Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 4 de 4
Más filtros

Base de datos
Intervalo de año de publicación
Int J Comput Dent ; 23(3): 245-255, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-32789312


AIM: The aim of the present study was to evaluate the number, strength, and position of occlusal contacts shown using an intraoral scanner (IOS) and a digital occlusal analysis system (T-Scan) compared with the current gold standard using occlusal foil (OF). MATERIALS AND METHODS: Occlusal contacts were analyzed for 70 volunteers using OF in maximum intercuspation (MI). The contact points obtained using the IOS were evaluated using a screenshot from Zirkonzahn.Modellier CAD software. Finally, the volunteers were asked to bite on the sensor sheet of the T-Scan system. For the evaluation of these data, the contact points of the OF and the IOS were graded as light, medium, and strong. Furthermore, the positions of the contact points were analyzed for the anterior region (premolars and molars). Parametric statistical tests were applied to analyze the differences among the three methods. RESULTS: The mean number of all contact points was similar: 29 ± 8 with the OF, 30 ± 12 with the IOS, and 24 ± 10 with the T-Scan. However, results were different in terms of the grading of the strength of contact points: mean number of light contacts: 8 ± 4 OF vs 17 ± 8 IOS and 17 ± 6 T-Scan; medium contacts: 12 ± 5 OF vs 8 ± 4 IOS and 5 ± 4 T-Scan; and strong contacts: 9 ± 5 OF vs 6 ± 6 IOS and 4 ± 2 T-Scan. The positions of the occlusal contact points were also different. CONCLUSION: The data sets showed that there were differences in the distribution of occlusal contact points evaluated using the OF, the IOS, and the T-Scan system. Although the number of detected occlusal contacts was similar, different occlusal contact protocols were determined by the three different methods.

Oclusión Dental , Diente Molar , Diente Premolar , Humanos , Programas Informáticos
Metab Eng ; 11(3): 178-83, 2009 May.
Artículo en Inglés | MEDLINE | ID: mdl-19558963


The highly productive whole-cell biotransformation of D-fructose to D-mannitol with recombinant, resting cells of Escherichia coli BL21(DE3) requires the combined expression of mdh, fdh and glf which encode mannitol and formate dehydrogenases and a sugar facilitator, respectively. However, long-term stability of the system was restricted, possibly due to loss of the cofactor NAD, high concentrations of formate, formation of CO(2) affecting the internal pH of the cells, accumulation of high intracellular concentrations of D-mannitol, and export of D-mannitol. Downstream of the mdh gene of Leuconostoc pseudomesenteroides, we identified an open reading frame encoding for a putative mannitol permease. The gene was cloned and expressed in E. coli. Biochemical analyses revealed an activity as secondary carrier for D-fructose. Therefore, the carrier was named FupL and participation in D-mannitol transport was excluded. In biotransformation experiments, the productivity of D-mannitol formation obtained with the strain expressing the additional fupL gene was enhanced by 20%.

Proteínas Bacterianas/metabolismo , Dióxido de Carbono/fisiología , Escherichia coli/metabolismo , Leuconostoc/metabolismo , Manitol/metabolismo , Proteínas de Transporte de Membrana/metabolismo , NAD/fisiología , Proteínas Bacterianas/genética , Biotransformación , Escherichia coli/genética , Formiatos/metabolismo , Leuconostoc/genética
J Biotechnol ; 132(4): 438-44, 2007 Dec 01.
Artículo en Inglés | MEDLINE | ID: mdl-17826859


The reduction of methyl acetoacetate was carried out in continuously operated biotransformation processes catalyzed by recombinant Escherichia coli cells expressing an alcohol dehydrogenase from Lactobacillus brevis. Three different cell types were applied as biocatalysts in three different cofactor regeneration approaches. Both processes with enzyme-coupled cofactor regeneration catalyzed by formate dehydrogenase or glucose dehydrogenase are characterized by a rapid deactivation of the biocatalyst. By contrast the processes with substrate-coupled cofactor regeneration by alcohol dehydrogenase catalyzed oxidation of 2-propanol could be run over a period of 7 weeks with exceedingly high substrate and cosubstrate concentrations of up to 2.5 and 2.8 mol L(-1), respectively. Even under these extreme conditions, the applied biocatalyst showed a good stability with only marginal leakage of intracellular cofactors.

Biotransformación , Escherichia coli/metabolismo , Cetonas/metabolismo , Acetoacetatos/metabolismo , Reactores Biológicos , ADN Recombinante , Formiato Deshidrogenasas , Glucosa Deshidrogenasas
Metab Eng ; 8(6): 587-602, 2006 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-16876450


In this study strains of Ralstonia eutropha H16 and Pseudomonas putida KT2440 were engineered which are suitable for biotechnological production of 2-methylcitric acid (2MC). Analysis of a previous mutant of R. eutropha able to accumulate 2MC recommended this strain as a candidate for fermentative production of 2MC. This knowledge was used for construction of strains of R. eutropha H16 and P. putida KT2440 capable of enhanced production of 2MC. In both bacteria the chromosomal genes encoding the 2-methyl-cis-aconitate hydratase (acnM) were disrupted by directed insertion of a copy of an additional 2-methylcitrate synthase gene (prpC) yielding strains R. eutropha DeltaacnM(Re)OmegaKmprpC(Pp) and P. putida DeltaacnM(Pp)OmegaKmprpC(Re). In both strains 2-methylcitrate synthase was expressed under control of the constitutive kanamycin-resistance gene (OmegaKm) resulting in up to 20-fold higher specific 2-methylcitrate synthase activities in comparison to the wild type. The disruption of the acnM gene by insertion of prpC led to a propionate- and levulinate-negative phenotype of the engineered strains, and analysis of supernatant of these strains revealed overproduction and accumulation of 2MC in the medium. A two stage cultivation regime comprising an exponential growth phase and a 2MC production phase was developed and applied to both engineered strains for optimum production of 2MC. Whereas gluconate, fructose or succinate were provided as carbon source for the exponential growth phase, a combination of propionate or levulinate as precursor substrate for provision of propionyl-CoA and succinate or fumarate as precursor substrate for provision of oxaloacetate were used in the production phase to make sure that the 2-methylcitrate synthase was provided with their substrates. Employing the optimised feeding regime P. putida DeltaacnM(Pp)OmegaKmprpC(Re) and R. eutropha DeltaacnM(Re)OmegaKmprpC(Pp) produced 2MC up to maximal concentrations of 7.2 g/L or 26.5 mM and 19.2 g/L or 70.5 mM, respectively, during 144 h of cultivation.

Reactores Biológicos , Vías Biosintéticas , Biotecnología/métodos , Citratos/biosíntesis , Cupriavidus necator/metabolismo , Ingeniería Genética/métodos , Oxo-Ácido-Liasas/genética , Pseudomonas putida/metabolismo , Ácidos Carboxílicos/metabolismo , Cromatografía Líquida de Alta Presión , Medios de Cultivo , Cupriavidus necator/genética , Cartilla de ADN , Fermentación , Cromatografía de Gases y Espectrometría de Masas , Plásmidos/genética , Pseudomonas putida/genética , Análisis de Secuencia de ADN