Morphological study of resin-dentin bonding with TEM and in-lens FESEM

To evaluate the morphological characteristics of the dentin-resin interface using high-magnification electron microscopy and correlate the TEM findings of resin-dentin interfaces with the corresponding in-lens Field Emission SEM (FEISEM) observation.

Twelve 800 microm-thick dentin disks were obtained from middle dentin and assigned to four groups: (1) a self-etching adhesive material, Clearfil SE Bond; (2) a solvent-free total-etch simplified adhesive, One Coat Bond; (3) an acetone-based total-etch simplified adhesive, Prime&Bond NT; (4) an acetone-based total-etch simplified adhesive, Prime&Bond NT, upon a short dentin deproteinization with 10% NaOCl gel (AD Gel) for 15 seconds. Disks were restored with a 1 mm thick layer of a low-viscosity composite. Four sticks with a cross section of 1 mm2 were taken from each restored dentin disk, decalcified in buffered 10% EDTA, fixed, and stained with lead citrate followed by uranyl acetate, or kept in water. The sticks were sectioned in 85 nm-thick slices, and mounted on Ni grids. After TEM observation, the same grids were coated with a 1.5 nm Pt-C film and observed under the FEISEM.

The TEM analysis revealed an intimate adaptation of all adhesive systems to dentin, with penetrating resin tags observed in transverse sections. The FEISEM revealed novel morphological features usually observed in the resin-dentin interface with distinctive arrangement for each of the adhesive systems. FEISEM and TEM appear as mutually complementary tools for the fine observation of the ultra-structure and the spatial relationship between the resin components and the collagen fibers of the hybrid layer.