| 1. |
- Adnan, Safdar, et al.
(author)
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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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In: Rapid prototyping journal. - : Emerald Group Publishing Limited. - 1355-2546 .- 1758-7670. ; 18:5, s. 401-408
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Journal article (peer-reviewed)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.
(author)
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Development of a Multispecies Biofilm Community by Four Root Canal Bacteria
- 2012
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In: Journal of Endodontics. - : Elsevier. - 0099-2399 .- 1878-3554. ; 38:3, s. 318-323
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Journal article (peer-reviewed)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. |
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| 4. |
- Chávez de Paz, Luis Eduardo, et al.
(author)
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Oral bacteria in biofilms exhibit slow reactivation from nutrient deprivation
- 2008
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In: Microbiology. - : Microbiology Society. - 1350-0872 .- 1465-2080. ; 154, s. 1927-1938
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Journal article (peer-reviewed)abstract
- The ability of oral bacteria to enter a non-growing state is believed to be an important mechanism for survival in the starved micro-environments of the oral cavity. In this study, we examined the reactivation of nutrient-deprived cells of two oral bacteria in biofilms, Streptococcus anginosus and Lactobacillus salivarius. Non-growing cells were generated by incubation in 10 mM potassium phosphate buffer for 24 h and the results were compared to those of planktonic cultures. When both types of cells were shifted from a rich, peptone-yeast extract-glucose (PYG) medium to buffer for 24 h, dehydrogenase and esterase activity measured by the fluorescent dyes 5-cyano-2,3-ditolyl-tetrazolium chloride (CTC) and fluorescein diacetate (FDA), respectively, was absent in both species. However, the membranes of the vast majority of nutrient-deprived cells remained intact as assessed by LIVE/DEAD staining. Metabolic reactivation of the nutrient-deprived biofilm cells was not observed for at least 48 h following addition of fresh PYG medium, whereas the non-growing planktonic cultures of the same two strains were in rapid growth in less than 2 h. At 72 h, the S. anginosus biofilm cells had recovered 78 % of the dehydrogenase activity and 61 % of the esterase activity and the biomass mm(-2) had increased by 30-35 %. With L. salivarius at 72 h, the biofilms had recovered 56 % and 75 % of dehydrogenase and esterase activity, respectively. Reactivation of both species in biofilms was enhanced by removal of glucose from PYG, and S. anginosus cells were particularly responsive to yeast extract (YE) medium. The data suggest that the low reactivity of non-growing biofilm cells to the introduction of fresh nutrients may be a survival strategy employed by micro-organisms in the oral cavity.
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| 5. |
- Chávez de Paz, Luis Eduardo
(author)
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Redefining the Persistent Infection in Root Canals : Possible Role of Biofilm Communities
- 2007
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In: Journal of Endodontics. - : Elsevier BV. - 0099-2399 .- 1878-3554. ; 33:6, s. 652-662
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Journal article (peer-reviewed)abstract
- Current concepts suggest that persisting infections subsequent to endodontic therapy are caused by one or two bacterial species that are "too robust" to be eliminated by conventional treatment measures. As a consequence, numerous studies are exploring the characteristics of these "most" resistant organisms to define an effective treatment strategy to eradicate them from root canals. By taking an ecological perspective, the main objective of this review is to present evidence that the nature of persisting endodontic infections depends not on the robustness of the organisms in the infected site, but on their capability of adapting their physiology to the new environmental conditions set by the treatment. Changes in the environment, such as an increase in pH by calcium hydroxide or the effect of antimicrobials, are capable of triggering genetic cascades that modify the physiological characteristics of bacterial cells. Surface adherence by bacteria to form biofilms is a good example of bacterial adaptation and one that is pertinent to endodontic infections. Increasing information is now available on the existence of polymicrobial biofilm communities on root canal walls, coupled with new data showing that the adaptive mechanisms of bacteria in these biofilms are significantly augmented for increased survival. This ecological view on the persisting infection problem in endodontics suggests that the action of individual species in persisting endodontic infections is secondary when compared to the adaptive changes of a polymicrobial biofilm community undergoing physiological and genetic changes in response to changes in the root canal environment.
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| 6. |
- Chávez de Paz, Luis Eduardo, et al.
