Biogas and bio-hydrogen: production and uses. A review

The first part of this essay aims at investigating the already available and promising technologies for the biogas and bio-hydrogen production from anaerobic digestion of different organic substrates. One strives to show all the peculiarities of this complicate process, such as continuity, number of stages, moisture, biomass preservation and rate of feeding. The main outcome of this part is the awareness of the huge amount of reactor configurations, each of which suitable for a few types of substrate and circumstance. Among the most remarkable results, one may consider first of all the wet continuous stirred tank reactors (CSTR), right to face the high waste production rate in urbanised and industrialised areas. Then, there is the up-flow anaerobic sludge blanket reactor (UASB), aimed at the biomass preservation in case of highly heterogeneous feedstock, which can also be treated in a wise co-digestion scheme. On the other hand, smaller and scattered rural realities can be served by either wet low-rate digesters for homogeneous agricultural by-products (e.g. fixed-dome) or the cheap dry batch reactors for lignocellulose waste and energy crops (e.g. hybrid batch-UASB). The biological and technical aspects raised during the first chapters are later supported with bibliographic research on the important and multifarious large-scale applications the products of the anaerobic digestion may have. After the upgrading techniques, particular care was devoted to their importance as biofuels, highlighting a further and more flexible solution consisting in the reforming to syngas. Then, one shows the electricity generation and the associated heat conversion, stressing on the high potential of fuel cells (FC) as electricity converters. Last but not least, both the use as vehicle fuel and the injection into the gas pipes are considered as promising applications. The consideration of the still important issues of the bio-hydrogen management (e.g. storage and delivery) may lead to the conclusion that it would be far more challenging to implement than bio-methane, which can potentially “inherit” the assets of the similar fossil natural gas. Thanks to the gathered knowledge, one devotes a chapter to the energetic and financial study of a hybrid power system supplied by biogas and made of different pieces of equipment (natural gas thermocatalitic unit, molten carbonate fuel cell and combined-cycle gas turbine structure). A parallel analysis on a bio-methane-fed CCGT system is carried out in order to compare the two solutions. Both studies show that the apparent inconvenience of the hybrid system actually emphasises the importance of extending the computations to a broader reality, i.e. the upstream processes for the biofuel production and the environmental/social drawbacks due to fossil-derived emissions. Thanks to this “boundary widening”, one can realise the hidden benefits of the hybrid over the CCGT system.

Clinical and microbiological findings at sites treated with orthodontic fixed appliances in adolescents

INTRODUCTION: Fixed orthodontic appliances can alter the subgingival microbiota. Our aim was to compare the subgingival microbiota and clinical parameters in adolescent subjects at sites of teeth treated with orthodontic bands with margins at (OBM) or below the gingival margin (OBSM), or with brackets (OBR). METHODS: Microbial samples were collected from 33 subjects (ages, 12-18 years) in treatment more than 6 months. The microbiota was assessed by the DNA-DNA checkerboard hybridization method. RESULTS: Bacterial samples were taken from 83 OBR,103 OBSM, and 54 OBM sites. Probing pocket depths differed by orthodontic type (P <0.001) with mean values of 2.9 mm (SD, 0.6) at OBSM sites, 2.5 mm (SD, 0.6) at OBM sites, and 2.3 mm (SD, 0.5) at OBR sites. Only Actinomyces israelii (P <0.001) and Actinomyces naeslundii (P <0.001) had higher levels at OBR sites, whereas Neisseria mucosa had higher levels at sites treated with OBSM or OBM (P <0.001). Aggregatibacter actinomycetemcomitans was found in 25% of sites independent of the appliance. CONCLUSIONS: Different types of orthodontic appliances cause minor differences in the subgingival microbiota (A israelii and A naeslundii) and higher levels at sites treated with orthodontic brackets. More sites with bleeding on probing and deeper pockets were found around orthodontic bands.

