Publications (9) View all
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Article: AFM characterization of bovine enamel and dentine after acid-etching.
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ABSTRACT: Teeth are constituted mainly of hydroxyapatite molecules (Ca(10)(PO(4))(6)(OH)(2)), grouped in different microstructural arrangements, depending on the dental layer considered (enamel or dentine). In the present work, these dental microstructural arrangements were characterized by atomic force microscopy. Enamel and dentine samples were cut from freshly extracted bovine incisor teeth. After metallographic polishing, the dental surfaces were etched with lactic acid (113.8 mmol/L, pH 3.3). Three etching times were tested: 1, 3 and 5 min. Atomic force micrographs showed that 1 min of etching time was effective to remove the smear layer, polishing debris and scratches, and display the characteristics of interest for both enamel and dentine. Although the bovine dental enamel rod cross-section presented keyhole-like shape, its measured dimensions (8.8 microm of major axis and 3.7 microm of minor axis) exhibited an insignificant discrepancy from human prisms diameters. Bovine dentinal tubules displayed larger mean diameters (4.0 microm) and a lower density (approximately 17,100 tubules/mm(2)) than human dentine, suggesting that the use of bovine dentine as a substitute for human dentine in resin adhesion investigations should be reconsidered. Apatite nanoparticles presented a mean radius (22-23 nm) considerably smaller than that of human teeth.Micron 01/2009; 40(4):502-6. · 1.53 Impact Factor -
Article: Influence of laser surface texturing on surface microstructure and mechanical properties of adhesive joined steel sheets
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ABSTRACT: This work discusses the resultant microstructure of laser surface treated galvanised steel and the mechanical properties of adhesively bonded surfaces therein. The surface microstructure obtained at laser intensities between 170 and 1700 MW cm?2 exhibit zinc melting and cavity formation. The wavy surface morphology of the treated surface exhibits an average roughness Ra between 1·0 and 1·5 ?m, and a mean roughness depth Rz of 8·6 ?m. Atomic force microscopic analyses revealed that the Rz inside the laser shot cavities increased from 68 to 243 nm when the incident laser intensity was increased from 170 to 1700 MW cm?2. X-ray fluorescence analyses were used to measure Zn coating thicknesses as a function of process parameters. Both X-ray fluorescence and X-ray diffraction analyses demonstrated that the protective coating remains at the material surface, and the steel structure beneath was not affected by the laser treatment. Tensile tests under peel strength conditions demonstrated that the laser treated adhesively joined samples had resistance strength up to 88 MPa, compared to a maximum of only 23 MPa for the untreated surfaces. The maximum deformation for rupture was also greatly increased from 0·07%, for the original surface, to 0·90% for the laser treated surfaces.This work discusses the resultant microstructure of laser surface treated galvanised steel and the mechanical properties of adhesively bonded surfaces therein. The surface microstructure obtained at laser intensities between 170 and 1700 MW cm?2 exhibit zinc melting and cavity formation. The wavy surface morphology of the treated surface exhibits an average roughness Ra between 1·0 and 1·5 ?m, and a mean roughness depth Rz of 8·6 ?m. Atomic force microscopic analyses revealed that the Rz inside the laser shot cavities increased from 68 to 243 nm when the incident laser intensity was increased from 170 to 1700 MW cm?2. X-ray fluorescence analyses were used to measure Zn coating thicknesses as a function of process parameters. Both X-ray fluorescence and X-ray diffraction analyses demonstrated that the protective coating remains at the material surface, and the steel structure beneath was not affected by the laser treatment. Tensile tests under peel strength conditions demonstrated that the laser treated adhesively joined samples had resistance strength up to 88 MPa, compared to a maximum of only 23 MPa for the untreated surfaces. The maximum deformation for rupture was also greatly increased from 0·07%, for the original surface, to 0·90% for the laser treated surfaces.Surface Engineering 03/2009; 25(3):180-186. · 0.94 Impact Factor -
Article: Cavity generation in dental enamel using a copper-HyBrID laser.
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ABSTRACT: Applications of Cu-HyBrID laser (copper laser with Hydrogen Bromide In Discharge) in Dentistry and AFM (atomic force microscopy) evaluations of dental tissues irradiated by laser are seldom reported in the literature. This work presents an AFM investigation of the cross-section of a cavity generated in human dental enamel by laser thermal evaporation using the Cu-HyBrID laser. The results exposed the structural and morphological differences between the fused and non-fused dental enamel, provide qualitative information about the susceptibility of these tissues to abrasive polishing, and revealed the extension of the thermal damage. Quantitative information concerning the wall thickness and the dimensions of the cross-section of non-fused enamel rod were also obtained.Journal of Materials Science Materials in Medicine 09/2007; 18(8):1507-13. · 2.32 Impact Factor -
Article: High beam quality in a HyBrID copper laser operating with an unstable resonator made of a concave mirror and a plano-convex BK7 lens
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ABSTRACT: This paper presents a very simple unstable resonator, made of a concave mirror (total reflector) and a bare plane–convex BK7 lens working as a convex coupling mirror, which is quite efficient for HyBrID copper laser. In addition to a good quality factor (M2=4.9), experimental results showed that it is possible to control the laser output power by introducing a variable aperture iris inside the cavity, close to the coupling lens, without spoiling beam quality. A rough theoretical model helped to explain these results as a combined effect of unstable resonator plus radial gain distribution.Optics & Laser Technology. -
Article: Phosphates nanoparticles doped with zinc and manganese for sunscreens
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ABSTRACT: The crescent number of skin cancer worldwide gives impulse to the development of sunscreen that can both prevent skin cancer and also permit gradual tanning. In this work, the synthesis of hydroxyapatite and tricalcium phosphate nanocrystalline powders was investigated in order to obtain materials with optical properties and appropriate size for sunscreen. Pure, Zn2+-doped and Mn2+-doped hydroxyapatite (HAP) and tricalcium phosphate (β-TCP) were produced by the wet precipitation process using diammonium phosphate, calcium nitrate, ammonium hydroxide, zinc nitrate and manganese nitrate as reagents. The pure and doped HAP precipitates were calcined at 500 °C for 1 h, while the β-TCP (pure and doped) were calcined at 800 °C for 2 h. The powder samples were characterized by X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDX), atomic force microscopy (AFM) and ultraviolet (UV)–vis spectroscopy. XRD and EDX showed the formation of the expected materials (HAP and β-TCP) without toxic components. AFM micrographs showed aggregated ellipsoidal particles with dimensions smaller than 120 nm. Optical absorption spectra showed that the calcium phosphate produced in this work absorbs in the UV region. The obtained materials presented structural, morphological and optical properties that allow their use as the active centers in sunscreens.Materials Chemistry and Physics. 124:1071-1076.
