Ramiro García-García

XRD and FTIR crystallinity indices in sound human tooth enamel and synthetic hydroxyapatite

The crystallinity index (CI) is a measure of the percentage of crystalline material in a given sample and it is also correlated to the degree of order within the crystals. In the literature two ways are reported to measure the CI: X-ray diffraction and infrared spectroscopy. Although the CI determined by these techniques has been adopted in the field of archeology as a structural order measure in the bone with the idea that it can help e.g. in the sequencing of the bones in chronological and/or stratigraphic order, some debate remains about the reliability of the CI values. To investigate similarities and differences between the two techniques, the CI of sound human tooth enamel and synthetic hydroxyapatite (HAP) was measured in this work by X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR), at room temperature and after heat treatment. Although the (CI)XRD index is related to the crystal structure of the samples and the (CI)FTIR index is related to the vibration modes of the molecular bonds, both indices showed similar qualitative behavior for heat-treated samples. At room temperature, the (CI)XRD value indicated that enamel is more crystalline than synthetic HAP, while (CI)FTIR indicated the opposite. Scanning (SEM) and transmission (TEM) images were also used to corroborate the measured CI values.

Structural and thermal behaviour of human tooth and three synthetic hydroxyapatites from 20 to 600 °C

The structural and thermal properties of human tooth enamel, dentine and three synthetic hydroxyapatite samples with Ca/P ratios of 1.57 (Ca deficiency), 1.67 and 1.77 (Ca excess), respectively, were analysed in the temperature range from 20 to 600??C to have information on the parameters involved in the ionic/electrical conductivities reported for human tooth enamel between 200 and 350??C approximately. Studies were carried out through x-ray diffraction, thermo-gravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy and temperature programmed desorption. Chemical analysis was performed by x-ray characteristic energy dispersive spectroscopy. Results indicate a strong correlation between the removal of the OH? groups from the hydroxyapatite unit cell and the expulsion of absorbed water and lattice water registered during heating.

Structural and thermal behaviour of carious and sound powders of human tooth enamel and dentine

Powder from carious human tooth enamel and dentine were structurally, chemically and thermally analysed and compared against those from sound (healthy) teeth. Structural and chemical analyses were performed using x-ray diffraction, energy-dispersive x-ray spectroscopy and transmission electron microscopy. Thermal analysis was carried out by thermogravimetric analysis, Fourier transform infrared spectroscopy and x-ray diffraction. Results demonstrate partially dissolved crystals of hydroxyapatite (HAP) with substitutions of Na, Mg, Cl and C, and a greater weight loss in carious dentine as compared with carious enamel. A greater amount of thermal decomposition is observed in carious dentine as compared with sound dentine, with major variations in the a-axis of the HAP unit cell than in the c-axis. Variations in shape and intensity of the OH−, and FTIR bands were also found.

Electron Microscopy Analysis of the Central Dark Line Defect of the Human Tooth Enamel

After some experimental results that indicated that HA is able to growth in an epitaxial way on the surface of OCP, it has been suggested that the central dark line (CDL) observed in the nanometric-sized grains of human tooth enamel corresponds to a one-unit-cell-thick layer of octacalcium phosphate (OCP). Based on this consideration, in this work we propose a model for CDL and we carried out the chemistry and structural analysis of the CDL with high resolution microscopy techniques such as Electron Energy Loss Spectroscopy (EELS) and Z-contrast (HAADF) with the aim of find the agreements and/or differences between the human tooth enamel HA and its CDL.

Holes drilling in gold and silver decahedral nanoparticles by the convergent beam electron diffraction electron beam

The 200 kV focused electron beam in the convergent beam electron diffraction patterns mode in a transmission electron microscope (TEM) with field emission gun is able to drill holes in gold and silver decahedral nanoparticles. However, although they are done under the same circumstances, the holes are shapeless in the silver and faceted in gold nanoparticles. In addition to this, the holes are closed during their high-resolution TEM observation in both materials. To comment their differences, displacement energy considerations are taken into account as function of the sputtering energy in order to modify the displacement cross-section of the processes.

X-ray diffraction study of the structure modification of aluminum samples by ion irradiation

This study shows the X-ray diffraction analysis of the structural changes registered in samples of highly pure aluminum (99.999%) of two different castings and of the aluminum alloy 7075 when they are irradiated at liquid nitrogen (LN2) temperature by protons of 300 keV first and of 700 keV thereafter, from a 0.7 MeV Van de Graff accelerator. The samples were also introduced in a magnetic field, and thereafter irradiated with a laser beam. The results indicated the loss of texture in the samples after proton irradiation and the magnetic field and laser beam treatments were found as contributors in the consolidation of the new structure. Without proton irradiation and without the LN2 temperature, no structural change was observed.

The low-loss EELS spectra from radiation damaged gold nanoparticles

The advantage of the EELS spectra in transmission electron microscopy is the ability to obtain plasmon information of the structure of individual nanoparticles. The EELS analyses of the plasmonic information of gold nanoparticles were obtained before and after irradiation by the convergent beam electron diffraction (CBED) technique. The results indicate that before irradiating the gold nanoparticles (35 nm in diameter) by the CBED technique, only the EELS spectrum of carbon is obtained. Nevertheless, the EELS spectra of gold were obtained after CBED irradiation of the nanoparticles. The spectrum of gold shows five plasmonic modes at 15.9, 24.8, 32.8, 45.4, and 63.2 eV, but theoretical surface and bulk plasmons of gold are at 6.378 and 9.020, respectively. When compared with the experimental plasmon peaks, we determined that peaks at energies above 9.026 eV are multiples of the surface and bulk (valence) plasmons of the gold nanoparticles.

The SEM electron-mirror effect in human tooth and synthetic hydroxyapatite samples

The characteristics of the electron‐mirror effect (EME) image depend on both the scanning electron microscope parameters and the samples physical properties. The behavior of human tooth (dentin and enamel) and synthetic hydroxyapatite samples submitted to the EME procedure is presented in this work. Polyethylene terephthalate (PET) and epoxy resin, two good EME producers, were used for comparison. A distorted EME image was observed in the obtained dentins surface, but enamel and synthetic hydroxyapatite surfaces did not produce the EME. After ex situ calcination treatments of the teeth at 700 and 1,200°C, the EME was observed in dentin, enamel, and synthetic hydroxyapatite, but highly deformed EME images were produced. We show that these last observations are the result of the well‐known charge‐edge effect. After EME analysis, the calculated dielectric constant was 8.7 for dentin and 3.8 for PET.