Papers by Author: Vitor Oliveira

Abstract: Laser treatment is a promising technique for dental applications such as caries prevention, dental hypersensitivity reduction and improvement of bond strength of restoration materials. In this study the morphological, structural and chemical changes of enamel surface due to treatment with KrF excimer laser radiation were evaluated using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. For radiation fluences near 1 J/cm², laser processing originates a relatively porous surface due to preferential removal of material in the enamel prism sheaths. Increasing the fluence leads to a relatively flat surface with clear evidence of surface melting. The X-ray diffractograms of both treated and untreated enamel are similar and correspond to hydroxyapatite. The only modification due to the laser treatment is a slight shift of the peaks, probably, due to a loss of the structural water of hydroxyapatite. X-ray photoelectron spectroscopy confirmed that organic matter is removed from the irradiated surface but no significant changes in the mineral phase occur.

Abstract: In the present paper, the influence of tubule orientation and areal density on the development of surface textures by excimer laser processing of dentin is analysed. Disks of dentin 2 mm thick were extracted from caries-free human teeth by cross-sectional cutting above the pulp cavity, polished and fixed using standard procedures. The samples were laser-processed using 100 laser pulses of 248 nm wavelength radiation at a fluence of 1 J/cm2, pulse duration of 30 ns and pulse frequency of 5 Hz. The surface texture after processing depends on the angle between the tubules and the laser beam. In inner dentin, where tubules are parallel to the laser beam, cone-like artefacts form, considerably increasing surface roughness. The cones are constituted by partially melted peritubular dentin and develop because the ablation rate of peritubular dentin is lower than the ablation rate of surrounding intertubular dentin. The areal density of cones is roughly identical to the areal density of tubules except when the tubule density is high enough to allow adjacent cones to coalesce. In outer dentin, where tubules are tilted with respect to the laser beam, the surface remains flat. The reason for this orientation dependence is that, when tubules are tilted towards the laser beam, preferential removal of intertubular dentin will expose an increased area of underlying peritubular dentin to laser radiation preventing cone development.