Conversion of Filtek Silorane Adhesive determined by Raman spectroscopy

Objectives: This study examined the adhesive interface created by Filtek Silorane Adhesive System (SIL, 3M ESPE, USA) using micro-Raman spectroscopy.

Methods: SIL (a photo-curing self-etching/primer+adhesive) was applied on 3 human dentin disks in accordance with manufacturer's instructions. Specimens were transversally cut to expose the bonded interfaces to the micro-Raman beam (Ranishaw InVia; laser wl 785 nm). Raman spectra were collected along the dentin/self-etching primer/adhesive interface. Measurements were performed at 1µm intervals. The relative intensities of bands associated with mineral dentin components (PO functional group at 960cm^-1) and adhesive (C-O-C group at 1115cm^-1) within the bonded interface were used to detect monomer penetration into the dentin matrix and to calculate SIL degree of conversion (DC) (C=C at 1640cm^-1 as reaction peak, COO at 605cm^-1 as reference peak) within the hybrid (HL) and adhesive layer.

Results: Depth of the HL was 3.1±1.3µm; primer thickness was 16.5±6.0µm while adhesive thickness ranged from 20 to 34µm. The resin monomer/mineral ratio within the HL was 1.0±0.5. DC of SIL was 68.3±7.1% in the adhesive layer, while it increased to 93.7±5.1% in the primer and 91.3±8.8% in the HL.

Conclusions: The HL thickness of the adhesive interface created by SIL was comparable with data previously reported on self-etch adhesives, while the adhesive layer was considerably thicker. As previous investigations revealed that high DC is a fundamental pre-requisite for the stability of the resin bond over time, the DC results of the present study support the hypothesis that optimal stability of SIL within the HL can be obtained. However, further studies are needed to investigate the mechanical properties of the hybrid layer created by SIL and its stability over time.

This study has been partially supported by 3M ESPE.