Alberto C. Barone

Surface morphology and mechanical properties of new-generation flowable resin composites for dental restoration

OBJECTIVES The purpose of this study was to characterize the surface morphology and the elastic properties of four dental restorative flowable composites currently on the market (Venus Diamond Flow, Vertise Flow, Filtex Supreme XT Flow, Surefil SDR Flow). Additionally, one adhesive system (Adhese One F) and one non-flowable composite (Venus Diamond) have also been characterized as the control materials. METHODS Surface morphology was studied by both scanning electron and atomic force microscopy, and the elastic modulus and the hardness measured by instrumented indentation. Grain analysis was performed on the microscopic images, and statistical analysis was carried out on the results of the nanoindentation measurements. RESULTS It was observed that Vertise, Filtek XT and Surefil SDR exhibit stiffness similar to the non-flowable Venus Diamond, whereas Venus Diamond Flow presents itself as the more compliant flowable composite, with Adhese showing intermediate stiffness. Grain analysis of the images confirmed the general rule that the mechanical properties improve with increasing filler loading, with the notable exception of Vertise Flow that shows modulus and hardness as high as 9.1±0.6 and 0.43±0.03GPa, respectively, for an estimated loading of only ∼40% by volume. SIGNIFICANCE Whereas generally flowable composites are confirmed not to possess sufficiently strong mechanical properties for bulk restorations, exceptions can eventually be found upon appropriate laboratory screening, as presently seems to be the case for Vertise Flow. However, real practice in actual restorations and respective clinical evaluation are required for final assessment of the suggested results.

Rigid biodegradable photopolymer structures of high resolution using deep-UV laser photocuring

Recently there has been increasing effort in using microstereolithography to produce scaffolds of crosslinkable and biodegradable polymers, with desired configurations of high spatial resolution, able to regulate the growth and distribution of cells and consequently the tissue development and engineering on them. The use of deep-UV radiation allows high resolution both in the transversal plane (optical resolution) and in the vertical direction (curing depth) due to the intrinsic large absorption of polymers in this region of the electromagnetic spectrum. Herein we present high-resolution photocrosslinking of the biodegradable poly(propylene fumarate) (PPF) and diethyl fumarate (DEF), using pulsed laser light at 248 nm. The curing depth can be modulated between a few hundreds of nanometers (nm) and a few micrometers (µm) by adjusting the energy dose, the number of incident pulses and the weight ratios of PPF, DEF and photoinitiator in the photocrosslinkable mixtures. The lateral resolution is evaluated by projecting a pattern of a grid with a specified line width and line spacing, and is found to be a few µm. Youngs modulus of the cured parts is measured and found to be several GPa, high enough to support bone formation. The results presented here demonstrate that the proposed technique is suitable for the fabrication of stiff and biocompatible structures with defined patterns of micrometer resolution in all three spatial dimensions, setting the first step toward deep-UV laser microstereolithography.

Calibration issues for nanoindentation experiments: Direct atomic force microscopy measurements and indirect methods

This article discusses calibration issues for shallow depth nanoindentation experiments with Berkovich tips with respect to the accurate measurement of the diamond area function (DAF). For this purpose, two different calibration procedures are compared: (i) the direct measurement of the DAF through atomic force microscopy (AFM) imaging of the Berkovich tip at shallow depth and (ii) a novel indirect calibration method based on an iterative robust and converging scheme in which both reduced modulus and indentation hardness are simultaneously used. These results are obtained by indentation measurements on a standard specimen of fused silica, performed in the 0.5–200 mN load range with a Berkovich indenter. Direct tip shape measurements were carried out through different AFM methods. Comparisons with the standard indirect calibration procedure are also reported. For both the indirect calibration procedures a sensitivity and convergence study is presented. Microsc. Res. Tech. 73:996–1004, 2010.

Thermal and Mechanical Characterization of PMMA TiO2 Nanocomposites

Hybrid composite films made of an organic polymeric matrix and an inorganic nanosized filler, namely titania prolate nanoparticles, have been prepared and characterized both thermally and mechanically. The filler content has been varied, while still being kept in the regime of unsaturated, homogeneous nanocomposites. On increasing, the filler content there is an abrupt increase in hardness at an intermediate load, while the elastic modulus increases almost linearly. The glass transition temperature is also increased, with a tendency to saturation. The morphological characterization of the films confirms a lack of phase separation, with only a continuous, slight increase in surface roughness, and no major effects on the top film features.