Evaluation of the Three-year Experience with All-ceramic Crowns with Polycrystalline Ceramic Cores

R e c e i ve d M a rc h 3 0 , 2 0 1 2 ; A c c e p t e d J a nu a r y 1 5 , 2 0 1 3 . Key words: Dentistry -Ceramic -All-ceramic crown -Retrospective study Abstract: The objective of the study was to evaluate the clinical outcomes of all-ceramic crowns three years after placement of the restoration in the oral cavity. The aim of the present clinical study were surveyed the Procera ® , Cercon ® and LAVA™ systems. In total, 121 crowns were followed in 33 patients (7 men and 26 women) with an average age of 53.5 years. The eighty crowns were placed in anterior and forty one crowns in posterior teeth. The crowns were fabricated in two dental laboratories and delivered in two private dental practices. The clinical trial was conducted according to American Dental Association guidelines. The patients were requested to provide their consent to the regular clinical examination including radiographic and photographic records. A total of 102 crowns were made of zirconium oxide ceramic cores -58 Cercon ® ; 43 LAVA™, while 19 crowns were made of aluminum oxide cores Procera ® . The veneering ceramic LAVA™ Ceram was used. The success rate was analyzed using Kaplan-Meier statistics and, in our case, the overall three-year success rate reached 96.7%. All-ceramic crowns with polycrystalline ceramic cores have low susceptibility to fracture, in this study just 3.3%

Fuel Processing for Solid Oxide Fuel Cells

Fuel flexibility is a major advantage of SOFC technology. In addition to H2, operations with synthesis gas, biogas, alcohols, and light hydrocarbons are feasible provided that appropriate conditions are respected. The chapter reviews the operational modes and the anodic materials that have been proposed in the literature to run SOFCs with non-H2 fuels, as well as the methods that can be applied to clean the fuel feedstock from impurities (tars and species based on sulfur, nitrogen, and halogen). SOFC stacks can be run under four main configurations, depending on the position of the reformer (external or integrated) and on the possibility of directly processing the incoming fuel in the anodic electrode (Sect. 4.3). The feasibility of direct reforming or oxidation operations needs to be evaluated based on thermodynamic (Sect. 4.4) and kinetic considerations (Sect. 4.5), in order to avoid impairing the anode due to carbon formation or poisoning with impurities. Although they are still the most widespread choice, the behavior of standard Ni-YSZ cermet anodes (Sect. 4.6) poses problems in terms of sulfur and C tolerance, especially when the steam supply is lowered to achieve direct oxidation modes. Several strategies can be adopted to overcome these issues, by modification of the anodic materials (Sect. 4.7): Ni can be partially substituted or alloyed with transition or noble metals; Ni can be entirely replaced by different metals or oxides; protective barriers or oxide ion transferring or storing materials (MIEC, OSM) can be added to the standard Ni-YSZ cermet. In the case of external reforming solutions, the catalyst also experiences coking and poisoning issues, and its lifetime can be improved by strategies similar to those applied in SOFC anodes (Sect. 4.8). Several methods are available to remove impurities from feedstock: Those based on the use of alkaline sorbents and on catalytic decomposition are reviewed (Sect. 4.9)