T he objective of this research was to evaluate, by three-dimensional (3D) finite element analysis (FEA), the stress distribution in three different fiveimplant mandibular protocol prosthesis models, when these three undergo a simulated occlusal load of 100 N in the area of the cantilever: (1) model A, temporary all-acrylic resin; (2) model B, metal-acrylic; and (3) model C, metal-ceramic. Materials and Methods Modeling of the External and Internal Portions of the MandibleThe external 3D modeling of the mandible was acquired from the laser digitization of a natural edentulous mandible in the sagittal, horizontal, and frontal planes (0.01mm precision) using Digimil 3D (Technodrill). The first 3D model was created using Geomatic Studio version 7.0, and then a continuous model was obtained using Rhynoceros 3D version 3.0.A tomographic image (70 transversal vertical slices, 1-mm thickness) of the same edentulous mandible was obtained using Helicoidal Tomographic Hispeed CTI System Series 6.3 (GE Healthcare). This image was superimposed over the external mandible model to develop the internal model (Rhynoceros 3D version 3.0). Modeling of Implants and Prosthetic ComponentsThe 3D shapes of implant and prosthetic components were obtained by manual measurements (eg, length, diameter, thread pitch) with magnifying lens and a digital caliper. These dimensions were used for generating digital surfaces (Rhynoceros 3D version 3.0), and then solid shapes were obtained (SolidWorks 2012, SolidWorks).

Purpose: This 3D-finite elements method study evaluated the effect of bone resorption on the stress distribution in overdentures with bone loss surrounding implants and resorption of the distal ridge. Methods: Tridimensional models were built from the images of a computerized tomography of a mandible and 3D laser digitalization of implants, abutments, mucosa, and complete denture. The geometric models of implants and abutments were mounted at the canine region to build reference model 1-absence of bone resorption. To build the test models the mandible geometric solid was modified to simulate 2-mm vertical bone loss surrounding the implants (model 2) and resorption of the distal ridge (model 3). Finite elements models were generated, and a 100 N static load was applied at the first molar region of each model to compare the von Mises stress distributions in selected points. Results: Von Mises stresses increased on the bone surrounding implants and on the prosthetic components in the model with 2-mm vertical bone loss. The combination of 2-mm vertical bone loss and resorption of the distal ridge did not increase the stresses compared with the model with only bone loss surrounding implants. The highest stress concentration at marginal bone and implants occurred on the same side of the vertical load application for all models. Conclusion: The results suggest that the bone loss surrounding implants increases stress concentration in dental implants, abutments, and marginal bone independently from the bone resorption of the distal ridge.

The present results suggest that Veracril® resin denture bases submitted to chemical polishing had decrease of internal adaptation in 30 days, although immediate adaptation was not affected.

OBJECTIVE: This 3-D FEA study compared the stress distribution in two-implant mandibular overdentures as a function of implant position and attachment system (LA: locator attachment vs. BA: ball attachment). METHODS: Four models of mandibular overdentures were tested: M1-LA -with implants at the canine regions (standard implant position) and LA; M2-LA -with implants placed at the first premolar regions (distalized implant position) and LA; M1-BA -with standard implant position and BA; and M2-BA -with distalized implant position and BA. The geometric models were converted into finite element models. A 100 N axial load was applied at the first molar region. The von-Mises stress distribution was compared in selected points. RESULTS: The models with BA had pattern of stress distribution was more uniform along the implant axis than the ones with LA, although the stress magnitude was larger. The largest area of von Mises stresses on the alveolar ridge was in the models with standard implant distribution. CONCLUSION: The findings showed that the models with BA had better biomechanical behavior than the ones with LA. For both types of attachment, the models with increased inter-implant distance presented a smaller area of stress distribution in the perimplant cortical bone tissue than the standard implant position.Keywords: dental implants; implant-supported overdenture; biomechanics; finite element analysis.Análise de elementos finitos em 3D de sobredentaduras mandibulares com diferentes posições de implante e tipos de encaixe RESUMO OBJETIVO: Este estudo de análise de elementos finitos em 3-D comparou a distribuição de tensão em sobredentaduras suportadas por implante em função da posição do implante e do sistema de encaixe (AA: tipo "locator" vs. BA: tipo "bola") METODOLOGIA: Foram testados quatro modelos 3-D de sobredentadura com implante mandibular: M1-LAcom implantes nas regiões dos dentes caninos (posição padrão dos implantes) e LA; M2-LA -com implantes nas regiões dos dentes primeiros pré-molares (posição distalizada dos implantes) e LA; M1-BA -com posição padrão de implante e BA; e M2-BA -com posição distalizada dos implantes e BA. Os modelos geométricos foram convertidos em modelos de elementos finitos. Uma carga axial de 100 N foi aplicada na primeira região molar. A distribuição de estresses von Mises foi comparada em pontos selecionados. RESULTADOS: Os modelos com BA apresentaram padrão de distribuição de estresse mais uniforme ao longo do eixo do implante do que os modelos com LA, embora a magnitude do estresse tenha sido maior. A maior área de tensões no rebordo alveolar ocorreu nos modelos com posição padrão de implantes. CONCLUSÃO: Os resultados sugerem que os modelos com BA apresentaram melhor comportamento biomecânico do que aqueles com LA. Para ambos os encaixes, implantes distalizados apresentam uma menor área de distribuição de estresse no tecido ósseo cortical do que posicionamento padrão dos implantes.Palavras-chave: implantes dentários; sobredentadura sobre implantes; biomecânica; anális...