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.

OCT has been used to evaluate dental materials, and is employed here to evaluate lumineers for the first time. Lumineers are used as esthetical indirect restoration, and after wearing and aging, several undesirable features such as gaps, bubbles and mismatch can appear in which would only be seen by invasive analysis. The OCT (spectral domain SD-OCT, 930nm central wavelength) was used to evaluate noninvasively the lumineer-cement-tooth interface. We analyzed 20 specimens of lumineers-teeth that were prepared in bovine teeth and randomly allocated in 4 experimental groups (n=5) with two different cementation techniques and two different types of cementing agent (RelyX U200 and RelyX Veneer, 3M ESPE, with the adhesive recommended by the manufacture). The lumineers were made of lithium disilicate and obtained using a vacuum injection technique. The analysis was performed by using 2D and 3D OCT images, obtained before and after cementing and the thermal cycling process to simulate thermal stress in a oral cavity. Initial measurements showed that the SD-OCT was able to see through the 500µm thick lumineer, as delivered by the fabricant, and internal stress was observed. Failures were found in the cementing process and also after ageing simulation by thermal cycling. The adhesive failures as bubbles, gaps and degradation of the cementation line are the natural precursors of other defects reported by several studies of clinical follow-up (detachments, fractures and cracks). Bubble dimensions ranging from 146 µm to 1427 µm were measured and the OCT was validated as an investigative and precise tool for evaluation of the lumineer-cement-tooth.

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The aim of this study was to evaluate the efficacy of commercial toothpastes containing sodium fluoride (NaF), stannous fluoride (SnF 2 ), or casein phosphopeptides (CPP)-amorphous calcium phosphate (ACP)/NaF regarding their potential to inhibit enamel erosion. Twenty-eight 4×4 mm enamel specimens were randomly allocated into 4 groups (n=7): negative control; Pronamel (NaF); Pro Health (SnF 2 /NaF); Mi Paste Plus (CPP-ACP/NaF). Erosive cycles with 0.5% citric acid, 5 times, 3 minutes/day for 7 days were performed. After the first and last cycle of each day, toothpaste slurries were applied for 2 min. The quantitative analysis was accomplished using Contact Profilometry and Optical Coherence Tomography (OCT), complemented by roughness and qualitative scanning electron microscopy (SEM) analysis. OCT and Profilometry analysis showed similar effectiveness in measuring the reduction of mineral loss. A significant increase in the mean roughness values was observed on eroded surface and also on treated surface as revealed by scanning electron microscopy. The use of SnF 2 /NaF toothpaste was the most effective method for reducing mineral loss. As quantitative methods, OCT and Contact Profilometry showed no statistical differences. OCT, which was used for this purpose for the first time, has the advantage of being noninvasive, and therefore have the potential for clinical application.