Abstract Objective: This study analyzed the effect of ionizing radiation on bone microarchitecture and biomechanical properties in the bone tissue surrounding a dental implant. Methodology: Twenty rabbits received three dental morse taper junction implants: one in the left tibia and two in the right tibia. The animals were randomized into two groups: the nonirradiated group (control group) and the irradiated group, which received 30 Gy in a single dose 2 weeks after the implant procedure. Four weeks after the implant procedure, the animals were sacrificed, and the implant/bone specimens were used for each experiment. The specimens (n=10) of the right tibia were examined by microcomputed tomography to measure the cortical volume (CtV, mm3), cortical thickness (CtTh, mm) and porosity (CtPo, %). The other specimens (n=10) were examined by dynamic indentation to measure the elastic modulus (E, GPa) and Vickers hardness (VHN, N/mm2) in the bone. The specimens of the left tibia (n=10) were subjected to pull-out tests to calculate the failure load (N), displacement (mm) up to the failure point and interface stiffness (N/mm). In the irradiated group, two measurements were performed: close, at 1 mm surrounding the implant surface, and distant, at 2.5 mm from the external limit of the first measurement. Data were analyzed using one-way ANOVA, Tukey’s test and Student’s t-test (α=0.05). Results: The irradiated bone closer to the implant surface had lower elastic modulus (E), Vickers hardness (VHN), Ct.Th, and Ct.V values and a higher Ct.Po value than the bone distant to the implant (P<0.04). The irradiated bone that was distant from the implant surface had lower E, VHN, and Ct.Th values and a higher Ct.Po value than the nonirradiated bone (P<0.04). The nonirradiated bone had higher failure loads, displacements and stiffness values than the irradiated bone (P<0.02). Conclusion: Ionizing radiation in dental implants resulted in negative effects on the microarchitecture and biomechanical properties of bone tissue, mainly near the surface of the implant.

Abstract Radiation-related caries are one the most undesired reactions manifested during or after head and neck radiotherapy. Fluoride application is an important strategy to reduce demineralization and enhance remineralizaton. Objective: To evaluate the effect of the topical application of fluoride during irradiation on dental enamel demineralization. Material and Methods: Thirty molars were randomly divided into three groups: Non-irradiated (NI), Irradiated (I), Irradiated with fluoride (IF). Each group was subdivided according to the presence or absence of pH-cycling (n=5). In the irradiated groups, the teeth received 70 Gy. The enamel's chemical composition was measured using Fourier Transform Infrared Spectrometry (organic matrix/mineral ratio - M/M and relative carbonate content - RCC). Vickers microhardness (VHN) and elastic modulus (E) were evaluated at three depths (surface, middle and deep enamel). Scanning electron microscopy (SEM) was used to assess the enamel's morphology. Results: The FTIR analysis (M/M and RCC) showed significant differences for irradiation, pH-cycling and the interaction between factors (p<0.001). Without pH-cycling, IF had the lowest organic matrix/mineral ratio and relative carbonate content. With pH-cycling, the organic matrix/mineral ratio increased and the relative carbonate content decreased, except for IF. VHN was influenced only by pH-cycling (p<0.001), which generated higher VHN values. ANOVA detected significant differences in E for irradiation (p<0.001), pH-cycling (p<0.001) and for the interaction between irradiation and pH-cycling (p<0.001). Increased E was found for group I without pH-cycling. With pH-cycling, groups I and IF were similar, and showed higher values than NI. The SEM images showed no morphological changes without pH-cycling. With pH-cycling, fluoride helped to maintain the outer enamel's morphology. Conclusions: Fluoride reduced mineral loss and maintained the outer morphology of irradiated and cycled enamel. However, it was not as effective in preserving the mechanical properties of enamel. Radiotherapy altered the enamel's elastic modulus and its chemical composition.

Quando uma espira circular formada por um circuito RLC começa a oscilar, a oscilação irá desaparecer, com uma corrente decaindo exponencialmente, mesmo considerando fios supercondutores, devido à emissão de radiações de dipolos eléctricos e magnéticos. Neste trabalho, propomos uma modificação da lei da voltagem de Kirchhoff, adicionando as contribuições radiativas associadas à perda de energia, através de resistências efetivas, cujos valores são relativamente pequenos quando comparados com os valores de resistências típicas, mas que são fundamentais para descrever circuitos reais de forma correta. Nós também analisamos as mudanças no espectro de radiação emitida pelo circuito à medida que se variam as resistências elétricas reais e efetivas.

When a circular loop composed by a RLC circuit begins to oscillate, the oscillation will eventually vanish as an exponentially decaying current, even considering superconducting wires, due to the emission of electric and magnetic dipole radiations. In this work we propose a modification of the Kirchhoff’s voltage law by adding the radiative contributions to the energy loss as effective resistances, whose values are relatively small when compared to typical resistance values, but are fundamental to describe real circuits correctly. We also analyse the change in the pattern of the radiation spectra emitted by the circuit as we vary the effective and electric resistances.

Discutimos o problema da descarga de um capacitor associado a outro, idêntico e inicialmente descarregado. É sabido que, com ou sem a presença de resistência elétrica no circuito, o estado final de equilbrio, assim como a energia dissipada no processo, são sempre os mesmos. O mecanismo de dissipação no caso em que não há resistência elétrica é a irradiação do sistema e no caso em que a resistência elétrica está presente ocorrem ambos, irradiação e dissipação por efeito Joule, devido à interação dos elétrons de condução com a rede cristalina, de forma a sempre satisfazer o teorema de Poynting. A diferença entre ambos os processos está no intervalo de tempo em que o sistema atinge o equilbrio e, consequentemente, no espectro da radiação eletromagnética emitida por este sistema.

We discuss the problem of the discharge of a capacitor associated with another identical and initially discharged capacitor. It is known that with or without the presence of an electrical resistance in the circuit, the final state of equilibrium, as well as the energy dissipated in the process, are always the same. The dissipation mechanism if there is no electric resistance is the irradiation of the system, and in the presence of electric resistance there are both irradiation and Joule dissipation, due to the interactions of the conduction electrons with the crystal lattice in order to always satisfy Poynting's theorem. The difference between both processes is the time interval in which the system reaches equilibrium and therefore the spectrum of electromagnetic radiation emitted by this system.