Ultra-morphological and chemical analysis of lased dentin for the adhesion promotion of resinous materials

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This study was carried out to investigate the ultra-morphological and chemically-analytical changes of the dentin surface induced by Er : YAG or CO_2 laser irradiation for the purpose of the adhesion promotion of resinous materials to lased dentin.Labial surface of freshly extracted bovine tooth was ground to expose flat dentin. The dentin surfaces were then polished with 600-grid SiC paper and were irradiated by Er : YAG laser (Erwin^R, 60mJ/pulse, 10pps) or CO_2 laser (Topal^R, 1W, 0.3 sec). The superficial layer of the lased dentin was ultra-morphologically examined by atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface characteristics of lased dentin were chemically analyzed using X-ray Photoelectron Spectroscopy (XPS).The SEM and AFM observation revealed that the smear layer was not produced on the lased dentin surface, where the structural defects such as micro cracks and stratified structure like fish scales were observed. By the TEM observations of non-decalcified specimens, such morphological changes as observed in the acid-etched dentin surface could not be detected in the subsurface layer of the lased dentin. Furthermore, the amorphous matrix substances of 10-15μm thickness, which consisted of denatured dentin collagen, were superficially observed. The analysis of XPS wide-scan spectrum of lased dentin surface showed the intensity of both C1s and N1s peaks obviously decreased. The SEM examination of resin-dentin interface revealed that the degenerated layer of 10-12μm thickness was observed beneath the hybrid layer.It was suggested that both the structural defects and the denatured layer affect the adhesive properties of resinous materials to the Er : YAG or CO_2 laser-irradiated dentin.