Influence of activation modes on diametral tensile strength of dual-curing resin cements.

In metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. The effect of the lack of photoactivation on the strength of these cements has been rarely studied. This study evaluated the influence of activation modes on the diametral tensile strength (DTS) of dual-curing resin cements. Base and catalyst pastes of Panavia F, Variolink II, Scotchbond Resin Cement, Rely X and Enforce were mixed and inserted into cylindrical metal moulds (4 x 2 mm). Cements were either: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated through mylar strips (chemical and photo-activation = dual-cured groups) (n = 10). After a 24 h storage in 37 masculineC distilled water, specimens were subjected to compressive load in a testing machine. A self-curing resin cement (Cement-It) and a zinc phosphate cement served as controls. Comparative analyses were performed: 1) between the activation modes for each dual-curing resin cement, using Students t test; 2) among the self-cured groups of the dual-curing resin cements and the control groups, using one-way ANOVA and Tukeys test (alpha = 0.05). The dual-cured groups of Scotchbond Resin Cement (53.3 MPa), Variolink II (48.4 MPa) and Rely X (51.6 MPa) showed higher DTS than that of self-cured groups (44.6, 40.4 and 44.5 MPa respectively) (p < 0.05). For Enforce (48.5 and 47.8 MPa) and Panavia F (44.0 and 43.3 MPa), no significant difference was found between the activation modes (p > 0.05). The self-cured groups of all the dual-curing resin cements presented statistically the same DTS as that of Cement-It (44.1 MPa) (p > 0.05), and higher DTS than that of zinc phosphate (4.2 MPa). Scotchbond Resin Cement, Variolink II and Rely X depended on photoactivation to achieve maximum DTS. In the absence of light, all the dual-curing resin cements presented higher DTS than that of zinc phosphate and statistically the same as that of Cement-It (p > 0.05).

A comparison of the film thickness of two adhesive luting agents and the effect of thermocycling on their microTBs to feldspathic ceramic.

The aim of the present study was to evaluate the effect of thermocycling (TC) on the microtensile bond strength (microTBS) of two luting agents to feldspathic ceramic and to measure their film thickness (FT). For the microTBS test, sixteen blocks (6.4 x 6.4 x 4.8 mm) were fabricated using a feldspathic ceramic, etched with 10% hydrofluoric acid, rinsed and treated with the silane agent. The ceramic blocks were divided into two groups (n= 8): Gr1: dual-cured resin cement and Gr2: flowable resin. The luting agents were applied on the treated surfaces. Microsticks (1 +/-0. 1mm2) were prepared and stored under two conditions: dry, specimens immediately submitted to the microTBS test, and TC (6,000 cycles; 5 degrees C-55 degrees C). The microTBS was evaluated using a universal testing machine (1 mm/min). The microTBS data (MPa) were submitted to two-way ANOVA and Tukey' test (5%). For the FT test (ISO 4049), 0.05 ml of each luting agent (n=8) was pressed between two Mylar-covered glass plates (150 N) for 180 seconds and light polymerized. FT was measured using a digital paquimeter (Model 727-2001). The data (mm) were submitted to one-way ANOVA. The luting cement did not influence the microTBS results (p= 0.4467). Higher microtensile bond values were found after TC (20.5 +/- 8.6 MPa) compared to the dry condition (13.9 +/- 4. 7MPa), for both luting agents. The luting agents presented similar film thicknesses: Gr1- 0.052 +/- 0.016 mm; Gr2-0.041 +/- 0.003 mm. The luting agents presented similar film thickness and microTBS values, in dry and TC conditions and TC increased the bond strength regardless of the luting agent.

Effect of light energy density on conversion degree and hardness of dual-cured resin cement

This study evaluated the effect of different light energy densities on conversion degree (CD) and Knoop hardness number (KHN) of RelyX ARC (RLX) resin cement. After manipulation according to the manufacturer's instructions, RLX was inserted into a rubber mold (0.8 mm X 5 mm) and covered with a Mylar strip. The tip of the lightcuring unit (LCU) was positioned in contact with the Mylar surface. Quartz-tungsten-halogen (QTH) and light-emitting diode (LED) LCUs with light densities of 10, 20 and 30 J/cm2 were used to light-cure the specimens. After light curing, the specimens were stored dry in lightproof containers at 37°C. After 24 hours, the CD was analyzed by FT-Raman and, after an additional 24-hours, samples were submitted to Knoop hardness testing. The data of the CD (%) and KHN were submitted to two-way ANOVA and the Tukey's test (α=0.05). QTH and LED were effective light curing units. For QTH, there were no differences among the light energy densities for CD or KHN. For LED, there was a significant reduction in CD with the light energy density set at 10 J/cm2. KHN was not influenced by the lightcuring unit and by its light energy density. © Operative Dentistry.

