL1 was included in the consortium. However, with OG1RF, L.salivarius and S.gordonii were outcompeted in a 24-h biofilm. Proteomic analysis revealed that OG1RF secreted higher levels of proteases, GelE (P=0.02) and SprE (P=0.002) and a previously unidentified serine protease (P=0.05), than GUL1. ConclusionsDifferent strains of E.faecalis can interact synergistically or antagonistically with a consortium of root canal bacteria. A possible mechanism underlying this, as well as potential differences in virulence, is production of different levels of proteases, which can cause detachment of neighbouring bacteria and tissue damage.
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| 5. |
- Dorkhan, Marjan, et al.
(författare)
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coating on adherence of Streptococcus oralis strains to titanium
- 2012
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Ingår i: Microbiology. - : Microbiology Society. - 1465-2080 .- 1350-0872. ; 158:2, s. 390-397
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Tidskriftsartikel (refereegranskat)abstract
- The use of dental implants to treat tooth loss has increased rapidly over recent years. 'Smooth' implants showing high long-term success rates have successively been replaced by implants with rougher surfaces, designed to stimulate rapid osseointegration and promote tissue healing. If exposed in the oral cavity, rougher surfaces may promote bacterial adhesion leading to formation of microbial biofilms which can induce pen-implant inflammation. Streptococcus oralis is an early colonizer of oral surfaces and has been recovered from titanium surfaces in vivo. The purpose of this study was to examine the adherence of clinical strains of S. oralis to titanium with smooth or moderately rough surface topography and to determine the effect of a saliva- or serum-derived coating on this process. Adherence was studied using a flow-cell system with confocal laser scanning microscopy, while putative adhesins were analysed using proteomics of bacterial cell wall proteins. This showed that adherence to moderately rough surfaces was greater than to smooth surfaces. Serum did not promote binding of any of the studied S. oralis strains to titanium, whereas a saliva coating increased adherence in two of three strains tested. The higher level of adherence to the moderately rough surfaces was maintained even in the presence of a saliva coating. The S. oralis strains that bound to saliva expressed an LPXTG-linked protein which was not present in the non-adherent strain. Thus strains of S. oralis differ in their capacity to bind to saliva-coated titanium and we propose that this is due to differential expression of a novel adhesin.
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| 6. |
- Dorkhan, Marjan, et al.
(författare)
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Effects of saliva or serum coating on adherence of Streptococcus oralis strains to titanium
- 2012
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Ingår i: Microbiology. - : Society for General Microbiology. - 1350-0872 .- 1465-2080. ; 158:2, s. 390-397
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Tidskriftsartikel (refereegranskat)abstract
- The use of dental implants to treat tooth loss has increased rapidly over recent years. 'Smooth' implants showing high long-term success rates have successively been replaced by implants with rougher surfaces, designed to stimulate rapid osseointegration and promote tissue healing. If exposed in the oral cavity, rougher surfaces may promote bacterial adhesion leading to formation of microbial biofilms which can induce peri-implant inflammation. Streptococcus oralis is an early colonizer of oral surfaces and has been recovered from titanium surfaces in vivo. The purpose of this study was to examine the adherence of clinical strains of S. oralis to titanium with smooth or moderately rough surface topography and to determine the effect of a saliva- or serum-derived coating on this process. Adherence was studied using a flow-cell system with confocal laser scanning microscopy, while putative adhesins were analysed using proteomics of bacterial cell wall proteins. This showed that adherence to moderately rough was greater than to smooth surfaces. Serum did not promote binding of any studied S. oralis strains to titanium whereas a saliva-coating increased adherence in two of three strains tested. The high level of adherence to the moderately rough surfaces was maintained even in the presence of a saliva coating. The S. oralis strains that bound to saliva expressed an LPXTG-linked protein which was not present in the non-adherent strain. Thus strains of S. oralis differ in their capacity to bind to saliva-coated titanium and we propose that this is due to differential expression of a novel adhesin.
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| 7. |
- Jaramillo, David E., et al.
