Effect of anaerobic cure of self-etch adhesive on degree of conversion and shear bond strength

Abstract

The main aim was to evaluate the effect of postponing the curing of the adhesive layer until the first layer of composite resin is applied-hereby oxygen-inhibited layer (OIL) formation and its detrimental effect on the degree of conversion (DC) of self-etch adhesives should be prevented. For this purpose, the degree of conversion and shear bond strength of four current market self-etch adhesives were evaluated, assessing the effect of curing the adhesives anaerobically and then under two different thicknesses of composite resin, and compare this to the samples cured alone and in air. The degrees of conversion were obtained by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, after the samples were prepared on a glass slide. The samples were either light-cured in air or anaerobically under a clear matrix strip alone, under 2mm of cured composite resin or under 4mm of cured composite resin. To determine the shear bond strength (SBS), extracted molars were halved and set in acrylic. Prefabricated cured cylinders of composite resin (TPH 3, 2.4mm in diameter) of two different lengths are placed over the adhesives under the following conditions: light-cured conventionally (2-mm-long cylinder) and light-cured anaerobically under the uncured end of the piece of composite resin (using both 2- and 4-mm-long cylinders as separate treatments). After another incubation for 24h at 37°C, the samples were subjected to shearing using the Bisco Shear Bond Strength Tester. The degree of conversion of the one-step self-etch adhesives was not statistically different when cured anaerobically under a clear matrix strip or cured anaerobically under 2mm of composite resin. These results were greater than those cured under 4mm. Shear bond strength between samples cured in air and anaerobically were similar under 2mm of composite resin tubes, while those cured anaerobically under 4mm of resin showed lower shear bond strength. When cured anaerobically, one-step self-etch adhesives show a greater degree of conversion and no significant difference in degree of conversion and shear bond strength when compared to those cured in air under the same thickness of composite resin. The results obtained from DC and SBS analysis show promise in placing the uncured adhesive under the composite resin and curing both the adhesive and restoration material simultaneously.