Rugosidade superficial do esmalte e de resinas compostas: avaliação de instrumentos de acabamento pelo microscópio de força atômica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Desenvolvimento e avaliação da efetividade de duas pastas polidoras em padrão nanométrico empregadas a materiais restauradores estéticos: análise comparativa por perfilometria digital e microscopia de força atômica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise comparativa da rugosidade superficial de resinas compostas de alta densidade

The success achieved by the use of composite resins in anterior teeth precipitately leads their use in posterior teeth. However, the indiscriminate application of these materials in cavities with several diverse sizes rapidly pointed out their lack of resistance to oclusal and proximal wear. OBJECTIVE: To evaluate the surface roughness of composite resin in relation to finishing and polishing technique. MATERIAL AND METHODS: Eight experimental groups (n = 15) were divided according to finishing and polishing technique: G1 – Z250TM composite resin without surface finishing and polishing; G2 – Z250TM composite resin plus surface finishing and polishing; G3 – P60TM composite resin without surface finishing and polishing; G4 – P60TM composite resin plus surface finishing and polishing; G5 – Prodigy CondensableTM composite resin without surface finishing and polishing; G6 – Prodigy CondensableTM composite resin plus surface finishing and polishing; G7 – SurefillTM composite resin without surface finishing and polishing; G8 – SurefillTM composite resin plus surface finishing and polishing. Three packable and one microhybrid (control group) composite resin was used. The surface roughness was measured using a profilometer at three points in each sample. The results were evaluated by ANOVA and Tukey test (p < 0.05). RESULTS: Prodigy CondensableTM composite resin showed the lowest surface roughness, while SurefillTM showed the highest surface roughness. Comparing the resins used, only between P60TM and SurefillTM there were no statistically significant differences (p > 0,05). CONCLUSION: Surface roughness was lower in all types of resin composites surfaces in contact with Mylar matrix strip than in areas submitted to finishing and polishing procedure.

Escape depth of secondary electrons from electron-irradiated polymers

Measurements on polymers (Teflon FEP and Mylar) have shown that the secondary electron emission from uncharged surfaces exceeds that from surfaces containing a positive surface charge. The reduced emission of charged surfaces is due to recombination between electrons undergoing emission and trapped holes within the charged layer. During the experiments the surface of the material was kept at a negative potential to assure that all secondary electrons reaching the surface from within the material are actually emitted. An analysis of the results yielded the maximum escape depth of the secondary electrons, and showed that the ratio of the maximum escape depth of the secondaries from Mylar to the maximum escape depth from Teflon is almost the same as the ratio of the corresponding second crossover energies of this polymers.

Design and development of new pressure sensors for aerodynamic applications

This artwork reports on two different projects that were carried out during the three years of Doctor of the Philosophy course. In the first years a project regarding Capacitive Pressure Sensors Array for Aerodynamic Applications was developed in the Applied Aerodynamic research team of the Second Faculty of Engineering, University of Bologna, Forlì, Italy, and in collaboration with the ARCES laboratories of the same university. Capacitive pressure sensors were designed and fabricated, investigating theoretically and experimentally the sensor’s mechanical and electrical behaviours by means of finite elements method simulations and by means of wind tunnel tests. During the design phase, the sensor figures of merit are considered and evaluated for specific aerodynamic applications. The aim of this work is the production of low cost MEMS-alternative devices suitable for a sensor network to be implemented in air data system. The last two year was dedicated to a project regarding Wireless Pressure Sensor Network for Nautical Applications. Aim of the developed sensor network is to sense the weak pressure field acting on the sail plan of a full batten sail by means of instrumented battens, providing a real time differential pressure map over the entire sail surface. The wireless sensor network and the sensing unit were designed, fabricated and tested in the faculty laboratories. A static non-linear coupled mechanical-electrostatic simulation, has been developed to predict the pressure versus capacitance static characteristic suitable for the transduction process and to tune the geometry of the transducer to reach the required resolution, sensitivity and time response in the appropriate full scale pressure input A time dependent viscoelastic error model has been inferred and developed by means of experimental data in order to model, predict and reduce the inaccuracy bound due to the viscolelastic phenomena affecting the Mylar® polyester film used for the sensor diaphragm. The development of the two above mentioned subjects are strictly related but presently separately in this artwork.

The recoil transfer chamber - An interface to connect the physical preseparator TASCA with chemistry and counting setups

Performing experiments with transactinide elements demands highly sensitive detection methods due to the extremely low production rates (one-atom-at-a-time conditions). Preseparation with a physical recoil separator is a powerful method to significantly reduce the background in experiments with sufficiently long-lived isotopes (t1/2≥0.5 s). In the last years, the new gas-filled TransActinide Separator and Chemistry Apparatus (TASCA) was installed and successfully commissioned at GSI. Here, we report on the design and performance of a Recoil Transfer Chamber (RTC) for TASCA—an interface to connect various chemistry and counting setups with the separator. Nuclear reaction products recoiling out of the target are separated according to their magnetic rigidity within TASCA, and the wanted products are guided to the focal plane of TASCA. In the focal plane, they pass a thin Mylar window that separates the ∼1 mbar atmosphere in TASCA from the RTC kept at ∼1 bar. The ions are stopped in the RTC and transported by a continuous gas flow from the RTC to the ancillary setup. In this paper, we report on measurements of the transportation yields under various conditions and on the first chemistry experiments at TASCA—an electrochemistry experiment with osmium and an ion exchange experiment with the transactinide element rutherfordium.

Green Man

Mixed Media/Mylar 24 x 24"

Being

Mixed Media/Mylar 72 x 42"

Animal

Mixed Media/Mylar 74 x 42"

Fruit

Mixed Media/Mylar 72 x 42"

Plant

Mixed Media/Mylar

Spring

Mixed Media/Mylar