Chemical and morphological characterization of self-etch primers incorporated with nanochitosan

This in vitro study evaluated experimental self-etch primers incorporated with different concentrations of nanochitosan gel (NC gel) and their action on the coronal and radicular dentin surface of bovine incisor teeth and the primer influence on the adhesive interface. Sections of 3 × 3 mm of coronal and root bovine dentin were flattened, and the smear layer was formed and standardized with 400 and 600-grit sandpaper. Root and coronal fragments (n=5) were treated with different primers: Clearfil _™ SE Primer, Primer 1 – without NC gel, Primer 2–5% NC gel, Primer 3–10% NC gel, and Primer 4–15% NC gel. Primers were actively applied and left on the surface for 20 s. Images were acquired before treatment and immediately after primer application by confocal 3D laser scanning microscopy (x2160) to assess the degree of surface modification and dentinal tubule alteration. For adhesive interface analysis, dentin specimens (n=5) were treated with the evaluated primers, followed by the bond agent from Clearfil _™ SE adhesive system, and restored with composite resin. Morphological analysis of the dentin surface and adhesive interface was performed using scanning electron microscopy (SEM) and chemical characterization using Fourier-transform infrared spectroscopy (FTIR). In coronal dentin, Clearfil _™ SE Primer exposed fewer tubules than the experimental primers (p<0.05), and the percentage of open tubules was similar for all groups in root dentin (p>0.05). Primer 2 and Primer 3 showed higher values of perimeter and area for root dentin compared to the other groups (p<0.05), while Primer 1 was similar to Clearfil _™ SE Primer (p>0.05). The incorporation of NC gel affected the behavior of the experimental primers. The addition of 10% of NC gel promoted a thicker and continuous hybrid layer with no gaps; however, higher concentrations of nanochitosan gel impaired the formation of a regular hybrid layer which is not favorable for an acceptable adhesion to the dentin substrate.