Complication and failure rates of fixed dental prostheses in patients treated for periodontal disease

Objectives: To evaluate the biological and technical complication rates of fixed dental prostheses (FDP) with end abutments or cantilever extensions on teeth (FDP-tt/cFDP-tt) on implants (FDP-ii/cFDP-ii) and tooth-implant-supported (FDP-ti/cFDP-ti) in patients treated for chronic periodontitis. Material and methods: From a cohort of 392 patients treated between 1978 and 2002 by graduate students, 199 were re-examined in 2005. Of these, 84 patients had received ceramo-metal FDPs (six groups). Results: At the re-evaluation, the mean age of the patients was 62 years (36.2–83.4). One hundred and seventy-five FDPs were seated (82 FDP-tt, 9 FDP-ii, 20 FDP-ti, 39 cFDP-tt, 15 cFDP-ii, 10 cFDP-ti). The mean observation time was 11.3 years; 21 FDPs were lost, and 46 technical and 50 biological complications occurred. Chances for the survival of the three groups of FDPs with end abutments were very high (risk for failure 2.8%, 0%, 5.6%). The probability to remain without complications and/or failure was 70.3%, 88.9% and 74.7% in FDPs with end abutments, but 49.8–25% only in FDPs with extensions at 10 years. Conclusions: In patients treated for chronic periodontitis and provided with ceramo-metal FDPs, high survival rates, especially for FDPs with end abutments, can be expected. The incidence rates of any negative events were increased drastically in the three groups with extension cFDPs (tt, ii, ti). Strategic decisions in the choice of a particular FDP design and the choice of teeth/implants as abutments appear to influence the risks for complications to be expected with fixed reconstruction. If possible, extensions on tooth abutments should be avoided or used only after a cautious clinical evaluation of all options.

In-vitro assessment of the forces generated by lingual fixed retainers

The aim of this article was to assess the effect of wire adaptation on the lingual surfaces of mandibular anterior teeth with 3 types of lingual retainers on the development of vertical and labiolingual forces.

Release of bisphenol-A from a light-cured adhesive bonded to lingual fixed retainers

Our aim was to quantitatively determine the bisphenol-A (BPA) released from a light-cured orthodontic adhesive used to bond lingual fixed retainers.

Unconventional implants for distal cantilever fixed full-arch prostheses: a long-term evaluation of four cases

Excessive cantilever lengths of fixed implant-supported prostheses may have functional and biomechanical disadvantages. This study reports the clinical outcomes of unconventional implants placed for distal support of a fixed implant-supported prostheses. Seven extraoral implants with intraosseous lengths of 2.5 to 4.0 mm were placed in four patients. Distal cantilevers had a mean length of 29.8 mm (range, 18.6 to 39.3 mm). No bone loss or other adverse events were found. The prosthetic plan was maintained in all patients. Within the limits of the employed research design, this concept seems to be a successful option for fixed complete implant-supported prosthesis treatment.

Curve Decomposition for Large Deflection Analysis of Fixed-Guided Beams With Application to Statically Balanced Compliant Mechanisms

Statically balanced compliant mechanisms require no holding force throughout their range of motion while maintaining the advantages of compliant mechanisms. In this paper, a postbuckled fixed-guided beam is proposed to provide the negative stiffness to balance the positive stiffness of a compliant mechanism. To that end, a curve decomposition modeling method is presented to simplify the large deflection analysis. The modeling method facilitates parametric design insight and elucidates key points on the force-deflection curve. Experimental results validate the analysis. Furthermore, static balancing with fixed-guided beams is demonstrated for a rectilinear proof-of-concept prototype.

Are endodontically treated incisors reliable abutments for zirconia-based fixed partial dentures in the esthetic zone?

This ex vivo pilot study tested the influence of defect extension and quartz-fiber post placement (QFP) on the ex vivo survival rate and fracture resistance of root-treated upper central incisors served as abutments for zirconia 2-unit cantilever fixed partial dentures (2U-FPDs) exposed to 10 years of simulated clinical function.