(author)
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Response to alkaline stress by root canal bacteria in biofilms
- 2007
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In: International Endodontic Journal. - : Wiley. - 0143-2885 .- 1365-2591. ; 40:5, s. 344-355
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Journal article (peer-reviewed)abstract
- To determine whether bacteria isolated from infected root canals survive alkaline shifts better in biofilms than in planktonic cultures. METHODOLOGY: Clinical isolates of Enterococcus faecalis, Lactobacillus paracasei, Olsenella uli, Streptococcus anginosus, S. gordonii, S. oralis and Fusobacterium nucleatum in biofilm and planktonic cultures were stressed at pH 10.5 for 4 h, and cell viability determined using the fluorescent staining LIVE/DEAD BacLight bacterial viability kit. In addition, proteins released into extracellular culture fluids were identified by Western blotting. RESULTS: Enterococcus faecalis, L. paracasei, O. uli and S. gordonii survived in high numbers in both planktonic cultures and in biofilms after alkaline challenge. S. anginosus, S. oralis and F. nucleatum showed increased viability in biofilms compared with planktonic cultures. Alkaline exposure caused all planktonic cultures to aggregate into clusters and resulted in a greater extrusion of cellular proteins compared with cells in biofilms. Increased levels of DnaK, HPr and fructose-1,6-bisphosphate aldolase were observed in culture fluids, especially amongst streptococci. CONCLUSIONS: In general, bacteria isolated from infected roots canals resisted alkaline stress better in biofilms than in planktonic cultures, however, planktonic cells appeared to use aggregation and the extracellular transport of specific proteins as survival mechanisms.
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| 7. |
- Chavez de Paz, Luis E., et al.
(author)
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Role of (p)ppGpp in Biofilm Formation by Enterococcus faecalis
- 2012
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In: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 78:5, s. 1627-1630
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Journal article (peer-reviewed)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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| 8. |
- Chavez de Paz, Luis E., et al.
(author)
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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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In: International Endodontic Journal. - : Wiley. - 0143-2885 .- 1365-2591. ; 48:10, s. 916-925
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Journal article (peer-reviewed)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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| 9. |
- Chávez de Paz, Luis Eduardo, et al.
(author)
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The effects of antimicrobials on endodontic biofilm bacteria
- 2010
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In: Journal of Endodontics. - : Elsevier. - 0099-2399 .- 1878-3554. ; 36:1, s. 70-77
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Journal article (peer-reviewed)abstract
- Introduction In the present study, confocal microscopy, a miniflow cell system, and image analysis were combined to test in situ the effect of antimicrobials and alkali on biofilms of Enterococcus faecalis, Lactobacillus paracasei, Streptococcus anginosus, and Streptococcus gordonii isolated from root canals with persistent infections. Methods Biofilms formed for 24 hours were exposed for 5 minutes to alkali (pH = 12), chlorhexidine digluconate (2.5%), EDTA (50 mmol/L), and sodium hypochlorite (1%). The biofilms were then characterized by using fluorescent markers targeting cell membrane integrity (LIVE/DEAD) and metabolic activity (5-cyano-2,3-ditolyl tetrazolium chloride and fluorescein diacetate). In addition, the biofilm architecture and the extent to which coating of the substrate surface with collagen influenced the resistance pattern to the chemicals were also analyzed. Results NaOCl (1%) affected the membrane integrity of all organisms and removed most biofilm cells. Exposure to EDTA (50 mmol/L) affected the membrane integrity in all organisms but failed to remove more than a few cells in biofilms of E. faecalis, L. paracasei, and S. anginosus. Chlorhexidine (2.5%) had a mild effect on the membrane integrity of E. faecalis and removed only 50% of its biofilm cells The effects were substratum-dependent, and most organisms displayed increased resistance to the antimicrobials on collagen-coated surfaces. Conclusions The biofilm system developed here was sensitive and differences in cell membrane integrity and removal of biofilm cells after exposure to antimicrobials commonly used in endodontics was discernible.
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| 10. |
- Chávez de Paz, Luis, 1974, et al.
(author)
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Gram-positive rods prevailing in teeth with apical periodontitis undergoing root canal treatment.
- 2004
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In: International endodontic journal. - : Wiley. - 0143-2885 .- 1365-2591. ; 37:9, s. 579-87
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Journal article (peer-reviewed)abstract
- AIMS: To identify Gram-positive rods from root canals of teeth with apical periodontitis and to examine their associations with other species. METHODOLOGY: Consecutive root canal samples (RCSs) from 139 teeth undergoing root canal treatment were analyzed prospectively for cultivable microbes. Gram-positive rods in the first RCS submitted after chemo-mechanical preparation were categorised to genus level by selective media and gas-liquid chromatography (GLC), and identified to species level by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Associations between organisms were measured by odds ratios (OR). RESULTS: In the first samples submitted a total of 158 Gram-positive rods, 115 Gram-positive cocci, 26 Gram-negative rods and 9 Gram-negative cocci, were identified. At genus levels Gram-positive rods were classified into: Lactobacillus spp. (38%), Olsenella spp. (18%), Propionibacterium spp. (13%), Actinomyces spp. (12%), Bifidobacterium spp. (13%) and Eubacterium spp. (6%). The most frequent species were Olsenella uli, Lactobacillus paracasei and Propionibacterium propionicum. In subsequent samples taken during treatment, Gram-positive rods were also identified, although the number of strains was considerably reduced. Positive associations were observed between members of the genus lactobacilli and Gram-positive cocci (OR>2). CONCLUSIONS: Olsenella uli and Lactobacillus spp. predominated over other Gram-positive rods. A possible association exists between Lactobacillus spp. and Gram-positive cocci in root canals of teeth with apical periodontitis receiving treatment.
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