M.A. Garrido

Early Hardness of Self‐Adhesive Resin Cements Cured under Indirect Resin Composite Restorations

PURPOSE To determine the influence of curing mode on the surface hardness of seven resin cements used to lute indirect composite restorations. MATERIALS AND METHODS Seven commercial dual-curing resin cements were tested: two were total-etch (RelyX ARC [3M ESPE, St. Paul, MN, USA] and Variolink II [Ivoclar Vivadent, Schaan, Liechtenstein]); one was self-etch (Multilink Automix [Ivoclar Vivadent]), and four were self-adhesive (RelyX Unicem [3M ESPE], Maxcem Elite [Kerr Corp., Orange, CA, USA], SmartCem2 [Dentsply, Detrey, GmbH, Konstanz, Germany], and G-Cem [GC CORPORATION, Itabashi-Ku, Tokyo, Japan]). Three specimens (0.5 × 6.5mm) of each material were prepared for each of three experimental groups: Group 1 (cements allowed to self cure); Group 2 (cements light-cured for 40 seconds); and Group 3 (cements light-cured for 80 seconds). All specimens were cured through a 4-mm-thick composite cylinder (Filtek Z250-A3). Surface microhardness numbers were determined at 20 min after preparation. Results were analyzed by two-way analysis of variance and Student-Newman-Keuls tests (p<0.05). RESULTS Superficial hardness was significantly influenced by the resin cement tested (p<0.0001), the curing mode (p<0.0001), and their interaction (p<0.0001). RelyX ARC exhibited the highest mean microhardness values regardless of the curing mode. Light-curing significantly increased the microhardness of all resin cements studied, and these values increased even further with a doubling of irradiation time. Self-adhesive cements exhibited different behavior according to the curing mode. RelyX Unicem was highly sensitive to light irradiation, showing the lowest mean values in the self-curing mode. After light irradiation for 40 or 80 seconds, Maxcem Elite exhibited the lowest mean hardness values of all the resin cements tested. CONCLUSION The microhardness of resin cements is highly dependent on the brand. Dual-curing resin cements should always be light irradiated for longer periods than that recommended by manufacturers. CLINICAL SIGNIFICANCE Dual-curing resin cements should always be light-cured for longer irradiation times, as light irradiation for 80 seconds yields the highest microhardness values in comparison with self-curing or light irradiation for 40 seconds. However, some self-adhesive resin cements exhibit low microhardness values when used to cement 4-mm-thick indirect composite restorations regardless of the curing mode applied.

Roughness Effect on the Mechanical Properties of Ceramic Materials Measured from Nanoindentation Tests

An experimental study was performed to evaluate the roughness effect on the determination of hardness and Young´s modulus of ceramic materials from nanoindentation tests. Several specimens polished at various stages were tested at different peak load values. Local roughness measurements have been done by means of atomic force microscopy. Results indicate that roughness and size effects are joined. Proportional Specimen Resistant Modified model (PSRM) was applied to avoid the scale effect, isolating the roughness influence. Indentations where the average roughness-elastic displacement ratio is lower than a critical value are needed to get consistent results.

Application of Gradient and Confocal Raman Spectroscopy to Analyze Silver Nanoparticle Diffusion in Medieval Glasses

In this work it has been carried out the diffusion of silver ions in medieval glasses by a heat treatment process. Silver ions are transformed into both silver nanoparticles and nanoclusters after redox reactions with reducing glass ions. Changes in glass colour due to the formation of these silver nanoparticles have been analysed by means of visible spectroscopy. At the same time, changes in glass structure have been analysed by means of Raman scattering. By using confocal Raman spectroscopy the in deep glass structural changes occurring after silver ion diffusion and silver nanoparticle formation have been studied. These changes have been corroborated by means of gradient Raman spectroscopy where the silver ion and silver nanoparticle diffusion have been analysed on a fractured glass surface. In all cases have been observed that silver nanoparticles produce a depolymerisation of the glass structure and that such depolymerisation increases with the amount of silver nanoparticles. By using Microprobe Analysis it has been found that the higher silver nanoparticle concentration is on the glass surface and it decreases with the distance to the surface according to a diffusion process. By using nanoindentation measurements on original and gradient glass surfaces it has been found an increase of the Young modulus from 60 to 85 GPa, being the first value that corresponding to the glass surface with high silver nanoparticle concentration, and the second one for the glass without silver. This result is in accordance with Raman and Microprobe analysis.

