Análises de falhas em eixo de laminadora

Pós-graduação em Engenharia Mecânica - FEG

Adaptação marginal e resistência à fratura de coroas totais executadas em diferentes sistemas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

3-D reconstruction by extended depth-of-field in failure analysis - Case study II: Fractal analysis of interlaminar fracture in carbon/epoxy composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Failure of miniplate osteosynthesis for the management of atrophic mandibular fracture

Fractures of the severely atrophic (<10 mm) edentulous mandible are not common, and these fractures with a vertical height of 10 mm or less have long been recognized as being particularly problematic. Although there are advances in the treatment of the atrophic mandibular fracture, the treatment remains controversial. There are some options for treatment planning because of using small miniplates to large reconstruction plates. However, when the fixation method fails, it causes malunion, nonunion, and/or infection, and sometimes it has been associated with large bone defects. The authors describe a clinical report of a failed miniplate fixation for atrophic mandibular fracture management. The authors used a load-bearing reconstruction plate combined with autogenous bone graft from iliac crest for this retreatment. The authors show a follow-up of 6 months, with union of the fracture line and no complication postoperatively. © 2013 by Mutaz B. Habal, MD.

3-D reconstruction by extended depth-of-field in failure analysis - Case study I: Qualitative fractographic investigation of fractured bolts in a partial valve

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determining the Optimum Processing Parameters of Glass-like Carbon Using Weibull Analysis of its Fracture Behaviour

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Postoperative renal function evaluation, through RIFLE criteria, of elderly patients who underwent femur fracture surgery under spinal anesthesia

Introduction. The postoperative acute renal failure (ARF) incidence in different kinds of surgery has rarely been studied. Age, cardiac dysfunction, previous renal dysfunction, intraoperative hypoperfusion, and use of nephrotoxic medications are mentioned as risk factors for ARF at the postoperative period. The postoperative ARF definition was based on the creatinine increase by the RIFLE classification (R = risk, I = injury, F = failure, L = loss, E = end stage), which corresponds to a 1.5 creatinine increase, two to three times, respectively, above the basal value. This study aimed to evaluate the postoperative ARF incidence in elderly patients who underwent femur fracture surgery under subarachnoid anesthesia and stratify it by the RIFLE criteria. Methods. Ninety patients older than 65 years under spinal anesthesia with fixed dosage of 15 mg of 0.5% isobaric bupivacaine associated with morphine 50 g were studied. Immediate postoperative creatinine was considered basal and compared with maximal creatinine evaluated at 24, 48, and 72 postoperative hours. Results. The mean age of the patients was 80.27 years. ARF incidence was 24.44% and stratified this way: R = 21.11% and I = 3.33%. Conclusions. In conclusion, the postoperative ARF incidence after femur fracture surgery in patients over 65 years was 24.44%. By analyzing the stratification based on the RIFLE classification, the incidence was categorized as Risk (R) = 21.11% and Injury (I) = 3.33%.

Effect of implant connection and restoration design (screwed vs. cemented) in reliability and failure modes of anterior crowns

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fracture strength of flared bovine roots restored with different intraradicular posts

Objective: The aim of this study was to evaluate the fracture strength and failure mode of flared bovine roots restored with different intraradicular posts. Material and Methods: Fifty bovine incisors with similar dimensions were selected and their roots were flared until 1.0 mm of dentin wall remained. Next, the roots were allocated into five groups (n=10): GI-cast metal post-and-core; GII-fiber posts plus accessory fiber posts; GIII-direct anatomic post; GIV-indirect anatomic post and GV-control (specimens without intraradicular post). A polyether impression material was used to simulate the periodontal ligament. After periodontal ligament simulation, the specimens were subjected to a compressive load at a crosshead speed of 0.5 mm/min in a servo-hydraulic testing machine (MTS 810) applied at 135 to the long axis of the tooth until failure. The data (N) were subjected to ANOVA and Tukey's post-hoc test (alpha=0.05). Results: GI and GIV presented higher fracture strength (p<0.05) than GII. GIII presented intermediate values without statistically significant differences (p>0.05) from GI, GII and GIV. Control specimens (GV) produced the lowest fracture strength mean values (p<0.05). Despite obtaining the highest mean value, GI presented 100% of unfavorable failures. GII presented 20% of unfavorable failures. GIII, GIV and GV presented only favorable failures. Conclusions: Although further in vitro and in vivo studies are necessary, the results of this study showed that the use of direct and indirect anatomic posts in flared roots could be an alternative to cast metal post-and-core.

Fracture resistance of bleached teeth restored with different procedures

This study evaluated the fracture resistance of teeth submitted to internal bleaching and restored with different non-metallic post. Eighty mandibular incisors were endodontically treated and randomly divided in 10 groups (n = 8): G1- restored with composite resin (CR), G2- CR + fiber-reinforced composite post (FRC, Everstick post, Sticktech) cemented with resin cement self-etch adhesive (RCS, Panavia F 2.0, Kuraray), G3- CR + FRC + self-adhesive resin cement (SRC, Breeze, Pentral Clinical), G4- CR+ glass fiber post (GF, Exacto Post, Angelus) + RCS, G5- CR + GF + SRC. The G6 to G10 were bleached with hydrogen peroxide (HP) and restored with the same restorative procedures used for G1 to G5, respectively. After 7 days storage in artificial saliva, the specimens were submitted to the compressive strength test (N) at 0.5 mm/min cross-head speed and the failure pattern was identified as either reparable (failure showed until 2 mm below the cement-enamel junction) or irreparable (the failure showed <2 mm or more below the cement-enamel). Data were analyzed by ANOVA and Tukey test (α = 0.05). No significant difference (p < 0.05) was found among G1 to G10. The results suggest that intracoronal bleaching did not significantly weaken the teeth and the failure patterns were predominately reparable for all groups. The non-metallic posts in these teeth did not improve fracture resistance.

