Comparison of different designs of implant-retained overdentures and fixed full-arch implant-supported prosthesis on stress distribution in edentulous mandible - A computed tomography-based three-dimensional finite element analysis

A finite element analysis was used to compare the effect of different designs of implant-retained overdentures and fixed full-arch implant-supported prosthesis on stress distribution in edentulous mandible. Four models of an human mandible were constructed. In the OR (O'ring) group, the mandible was restored with an overdenture retained by four unsplinted implants with O'ring attachment; in the BC (bar-clip) -C and BC groups, the mandibles were restored with overdentures retained by four splinted implants with bar-clip anchor associated or not with two distally placed cantilevers, respectively; in the FD (fixed denture) group, the mandible was restored with a fixed full-arch four-implant-supported prosthesis. Models were supported by the masticatory muscles and temporomandibular joints. A 100-N oblique load was applied on the left first molar. Von Mises (sigma(vM)), maximum (sigma(max)) and minimum (sigma(min)) principal stresses (in MPa) analyses were obtained. BC-C group exhibited the highest stress values (sigma(vM) = 398.8, sigma(max) = 580.5 and sigma(min) = -455.2) while FD group showed the lowest one (sigma(vM) =128.9, sigma(max) = 580.5 and sigma(min) = -172.1). Within overdenture groups, the use of unsplinted implants reduced the stress level in the implant/prosthetic components (59.4% for sigma(vM) 66.2% for sigma(max) and 57.7% for sigma(min) versus BC-C group) and supporting tissues (maximum stress reduction of 72% and 79.5% for sigma(max), and 15.7% and 85.7% for sigma(min) on the cortical and trabecular bones, respectively). Cortical bone exhibited greater stress concentration than the trabecular bone for all groups. The use of fixed implant dentures and removable dentures retained by unsplinted implants to rehabilitate edentulous mandible reduced the stresses in the periimplant bone tissue, mucosa and implant/prosthetic components. (C) 2013 Elsevier Ltd. All rights reserved.46713121320[2007/58926-5][2010/09857-3][2007/58926-5][2010/09857-3

Influence of abutment-to-fixture design on reliability and failure mode of all-ceramic crown systems

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Objective. Evaluate the effect of implant connection designs on reliability and failure modes of screw-retained all-ceramic crowns. Methods. Central incisor ceramic crowns in zirconia abutments were screwed and torqued down to external hexagon (EH), internal hexagon (IH) and Morse taper (MT) implant systems. Single-load-to-fracture (SLF) test (n = 4 per group) determined three step-stress fatigue profiles with specimens assigned in the ratio of 3:2:1. Fatigue test was performed under water at 10 Hz. Use level probability Weibull curves and reliability for missions of 50,000 cycles at 400 N and 200 N were calculated (90% confidence bounds-CB). Weibull probability distribution (90% CB) was plotted (Weibull modulus vs characteristic strength) for comparison between the groups. Fractographic analyses were conducted under polarized-light microscopy and SEM. Results. Use level Weibull probability calculation indicated that failure was not associated with fatigue in groups EH (beta = 0.63), IH (beta = 0.97) and MT (beta = 0.19). Reliability data for a mission of 50,000 cycles at 400 N revealed significant reliability differences between groups EH (97%), IH (46%) and MT (0.5%) but no significant difference at 200 N between EH (100%) and IH (98%), and IH and MT (89%). Weibull strength distribution (figure) revealed beta = 13.1/eta = 561.8 for EH, beta = 5.8/eta = 513.4 for IH and beta = 5.3/eta = 333.2 for MT. Groups EH and IH exhibited veneer cohesive and adhesive failures. Group IH also presented adhesive failure at zirconia/titanium abutment insert while MT showed fracture at abutment neck. Significance. Although group EH presented higher reliability and characteristic strength followed by IH and MT, all groups withstood reported mean anterior loads. (C) 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.304408416Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [2009/11491-0, 2009/15060-3

La administración pública en Colombia Reflexiones en torno a un escenario de transición: Privatización de lo público, excepcionalidad política y desafíos disciplinares

Este trabajo desarrolla de manera preliminar los desafíos de la administración pública -AP- y su formación ad portas de un escenario transicional en Colombia. Referidos los planteamientos generales de A. Rosembaum en torno a asumir la gestión gubernamental en la actualidad, movida entre una hegemonía privatizadora y una urgencia del llamado al sector público en el mundo, se aborda el caso colombiano en el que si bien es evidente la crisis del papel privatizador en la AP, se insiste en su acción. La hipótesis explicativa de dicha insistencia se da por una nueva excepcionalidad política acogida por el Estado dentro de la reestructuración capitalista neoliberal. Llegada la transición con la paz, se pregunta  si la AP hará la diferencia y qué retos desafiará su formación. 

The influence of bone quality on the biomechanical behavior of full-arch implant-supported fixed prostheses

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)We evaluated the influence of bone tissue type on stress distribution in full-arch implant-supported fixed prostheses using a three-dimensional finite element analysis. Stresses in cortical and trabecular bones were also investigated. Edentulous mandible models with four implants inserted into the interforaminal region were constructed from different bone types: type 1 - compact bone; type 2 - compact bone surrounding dense trabecular bone; type 3 a thin layer of compact bone surrounding trabecular bone; and type 4 - low-quality trabecular bone. The mandible was restored with a full-arch implant-supported fixed prosthesis. A 100-N oblique load was applied to the left lower first molar of the prosthesis. The maximum (sigma max) and minimum (sigma min) principal stress values were determined. The sigma max in the type 4 cortical bone was 22.56% higher than that in the type 1 bone. The sigma min values in the cortical bone were similar among all the bone types. For the superstructure, increases of 9.04% in the sigma max and 11.74% in the sigma min in G4 (type 4 bone) compared with G1 (type 1 bone) were observed. For the implants, the highest stress values were located in G4, and the lowest values were observed in GI. In the trabecular bone, the highest stress was generated in G1 and G2. In conclusion, the more compact bones (types 1 and 2) are the most suitable for supporting full-arch implant-supported fixed prostheses, and poor bone quality may increase the risk of biological and mechanical failure. (C) 2014 Elsevier B.V. All rights reserved.37164170Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [2010/09857-3