Publication

Abstract : In the present work, dentin samples extracted from human molar teeth were treated with 248 nm wavelength pulsed laser radiation at fluences between 0.5 and 20 J/cm2. The surfaces were characterised by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and x-photoelectron spectroscopy (XPS). Two distinct behaviours were observed in what concerns the evolution of surface morphology with fluence and number of pulses. In some samples the surface remained flat, independently of the fluence and covered by a layer of resolidified material and redeposited ablation particles, which often occluded the dentinal structure. In other samples the surface topography depended on radiation fluence. For fluences below 1 J/cm2, intertubular dentin was preferentially removed, originating a columnar structure where columns were centred on the dentinal tubules and constituted by peritubular dentin. The height of the columns increased with the number of laser pulses. When fluence exceeded 1 J/cm2 the processed surface remained flat, covered with a fine resolidified layer. These distinct behaviours of dentin can be explained by differences in the constitution of this composite biological material. Despite the topographic changes observed, the mineral phase of dentin (apatite) remained unaltered and collagen was removed only from the outermost superficial layers of the processed material. This fact is explained by the constitution and structure of dentin and by the physical properties and electronic structure of its main constituents. Taking into consideration the results obtained and the bond type and properties of the constituents of dentin, it is suggested that the ablation of collagen occurs by a photochemical mechanism while the ablation of apatite is photothermal.