(författare)
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Decreased Bacterial Adherence and Biofilm Growth on Surfaces Coated with a Solution of Benzalkonium Chloride
- 2012
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Ingår i: Journal of Endodontics. - : Elsevier. - 0099-2399 .- 1878-3554. ; 38:6, s. 821-825
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Tidskriftsartikel (refereegranskat)abstract
- Introduction Secondary biofilm formation by oral bacteria after breakdown/fracture of temporary or permanent restorations imposes a challenge to the outcome of root canal treatment. This study focuses on benzalkonium chloride (BAK) coating on dentin or polystyrene surfaces and its influence on the early adhesion and biofilm formation by oral and root canal bacteria. Methods Microbial adhesion and biofilm growth on surfaces coated with BAK were analyzed qualitatively with a dentin disk model and quantitatively with a mini-flow cell biofilm model. Cell viability and total biovolume were analyzed by the LIVE/DEAD technique. The repelling effect of surfaces coated with BAK was compared with NaOCl. Uncoated surfaces were used as controls. Results Scanning electron microscope images in the dentin disk model revealed that very sparse biofilms were formed on NaOCl- and BAK-coated dentin surfaces. In contrast, biofilms formed on uncoated dentin were clearly visible as numerous irregularly distributed aggregates of rods and cocci. In the mini-flow cell system, confocal laser scanning microscope analysis confirmed that biofilms formed on NaOCl- and BAK-coated surfaces showed significantly less adhesion (2 hours) and biovolume accumulation (24 and 96 hours) compared with the uncoated controls (P < .01). Furthermore, cell viability assessments showed that on uncoated controls the viability measurements were high (>89%) as well as on BAK-coated surfaces (88% viable cells). However, cell viability was significantly reduced on NaOCl-coated surfaces (59% viable cells). Conclusions This study illustrates that surface coating with a surfactant solution containing BAK does not cause cell membrane damage but might interfere with cell mechanisms of adhesion. Investigations into the clinical utility of BAK as an antibiofilm medication are warranted.
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| 8. |
- Kinnby, Bertil, et al.
(författare)
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Plasminogen coating increases initial adhesion of oral bacteria in vitro
- 2016
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Ingår i: Microbial Pathogenesis. - : Elsevier. - 0882-4010 .- 1096-1208. ; 100, s. 10-16
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Tidskriftsartikel (refereegranskat)abstract
- Plasminogen is a major plasma protein and the zymogen of the broad spectrum protease plasmin. Plasmin activity leads to tissue degradation, direct and through activation of metalloproteinases. Infected tooth root canals, as a consequence of the inflammatory response and eventual necrosis, contain tissue fluid and blood components. These will coat the root canal walls and act as conditioning films that allow bacterial biofilms to grow and be a potential source of hematogenously spreading bacteria. We investigated the effect of in vitro surface conditioning with human plasminogen on the initial adhesion of bacteria. Four bacterial species, L. salivarius, E. faecalis, A. naeslundii, and S. gordonii, isolated from dental root canals, and three other oral streptococci, S. oralis, S. anginosus, and S. sanguinis, were grown in albumin- or plasminogen-coated flow chambers and studied by confocal laser scanning microscopy using the cell viability staining LIVE/DEAD and 16S rRNA fluorescence in situ hybridization (FISH). A. naeslundii, L. salivarius and in particular S. gordonii showed a higher initial adhesion to the plasminogen-coated surfaces. E. faecalis did not show any preference for plasminogen. Four-species biofilms cultured for 96 h showed that streptococci increased their proportion with time. Further experiments aimed at studying different streptococcal strains. All these adhered more to plasminogen-coated surfaces than to albumin-coated control surfaces. The specificity of the binding to plasminogen was verified by blocking lysine-binding sites with epsilon-aminocaproic acid. Plasminogen is thus an important plasma component for the initial adhesion of oral bacteria, in particular streptococci. This binding may contribute to their spread locally as well as to distant organs or tissues.
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