Compressive fatigue in titanium dental implants submitted to fluoride ions action

The aim of this study was to assess the influence of a fluoridated medium on the mechanical properties of an internal hexagon implant-abutment set, by means of compression, mechanical cycling and metallographic characterization by scanning electronic microscopy. Five years of regular use of oral hygiene with a sodium fluoride solution content of 1500 ppm were simulated, immersing the samples in this medium for 184 hours, with the solutions being changed every 12 hours. Data were analyzed at a 95% confidence level with Fisher's exact test. After the action of fluoride ions, a negative influence occurred in the mechanical cycling test performed in a servohydraulic machine (Material Test System-810) set to a frequency of 15 Hz with 100,000 cycles and programmed to 60% of the maximum resistance of static compression test. The sets tended to fracture by compression on the screw, characterized by mixed ruptures with predominance of fragile fracture, as observed by microscopy. An evidence of corrosion by pitting on sample surfaces was found after the fluoride ions action. It may be concluded that prolonged contact with fluoride ions is harmful to the mechanical properties of commercially pure titanium structures

Pre-heating mitigates composite degradation

Dental composites cured at high temperatures show improved properties and higher degrees of conversion; however, there is no information available about the effect of pre-heating on material degradation. Objectives This study evaluated the effect of pre-heating on the degradation of composites, based on the analysis of radiopacity and silver penetration using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS). Material and Methods Thirty specimens were fabricated using a metallic matrix (2x8 mm) and the composites Durafill VS (Heraeus Kulzer), Z-250 (3M/ESPE), and Z-350 (3M/ESPE), cured at 25°C (no pre-heating) or 60°C (pre-heating). Specimens were stored sequentially in the following solutions: 1) water for 7 days (60°C), plus 0.1 N sodium hydroxide (NaOH) for 14 days (60°C); 2) 50% silver nitrate (AgNO3) for 10 days (60°C). Specimens were radiographed at baseline and after each storage time, and the images were evaluated in gray scale. After the storage protocol, samples were analyzed using SEM/EDS to check the depth of silver penetration. Radiopacity and silver penetration data were analyzed using ANOVA and Tukey’s tests (α=5%). Results Radiopacity levels were as follows: Durafill V

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear un derstanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5–7 vast areas of the tropics remain understudied.8–11 In the American tropics, Amazonia stands out as the world’s most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepre sented in biodiversity databases.13–15 To worsen this situation, human-induced modifications16,17 may elim inate pieces of the Amazon’s biodiversity puzzle before we can use them to understand how ecological com munities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple or ganism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region’s vulnerability to environmental change. 15%–18% of the most ne glected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lostinfo:eu-repo/semantics/publishedVersio

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time,1,2 and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space.3,4 While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes,5,6,7 vast areas of the tropics remain understudied.8,9,10,11 In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity,12 but it remains among the least known forests in America and is often underrepresented in biodiversity databases.13,14,15 To worsen this situation, human-induced modifications16,17 may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge,18,19 it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Comportamento biomecânico do sistema prótese/implante em região anterior de maxila: análise pelo método de ciclagem mecânica

INTRODUÇÃO : O adequado posicionamento tridimensional dos implantes é indispensável para garantir a previsibilidade no tratamento com implantes dentários. OBJETIVO : Analisar comparativamente o comportamento mecânico do sistema prótese/implante em região anterior de maxila, diferindo os sistemas de encaixe e posicionamento dos implantes. MATERIAL E MÉTODO : Utilizando um modelo prototipado de maxila, as situações estudadas foram: Grupo IC - implantes nos incisivos centrais e cantilever nos incisivos laterais; Grupo IL - implantes nos incisivos laterais e pônticos nos incisivos centrais; Grupo ICIL - implantes no incisivo central e no incisivo lateral, intercalados com elementos suspensos. Para cada situação estudada, foram utilizadas as três conexões protéticas: hexágono externo, hexágono interno e cone-Morse. O ensaio de ciclagem mecânica foi realizado com a aplicação de 100 N de carga e frequência de 15 Hz no cíngulo dos incisivos a 45° com o longo eixo do dente, para simular o movimento mastigatório. RESULTADO : No ensaio de ciclagem mecânica, todos os modelos de todos os grupos com os três tipos de conexões protéticas atingiram um milhão de ciclos sem que ocorresse ruptura do parafuso, do componente protético ou da estrutura metálica. CONCLUSÃO : Com a metodologia e as condições empregadas, pode-se concluir que o comportamento mecânico das reabilitações implantossuportadas foi semelhante para os diferentes posicionamentos dos implantes e diferentes conexões protéticas

CORROSIÓN EN MEDIO ÁCIDO CÍTRICO DE UNA ALEACION METÁLICA DE COBRE APLICADA EN LA ODONTOLOGIA

ABSTRACTThe aim of this work went characterize and to study the effect of heat treatment in based copper metallic alloy for application in dentistry, with relationship to its behavior before the corrosion, in a solution that simulates the aggressiveness of the oral environment. The characterization of the alloy was made by means of chemical analysis and optical microscopy and the corrosion tests consisted in obtaining the potentiostatic polarization curves, in acid citric solution 1g/L. Analyzing the obtained results it was observed that the alloy when submited to the thermal treatment there is a transformation of the dendritic structure for a phase granular structure. In relation to the corrosive process it was verified by means of potentiostatic polarization curves didn't happen passivation, as well as there were not differences in the resistance the corrosion between the samples with and without thermal treatment.RESUMENEl objetivo de este trabajo fue caracterizar y estudiar el efecto del tratamiento térmico hecho en una aleación metálica de cobre para el uso odontológico, con relación a su comportamiento frente a la corrosión, en un medio que simula la agresividad del ambiente bucal. La caracterización de la aleación fue hecha por medio de análisis de la composición química y microscopia óptica y los ensayos de corrosión comprendieran en la obtención de las curvas de polarización potenciostáticas en solución arenosa de ácido cítrico 1g/L. De acuerdo con los resultados obtenidos se observó que la aleación cuando sometida al tratamiento térmico, sufre una transformación de la estructura dendrítica para una estructura con fases bien definidas. En relación al proceso corrosivo, se verificó por medio de las curvas de polarización potenciostáticas que no ocurre pasivacíon, bien como no ha diferencia en la resistencia a la corrosión entre las muestras con y sin tratamiento térmico en el medio estudiado