Customized fiber glass posts. Fatigue and fracture resistance

Purpose: To evaluate the root fracture strength of human single-rooted premolars restored with customized fiberglass post-core systems after fatigue simulation. Methods: 40 human premolars had their crowns cut and the root length was standardized to 13 mm. The teeth were endodontically treated and embedded in acrylic resin. The specimens were distributed into four groups (n=10) according to the restorative material used: prefabricated fiber post (PFP), PFP+accessory fiber posts (PFPa), PFP+unidirectional fiberglass (PFPf), and unidirectional fiberglass customized post (CP). All posts were luted using resin cement and the cores were built up with a resin composite. The samples were stored for 24 hours at 37 degrees C and 100% relative humidity and then submitted to mechanical cycling. The specimens were then compressive-loaded in a universal testing machine at a crosshead speed of 0.5 mm/minute until fracture. The failure patterns were analyzed and classified. Data was submitted to one-way ANOVA and Tukey's test (alpha= 0.05). Results: The mean values of maximum load (N) were: PFP - 811.4 +/- 124.3; PFPa - 729.2 +/- 157.2; PFPf - 747.5 +/- 204.7; CP - 762.4 +/- 110. Statistical differences were not observed among the groups. All groups showed favorable restorable failures. Fiberglass customized post did not show improved fracture resistance or differences in failure patterns when compared to prefabricated glass fiber posts. (Am J Dent 2012;25:35-38).

In Vitro Study of Fracture Load and Fracture Pattern of Ceramic Crowns: A Finite Element and Fractography Analysis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Interfacial fracture of dentin adhesively bonded to quartz-fiber reinforced composite

The paper presents the results of an experimental study of interfacial failure in a multilayered structure consisting of a dentin/resin cement/quartz-fiber reinforced composite (FRC). Slices of dentin close to the pulp chamber were sandwiched by two half-circle discs made of a quartz-fiber reinforced composite, bonded with bonding agent (All-bond 2, BISCO, Schaumburg) and resin cement (Duo-link. BISCO, Schaumburg) to make Brazil-nut sandwich specimens for interfacial toughness testing. Interfacial fracture toughness (strain energy release rate, G) was measured as a function of mode mixity by changing loading angles from 0 degrees to 15 degrees. The interfacial fracture surfaces were then examined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) to determine the failure modes when loading angles changed. A computational model was also developed to calculate the driving forces, stress intensity factors and mode mixities. Interfacial toughness increased from approximate to 1.5 to 3.2 J/m(2) when the loading angle increases from approximate to 0, 0 to 15 degrees. The hybridized dentin/cement interface appeared to be tougher than the resin cement/quartz-fiber reinforced epoxy. The Brazil-nut sandwich specimen was a suitable method to investigate the mechanical integrity of dentin/cement/FRC interfaces. (C) 2011 Elsevier B.V. All rights reserved.

The effect of porcelain thickness and surface liner application on the fracture behavior of a ceramic system

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effects of cement thickness and bonding on the failure loads of CAD/CAM ceramic crowns: Multi-physics FEA modeling and monotonic testing

Objective. To determine the influence of cement thickness and ceramic/cement bonding on stresses and failure of CAD/CAM crowns, using both multi-physics finite element analysis and monotonic testing.Methods. Axially symmetric FEA models were created for stress analysis of a stylized monolithic crown having resin cement thicknesses from 50 to 500 mu m under occlusal loading. Ceramic-cement interface was modeled as bonded or not-bonded (cement-dentin as bonded). Cement polymerization shrinkage was simulated as a thermal contraction. Loads necessary to reach stresses for radial cracking from the intaglio surface were calculated by FEA. Experimentally, feldspathic CAD/CAM crowns based on the FEA model were machined having different occlusal cementation spaces, etched and cemented to dentin analogs. Non-bonding of etched ceramic was achieved using a thin layer of poly(dimethylsiloxane). Crowns were loaded to failure at 5 N/s, with radial cracks detected acoustically.Results. Failure loads depended on the bonding condition and the cement thickness for both FEA and physical testing. Average fracture loads for bonded crowns were: 673.5 N at 50 mu m cement and 300.6 N at 500 mu m. FEA stresses due to polymerization shrinkage increased with the cement thickness overwhelming the protective effect of bonding, as was also seen experimentally. At 50 mu m cement thickness, bonded crowns withstood at least twice the load before failure than non-bonded crowns.Significance. Occlusal "fit" can have structural implications for CAD/CAM crowns; pre-cementation spaces around 50-100 mu m being recommended from this study. Bonding benefits were lost at thickness approaching 450-500 mu m due to polymerization shrinkage stresses. (C) 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.