On the possibility of estimating the fracture toughness of enamel

OBJECTIVES There are many works that have attempted to estimate the fracture toughness of enamel by indentation techniques using equations whose success in determining the actual value of fracture toughness, rely on a particular three-dimensional pattern consisting of cracks growing from the edges of the indentation. Recently, an alternative methodology based on an energetic approach has been developed to estimate the fracture toughness of coatings by depth sensing indentation that is not less affected by the cracks pattern generated. In this work, the energetic approach to indentation fracture toughness of bovine enamel is presented and compared with those toughness values obtained using the traditional expressions reported in the literature. METHODS Indentation tests were carried out using a diamond Berkovich indenter onto the enamel surface of eight incisors from bovines of two years old. A continuous stiffness measurement methodology was used with a frequency of 45 Hz and displacement amplitude of 2 nm up to a maximum penetration depth of 2000 nm. RESULTS The results showed that some modifications in the energetic methodology should be performed in order to apply it successfully. SIGNIFICANCE The fracture toughness values obtained using the traditional equation and applying the energetic methodology, were significantly different, although the values were within the range obtained by other authors.

Evaluation of mechanical properties of Ti6Al4V cold sprayed coatings

ABSTRACT The majority of the mechanical components in aeronautical applications show a reduction of their performance during their service life. Sometimes the component replacement is necessary, with the consequent cost of material and time. An alternative is to repair the component depositing a coating onto the metallic alloy. In this work, a cold spray technique was used to generate Ti6Al4V coatings onto a bulk of the same material. The mechanical response of these coatings was investigated by instrumented indentation tests. Additionally, instrumented indentation tests were also conducted on the particles used for the spraying process and on the substrate. The Young’s modulus and the hardness of the coatings were compared to those obtained on the particles and on the substrate. The mechanical properties obtained on the coatings presented values similar to those obtained on the substrate. Also, the sprayed particles showed a hardness significantly lower than that obtained on the coatings.

Wear resistance of cold sprayed Al alloys for aeronautical repairs

ABSTRACT Al–Cu alloys, like Al 2024, and Al–Si alloys, like Al F357 and Al C355, are used in aeronautic gearboxes and fuselage parts operating in severe conditions. It is necessary to develop maintenance and overhaul technologies to extend the life of metallic components used in the aeronautical sector. Cold Spray (CS) could be an alternative as it is real solid-state processing technique. However, the repaired component should exhibit similar properties as the original substrate. This paper evaluates the wear performance of Al coatings CS onto the same Al substrates in sliding and oscillating conditions. The results were compared with the corresponding substrates. The wear rate of coatings processed using new conditions, developed to enhance the coatings performance, was similar or smaller than that measured in the substrate bulk alloys. For Al 2024 and Al C355 CS could be used for repairing, from the tribological point of view.

Nanoindentation by Multiple Loads Methodology: A Pile Up Correction Procedure

Young’s modulus and hardness data obtained from nanoindentation are commonly affected by phenomena like pile up or sink in, when elastic-plastic materials are tested. In this work, a finite element model was used to evaluate the pile up effect on the determination of mechanical properties from spherical indentation in a wide range of elastic-plastic materials. A new procedure, based on a combination of results obtained from tests performed at multiple maximum loads, is suggested.

Hardness and Young´s Modulus Determination of Nanostructured Alumina-Titania Coatings

It has been generally accepted that a nanostructured material exhibits better properties than conventional ones. Nanostructured ceramic coatings fabricated by plasma spray have been developed for a wide variety of applications where a surface protection is required. Alumina - titania coatings are usually used as protective layers in many industrial applications requiring a high wear resistance during dry sliding contact. In this work, nanostructured and conventional Al2O3 – 13% TiO2 coatings deposited via atmospheric plasma spray were compared. Mechanical characterization was carried out using depth sensing indentation to determine hardness and Young´s modulus of the coatings. Size independent properties can be determined after considering geometrical factors such as tip rounding and indenter deformation. Nanostructured coatings show slightly better mechanical properties than conventional coatings.