Apparent conversion of adhesive resin in the hybrid layer, Part II: In situ studies of the resin-dentin bond

Penetration and conversion of adhesives into the hybrid layer (HL) is important to the quality and longevity of the adhesive, resin (AR)-dentin bond. In this Study, a methodology is developed to examine the degree of conversion and relative HEMA concentration with respect to Bis-GMA using Raman spectroscopy. This methodology will be used in the future reports related to this topic. Conversion in the AR of water-stored resin-dentin samples (84%+/- 3%) agreed well with that measured in commercial adhesive (Comm Adh) resin samples after 24-h water storage (80%+/- 2% from Part 1) and was significantly higher than Comm Adh Without water storage (58%+/- 3% from Part 1) (p=0.0005). Adhesive conversion was not significantly different (p=0.5036) through the middle of the HL, with a mean of 83%+/- 6%. HEMA mole fraction, relative to Bis-GMA, was significantly higher (p=0.0028) in the top half of the HL (0.67 +/- 0.03), when compared to HEMA in the AR (0.60 +/- 0.01). HEMA and EDMAB were identified through GC/MS as leachable components in the aqueous 24-h storage media. The effect of this elution explains the change in conversion measurements observed between dry and water-stored conditions, which is more appropriately described as the "apparent" conversion. (C) 2008 Wiley Periodicals, Inc. J Biomed Mater Res 89A: 355-362, 2009