LAUSR

The aim of this in vitro study was to assess the microshear bond strength (μSBS) of an adhesive system in sound (SD) and demineralized dentin (DD) after femtosecond (fs) laser treatment. Twenty specimens of human dentin were randomly divided into two main groups: sound and demineralized dentin (n = 10). In each of them, three different tissue conditions were produced: SD control group, SD etched with two different fluences of an fs laser (11 and 18 J/cm2, SD11 and SD18, respectively), DD control group, and DD irradiated with the same laser parameters (DD11 and DD18). An adhesive system was applied to the dentin surface, and a resin composite was light-cured to bond to the dentin surface. The μSBS was measured, and the fracture analysis was performed using an optical microscope. The data were analyzed using the Mann Whitney test (p < 0.05). Tissue morphology was assessed via 2D and 3D optical coherence tomography images, scanning electron microscopy, and atomic force microscopy. The optimum bond strength was recorded for the SD11 group (16.42 ± 4.63 MPa), and the minimum bond strength was recorded for the DD (8.89 ± 0.99 MPa) group. The Kruskal Wallis test revealed that sample groups were significantly different (p < 0.01). The Mann Whitney test demonstrated statistical differences between DD and all the other groups. The imaging techniques showed the opening of the dentinal tubules and that the bond strength could be related to laser-induced roughness. Femtosecond laser radiation was successfully able to remove smear layers, producing surface alterations that caused higher dentin-resin adhesion.